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Clever Controller for a Dumb Battery Charger BY JOHN CLARKE Most cheap battery chargers – the type you might buy at a hardware store or auto retailer – are pretty dumb. As many people have discovered (because these chargers are so dumb) they can actually destroy the battery under charge! If you have one of these chargers, you can upgrade it to one with a clever controller, suitable for flooded lead-acid, sealed lead-acid (SLA) or even LiFePO4 rechargeable batteries. M any manufacturers’ idea of a battery charger is a transformer, a diode or two and a pair of clip leads... and not much else. You may even have one of these sitting on a shelf in the garage. They’re everywhere! Sure, it will charge a flat battery but the chances are if you don’t unclip it, it will keep on charging and charging and charging... until the battery electrolyte is boiled dry, the plates are buckled or, worst case, you have a fire on your hands that may be very difficult to control! Our new Charge Controller is used in conjunction with one of these basic, low-cost lead-acid battery chargers. It transforms this ‘dumb’ charger into a more advanced device that can still charge at the same maximum rate, but also offers proper charge termination, float charging and temperature compensation. Since it’s fully adjustable, it caters for the lithium-iron-phosphate (LiFePO4) batteries that are starting to become available as a replacement for lead-acid types. Compared to lead-acid, LiFePO4 offers faster charging and discharging, more charge cycles, smaller volume and lighter weight, albeit at a higher cost. A 12V A 2 3 0V AC 0V DIODE 1 330Ω 12V A A N 12V TRANSFORMER + K K  DIODE 2 THERMAL CUTOUT K K Basic charger flaws The configuration of a typical low cost lead-acid battery charger is shown in Fig.1. It comprises a mains transformer with a centre-tapped secondary output. The output is rectified using two power diodes to provide raw DC for charging the battery. A thermal cutout opens if the transformer is delivering too much current. Charge indication – if it is present at all – may be as simple as a zener diode, LED and resistor. The LED lights when the battery voltage exceeds the breakdown voltage of the zener diode (12V) and the forward voltage of the green LED (at around 1.8V). Thus the LED begins to glow at 13.8V and increases in brightness as the voltage 17V PEAK 12V RMS TO BATTERY 12V ZENER A  16 GREEN LED Adding a fully automatic Charge Controller to a basic charger will also prolong the life of your batteries, and you can leave a battery on a float charge as long as you want, ready for use when required. LiFePO4 batteries usually are not float charged, so you can disable that step for these batteries. – 0V Fig.1: the basic arrangement of a typical low-cost lead-acid battery charger. It consists of a centre-tapped mains transformer and a full-wave rectifier (D1 and D2). There’s usually a thermal cutout and perhaps an LED indicator to show when the battery is charged. The output voltage of this simple arrangement is shown above. Practical Electronics | December | 2020 VOLTS UNLOADED CHARGER OUTPUT Features BATTERY VOLTAGE 0 10ms 20ms 30ms TIME • Charges 6V, 12V or 24V flooded lead-acid, SLA or LiFePO4 batteries at up to 10A (with a suitable charger) • Charge rate: adjustable from 1-100% of charger capability in 1% steps • One, two or three charging phases: bulk, absorption and float • Adjustable or pre-set charge termination and float voltages • Adjustable temperature compensation for lead-acid batteries with an internal or external thermistor CURRENT • Automatic slow charge mode for batteries that are heavily discharged TIME A CHARGING VOLTAGE AND CURRENT BATTERY VOLTAGE • Battery discharge protection • Cold battery charge protection (won’t charge below 1°C) UNLOADED CHARGER OUTPUT • Thermistor fault protection (won’t charge lead-acid batteries if the thermistor is open or short circuit) • Six status indicator LEDs with error indication REQUIRED BATTERY VOLTAGE CHARGING TIME B CHARGING CHARACTERISTIC Fig.2. in more detail, the charging current from the circuit shown in Fig.1 consists of a series of high-current pulses at 100Hz. As shown in part (b), the relatively high peak voltage can result in the battery being over-charged if the charger is left on long enough. rises. Some chargers may also have an ammeter to show the charging current. The charging current to the battery is a series of highcurrent pulses at 100Hz, as shown in Fig.2(a). The nominal 17V peak output from the charger will eventually charge a battery to over 16V if left connected long enough, which will damage the battery. As shown in Fig.2(b), the maximum battery voltage for a full charge (called the cut-off voltage) is exceeded when left on charge for too long. The solution By adding in the Charge Controller to that simple charger, we can do much better. Fig.3 shows how the Charge Controller is connected in between the charger and the battery. The Charge Controller is housed in a compact diecast aluminium case. In effect, the Charge Controller is a switching device that can connect and disconnect the charger to the battery. This allows it to take control over charging and to cease charging when the correct voltage is reached. The various charging phases for lead-acid batteries are shown in Fig.4. The Charge Controller can switch the current on or off and apply it in a series of bursts, ranging from 20ms every two seconds through to a continuous current. During the first phase, called ‘bulk charge’, current is typically applied continuously to charge as fast as possible. After the bulk charge phase, the Charge Controller switches to the ‘absorption phase’. This maintains the cut-off voltage for an hour by adjusting the burst width while it brings the battery up to an almost full charge. After that, the Charge Controller switches to ‘float charge’. This uses a lower cut-off voltage and a low charge rate, to keep the battery fully charged. Practical Electronics | December | 2020 • Low-cost, easy to build and easy to use • Microprocessor controlled The switch from absorption to float occurs when the charging current drops to 3% of the original bulk charge rate or after an hour, whichever comes first. The absorption phase is optional; you can choose to skip this phase and go straight from bulk charging to float charging. When absorption is enabled, this phase will be bypassed if the bulk charge takes less than an hour. This prevents excessive absorption phase charging with an already fully charged battery. While the bulk phase is usually done at the full rate, for lower capacity batteries where this charging current would be too high, the burst width can be reduced to limit the average current. For example, if you have a 4A battery charger, the current can be reduced from 4A anywhere down to 40mA in 1% steps, using the charge rate control. Lithium-iron-phosphate battery charging Typically, LiFePO4 batteries are charged to 3.47V per cell, although 3.6V per cell is also used. A nominally 12V LiFePO4 battery therefore has four cells, and the cut-off voltage is either 13.88V or 14.4V, depending on which percell figure you use. The Charge Controller can cease charging once the cut-off voltage is reached, or you can opt for an absorption phase. During this phase, the cut-off voltage is maintained for an hour, or until charging pulses drop to 3% of the original bulk charge setting. + + + – – – LEAD-ACID BATTERY CHARGER + – CHARGE CONTROLLER BATTERY Fig.3. the Charge Controller is connected between the charger and battery. It takes control over charging and ceases charging the battery at the correct voltage; ie, when it is fully charged but before it becomes over-charged and starts out-gassing (or worse). 