Fullscreen HTML5Med Res (??MB)HTML4

Fit this oil change timer to your car Can’t remember when you last changed your car’s oil? Build this Oil Change Timer & you won’t need to rely on your memory. It beeps a buzzer & flashes a LED after the engine has run for a preset number of hours. By DARREN YATES Keeping your car running in tip-top condition is something that everyone sees as an obvious necessity. However, it’s surprising to think how little time we spend making sure of that fact. Keeping an eye on the oil and water levels is something everyone is used to doing. And if you own a VW Beetle, it’s even easier – scrub one radiator. 72  Silicon Chip But how often do you think of changing the oil? Do you change it every six months or after a set number of kilometres? Or are you like most people and only think about it when the car is put in for other service work? Regular oil changes at the recommended service intervals are vital if engine wear is to be kept to a minimum. In fact, most car manufacturers recommend that the oil be changed every 6000-8000kms (or 5000 miles for us Beetle owners). However, depending on how the car is used, that 8000kms could be chalked up in a couple of months or it may take all year. If you don’t keep track of the kilometres, you have to rely on the 6-month rule and this is only a rough guide at best. So just how do you keep track of the oil change intervals? If you have your oil changed at a garage, a windscreen sticker will serve as the reminder although that’s easily ignored. This electronic reminder is more insistent. It flashes a LED and sounds an (optional) buzzer after the engine has run for a set number of hours. When you think about it, changing D2 1N4004 +5V 0.1 D4 1N4004 RESET S5 10k 3V BACK-UP 0.1 D1 D1 1N914 1N914 11 10M 16 IC1 4060 Q14 Q14 10 3 12 11 16 RST IC3 Q8 13 4040 4 10 Q7 CLK 2 Q6 3 Q5 +16384 +16384 4.7k X1 32.768kHz 39pF 100k 100k 11 RST IC2 4020 3 10 CLK Q14 Q14 16 8 8 E +12V FROM IGNITION SWITCH GND C IN OUT A S3 D7 S1 D8 4x1N914 D9 1N4004 F1 250mA IN 22 25VW K VIEWED FROM BELOW D6 D3 1N914 CHASSIS ZD1 18V 1W REG1 78L05 GND PIEZO BUZZER 1k S2 8 39pF B 10k D5 S4 CHANGE OIL LED1 A  10k B 10k OUT S6 K C Q1 BC548 E +5V 10 16VW OIL CHANGE TIMER Fig.1: the circuit is based on three low-cost CMOS counter ICs (IC1-3). IC1 & IC2 both divide the 32.768kHz clock frequency by 214, while IC3 provides four division ratios ranging from 25 to 28 at its Q5-Q8 outputs. These outputs are then selected by DIP switches S1-S4 to obtain the required timing period. S1 S2 S3 S4 Timer Period 0 0 0 0 Test 1 0 0 0 36 0 1 0 0 73 1 1 0 0 109 0 0 1 0 146 1 0 1 0 182 0 1 1 0 218 1 1 1 0 255 0 0 0 1 291 1 0 0 1 328 Circuit diagram 0 1 0 1 364 Fig.1 shows the circuit diagram for the Oil Change Timer. It uses three low-cost CMOS ICs to do the timing and a single transistor to beep the piezo buzzer and flash the LED. 1 1 0 1 401 0 0 1 1 437 1 0 1 1 473 0 1 1 1 510 coupled to the clock input of IC2, a 4020 14-bit counter IC. The difference between the 4020 and 4060 is that the 4020 doesn’t have an inbuilt oscillator. This IC further divides the frequency by 214, so that the output at its pin 3 is now just 0.00012Hz. This is equivalent to a period of 8192 seconds, or just under 2.3 hours. The output at pin 3 of IC2 then couples into divider stage IC3 which is a 4040 12-stage binary counter. We don’t need all of the stages of division here and only use the Q5-Q8 outputs. These outputs are fed via a 4-way DIP switch to diodes D8-D5 which, together with D3, form a simple but effective 5-input AND gate. D3 is driven directly by the 2Hz signal from IC1. The timing period is set by the DIP switches – see Table 1. Normally, one or more of these DIP switches is closed and so Q1’s base is pulled low by the corresponding outputs of IC3. This means that Q1, LED 1 and the buzzer are all off. At the end of the timing period, the relevant Q outputs of IC3 go high and so their corresponding diodes are now reverse biased. Q1’s base is now alternately