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REMOTE CONTROL RANGE EXTENDER Most remote controls use pulses of infrared light to control equipment. This usually only works reliably up to a few metres and is easily blocked by furniture, people, plants... just about anything. Convert an IR remote to use UHF instead, and it will work at much longer ranges. It will even work when something is between the remote and the device, regardless of where the remote is pointed! M ost of the time, infrared remote controls work very well. But there are times where they are woefully inadequate. This could be because there is an obstruction between the remote control and appliance to be controlled. Or the receiver on the device may be awkwardly placed, making it difficult to direct the infrared beam to it. Sometimes you might even want to use the remote control in a different room from the appliance being controlled. Or you might need to position the appliance so that the receiver is not facing where you will usually be located, such as a projector, where it will typically be behind you. Sometimes you can reflect the IR signals using the projector screen, but that doesn’t always work reliably. Regardless of why the IR signal doesn’t work well, this device is a great solution. It allows you to convert the infrared remote to transmit using UHF radio signals rather than infrared light. Another small box positioned in front of the infrared receiver on the appliance picks up these radio signals and transmits IR directly into the device’s receiver. Note that if you have more than one appliance to be controlled, you could convert all their remotes to transmit on UHF and use a single UHF-to-IR converter to relay the signals to all those devices. That’s provided the appliances are in the same vicinity, so that the light from a single transmitter can reach all their receivers. Concept Fig.1 shows the general arrangement for the Range Extender. Fig.1(a) shows how the IR-to-UHF Converter works, while Fig.1(b) shows the UHF-to-IR Converter. The IR-to-UHF Converter monitors the signal that would normally be fed to the IR LED. When a button on the remote control is pressed, it produces a ~36kHz modulated signal to drive that LED. IC1 instead demodulates that signal, and its output (waveform B) is shown in scope grabs Scope 1 and Scope 2 (which can be seen overleaf, with the other scope grabs). Fig.1(a): the Remote Control Range Extender has two parts. The first is the IR-to-UHF Converter which runs from the remote’s battery and converts its IR LED drive signal to a UHF transmission. The second is the UHF-to-IR Converter which picks up those UHF signals and drives an infrared LED with appropriate modulation to control the appliance(s). 32 Practical Electronics | January | 2023 IR-to-UHF Converter n Transmission range: 25m through one weatherboard and Gyprock wall n Signal delay: 56μs n UHF transmitter power-down period: 600ms after the last signal n Standby current: 80nA typical at 3V supply (90nA measured) n Operating current: 8mA average during transmission UHF-to-IR Converter n Valid transmission detection: requires 3ms minimum quieting period n Acknowledge LED lighting: 654ms time-out after a valid signal n Modulation frequency: 32.4kHz to 41.4kHz in 32 steps n Modulation duty cycle: 33.3% n Current consumption: close to 50mA during signal reception n IR transmission range: typically 2m to appliance receiver By John Clarke ‘Demodulation’ converts the series of brief 36kHz pulses to a signal that’s high when the pulses are present and low otherwise. When IC1 detects it is receiving a signal, it powers the UHF transmitter (IC2) and sends the demodulated signal to the UHF transmitter’s input. The result is that the UHF transmitter produces a 433.92MHz modulated signal to the transmitting antenna. This is waveform C. So overall, the original 36kHz modulated signal is converted to a 433.92MHz modulated signal for wireless transmission. The corresponding UHF-to-IR Converter has a UHF receiver (RX1) that provides the demodulated waveform, shown as waveform D. This matches the B waveform – see Scope 3. Processor IC1 on the second board then uses a new 36kHz carrier to produce a modulated waveform, waveform E, that matches the original waveform A, as shown in Scope 4 and Scope 5. This modulated signal then drives an infrared LED that sends the signal onto the appliance(s) via their onboard IR receivers. Note that 36kHz is a typical modulation frequency used in infrared remote controls. You can adjust the modulation frequency of the final infrared output to match that of the original remote control, since the remote control could use another frequency between about 32kHz and 41kHz. Overall, the original handheld remote signal is duplicated at the output of the UHF-to-IR Converter. The appliance