17 Specifications • • • • • • • • • • • • • • • • Charging pulse width: 20ms-1980ms in 20ms steps, or continuous Charging cut-off voltage: 0-30.5V in 29.8mV steps. Independent LiFePO4, SLA and lead-acid battery settings (presets are also available, see Table 1) Temperature compensation: 0-50mV/°C in 256 steps (separate SLA and lead-acid battery adjustments) Minimum battery charging temperature: 1°C Maximum compensation temperature: 60°C Under-voltage burst charge: 5.25V for a 6V battery, 10.5V for a 12V battery, 21V for a 24V battery Under-voltage burst rate: 200ms burst every 2s at maximum charge rate. The burst width is reduced with a lower charge rate (10% of the normal rate). Battery discharge protection: if charger power is lost, it switches off after two hours with battery voltage below 6.25V (for a 6V battery), 12.5V (for a 12V battery) or 25V (for a 24V battery) Power on: LED1 lights Thermistor error: LED2 lights Temperature too low: LED2 flashes at 1Hz Bulk charging: LED3 lights Absorption charging: LED4 lights; optionally, LED3 flashes to indicate charge rate Float charging: LED5 lights; optionally, LED3 flashes to indicate charge rate Battery detected: LED6 lights Battery voltage low, charging slowly: LED3 flashes; if charging a lead-acid battery, LED4 and LED5 also flash Lead-acid cut-off and float voltages The actual cut-off and float voltages for lead-acid batteries are dependent on the particular battery, its construction and the operating temperature. Typical cut-off and float voltages at 20°C are 14.4V and 13.8V, respectively. For sealed lead-acid (SLA) batteries, the voltages are lower at 14.1V and 13.5V respectively. These values, plus 13.88V for the LiFePO4 battery, are pre-set within the Charge Controller and selected using the Lead-Acid/SLA/Lithium jumper shunts, but only when the ‘default’ shunt is inserted (not ‘adjustable’). See Table 1. Other settings are possible, and can be set manually from 0-30.5V in 29.8mV steps – see Table 2. These voltage settings can also be compensated for temperature changes; as the temperature rises, the charge voltages for a lead-acid battery are normally reduced. A typical temperature compensation value is –20mV/°C for flooded CUTOFF VOLTAGE CUTOFF POINT BATTERY VOLTAGE cells and –25mV/°C for SLA batteries. LiFePO4 batteries do not require temperature compensation. Temperature compensation values can be set from between 0 to –50mV/°C in 256 steps. Temperature compensation is applied for temperatures between 0°C and 60°C. No charging is allowed at temperatures at or below 0°C, to protect the battery. A negative temperature coefficient (NTC) thermistor is used for temperature measurement, and the Charge Controller will use the internal thermistor if an external one is not connected via its jack socket. The external thermistor provides for a more accurate measurement when it is placed against the battery. Four trimpots are used to make the settings. One sets the charge rate, as a percentage of the full charge current available from the charger. The remaining three are for setting the cut-off voltage, float voltage and temperature compensation adjustments. When charging the battery, the microcontroller adjusts the pulse duty cycle to reach the desired battery terminal voltage using negative feedback. FLOAT VOLTAGE BULK CHARGE ABSORPTION FLOAT CHARGE CURRENT Setting SLA Flooded lead-acid 14.4V 13.8V LiFePO4 Cut-off voltage Float voltage Temperature compensation 14.1V 13.5V -25mV/°C -20mV/°C None 13.88V None Table 1 – default settings TIME Fig.4: the three typical charging phases for a lead-acid battery. It starts with the bulk charge phase, then switches to the absorption phase (optional, selected using JP2) for an hour or so, and then finally switches to float charging to finish charging and keep the battery charged. For LiFePO4 batteries, there is no float phase. The charger switches off when the battery is fully charged and switches back on again later if it becomes discharged. 18 Setting Set by VR2 VR3 SLA and Flooded lead-acid 0-30.5V* 0-30.5V* Cut-off voltage Float voltage Temperature compensation 0-30.5V* None VR4 0 to -50mV/°C None Table 2 – adjustable settings LiFePO4 *in 29.8mV steps Practical Electronics | December | 2020 TO CHARGER F1 – 10A 100  1W Q1 IRF1405N K D1 1N4004 A A G TP5V REG1 LM317T K K ZD1 18V 220 F ADJ 8 120 1 +5V 1k 7 A 50V 100 F 330 K ZD2 18V 16V A 3 POWER D2 1N4004 RLY1 (5V) 2k 15 Q3 BC337 VR1 10k 3.3k 18 Vdd RA3 /AN3 AN1/RA1 10nF E RA4 TP2 VR2 10k OUT: DEFAULT 12V IN: ADJUST. 17 AN0/RA0 10nF VR3 10k +5V 13 12 4 16 AN5/RB6 RA2/AN2 RB4 A 7 100nF A RLY1b RB5 1k 1k 1k 1k 1k LED2  K A A LED3  K LED4  K A 100nF BATTERY  LED6 K LED2: THERMISTOR LED3: CHARGE LED4: ABSORPTION LED5: FLOAT  K C Q2 BC337 B E 10k 1 11 STORE RA7/OSC1 EXTERNAL THERMISTOR T S2 R THERMISTOR 100nF TH1 5 S CON1 BC 33 7 LEDS K A 10k A 10k LED5 A Vss ZD1, ZD2 K 8 RA5/MCLR 10nF K 6 RB1 AN6/RB7 10nF 1k 1: SLA 1 2: FLOODED LEAD-ACID 2 OPEN: LITHIUM 3 RB2 10 JP3 1N4004 100k 51k RB0 TP4 VR4 10k 2 2: ABSORPTION 4 2 10nF +5V 1: STANDARD 1 2 TTC 9 IC1 PIC1 6F8 8 PIC16F88 TP3 JP2 RB3 RA6/OSC2 B JP1 INPUT 100nF 14 TP1 C IC2 +5V A 56 SOURCE 6 Mcap2 Mcap1 Si87 51 100nF K +5V K 5 GATE +5V GND  LED1 VR5 100 A – 10pF +5V OUT IN S1 POWER + D3 1N4004 RLY1a  + TO BATTERY S D B E C 8 Universal Battery Charge Controller SC UNIVERSAL BATTERY CHARGE CONTROLLER 20 1 9 IRF1405N IC2 4 1 G LM317T D D S OUT ADJ OUT IN Fig.5: the Charge Controller circuit is based around a PIC16F88 microcontroller (IC1). This monitors the battery voltage at its AN3 input and switches MOSFET Q1 on and off via isolated driver IC2, to control the charging. The duty cycle is reduced by 15% every two seconds if the battery voltage is above the required value by more than 0.25V, or reduced by 1% every two seconds if the battery voltage is above the required value by less than 0.25V. Conversely, the charge duty cycle is increased at a fast rate (3% per two seconds) if the battery voltage is more than 0.25V below the required value and increased at a slow rate (1% per two seconds) if the battery voltage is low by less than 0.25V. LED indicators The Charge Controller has