pulled high and low at a 2Hz rate due to a 10kΩ pullup resistor and the clock signal driving D3. Thus, Q1 pulses on and off at a 2Hz rate to flash the LED and beep the buzzer. Switch S6 allows the buzzer to be 1 1 1 1 546 February 1995  73 your engine oil after a set number of hours makes a lot of sense. For example, if you spend a lot of your time travelling in the city, your average speed will probably be about 40km/h. Multiply this by 200 hours and you have your 8000kms. On the other hand, if you do a lot of highway driving, then you’ll clock up the kilometres in much less time. That’s why we’ve designed the unit so that you can choose from a number of presettable times from 36 to 546 hours (see Table 1). You should be able to find one that suits your style of driving. The Oil Change Timer uses only common ICs and components, most of which you’ll probably have lying around in your junkbox. It simply connects to your car’s ignition switch and to chassis. It then automatically starts timing whenever the engine is start­ed and backs up the accumulated time when the ignition is switched off using two nicad cells. Let’s look at Fig.1 more closely. IC1 is a 4060 14-bit binary counter with its own inbuilt oscillator. The crystal network on pins 10 and 11 ensures that its frequency is 32.768kHz. IC1 divides this frequency down by 16,384 (214) so that it is just 2Hz at the Q14 output (pin 3). This output from pin 3 is then Table 1: DIP Switch Settings 10k 4.7k 10M 2x39pF S1 IC1 4060 0.1 S2 1 S4 D4 IC3 4040 100k IC2 4020 D2 1k 10uF S3 D3 1 PIEZO BUZZER 1 78L05 22uF 10k 10k X1 10k D8 D7 D6 D5 D1 Q1 D9 12V FROM IGN 0.1 ZD1 S6 S5 3V BACKUP BATTERY K A LED1 Fig.2; make sure that all polarised parts are correctly oriented & note that the positive connection to the ignition switch must be run via a 250mA in-line fuse. The buzzer & switch S6 can be regarded as optional. switched out of circuit after it has sounded, to prevent annoyance. However, the LED continues to flash until the circuit is reset and this is done by pressing S5 to reset counters IC2 and IC3 (ie, when the oil is changed). If all four DIP switches are open, the 2Hz signal from IC1 is fed straight to Q1 which means that the LED flashes (and the buzzer sounds) as soon as power is applied. This is useful for checking that IC1, Q1, LED 1 and the buzzer are all operating correctly. Note also that once the LED starts flashing, it will con­tinue flashing for a period equal to the current time setting (unless the Reset switch is pressed). This means that if you set the unit to 146 hours, for example, the LED will flash for anoth­er 146 hours, or until the reset button is pressed. Power supply Power for the Oil Change Timer is derived from the ignition switch and is fed to a 78L05 3-terminal regulator via fuse F1 and reverse-polarity protection diode D9. ZD1, an 18V 1W zener diode, limits any high voltage spikes that may appear on the line due to the operation of other equipment. The 7805 regulator delivers a +5V rail and this is filtered using a 10µF electrolytic capacitor. This rail then directly powers the buzzer and LED circuitry, while the ICs are powered via isolation diode D2. D4, a 10kΩ resistor and two nicad cells form the battery backup circuit (you could also use two alkaline batteries if you prefer). When the ignition is on, D2 is forward biased and the nicad cells are trickle charged via the 10kΩ resistor. Converse­ly, when the ignition is off, D4 is forward biased and the backup battery provides power to the three ICs. Note that although the minimum operating voltage of CMOS 4000 series ICs is quoted as 3VDC, we’re only using a nominal 2.4V rail here due to the voltage drop across D4. However, we’ve found that a CMOS counter IC will remember its internal count even when the supply rail drops down to as low as 1VDC. At this voltage, you don’t get any output level and they won’t advance the count if you try to clock them. However, the applied voltage is enough to keep the internal flipflops powered