receiving the signal is none the wiser that any processing has occurred. Previously Note that we published a similar project named Add a UHF link to a universal remote control (PE, August 2014). While that project is still valid, this one has a much smaller transmitter circuit that can be fitted into small infrared remote controls, unlike the one from 2013. This became apparent when we tried to install our earlier design inside a small remote control for an LCD projector. There just wasn’t any room for it. Subsequently, the entire IR-to-UHF circuit has been redesigned using surface mount components. Instead of using a large pre-built UHF transmitter module, we use a very small UHF transmitter IC with a few discrete components. Remote’s battery life One question that arises is what happens to the battery life of the modified remote. Will the battery be flattened in a short time when the UHF transmitter circuitry is added? We have made sure that there will be a negligible effect on battery life by keeping the circuitry in a sleep mode when the remote is not being used. A typical infrared remote control draws about 1-2μA from the battery continuously and around 10-20mA during infrared transmission. The UHF transmitter’s added power draw has almost no effect on these figures. With the IR-to-UHF Converter installed, we measured the standby Fig.1(b): the waveforms at right, both here and in Fig.1(a) opposite, show how the original IR LED drive signal is demodulated, then remodulated to 433.92MHz, then demodulated, and then finally remodulated to around 36kHz to drive the IR LED. Practical Electronics | January | 2023 33 A real soldering challenge! One of the main goals of this design was for the UHF transmitter to be tiny enough to fit inside just about any remote control case. That rules out using a pre-built UHF transmitter module, and due to the relatively high frequencies involved, the components need to be small. Very small. This project uses by far the smallest components we’ve ever specified in a design. The 68nH inductor comes in a metric 0603 SMD package (imperial 0201) – that’s 0.6 x 0.3mm! Unless you have excellent vision, it will just look like a dot to you (if you can see it at all). And the metric 1206 SMD inductors (imperial 0402) aren’t all that much bigger at 1.2 x 0.6mm. Soldering these devices is a challenge, to put it mildly. If you decide to go ahead, we suggest you purchase at least 10 of each (hey, they’re cheap!). That way, if you mangle or lose them, you can grab another one and try again. Even the larger (by comparison) devices on this board are a little tricky to solder because it’s so packed with components – again, to keep it small and also so it can transmit 434MHz signals efficiently. Besides being a useful little device to build, if you have reasonable SMD soldering skills and want to push yourself to achieve the next level of skill, assembling the transmitter module described here would be a great way to do that. current increasing by a mere 90nA (0.09μA)! The current drain when a button is pressed is essentially unaltered and possibly even a little less than before, as the remote’s IR LED is not used and replaced by UHF transmission, which is on average 8mA when active. By the way, we measured the 90nA figure by connecting a 100kW resistor in series with the device’s supply and shorting it out until it went into sleep mode. We then measured 9mV across this resistor, which equates to 90nA (9mV ÷ 100kW). 9-12V DC plugpack or USB power source should be suitable. demodulated output at pin 4. That pin goes high when a modulated signal is present and low when the modulation is absent. IC2 is a UHF transmitter that sends digital data using two different carrier wave amplitudes. This is known as Amplitude Shift Keying (or ASK). For our purposes, there is no UHF transmission when the digital signal is low (near 0V) and a 433.92MHz carrier transmission when the digital signal is high (near 3V). IC1’s demodulated signal at pin 4 is suitable for driving IC2 at its ASK input (pin 6). Note that the pin 3 output of IC1 drives the supply input for IC2, at its pin 3. This way, IC2 can be shut down when not needed, drawing no power at idle. The transmission frequency is set using a crystal oscillator that is multiplied by 32 within IC2 to produce the UHF carrier. So the 13.56MHz crystal gives a carrier at 433.92MHz. This matches the carrier frequency used in most UHF ASK transmitter/receiver modules that are available for lowpower UHF data transmission. Receiver The companion UHF-to-IR Converter is housed in a small plastic case. One end of the case has a red acknowledge LED and an IR LED to re-transmit the received UHF signal as an IR signal. There is also a 3.5mm jack socket to allow the connection of an external IR LED via a cable. This device either