six LED indicators. LED1 (green) shows power is applied, while LED2 (orange) flashes when the thermistor temperature is below 0°C but otherwise does not light unless the thermistor connection is broken or shorted. LED3 (red) indicates the bulk charge phase, while LED4 (orange) and LED5 (green) indicate the absorption and float phases. LED6 (green) indicates that a battery is connected, but is not an indication that charging is occurring. Practical Electronics | December | 2020 There is an option for LED3 to indicate when current is being fed to the battery during the absorption and float phases. This is useful, as it flashes whenever current is being fed to the battery. So it indicates the duty cycle of power bursts. Brief bursts indicate that the battery is close to the required voltage, while longer bursts indicate that the battery requires further charging. If this is not required, it can be disabled so that LED3 only lights during the bulk phase. The absorption LED (LED4) will never light if you set up the charger to skip this phase. Similarly, the float LED (LED5) does not light when charging LiFePO4 batteries, since that phase is not used for lithium batteries. Isolated MOSFET drive The circuit of the Charge Controller is shown in Fig.5. It uses a PIC16F88-I/P microcontroller (IC1) to monitor the battery voltage and adjust the switching of an N-channel 19 Transmitter Receiver MODULATOR A SemiconductorBased Isolation Barrier Input Signal DEMODULATOR Modulation Signal B RF OSCILLATOR Output Signal Fig. 6(a): Simplified Channel Diagram Fig 6(b): Modulation Scheme Fig.6: an excerpt from the Si8751 data sheet, showing its internal arrangement. It comprises an RF transmitter and RF receiver to transmit gate drive power and control from the input side to the output. The receiver is isolated from the transmitter by a semiconductor isolation barrier, rated at 2.5kV. When the RF transmitter is producing an RF signal, a gate-drive voltage appears at the output. When there is no RF transmission, there is no gate-drive voltage. MOSFET (Q1) to control the charging rate. Q1’s channel is connected between the incoming positive supply (drain) and the battery positive terminal (source). To switch Q1 on, its gate needs to be brought several volts higher than its source. Since the source is at the battery voltage, we need a way to generate a voltage above this. This needs to be controlled by a 0-5V control signal from microcontroller IC1. To accomplish this, we use an Si8751 isolated FET driver (IC2). It provides up to 2.5kV of isolation between its input and output, but here, 45V is sufficient. IC2 runs from the same 5V supply as microcontroller IC1, and Q1’s gate is driven from pin 8. The MOSFET source is connected to pin 5. The gate drive output at pin 8 typically charges the gate to 10.8V with respect to the source when the input at pin 3 is high (5V). The gate output is pulled down to the source voltage with a 0V input. The 10pF capacitor between drain and MCAP1 (pin 7) enables a feature of the chip to prevent a fast voltage rise at the MOSFET drain from coupling into its gate and spuriously switching it on. Internally, IC2 comprises an RF transmitter and RF receiver to send gate drive power from the input side to the isolated output. Isolation is provided by a semiconductor oxide barrier. When the transmitter is producing an RF signal, this is detected in the receiver to produce the gate drive voltage. When there is no RF transmission, there is no gate drive. See Fig.6 for details of its internal operation. The gate drive current is set by the resistor at pin 2. In combination with the MOSFET’s gate capacitance, this determines the MOSFET switch-on time. With the 100kΩ resistor we’ve used, the switch-on time is around 5ms to a gate voltage of 5V. It continues to rise to about 10V, but the MOSFET is already mostly in conduction by 5V. The 100kΩ resistance we have chosen reduces the supply current for IC2 from 13.8mA down to 1.8mA, compared to the fastest option of connecting pin 2 directly to ground, which would give a 1ms switch-on time. The 100nF capacitor across the 100kΩ resistor speeds up switch-on without increasing current consumption. The switch-off time is typically 15µs, regardless of the resistor value at pin 2. Fast switching isn’t required in this application, as we’re only switching the MOSFET on/off once every two seconds. Low current consumption is important, so that REG1’s dissipation is below 1W when charging a 24V battery. Otherwise, the regulator will run very hot and need heatsinking beyond that provided by the PCB. Switching losses increase when the switching is slow because the MOSFET’s dissipation is at a maximum when it is in partial conduction. The instantaneous losses can be high (hundreds of watts at many amps), but as they are infrequent, the average is low. Switching losses are: (switchon loss + switch-off loss) × switching frequency. So losses are directly proportional to frequency. Fig.7 is an oscilloscope screen grab showing the gate drive waveform for MOSFET Q1. The period for the gate to rise from 0V, with the MOSFET off, to fully conducting (4.5V) is 5ms. The switch-off time is relatively fast at around 35µs for the full gate-voltage excursion. Scope1: scope grab of the Charge Controller with a 2A charger and a lead-acid car battery. The yellow trace shows the charger output, the green trace the battery voltage and the blue trace the charge current. Note how the battery voltage varies with the charging current. The difference in voltage between the charger and the battery is due to the current shunt and cable losses. Scope2: the same charging scenario as Scope1 but at a much longer timebase, showing the many pulses that make up two seconds of charging. 20 Practical Electronics | December | 2020 The overall energy loss in the MOSFET (and therefore heating) is the switching losses plus the static losses. We’ve already explained that the switching losses are reasonably low. The static losses are simply the average current times the MOSFET’s on-resistance. Its on-resistance is low enough that even at 10A, the static losses are within reason. Circuit description Power for the circuit is usually obtained from the ‘dumb’ charger via reverse-polarity protection diode D1, although it can also flow from the battery via the body diode within Q1. However, the latter has no useful function and can eventually discharge the battery. We have a solution for that, which is described below. The incoming supply also passes through a 100Ω dropper resistor and either power switch (pushbutton) S1 or the contacts of RLY1, and is then filtered by a 220µF electrolytic capacitor and fed to an LM317T adjustable regulator (REG1), set to deliver a precise 5.0V. For REG1, the voltage between the OUT and ADJ terminals is a fixed reference value of typically 1.25V, but it could be between 1.2 and 1.3V. Assuming it is 1.2V, the 120Ω resistor between these pins has 10mA (1.2V ÷ 