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A multi-purpose timer with external triggering and several modes of operation Design by JOHN CLARKE Special Function Timer This automatic timer has a wide range of applications whereby a timing cycle is initiated in response to a trigger signal. There are quite a few uses for it in a car or you could use it on a model railway layout, in a home security system or whatever. T HIS PROJECT WAS originally presented as a “Versatile Auto Timer” in our book, “Performance Electronics for Cars” but since it has considerably wider applications than in cars, we have decided to give it a wider audience by publishing it in SILICON CHIP with an updated microcontroller, the PIC16F628A. Since it is based on a microcontroller, it can be easily configured to give a wide range of times and triggering options. As well, it can run as a “one-shot”, giving a fixed ON time for a device after being triggered or it can cycle the device on and off repeatedly 62  Silicon Chip after being triggered. There are a number of triggering operations. For example, you could just use a pushbutton to start the timer or it might be triggered by the application or removal of more than 6V to the input. As you might imagine, there are any number of applications for this timer in a car. For example, it could run a fan for 10 minutes at the push of a button or it could run the ventilation fan for a couple of minutes every 10 minutes when the car is locked in a sunny car park. When you come back to the car, it would not be stifling inside and there would not have been too much drain on your battery. Or what if you have a model railway layout with points switching? Say you have just changed over the points and you want lights to flash and bells to sound at a road crossing for three minutes after? That’s a job for this timer. There are many others. Basically, the Special Function Timer is just a small PC board with a 12V relay on it. You can run it anywhere that 12V DC is available. Want to run it off 24V DC? Simple; just substitute a 24V relay. Want to run it at 6V? Again, it is simple; just substitute a 6V relay. siliconchip.com.au D1 * +11.4V REG1 1N4004 LM2940-5 A +12V K IN ZENER, 1N4004 +5V OUT GND 100 µF* 16V 10 µF 100nF 16V 10k A K 10k LED BC327, BC337 GND B * USE 1N5819 FOR 6V SUPPLY * 1k FOR 6V SUPPLY 4.7k FOR 24V SUPPLY * 10k SIGNAL INPUT A RB6 RB4 10k K MCLR 10k Q1 BC337 ZD1 16V 1W B 150Ω 6 RB5 RB0 RB7 1nF IC1 PIC16F628A 100k SC  2004 RB1 RA4 RA3 X1 4MHz 15 OSC1 RA2 OSC2 RA1 OUT GND RB2 RB3 16 22pF 22pF SPECIAL FUNCTION TIMER A 10 2 11 Vss 5 RA0 7 3 9 +11.4V COM 4 13 8 BCD SWITCH 0–9 (1's) 1 A 8 TP1 LM2940CT-5 IN S1 12 C E C 4 14 Vdd USE 100 µF 35V FOR 24V SUPPLY K E +5V S2 λ LED1 D2 1N4004 K BCD SWITCH 0–9 (10's) 1 K 2.2k* 2 COM 4 A 8 Q2 BC337 10k 2 B NO COM NC E +5V 1 NO COM NC C RELAY1 18 17 100 µF* 16V LK2 10k LK1 LK3 1-SH H/L x10 ALT L/H x0.1 TRIGGER MULTIPLIER (OPEN = x1) MODE Fig.1: the circuit is based on a PIC16F628A microcontroller that’s programmed to provide a timed output after being triggered. The output at pin 2 drives a double-pole relay via transistor Q2. OK, there are a couple of other component variations which might need to be made and we will detail those later in this article. Circuit description The full circuit is shown in Fig.1. As already noted, it is based on IC1, a PIC16F628A microcontroller programmed to provide a timed output after being triggered. The output drives a relay which is closed during the timing period. A LED also lights whenever the relay is activated. The relay has changeover (DPDT) contacts so that it activates or de-activates a circuit for the set time. The time duration is set using two 10-position BCD (binary coded decimal) rotary switches that provide a timing range of 1-99 seconds in steps of one second. A separate jumper connection (link LK3) selects either x 0.1, x1 or x10 multipliers of the set time siliconchip.com.au duration. In the standard x1 position (LK3 open), the time duration is in seconds, as already noted. When LK3 is in the 0.1 