draws power from a 9-12V DC plugpack or from USB 5V. The circuit draws a maximum current of 50mA when transmitting, so any Circuit details Fig.2 shows the circuit of the IR-toUHF Converter that’s designed to be built into the remote control. It comprises a PIC10LF322 microcontroller (IC1), a MICRF113 UHF transmitter (IC2) and associated components. IC1 monitors the infrared LED drive signal originally used to drive the infrared LED. The handheld remote output will drive either low or high to power the LED. An open-collector driver transistor or MOSFET in the remote control IC is normally used. This output requires a pull-up resistance to turn it into a digital signal for sensing, which is supplied by a MOSFET we enable inside IC1. A 1kW pull-down resistor is shown on the circuit, but this is only required if the remote control has an open-collector (or open-drain) output that drives high to power the LED. We will describe how to check for this later. IC1 converts the LED drive modulation (typically 36kHz) into a IR-to-UHF Converter V2 Fig.2: the IR-to-UHF Converter section circuit deliberately uses few components to make the PCB as small as possible. It’s powered by the typically 3V supply of the remote control (from two 1.5V cells). IC1 demodulates the drive signal that would normally go to an infrared LED. When it detects a button press, it powers up UHF transmitter IC2 and feeds it the demodulated signal that is then radiated by the antenna at 434MHz. 34 Practical Electronics | January | 2023 Scope 1: the top yellow trace is the infrared LED drive signal from the remote control, applied to pin 1 of IC1. This is a series of 36kHz pulses. The lower blue trace shows the output of IC1 at pin 4 that drives the ASK input (pin 6) of the MICRF113 434MHz transmitter (IC2). This signal is high whenever there is a 36kHz signal at the input and low otherwise. The MICRF113 and its associated components are tiny, fitting in a much tighter space than most pre-built UHF transmitter modules that are available. The supply current for IC2’s RF output stage is via two series-connected 220nH inductors, also acting as a 440nH driver load. The following 12pF series capacitor and 68nH inductor plus the 5pF capacitor to ground act as a filter that removes second and third harmonics from the UHF signal before it passes to the antenna. We mainly use two 220nH inductors instead of one 470nH inductor because we found suitable 220nH inductors easier to source. Any inductor used in the circuit must have a self-resonance (SR) frequency above 433.92MHz; otherwise, it will not function as an inductor at that frequency. Scope 2: this is the same capture as Scope 1 except with a faster timebase, so the 36kHz modulation is visible. Note the delay of about 56μs between IC1 receiving the 36kHz pulses and producing the demodulated pulses at its output. This does not distort the signal because it is symmetrical. Power for IC2 IC2’s power rail at pin 3 is bypassed with a 1μF ceramic capacitor, while a 100nF capacitor bypasses the output stage supply. These two capacitors are essentially in parallel but are at different locations on the PCB so that the supply for each part is bypassed directly at its supply connection. We include schottky diode D2 between the ASK signal and the IC2 supply to boost the supply whenever the IC is transmitting. The pin 3 output drops in voltage when supplying current; and the current flowing from pin 4 of IC1 via diode D2 assists in maintaining a stable supply voltage for IC2. While IC2 can operate down to 1.8V, it’s best to keep its supply voltage as close as possible to the 3V from the remote battery for the best efficiency. IC1’s supply is bypassed by another 100nF ceramic capacitor. Diode D1 is included in case the cells in the remote are inserted the wrong way around, causing a reverse polarity to be applied. In this case, D1 will conduct and reduce the reverse voltage applied to IC1, preventing it from being damaged (at least in the short term). UHF-to-IR Converter The UHF signal needs to be detected and converted back to a stream of infrared pulses to control the appliance being operated. The UHF-to-IR Converter circuit is shown in Fig.3, and comprises UHF receiver RX1, a PIC12F617 microcontroller (IC1) and an infrared LED (LED1). The circuit is powered via either DC socket CON1 or micro-B USB socket CON2. The UHF receiver is powered continuously, ready to receive a transmission from the IR-to-UHF Converter in the handheld remote. Practical Electronics | January | 2023 Scope 3: the top yellow trace shows the IR drive signal from the handheld remote as in Scope 1, but the lower trace is the output from the UHF receiver in the UHF-to-IR Converter, ie, after it has passed over the wireless link. Scope 4: the top yellow trace is the infrared LED drive signal from the