120Ω) flowing through it, which also passes through the 330Ω resistor and trimpot VR5. We need 3.8V at the ADJ terminal for a 5V output (3.8V + 1.2V), so the total resistance of VR5 and the 330Ω resistor needs to be 380Ω for the 10mA current to produce this voltage. VR5 is therefore adjusted to give 50Ω. This adjustment is provided to allow for variations in REG1’s reference voltage and the resistor values. The 5V supply feeds both IC1 and IC2. The accuracy of the 5V setting adjustment determines the precision of the battery-charge voltage settings. That is because IC1 uses the 5V supply as a voltage reference to compare the measured battery voltage against. Preventing battery discharge To switch the Charge Controller on, momentary pushbutton S1 is pressed, allowing current to flow into REG1. IC1 then switches on RLY1, shorting out S1 so that the circuit remains powered after it is released. RLY1 is controlled by digital output RA6 of IC1 (pin 15), which goes high to Scope3: we have now reduced the charging duty cycle to around 75% and the average current delivered to the battery has dropped (the reading is unrealistically low due to the timing of the pulses). Note how the battery voltage rises during the bursts, then falls a little between them, averaging lower than before. The charger output voltage rises substantially when it is not delivering current. Practical Electronics | December | 2020 Using the Charge Controller with 6V batteries The circuit as presented is suitable for use with 12V or 24V batteries and chargers, but it can easily be modified for 6V batteries and chargers with a few changes. Note that if you make these changes, you can only use the unit with a 6V charger. The changes required are: replace D1 with a 1N5819 Schottky diode, change the 100Ω 1W resistor to 10Ω 1W and change REG1 to the low-dropout version, LD1117V. ZD1 should be changed to a 15V 1W type and ZD2 replaced with a wire link. The default position for JP1 cannot be used with 6V batteries; set the adjustable cut-off voltage, float voltage and temperature compensation values to suit your particular 6V battery. drive the base of NPN transistor Q3, energising the relay coil via a 56Ω resistor. This resistor reduces the current through the relay coil, as the relay will operate down to 3.75V and so we save a little power this way. Without the resistor, the relay coil current is 28mA, and with it, it is 21mA. The other set of contacts in RLY1 make the connection between the battery and the 51kΩ and 10kΩ battery-voltage-measuring resistors. If the charger is switched off or a blackout occurs with the battery still connected, the battery powers the Charge Controller and it could become over-discharged and damaged if this continues long enough. With the charger power off, the circuit draws around 50mA from the battery. To prevent this, IC1 monitors battery voltage and when the battery voltage falls below 12.5V for a 12V battery or 25V for a 24V battery for at least two hours, the RLY1 switches off. This totally removes the load from the battery, as current can no longer flow from it into REG1 or the voltage divider. Battery voltage measurements When the Charge Controller is powered up, the 51kΩ and 10kΩ resistors allow IC1 to monitor the battery voltage at its AN3 analogue input (pin 2). The resistors reduce the battery voltage to be within its 0-5V measurement range. So, for example, if you have a 24V battery at its maximum standard charge voltage of 28.8V, the battery voltage is Scope4: now the duty cycle has been reduced to 50% and the battery voltage and average charge current have dropped a little further. 21 Making a fully self-contained charger While the emphasis in this project has been to make a dumb battery charger clever, we can already hear the question: What do you do if you don’t have a dumb battery charger? The answer to that is simple! There is absolutely nothing to stop you making one, as per Fig.1 in this article, and add it to the project. You won’t need the LED/zener indicator (the Charge Controller tells you everything you need); the thermal cutout wouldn’t do any harm, though. In fact, you could place a 12V CT transformer and a pair of diodes in a larger case and include this project to have a fully self contained, clever battery charger. If you can’t lay your hands on a 12V CT transformer, a single-ended 12V with a bridge rectifier will do the same job. Just remember that the transformer (in either case) must be a standard iron-core type (not an electronic type) rated high enough – we’d suggest 4A or 50W (did we hear someone say an old 12V downlight transformer?). And the diodes or bridge need to be pretty beefy, too – a pair of automotive diodes or a 30A bridge, for example. Make sure the mains wiring side is exemplary – in fact, all wiring must be workmanlike, properly anchored and so on. Any metal case should be properly earthed (via the power cord). So away you go . . . divided down by a factor of 6.1, giving 4.72V at pin 2 of IC1. The voltage is filtered with a 100nF capacitor to remove noise from the measurement. IC1 converts the voltage to a 10bit digital value (0-1023), which gives a 29.8mV resolution (5V × 6.1 ÷ 1023). Battery voltage measurements are made when Q1 is switched off, so voltage fluctuations due to the charging current in the leads to the battery don’t affect it. Temperature measurement An NTC thermistor is used to measure the battery temperature. One thermistor mounts on the PCB and connects to pin 1 of micro IC1 via the switched tip contact of 3.5mm jack socket CON1. When an external thermistor is connected via CON1, the internal thermistor is switched out and the external thermistor connects to pin 1 of IC1 instead. Note that the external thermistor is connected to ground via the ring connection. The sleeve is left open. This allows the metal enclosure of the Charge Controller to remain floating from the controller circuit. Scope5: the duty cycle has now been reduced to 10% but the battery is still charging (slowly), with an average terminal voltage of 13.2V. 22 In either case, the thermistor is connected in series with a 10kΩ resistor across the 5V supply. It therefore forms a voltage divider and the resulting voltage, which is related to the thermistor temperature, appears at the AN2 input (pin 1) of IC1 and is converted to an 8-bit digital value. IC1 then uses a look-up table to convert the voltage to a temperature value, as the relationship is non-linear. IC1 can sense whether the thermistor is disconnected; eg, if the wire to the external thermistor is broken. Pin 1 would then be at +5V. Similarly, if the resistor is shorted to ground, IC1 can detect this as pin 1 will be at 0V. The thermistor LED lights in either case, and charging ceases. The thermistor LED flashes when the measured temperature is 0°C or below. Charging also ceases in this case. Set-up adjustments Analogue inputs AN5, AN6, AN0 and AN1 (pins 12, 13, 17 and 18) are used to monitor the