multiplier position, the timer provides 0.1s to 9.9s timing periods, selectable in 0.1s steps. Similarly, when LK3 is in the x10 multiplier position, it allows timing from 10s through to 990s, in steps of 10s. Three modes are available: (1). The standard one-shot mode provides a timing period where the relay is activated for the set period after triggering. (2). The alternating mode switches the relay on and off at the rate set by the time selection rotary switches. (3). The variable on/off alternating mode allows you to independently set the length of the on and off periods when the timer is alternating. The triggering options are a rising edge or falling edge trigger for the one-shot mode, or a low-to-high (L/H) or high-to-low (H/L) signal for the alternating mode. These options are set using links LK1 and LK2. The trigger signal is applied via a 10kW resistor and 16V zener diode ZD1 to limit transient voltages. This Main Features • Triggered on rising or falling voltage (user selectable) • One-shot or alternating (pulse) operation • Pulse mode can be set for variable on/off periods • Precise 0.1s to 16.5-minute timing period • Relay output with dual doublethrow contacts rated at 5A • LED indicator for timing October 2008  63 10k x10 MULTIPLIER (OPEN = x1) + 100 µF* O NNO C 10k NC CN 1 C 4 LED1 A 2.2k* COM s'PERIOD 01 SWITCHES 1nF A D2 K Q2 S2 10'S 18001150 NC CN 901 S1 1'S 23 10k LK3 COM 8 C 2 150Ω x0.1 D1: 1N4004 1 C 4 NO C ON X1 4MHz L/H H/L 1-SHOT ALT ZD1 10k 10k A 1 23 901 INPUT 100nF 22pF IC1 PIC16F628A BC337 K TP1 456 +12V DNG GND Q1 D1* NI 2 1 + GND K s'1 8 C 2 456 LM2940-5 100k 10k REG1 LK2 LK1 78 ➡ + A 78 ➡ + RE MIT OTUA TP GND 22pF 10k 10 µF 100 µF* RELAY 1 K BC337 * SEE TEXT & CIRCUIT FOR 6V & 24V OPERATION Fig.2: follow this parts layout diagram to build the Special Function Timer. Jumpers LK1-LK3 are installed to suit your application (see Fig.1 & Figs.3-6). Link LK1 sets the mode (1-shot or alternating); LK2 sets the input signal trigger sense (low to high or high to low); and LK3 sets the timing multiplier. BCD switches S1 & S2 set the timing period. Resistor Colour Codes Value 4-Band Code (1%) 5-Band Code (1%) 100kΩ 10kΩ 2.2kΩ 150Ω brown black yellow brown brown black orange brown red red red brown brown green brown brown brown black black orange brown brown black black red brown red red black brown brown brown green black black brown effectively clamps the signal at a maximum of +16V and -0.6V above and below ground. This signal then drives transistor Q1 via another 10kW resistor. Q1’s collector inverts the input signal and drives pin 6 of IC1 via a 10kW pull-up resistor and a 150W series resistor. A 1nF capacitor filters any high-frequency voltage fluctuations, while the pin 6 input of IC1 includes an internal Schmitt trigger to ensure a clean signal for measurement. Rotary BCD switches S1 & S2 are monitored by IC1’s RB1-RB7 and RA4 inputs. The RB inputs are normally held high via internal pull-up resistors within IC1, while RA4 has a 10kW pullup resistor to ensure it is high unless pulled low via S2. In operation, the switches provide a unique BCD (binary coded decimal) code on these inputs for each setting and these codes are processed by the program within IC1 to determine the timing period. The RA0 and RA1 inputs of IC1 are held either high or low via links LK1 and LK2 to select the Mode and Trigger options. The RA2 input operates slightly differently. It can be held either high or low using the x10 or x 0.1 jumper (LK3) and this level is checked by IC1. Initially, this pin is set as an output and is driven low. The pin is then set as an input and the level is checked. If the input is high, then IC1 “knows” that the x10 jumper must be in place. The pin is then set as an output and is set high. When set as an input again, the level is checked and if it is low, then the x0.1 jumper must be in place. If the level does not change in both cases, then the input must be open-circuit and the microcontroller assumes the setting is for the x1 range. The RA3 output drives transistor Q2 which in turn