original infrared remote, while the lower blue trace is the IR LED drive signal in the UHF-to-IR Converter. The two waveforms are essentially the same except for the slight delay in the second trace, and the different voltage levels due to the UHF-toIR circuit being powered from 5V instead of 3V. The signal inversion is of no consequence. Scope5: a zoomed-in version of Scope 4 showing the modulation on both signals. The rise time of the original waveform at the top is slow due to the low pull-up current from pin 1 of the PIC10LF322. The lower blue trace is the IR LED drive from the UHF-to-IR Converter. The frequency has been set to about 36kHz to match the handheld remote. The top trace is inverted compared to the lower trace, as the original LED in the handheld remote was on when the output was low, whereas the IR LED in the UHF-to-IR Converter LED drive is active-high. With no signal present, the data output from the UHF receiver is just random noise with an amplitude of 5V. In this state, the receiver operates at maximum gain due to its automatic gain control (AGC). When a UHF signal is received, the AGC reduces the receiver’s sensitivity so that the detected signal is essentially noisefree. This is fed to the GP5 input (pin 2) of PIC micro IC1. To determine if a signal is valid, IC1 checks for periods where the data line from the UHF receiver is at 0V for 35 at least 3ms. This indicates that the AGC has reduced the sensitivity of the receiver and that a transmission is occurring. The data output from the UHF receiver matches that data applied to the UHF transmitter. This data signal, in part, becomes the Acknowledge waveform that drives LED2 via digital output GP0. The 1kW resistor limits the LED current to around 3mA. IC1 drives the IR LED (LED1) from its GP1 and GP2 outputs in parallel to provide sufficient current. The 220W resistor limits this current to around 18mA. The infrared LED drive signal needs to include the same or similar modulation as that used by the original remote. So when the data output from the UHF receiver goes high, the GP1 and GP2 outputs are driven with pulse-width modulated signals. The duty cycle is 33.3%, so they are high 1/3 of the time and low 2/3 of the time. The GP4 input of IC1 monitors the voltage set by trimpot VR1, connected across the 5V supply rail. Its wiper voltage is converted to a digital value within IC1, allowing the IR carrier frequency to be adjusted to match the original transmitter. The adjustment range is from 32.4kHz to 41.4kHz in 32 steps. Setting VR1 to its mid-position gives 37kHz. Usually, somewhere near the middle setting is satisfactory, but some devices might require a different carrier frequency to operate reliably. A second output is provided via a 3.5mm jack socket (CON3) for an external IR LED (if necessary). This IR LED can be mounted near the IR receiver of the appliance(s) which are being operated. Power from a 9-12V DC plugpack is fed in via diode D1, providing reverse polarity protection. A 78L05 3-terminal regulator then provides a 5V supply for RX1 and IC1. Power via the USB connector is applied to the 5V supply rail via a 4.7W resistor. This resistor prevents excess current flow between the REG1 output and the 5V from the USB should be connected. Construction The IR-to-UHF Converter PCB is coded 15109212, measures 15mm x 12mm and is available from the PE PCB Service. It has components mounted on both sides. Refer to the PCB overlay diagrams, Fig.4a and Fig.4b, to see which parts go where. Now is the time to program IC1 – the code is available for download from the January 2023 page of the PE website: https://bit.ly/pe-downloads Begin assembly by fitting the surface-mount parts on the top side of the PCB. These can be soldered using a fine-tipped soldering iron. Good close-up vision is necessary; you might need a magnifying lens or glasses to see well enough. Fine-point tweezers can help to hold the components in place. It will be easier to install the two 220nH inductors first. Solder one pad and then check alignment. Reheat the soldered pad and move the device if the inductor needs moving before soldering the second pad. Next, mount the two ICs. IC1 and IC2 are positioned so that the small pin 1 location dot aligns with that on the PCB. When the IC is held with pin 1 at lower left, the writing on the IC top face will be the right way up. IC1 will be marked LF followed by two traceability code numbers. IC2 will have ‘F_113’ etched on the top face. Orient the ICs on the PCB with the pin 1 dot at upper left. For each IC, solder one pad first and then check their alignment. Readjust the component positioning by reheating the solder joint if necessary before soldering the remaining pins. Any shorts between pins can be cleared using solder wick to draw up the excess solder (adding flux paste