settings for charge rate percentage, cut-off voltage, float voltage and temperature compensation, as set with trimpots VR1 to VR4. Switch S2 is pressed to store the settings in IC1’s Flash. S2 is normally open, and an internal pull-up resistor within IC1 holds the RB5 input (pin 11) at 5V. When S2 is pressed, the pin 11 input is pulled low (to 0V) and this signals the program within IC1 to store the settings for VR2, VR3 and VR4 as the adjustable values for either SLA, lead-acid or lithium batteries. These values are only stored if the jumper JP1 is in the ‘adjustable’ position. Where the values are stored depends on the position of the battery chemistry selection jumper JP3. This is monitored by IC1’s RA7 digital input (pin 16). Jumper link JP1 sets whether the Charge Controller uses the standard (or default) values or the adjustable settings referred to above. JP2 selects the absorption option. If this jumper is not in the ‘absorption’ position, when charging lead-acid batteries, the charger switches to float charging as soon as bulk charging is complete. For LiFePO4 batteries, in this position, charging ceases as soon as the bulk charge is complete. If absorption charging is enabled by JP2, the absorption phase will run after the bulk charge, provided that the charging process has been going for more than one hour. At the end of the absorption phase, the unit either switches to float charging (for lead-acid) or ceases (for LiFePO4). Since the battery chemistry selection jumper (JP3) can have three possible states, including ‘open’, there is a 10nF Fig.7: this scope grab shows the voltage at the gate of Q1 for a single, short pulse. The vertical scale is 2V/div and the horizontal scale is 2.5ms/div. The MOSFET switches on at around 4-5V, so we can determine from this that the switch-on time is around 5ms, while the switch-off time is much shorter, les than 0.1ms (100µs). Practical Electronics | December | 2020 10nF TH1 A Power 1k LED1 10nF 10nF IC1 PIC16F88-I/P 100nF 100nF 100nF 1 CON1 LED2 A Thermistor 10k 10nF S2 SILICON CHIP Q2 BC337 STORE LED3 A Charge LED4 A Absorption 51k 100k TP3 TP4 10k JP1 10k  <at>25 °C 100nF 100nF 1k 2 VR4 3.3k 10k  VR3 JP3 10nF 1 LED5 1k 18V ZD1 ZD2 S1 1 18V 5V ADJUST JP2 Si8751 COMP. FLOAT 1k TP GND TP5V 330 VR2 TP1 TP2 10k 120 D3 VR1 1k + 100 F CUTOFF IC2 1k CHARGE % JP1 IN: ADJUSTABLE OUT: DEFAULT (12V only) JP2 1: STANDARD 2: ABSORPTION JP3 1: SLA, 2: Flooded LA OPEN : LiFePO4 2k F1 10A 1k + 220 F 50V Q3 BC337 10k 4004 COIL 56 14107191 REV.B C 2019 TO BATTERY + 10pF REG1 LM317T LED6 A A Float Battery Fig.8: fit the parts to the PCB as shown above and the photo below. Watch the orientation of the diodes, ICs, LEDs, trimpots and relay. Note that the LEDs should be fitted at right-angles, as shown here, to project through the side of the case. Q1 is fitted last as it’s attached to the bottom of the case before soldering its leads on the top side of the board. Jumper JP1 selects between default or adjustable charging parameters, JP2 enables or disables the absorption phase, and JP3 selects the battery chemistry. Construction The Charge Controller is built on a PCB coded 14107191, measuring 111 × 81mm and available from the PE PCB Service. This is housed in a 118 × 93 × 35mm diecast aluminium box. It’s best to start by preparing the box. This way, you can use the blank PCB as a template. First, locate the PCB in the bottom of the box with the edge closest to the LEDs against that edge of the box. Mark out the four corner mounting hole positions, then drill these holes to 3mm and deburr them. Copy the panel artwork (Fig.8) and use it as a template to drill out the holes in the front of the enclosure for the switch, 3.5mm socket and LEDs. Make sure the template is lined up with your PCB mounting location before drilling the holes. The power switch hole is 4.5mm in diameter (5mm is OK) and the thermistor socket is 6.5mm (7mm is OK). The other panel holes are 3mm. You can now start assembling the PCB. Fig.8 shows the overlay diagram, which you can use as a guide during construction. Start by fitting IC2. This is an 8-pin surface mount device that’s relatively easy to solder using a fine-tipped soldering iron. The pin 1 location is marked with a small dot on the package. Line the IC up on the PCB pads and tack-solder one of the corner pins. Check that the IC is still aligned correctly on all the pads. If not, re-heat the solder and adjust again. When aligned correctly, solder all the pins including the original tack-soldered pin. If any pins are bridged together, use flux paste and solder wick to clear the bridge. Next, insert the three M4 screws from the underside of the PCB at each of the eyelet mounting positions and secure using M4 nuts on the top of the PCB. Using a soldering iron, preheat each screw and solder it to the board. Make sure the solder adheres to each screw head. When cool, the nuts can be removed. Note that you may be able to build the unit without having to solder the screw heads if you use M4 copper crinkle Practical Electronics | December | 2020 Q1 IRF1405N (UNDER) TO CHARGER + VR5 100 D1 1 9 1 7TO 0 1 4BATTERY 1 – TO CHARGER – 4004 100 1W 12/24V Universal Battery Charge Controller Indicator LED driving Power indicator LED1 runs from the 5V supply via a 1kΩ current-limiting resistor. LED2, LED3, LED4 and LED5 are driven from the RA4, RB0, RB1 and RB2 digital outputs of IC1 (pins 3 and 6-8), via 1kΩ resistors. LED6 is the battery detection indicator and is driven via transistor Q2 via a 1kΩ resistor from the 5V supply. The base of this transistor connects to the switched side of RLY1’s second set of contacts via a 10kΩ resistor. This transistor switches on when battery voltage is present. This prevents the LED brightness from varying significantly between different battery types. D2 RLY1 4004 capacitor connected from pin 16 of IC1 to ground. IC1 can therefore briefly pull this pin high or low, then cease driving it and sample the voltage at it. If no jumper is inserted, the voltage will be as expected, but if a jumper is in place, it will prevent the capacitor from charging or discharging. washers under each screw head instead, but they are not that easy to find. Construction can now continue by installing the fixed resistors. Take care to place each resistor in its correct position. It’s best to use a multimeter to check each set of resistors before fitting them because the colour bands can be hard to read. Next, fit the optional PC stakes for the test points labelled TP GND, TP5V and TP1-TP4. They make it easier to attach clip leads during set-up. Then mount the 2-way header for JP1 and the 3-way headers for JP2 and JP3. Now install the diodes and zener diodes, with the orientations and positions shown in Fig.8. IC1’s socket can then be installed, and this must also be oriented correctly. Follow with tactile pushbutton switch 23 Fifteen holes are required in the diecast box – eight on the front panel (see below), two on the