up so that they remember their current settings. The other interesting point to note here is that the quies­ cent current is only about 0.2µA. As a result, the voltage devel­oped across D4 is only about 100mV and not the more normal 600mV. This low quiescent current also means that the backup battery will last for the length of its shelf life. To preserve the counts in IC2 and IC3, it is also necessary to disable IC1’s oscillator when the ignition is switched off. This is done using diode D1. When the ignition is on, D1 is reversed biased and the oscillator operates in its normal fash­ion. However, when the ignition is switched RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 4 1 1 74  Silicon Chip Value 10MΩ 5% 100kΩ 10kΩ 4.7kΩ 1kΩ 4-Band Code (1%) brown black blue gold brown black yellow brown brown black orange brown yellow violet red brown brown black red brown 5-Band Code (1%) not applicable brown black black orange brown brown black black red brown yellow violet black brown brown brown black black brown brown PARTS LIST 1 PC board, code 05102951, 102 x 56mm 1 plastic case, 130 x 68 x 41mm 1 front panel label, 127 x 63mm 1 momentary NO pushbutton switch 1 SPDT toggle switch 1 mini piezo buzzer (7.5mm pin spacing) 1 in-line fuseholder & 250mA fuse 2 AA nicad cells 1 2 x AA cell holder 1 battery snap connector 1 4-way DIP switch 1 32.768kHz watch crystal The batteries can be secured inside the case by wrapping them in foam rubber & then sandwiching them between the board & the lid when the lid is closed. The 4-way DIP switch allows 16 possible settings between 36 hours & 546 hours. In general, the lower settings will be suitable for cars, while the high settings can be used for stationary engines. Semiconductors 1 4060 14-bit counter/oscillator (IC1) 1 4020 14-bit counter (IC2) 1 4040 12-bit counter (IC3) 1 78L05 3-terminal regulator 1 BC548 NPN transistor (Q1) 1 18V 1W zener diode (ZD1) 3 1N4004 diodes (D2,D4,D9) 6 1N914 signal diodes (D1,D3,D5-D8) 1 5mm red LED (LED 1) 4 12mm x 3mm-dia. machine screws plus 8 nuts off, D1 becomes forward biased and pulls pin 11 of IC1 down to 0.6V. This stops the oscillator and so no further clock pulses are produced to clock IC2 and IC3. mounted with its ON position towards diodes D5-D8. The buzzer must be mounted with its positive terminal adjacent to the edge of the PC board –see Fig.2. Capacitors 1 22µF 25VW electrolytic 1 10µF 16VW electrolytic 2 0.1µF 63VW MKT polyester 2 39pF ceramic Construction Final assembly All the components for the Oil Change Timer are installed on a PC board measuring 102 x 57mm and coded 05102951. Before you begin construction, check your etched board carefully against the published pattern to ensure that there are no shorts or breaks in the tracks. If you find any, use a small artwork knife or a touch of your soldering iron where appropriate to fix the problem. Fig.2 shows the layout on the PC board. Begin by installing PC stakes at the eight external wiring points, then mount the remaining parts as shown. Leave the DIP switch and the buzzer until last and take care to ensure that the semiconductors are all correctly oriented. Note that the pins on the 4-way DIP switch can be somewhat flimsy so be careful not to break them. It should be The prototype board was housed in a small plastic case but this can be considered optional. In a practical installation, you might elect to wrap the PC board in foam and hide it behind the dashboard. That way, the LED and the two switches could all be mounted on a small satellite panel situated somewhere on the console. You could even elect to delete the buzzer and toggle switch altogether and just settle on the flashing LED to provide the oil change indication. If you do elect to mount the unit in the specified case, then proceed as follows. First, use the board as a template for marking out and drilling its mounting holes. This done secure the board in position using machine screws and nuts, with an addi­tional nut under each corner serving as