first will help this process). Now diode D2 can be soldered in before fitting crystal X1. Make sure D2 is oriented as shown in Fig.4(a). You can then install the remaining top-mounted components. Note that many of the capacitors and inductors in surface-mount packages are unmarked, so you will need to rely on the packaging to show what they are and their value. Mount one component at a time to avoid mixing them up. We are using capacitors and a resistor in slightly smaller M2012/0805 packages compared to the M3216/1206 packages we use elsewhere. This makes it easier to avoid accidentally making solder bridges to adjacent components when fitting them. It is also possible to lose components, so be careful and, if possible, get spares. SMD resistors and Fig.3: the UHF-to-IR Converter PCB uses a pre-built UHF receiver module (RX1) to pick up the signals from the transmitter, then microcontroller IC1 adds modulation at a frequency adjustable by VR1, and drives onboard infrared LED1 plus an external LED when plugged in via CON3. It can run directly from a 5V USB source via CON2 or 9-12V DC from barrel socket CON1, regulated to 5V by linear regulator REG1. UHF-to-IR Converter V2 36 Practical Electronics | January | 2023 capacitors are generally very cheap and sold in useful sets which are well worth investing in. Incidentally, we recommend that you mount the 68nH inductor after fitting the 12pF and 5pF capacitors; otherwise, you might accidentally desolder this inductor. Now turn your attention to the underside of the PCB. There are two 18pF capacitors, one 1kW resistor and diode D1. Take care to position the diode correctly, with the cathode stripe, as shown in Fig.4(b). Note that the resistor might not be required, so leave it off for the moment. If you want to be sure that the components have been soldered correctly, you can trace the connections to the other sections of the PCB to where there should be continuity. For example, pin 3 of IC1 should provide a low resistance reading to pin 3 of IC2. Additionally, check that there are no short circuits between component pins on the PCB that shouldn’t be connected. Pull-up or pull-down As mentioned, the handheld remote control might drive its output high or low to turn the IR LED on. The way the LED is driven determines whether you need to install the 1kW pull-down resistor. The internal pull-up within IC1 is automatically activated if the pull-down resistor is not fitted. To determine this, first you will need to open the remote control case. Some remote cases are secured using screws that are easy to spot, but they also could be hidden under the cells. Open the battery compartment and remove the cells to check for screws. Once these are out, open the case by gently working around the sides Before mounting the IR-to-UHF Converter inside a remote, you will need to check whether a pull-down resistor is needed. with a thin implement to separate the two halves. Once inside, locate the positive and negative battery terminals. To check whether the resistor is needed, it is just a matter of making some measurements with a multimeter. First, check the resistance between the battery’s positive terminal and the anode (+) of the LED. If it is low (less than 30W), you can expect that the pulldown resistor is not needed. That is because the cathode of the LED would be pulled down to power the LED. If the resistance between the cathode (–) of the LED and the negative battery terminals is low (less than 30W), that means the LED drive is active-high, so the 1kW pull-down resistor is needed. After the pull-down resistor is soldered in place (if needed), the assembled PCB can be mounted in the remote’s case. The IR LED should be removed. Wire up the supply connections: ‘+’ to the +3V on the remote, GND to the 0V terminal and IN to the LED drive pin on the remote’s IC (eg, to the pad where the LED was soldered). You might need to trace out the PCB to figure out which one to connect. Now place the PCB in a suitable spare space within the remote. Next, solder the antenna wire, and route this around the case in a position where it will not be caught when it is reassembled. Note that while we specify a 170mm length of antenna wire, the transmission range does not suffer significantly if it is shortened. We found that a 53mm length of antenna wire only reduced the range by 5m compared to the 170mm length. Finally, clip the case together and reinstall the securing screws if they were present. These two photos show the top and bottom of the IR-to-UHF PCB at approximately triple actual size. Fig.4 (right): the IR-to-UHF converter PCB is packed so it can fit inside just about any remote control case. Don’t worry too much about bridging the pins of IC1 and IC2 when soldering them as that can be fixed quite easily using solder wick and flux paste, but