rear panel (for the cable glands) and five in the base. Four of these are for PCB mounting, with the 6.3mm pillars already shown fitted here. The last hole, just visible in the top right corner, is for mounting Q1 on its insulating washer and bush. And here’s the PCB fitted inside the case with the six LEDs just poking through. As yet, we haven’t fitted the front panel artwork (Fig.9, below). And the wiring we used here was just for testing – polarised 15A auto figure-8 should be used. S2, then jack socket CON1. Push both all the way down Then remove the board, drill the MOSFET mounting onto the PCB before soldering their pins. hole to 3mm and deburr. Also drill the cable gland holes Fit the on-board NTC thermistor and capacitors next. and check that they fit securely. Note that the electrolytic capacitors must be oriented with The MOSFET is secured with a 10mm M3 machine screw the polarity shown. and nut. If you find it awkward to secure it, the screw can In each case, the longer lead is positive, and the stripe be fed in from the top instead. on the can indicates the negative lead. Install transistors Q1’s tab must be isolated from the case by an insulating Q2 and Q3, then trimpots VR1-VR5, taking care to fit the washer and mounting bush. For details, see Fig.10. Now 100Ω trimpot for VR5. check that the tab of Q1 is insulated from the metal box by Mount REG1 on the top side of the PCB, with its leads measuring the resistance between the two with a multimebent down to insert into its pads. Secure the regulator tab ter. The reading should be high, above 1MΩ. to the PCB with a 10mm M3 screw and nut before solderThe box is isolated from the electrical connections so ing and trimming the leads. that accidental contact of the box to a battery terminal will Follow by fitting RLY1, ensuring that its striped (pin 1) not cause a short circuit. The PCB can now be mounted end faces to the right as shown. inside the box using the remaining M3 screws in from the Fuse F1 comprises the two fuse clips and the fuse. The base of the enclosure into the spacers. fuse clips must be oriented with the end stops facing outFit the two cable glands and feed the figure-8 cable wards so that the fuse can be clipped into place. Make sure through them, ready to attach the crimp eyelets. We used they’re sitting flat on the PCB and then attach them using the striped side of the wire as the negative and the plain a hot iron and plenty of solder. wire as the positive, but some people prefer the opposite. The LEDs are mounted at right angles to the PCB. Bend Just make sure you’re consistent. the leads 11mm back from the front lens of each, taking Attach the crimp eyelets to the wire using a suitable care to have the anode (longer lead) to the right and then crimping tool and secure them to the PCB using the M4 bend the leads downward. Insert into the PCB and solder nuts and star washers. Make sure the eyelets are not shortthem so that the bottom of the lenses are 6mm above the ing to adjacent parts, especially the fuse holder. top surface of the board. Attach the large insulated clips to the end of the battery Now mount pushbutton S1, ensuring it is pressed down leads; red for positive and black for negative. The Charge Controller leads can be terminated in bare copper, for clampfirmly onto the board before soldering its pins. Secure the tapped spacers to each corner of the PCB us- ing in your charger clips, or they can be permanently wired ing 5mm M3 screws, then mount Q1. It’s fitted to the un- to the charger. Finally, push the button cap onto S1 and fit the four stick-on rubber feet to the underside of the box. derside of the PCB and bolted to the case for heatsinking. Bend Q1’s leads up at right angles, as in Fig.10. It is placed Preparing the external thermistor so that the metal face will sit at the base of the enclosure. Note that the tab of Q1 must be at least 1mm away from The NTC thermistor on the PCB gives acceptable results the back edge of the case, to prevent the tab shorting to it. with the Charge Controller close to the battery, as the metTest that it is in the right position by temporarily mounting al box will not usually heat up too much above ambient the PCB in position and mark out the mounting hole for Q1. Also mark out Hole sizes: 4.5 3 6.5 3 3 3 3 3mm the two holes for the cable glands. Fig.9: this front panel artwork can be copied, laminated and glued to the front panel. It could also be photocopied and used as a template for drilling the front panel holes, once you have established the PCB position. You can also download the panel artwork from the December 2020 page of the PE website. 24 SILICON CHIP 12/24V Battery Charge Controller Float Charge + + Power + External Thermistor + Thermistor + + Absorption + + Battery Practical Electronics | December | 2020 LEDS INSULATING SLEEVE M3 NUT Q1 5mm LONG M3 SCREWS SILICONE INSULATING WASHER PCB 6.3mm x M3 TAPPED SPACER BOX 10mm LONG M3 SCREW 5mm LONG M3 SCREWS Fig.10: this diagram clarifies how Q1, the LEDs and the PCB itself are mounted in the case. Note the insulating washer and bush (sleeve) under the M3 nut securing Q1, which are critical, as Q1’s tab must be electrically isolated from the case. temperature. As a consequence, its temperature should be similar to the battery temperature. But a thermistor on the battery is going to give more accurate results and therefore a safer and more complete charge. To make this external thermistor, a stereo 3.5mm jack plug is soldered to one end of the twin-core cable, with the thermistor soldered across the wires at the other end. For the jack plug, connect the internal wires to the tip and ring terminals, and the wire sheath to the jack plug sleeve. The thermistor can be covered in heatshrink tubing and attached to the side of the battery using adhesive-backed hook-and-loop tape (eg, Velcro) or good quality doublesided tape for a more permanent installation. Testing Before applying power, it is vital to adjust VR5 to its lowest resistance by turning the adjusting screw 20 full turns anti-clockwise. You can check that this has been done correctly by measuring the resistance between TP GND and the 330Ω resistor at the end near the cathode of ZD1. The resistance should be near to 0Ω. This prevents REG1 from producing more than 5V when power is first applied. Now connect a multimeter set to read DC voltage between TP GND and TP5V. Connect a power supply to the charger input (eg, a 12V DC plugpack or bench supply), press and hold S1 and adjust VR5 for a 5.0V reading on the multimeter. Check that the voltage between the pin 5 and pin 14 pin on IC1’s socket is also 5V. If so, switch off power and insert IC1, taking care to orient it correctly and make sure all its pins go into the socket and don’t fold up under the IC body. Plug jumpers into JP1, JP2 and JP3 as required for your battery. Determine the maximum safe charging current Most lead-acid batteries can accept up to 30% of the quoted Ah capacity