a spacer. Resistors (1%, 0.25W) 1 10MΩ 5% 1 4.7kΩ 1 100kΩ 1 1kΩ 4 10kΩ Miscellaneous Light-duty hook-up wire, auto­ motive cable (for power supply connections), automotive connect­ ors, heatshrink tubing. Once the board is in position, drill a 6mm hole in the side of the case adjacent to the buzzer to allow the sound to escape. An additional hole is also required in one end of the case to accept the ignition switch leads. The front panel artwork can now be affixed to the lid and the holes drilled for the warning LED and the two switches. Complete the construction by February 1995  75 OIL CHANGE TIMER OIL WARNING RESET mounting the front panel items and running the wiring as shown in Fig.2. You can use light-duty hook-up wire for this job. Take care with the orientation of the LED; its anode lead is the longer of the two (see Fig.1). Take care also to ensure that the leads to the battery snap connector are wired with the correct polarity. This clips onto a 2-AA cell holder. The ignition leads should be run using medium-duty automotive cable. Before you screw the lid down, connect the circuit to a 12VDC source. This can be either a power supply or a 12V battery. With all of the DIP switches open, the LED and buzzer should start immediately and should pulse on and off at 0.5-second intervals. The supply voltage on pin 16 of each IC should be about 4.4V. Setting the DIP switches Assuming everything works correctly, you can set the DIP switches to give ALARM ON The 4-way DIP switch is used to set the required timing period. Refer to Table 1 for the various settings – there are 16 combinations to choose from. the required number of hours. Table 1 shows the period provided by each combination. In fact, you might want to give yourself a trial period over a few days to arrive at a reasonable average speed. This is easy to do. Just set your odo­ meter to zero and keep a record of your driving periods over the next few days. Fig.4: check your PC board against this full-size etching pattern before mounting any of the parts. 76  Silicon Chip Fig.3 (left): this full-size artwork can be used as a drilling template for the front panel. Alternatively, you can mount the board under the dashboard somewhere & simply mount the switches & the warning LED on a small panel. You can then use the odometer reading and the accumulated period to calculate your average speed. From there, you can then calculate the number of engine hours it will take to cover the required dis­tance. An example will serve to demonstrate this. Let’s say that, over several days, you cover a total distance of 400km in an accumulated time of 12 hours. In that case, your average speed will be 400/12 = 33.3km/h. If we now assume an oil change service interval of 7500km, then the approximate number of engine hours required to cover this distance will be 7500/33.3 = 225.2 hours. If we look now at Table 1, we see that 218 hours is the closest available setting. To obtain this setting, we simply leave S1 & S4 off and set S2 & S3 on. Installation The unit is relatively easy to install, since there are only two external wiring connections. One connection goes to chassis, while the other goes to the switched side of the igni­tion switch. The latter connection is best made at the fuse panel and should be run via a 250mA in-line fuse. Alternatively, you can run this lead to the ignition switch via one of the accessory fuses (eg, for the car radio). Do not leave out the fuse; it is a necessary safety precau­ tion in the event of a short inside the unit. Also, make sure that you install all wiring in a professional manner and use automotive connectors and heatshrink tubing to terminate the leads. Finally, you must press the reset button the first time the unit is powered up, to make sure that the counters start from scratch. After that, the reset button is pressed only when the engine oil is changed. For this reason, you might like to mount the reset button in some inconspicuous location, away SC from prying fingers.