do be careful to orient those ICs correctly and don’t mix them up. The 68nH inductor is minuscule, so be careful not to lose it. After soldering it, check for a low resistance reading between the antenna terminal and left end of the 12pF capacitor. Practical Electronics | January | 2023 37 Parts List – Remote Control Range Extender IR-to-UHF Converter 1 double-sided PCB coded 15109212, 15mm x 12mm, from the PE PCB Service 1 13.56MHz surface-mount crystal (X1) [RS Components 171-0468] 2 220nH 500MHz inductors, M1005/0402 SMD (L1) [RS 741-3797] 1 68nH 1.2GHz inductor, M0602/0201 SMD (L2) [element14 3386563] 1 170mm length of light-duty hook-up wire (for the antenna) 1 200mm-length of red hook-up wire 1 200mm-length of green hook-up wire 1 200mm-length of blue hook-up wire Semiconductors 1 PIC10LF322-I/OT 8-bit microcontroller programmed with 1510921M.HEX, SOT-23-6 (IC1) [download from the January 2023 page of the PE website: (https://bit.ly/pe-downloads] 1 MICFR113YM6 ASK UHF transmitter chip, SOT-23-6 (IC2) [RS 177-3314P] 1 1A SMD diode, DO-214AC (D1) [SM4004 or GS1G; Altronics Y0174, Jaycar ZR1003] 1 BAT54S ➊ small signal schottky diode, SOT-23 (D2) [Altronics Y0075] ➊ BAT54, BAT54S, BAT54C, BAT54FILMY and BAT54SFIMLY are all suitable Capacitors (all SMD M2012/0805 size ceramic) 1 1μF 16V X7R (preferred) or Y5V [Altronics R8650] 2 100nF 50V X7R (preferred) or Y5V [Altronics R8638] 2 18pF 50V C0G/NP0 [Altronics R8533] 1 12pF 50V C0G/NP0 [Altronics R8527] 1 4.7pF or 5pF 50V C0G/NP0 [Altronics R8512] Resistors 1 1kW SMD M2012/0805 ⅛W (might not be required; see text) [Altronics R1220] 1 10kW to 470kW ¼W axial leaded resistor (for testing) UHF-to-IR Converter 1 double-sided PCB coded 15109211, 79 x 47mm, from the PE PCB Service 1 UB5 Jiffy box, 83 x 54 x 31mm 1 lid label, 78 x 49mm 1 433.92MHz receiver module (RX1) [eg, Jaycar ZW3102, Altronics Z6905A] 1 PCB-mount barrel socket to suit plugpack (CON1) 1 micro-USB SMD Type-B USB socket (CON2) [Jaycar PS0922, Altronics P1309] 1 3.5mm PCB-mount switched jack socket (CON3) [Jaycar PS0133, Altronics P0092] 1 8-pin DIL IC socket (for IC1) 1 170mm-length of light-duty hookup wire 1 10kW miniature horizontal trimpot (VR1) Semiconductors 1 PIC12F617-I/P 8-bit microcontroller, DIP-8, programmed with 1510921A.hex (IC1) [download from the January 2023 page of the PE website: (https://bit.ly/pe-downloads] 1 78L05 5V 100mA linear regulator, TO-92 (REG1) 1 3mm infrared LED (LED1) 1 3mm red LED (LED2) 1 1N4004 400V 1A diode (D1) Capacitors 2 100μF 16V PC electrolytic 1 100nF 63V MKT polyester Resistors (all ¼W 1% thin film axial) 2 1kW 2 220W 1 4.7W Optional parts for extended IR transmitter lead 1 3.5mm mono jack plug 1 1m length of single-core screened cable 1 3mm infrared LED 1 100mm length of 3mm diameter heatshrink tubing UHF-to-IR Converter assembly The companion UHF-to-IR Converter is built on a double-sided PCB coded 38 151009211 that measures 79 x 47mm and is available from the PE PCB Service. This clips neatly into an 83 x 54 x 31mm UB5 plastic utility box. A 78 x 49mm lid panel label can be attached to this. Now is the time to program this IC1 – the code is available for download from the January 2023 page of the PE website: https://bit.ly/pe-downloads Fig.5 shows the parts layout for this board. Start with the micro USB socket, which is surface-mounted. Align the solder pads with the leads on the connector and solder one of the mounting tabs to the PCB. Re-check the alignment of the small signal pins before soldering the signal pins and then the remaining tabs. The solder on the mounting tab can be remelted, and the connector realigned if it is not correct. Check the signal pins for solder bridges; if you find any, clear them using solder wick. Make sure the pins are still soldered to the PCB. Now fit the resistors. The resistor colour codes can be used as a guide to their values but checking the resistances with a multimeter is always a good idea. Next, mount diode D1, ensuring it is correctly oriented. The capacitors can go in next; only the two 100μF electrolytics are polarised. As well as ensuring their longer leads go to the pads marked with ‘+’ symbols, they must be bent over to clear the lid when the PCB is mounted in its case. REG1 can then be mounted, followed by the DC socket (CON1), the 3.5mm jack socket (CON2) and trimpot VR1 (set it mid-way now). Next, fit the UHF receiver (RX1), making sure it goes in the right way around. Installing the LEDs LED1 must be mounted at full lead length (25mm) so that later it can be bent over and its lens pushed through a hole in the side of the box (above the 3.5mm socket). LED2 is mounted with the top of its lens 20mm above the PCB surface. Make sure the LEDs are oriented correctly, with their anode (longer) leads going to the pads marked ‘A’. Now solder in an 8-pin DIL socket