as charge current. For example, a 30Ah battery can be charged at 9A. In this case, as long as your charger is rated at no more than 9A, the 100% setting can be used. If your battery is rated in RC (reserve capacity), you will need to convert to Ah to calculate its maximum charge current. Reserve capacity indicates how many minutes a fullycharged battery can deliver 25A before the voltage drops significantly. A battery with an RC of 90 will supply 25A for 90 minutes. The amp-hour specification (Ah) refers to the total current that can be supplied over a long period, usually 20 hours. So a 100Ah battery can supply 5A for 20 hours. To convert from RC to Ah, multiply the RC value by 0.42, which is the same as multiplying by 25A to get the capacity in amp-minutes, then dividing by 60 to convert from minutes to hours. In practice, because the RC capacity specification uses 25A, the conversion from RC to Ah often gives a lower Ah value than the battery’s actual capacity. This is because the Practical Electronics | December | 2020 Parts list – Clever Charger 1 double-sided PCB, code 14107191, 111 × 81mm 1 diecast aluminium box, 119 × 94 × 34mm [eg, Jaycar HB5067] 1 2A DPDT 5V coil telecom relay (RLY1) [eg, Altronics S4128B] 1 PCB-mount SPDT momentary pubutton switch (S1) [Jaycar SP0380, Altronics S1498] 1 pushbutton switch cap for S1 [Altronics S1482, Jaycar SP0596] 1 SPST micro tactile switch with 0.7mm actuator (S2) [Jaycar SP0600, Altronics S1122] 1 PCB-mount 3.5mm stereo switched socket (CON1) [Altronics P0092, Jaycar PS0133] 2 PCB-mount M205 fuse clips (F1) 1 10A M205 fuse (F1) 2 NTC thermistors (10kΩ at 25°C) (TH1 and external thermistor) 1 2-way header with 2.54mm spacing (JP1) 2 3-way headers with 2.54mm spacing (JP2,JP3) 3 jumper plugs/shorting blocks (JP1-JP3) 1 18-pin DIL IC socket (for IC1) 1 3.5mm stereo jack plug 1 TO-220 silicone insulating washer and mounting bush (for Q1) 4 6.3mm-long M3 tapped spacers 3 M4 × 10mm machine screws 3 M4 star washers 3 M4 hex nuts 2 M3 × 10mm machine screws 8 M3 × 5mm machine screws 2 M3 hex nuts 4 insulated crimp eyelets (wire size 4mm, eyelet for M4 screw) 2 cable glands for 4-8mm diameter cable 1 2m length of 15A figure-8 automotive cable 1 1m length of twin-core shielded cable (for thermistor) 1 20mm length of 6mm diameter heatshrink tubing 2 large insulated battery terminal alligator clips (red and black) 6 PC stakes (optional) 4 small adhesive rubber feet Semiconductors 1 PIC16F88-I/P micro programmed with 1410719A.HEX (IC1) 1 Si8751AB-IS isolated FET driver (IC2) (mouser.co.uk) 1 LM317T 1.5A adjustable positive regulator (REG1) 1 IRF1405N N-channel MOSFET (Q1) 2 BC337 NPN transistors (Q2,Q3) 3 green 3mm LEDs (LED1,LED5,LED6) 2 orange 3mm LEDs (LED2,LED4) 1 red 3mm LED (LED3) 2 18V 1W zener diodes (ZD1,ZD2) 3 1N4004 1A diodes (D1-D3) Capacitors 1 220µF 50V PC electrolytic 1 100µF 16V PC electrolytic 5 100nF MKT polyester 5 10nF MKT polyester 1 10pF ceramic Resistors (all 0.25W, 1% metal film unless otherwise stated) 1 100kΩ 1 51kΩ 3 10kΩ 1 3.3kΩ 1 2kΩ 7 1kΩ 1 330Ω 1 120Ω 1 100Ω 1W, 5% 1 56Ω 4 10kΩ multi-turn top adjust trimpots, 3296W style (VR1-VR4) (code 103) 1 100Ω multi-turn top adjust trimpot, 3296W style (VR5) (code 101) Small Capacitor Codes Qty. Value µF value IEC code EIA code  5  5  1 100nF 10nF 10pF 0.1µF 0.01µF n/a 100n 10n 10p 104 103 10 25 TO BATTERY TO CHARGER Fig.11: once the PCB is mounted in the case, wire it up as shown here. Make sure that the crimp eyelets are firmly secured to the board using the specified washers and nuts. CABLE GLANDS Reproduced by arrangement with SILICON CHIP magazine 2020. www.siliconchip.com.au 18V 18V 4004 4004 + Ah capacity usually requires much less current from the battery, over a longer period. Setting the charge current For most large batteries, you would set the charge rate to 100%. To do this, adjust VR1 to get a reading of at least 1V at TP1 relative to TP GND. You can use the 100% setting for all batteries that can accept the full charge rate from your charger. If you need a lower current than your charger would normally supply, as explained above, adjust VR1 to reduce the maximum charge rate. This still applies the full current from the charger to the battery but in bursts. For example, when the charge percentage is set at 50%, the charge will be bursts of full current for 50% of the time. This would be suitable, for example, with a charger that is rated at 4A and a battery that can only accept a 2A charge current. Divide the desired charge rate percentage by 100 and adjust VR1 to get this voltage at TP1. So for our 50% example, you would adjust for 0.5V at TP1. Note that when charging a 12V battery that initially has less than 10.5V across its terminals, or a 24V battery with less than 21V, the actual charge rate will be 1/10th of that set. So for example, if you have set the charge rate to 100%, it will be charged with a burst for 200ms every two seconds. During this process, the Charge, Absorption and Float LEDs flash. Once the voltage comes back up into the normal range, full-rate charging will start. Current limiting Very small batteries may not tolerate these high-current bursts, even if they are limited in time. In this case, you could add a series power resistor between the Charge Controller and your battery. 26 For example, when using a 12V battery and with a charger that typically provides up to 17V peak, there will be 14107191 5V peak across the resistor. So the resisREV.B C 2019 tor value required is 5V divided by the peak current that the battery can tolerate. If the peak current is 1A, then the resistance can be 5Ω (eg, one 4.7Ω re1 sistor or two 10Ω resistors in parallel). Its wattage rating will need to be 5V squared (25) divided by 5Ω. That gives us a 5W dissipation, so to be safe, you would use a 4.7Ω 10W resistor, or two 10Ω 5W resistors in parallel. This is a conservative figure since 5W is the peak power, not necessarily the average power. The actual RMS voltage across the resistance will be around 30% lower than this, so the dissipation will be around 50% lower. Therefore, you could probably get away with a 5W resistor. As mentioned, the charge LED can be set to flash when current is applied during the absorption and float phases. This indicates the duty cycle used to charge the battery. If the LED is off, then the battery is over the required voltage for absorption or float. If the LED is not lit very often, then the battery is at the required voltage. If the LED is lit continuously, then the battery voltage is still being brought up. SILICON CHIP + 4004 COIL 19170141 LED option setting The flashing LED option is on initially. If you do not require the charge LED to show during these phases, you can disable this. Switching off power and holding S2 while the power is re-applied using S1 will disable this feature. The change is acknowledged by a minimum of two fast (two per second) flashes of the Charge LED. The acknowledgement flashing continues until