for IC1, but do not plug the PIC micro in at this stage. That step comes later after the power supply has been tested. Complete the PCB assembly by fitting the 170mm-long antenna wire made from insulated hookup wire. Final assembly The PCB simply clips into the integral ribs of the UB5 case. Before doing this, you need to drill holes in the case ends for the USB socket, the DC socket, the 3.5mm socket and the two LEDs. The drilling diagrams are shown in Fig.6. Practical Electronics | January | 2023 ► ► The IR LED in the remote is replaced with our IR-to-UHF PCB. This PCB can then be covered with heatshrink and placed in the remote’s housing. The DC socket hole can be drilled first. This is positioned 6.5mm down from the top lip of the base at the lefthand end. Start this hole using a small pilot drill, then carefully enlarge it to 6.5mm using a tapered reamer. The 3.5mm socket hole is centred along the horizontal axis at the other end of the case, 10.5mm down from the lip. Again, use a pilot drill to start it, then enlarge it to 6.5mm. The hole for LED1 can then be drilled 3.5mm down from the lip, directly above the socket hole. Drill this hole to 3mm, then drill a similar hole for LED2 about 12mm to the right. The rectangular USB cut-out can be first drilled and then filed to shape with needle files. Now clip the PCB into the slots in the side ribs of the box (push the 3.5mm jack socket into its hole first). Once it’s in place, bend the two LEDs over and push them through their respective holes in the adjacent end. Secure the assembly by fitting the nut to the jack socket. The lid label can be downloaded (in PDF format) from the January 2023 The UHF-to-IR PCB can be mounted inside a UB5 case and placed near the receiving device. You will need to drill holes in the UB5 case for the sockets and LEDs, as shown in Fig.6. page of the PE website: (https://bit.ly/ pe-downloads) printed onto a suitable label and affixed to the lid. The four corner holes for the case screws can be cut out using a sharp hobby knife. Making an extension cable Depending on how your gear is arranged, you may want to make up a cable with a 3.5mm jack plug at one end and an external IR LED at the other. Fig.7 shows the details. You will need to use a suitable length of single-core shielded cable, while the LED leads should be insulated from each other using heatshrink tubing. The front panel label for the Remote Control Range Extender can be downloaded as a 1-1 scale PDF from the January 2023 page of the PE website: (https://bit. ly/pe-downloads). Fig.5: the assembly of this board is straightforward as the components are much larger than on the other board. Watch the orientations of the UHF receiver, IC1 and diode D1. Practical Electronics | January | 2023 39 Fig.6: shown here are the holes that need to be drilled or cut in the UB5 Jiffy box. The hole for the jack socket in the right-hand end of the box can be left out if you aren’t using the IR extension lead, and similarly, you only need to make one hole in the left-hand end, depending on whether you will be using the USB or barrel socket to supply power. Fig.7: if you need to mount the IR LED away from the receiver unit (eg, mounting it directly in front of the appliance’s receiver), you can make up an extension cable as shown here. It plugs directly into the socket on the receiver. ► Testing First, check that IC1 has not been installed. Apply power and check there is 5V between pins 1 and 8 of the IC socket. If not, verify the supply polarity and ensure that D1 and REG1 are correctly oriented. If you measure 5V, switch off and install IC1 with its notched end towards the adjacent 100nF capacitor. Now reapply power and check that the red acknowledge LED flashes when the remote control buttons are pressed. Next, test the appliance. The UHFto-IR Converter needs to have its IR LED pointing towards the appliance at a range of about 1m. If it doesn’t work, adjust VR1 as you operate the remote control until the appliance responds. Usually, setting VR1 mid-way (corresponding to a carrier frequency of around 37kHz) will be suitable. Once it’s operating correctly, try using the remote to control the appliance from another room. You should get a free-air range of 20-25m, but the range will be less than this inside a house, depending on any obstacles (walls, doors, furniture and so on) between the remote and the UHFto-IR Converter. ► Use a length of larger diameter heatshrink tubing to cover the end of the cable, including both LED leads and part of the lens, as shown below. Reproduced by arrangement with SILICON CHIP magazine 2022. www.siliconchip.com.au An extension cable can be made and attached to the UHFto-IR Converter via the 3.5mm jack socket (CON3); Fig.7 has the details for how to design this cable. 40 Practical Electronics | January | 2023