S2 is released. You can re-enable the feature by holding S2 again at power up. Setting the parameters Most battery manufacturers will specify the required cutoff voltage (also called the cyclic voltage) for a given battery. For lead-acid types, the manufacturer will typically also specify the float voltage (also called the trickle voltage) and the temperature compensation coefficient. Note that the cut-off and float voltages must be the values specified at 20°C. The temperature compensation required by manufacturers is usually shown as a graph of voltage versus temperature. You can convert this to mV/°C by taking the difference between the voltages at two different temperatures and divide by the temperature difference. For example, a battery graph may show the cut-off or cyclic voltage at 0°C to be 14.9V. At 40°C, it may be 14.2V. So (14.2V – 14.9V) ÷ 40°C = –700mV ÷ 40°C = –17.5mV/°C. Where the float temperature compensation is different from the cyclic temperature compensation, a compromise between the two values will have to be made. Practical Electronics | December | 2020 Note that you can do this calculation over a smaller temperature range if that is consistent with the temperatures under which you expect to be charging the battery, eg, 10-35°C if you live in coastal Sydney, but different in the UK! To set the adjustable parameters, apply power to the Charge Controller via a battery or charger and select the battery type with JP3. Then connect a multimeter between TP2 and TP GND and adjust for one-tenth of the required cut-off voltage using VR2. So 1V at TP2 represents a 10V cut-off, 1.44V sets it to 14.4V, and so on. Now monitor the voltage at TP3 and adjust VR3 for the required float voltage with the same 10:1 ratio. For the temperature compensation, monitor TP4 and adjust VR4 for the required compensation, with 1V representing –10mV/°C. So 5V represents –50mV/°C and 2V represents –20mV/°C, and so on. Once you’ve adjusted all these, make sure JP1 is inserted and then press S2 to store the values. The Thermistor, Charge and Float LEDs will all flash twice to acknowledge that these values have been stored successfully for lead-acid batteries. If adjusting the thresholds for LiFePO4 batteries, just the charge LED and absorption LED will flash. You can store the parameters for each battery type by changing the settings for JP3 and readjusting the trimpots, then store the values again using switch S2. Adjusting the trimpots without pressing S2 has no effect. The adjustment of VR1, for the charge rate, is different. This has an immediate effect. You will have to re-adjust it each time you switch to charging a different battery that needs a different charge rate than the last one. To round out our description of this project, we should also mention its possible shortcomings. These do not matter in most cases, but may be significant in specific charging applications. (1) Pulsed operation The pulsed charging current can cause extra heating within the battery as losses are proportional to the square of the current. For example, when charging at an average of 1A from a 4A charger, a 25% duty cycle is used. This averages to 1A, however, the losses are equivalent to charging at 4A2 × 25% = 4 times that of charging at 1A continuously. (2) Absorption and float charge We pulse the charge current, therefore the battery voltage fluctuates during charging. We measure the battery voltage just after the charge pulse finishes. Compared to a charger that has continuous charging at a lower current, the battery voltage may be maintained at a different value. (3) Charge indication As the battery supplies the circuit power via Q1’s body diode, it can appear that charging is taking place even when the charger is not connected or powered. It is important to check that the charger is connected and is switched on when you start charging. (4) Battery discharge If the ‘dumb’ charger is switched off with the battery connected, the battery will eventually discharge due to the 50mA load of the Charge Controller. This is prevented using a relay to switch off the power to the charge controller if the battery voltage drops too low, but if this happens, you will have to recharge the battery. Order direct from Electron Publishing GET T LATES HE T COP Y OF TEACH OUR -IN SE RIES A VAILA B NOW! LE Charge Controller limitations PRICE £8.99 (includes P&P to UK if ordered direct from us) EE FR -ROM CD ELECTRONICS TEACH-IN 9 £8.99 FROM THE PUBLISHERS OF GET TESTING! Electronic test equipment and measuring techniques, plus eight projects to build FREE CD-ROM TWO TEACH -INs FOR THE PRICE OF ONE • Multimeters and a multimeter checker • Oscilloscopes plus a scope calibrator • AC Millivoltmeters with a range extender • Digital measurements plus a logic probe • Frequency measurements and a signal generator • Component measurements plus a semiconductor junction tester PIC n’ Mix Including Practical Digital Signal Processing PLUS... YOUR GUIDE TO THE BBC MICROBIT Teach-In 9 Teach-In 9 – Get Testing! A LOW-COST ARM-BASED SINGLE-BOARD COMPUTER Get Testing Three Microchip PICkit 4 Debugger Guides Files for: PIC n’ Mix PLUS Teach-In 2 -Using PIC Microcontrollers. In PDF format This series of articles provides a broad-based introduction to choosing and using a wide range of test gear, how to get the best out of each item and the pitfalls to avoid. It provides hints and tips on using, and – just as importantly – interpreting the results that you get. The series deals with familiar test gear as well as equipment designed for more specialised applications. The articles have been designed to have the broadest possible appeal and are applicable to all branches of electronics. The series crosses the boundaries of analogue and digital electronics with applications that span the full range of electronics – from a single-stage transistor amplifier to the most sophisticated microcontroller system. There really is something for everyone! Each part includes a simple but useful practical test gear project that will build into a handy gadget that will either extend the features, ranges and usability of an existing item of test equipment or that will serve as a stand-alone instrument. We’ve kept the cost of these projects as low as possible, and most of them can be built for less than £10 (including components, enclosure and circuit board). © 2018 Wimborne Publishing Ltd. www.epemag.com Teach In 9 Cover.indd 1 01/08/2018 19:56 FREE COVER-MOUNTED CD-ROM On the free cover-mounted CD-ROM you will find the software for the PIC n’ Mix series of articles. Plus the full TeachIn 2 book – Using PIC Microcontrollers – A practical introduction – in PDF format. Also included are Microchip’s MPLAB ICD 4 In-Circuit Debugger User’s Guide; MPLAB PICkit 4 In-Circuit Debugger Quick Start Guide; and MPLAB PICkit4 Debugger User’s Guide. ORDER YOUR COPY TODAY JUST CALL 01202 880299 OR VISIT www.electronpublishing.com Practical Electronics | December | 2020 27