switches on the relay. Q2 also turns on LED1 to indicate when the relay is activated. Diode D2 prevents damage to Q2 from any backEMF spikes produced when the relay coil is switched off. IC1 is operated at 4MHz using crystal X1. The two 22pF capacitors provide the correct loading for the crystal, so that the clock starts reliably. Power supply Power for the circuit is derived via the vehicle’s fuse box if used in a car or truck and is fed via diode D1 which provides reverse polarity protection. Alternatively, the circuit may be powered from a battery or other source of DC power at 6V, 12V or 24V, depending on the relay fitted (see parts list). If the circuit is run from 6V, then D1 should be changed to a 1N5819 Schottky diode to minimise voltage Looking for real performance? • • • • Learn how engine management systems work Build projects to control nitrous, fuel injection and turbo boost systems Switch devices on and off on the basis of signal frequency, temperature and voltage From the publ ishe rs of 160 PAGES 23 CHAPTE RS Build test instruments to check fuel injector duty cycle, fuel mixtures and brake & temperature Mail order prices: Aust. $A22.50 (incl. GST & P&P); Overseas $A26.00 via airmail. Order by phoning (02) 9939 3295 & quoting your credit card number; or fax the details to (02) 9939 2648; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 64  Silicon Chip Intelligent turbo timer I SBN 09585 2294 9 78095 8 -4 TURBO BO OST & nitrous fuel con 5229 46 $19.80 (inc GST) NZ $22.00 (inc GST) trollers How engin e management works siliconchip.com.au Helping to put you in Control Control Devices New PLC With Analogs This PLC is great value. Features 9 Digital in, 10 Relay out, 8 Analog In and 2 Analog Out. Can accept quadrature encoder input and high speed counters $425+GST. This view shows the fully assembled unit, which was built from a Jaycar Auto Timer kit. Note that if your kit comes with a PIC16F628A for IC1, then IC2 is left out of circuit. Conversely, if you get the original kit with a PIC16F84 microcontroller, then IC2 must be installed. drop and reduce the possibility of regulator dropout. Conversely, if the circuit is run at 24V, the two 100mF capacitors should be rated at 35V instead of 16V. In addition, the current-limiting resistor in series with LED1 will need to be varied according to the supply voltage: 1kW at 6V, 2.2kW at 12V and 4.7kW at 24V. The +5V rail for IC1 is derived from an LM2940CT-5 regulator which is designed specifically for automotive applications and includes transient voltage protection. The 100mF capacitor at REG1’s input provides further transient voltage suppression. other suppliers will have the PC board encoded as 05110081. When assembling the PC board, make sure that you insert the polarised components the right way around. These parts include the two rotary switches, diodes, ICs, LED1, the transistors, the voltage regulator and the electrolytic capacitors. You should also carefully compare the photos with the parts layout diagram (Fig.2) to avoid making any mistakes. If you are assembling a PIC16F84 version of the circuit, make sure that you do not swap the MC34064 for one of the transistors – that could lead to smoking components! Construction Testing All of the timer components are mounted on a PC board which measures 106 x 61mm. A complete kit of parts for the 12V version of the kit is available from Jaycar Electronics (Cat. KC5379). In this case the PC board will have the code number 05car81. However, since this is the previous version of the circuit which was based on a PIC16F84, it also needs an MC34064 5V supply supervisory chip. This device performs a power-on reset for IC1 to ensure that pin 4 of IC1 is only switched high when the supply is above about 3.5V. For voltages below this, IC1 is held in the reset state. We expect that, once existing stocks are exhausted, Jaycar will upgrade their kit to use the PIC16F628A, in which case the MC34064 is simply omitted from the PC board. Kits from The timer should now be benchtested for correct operation and to configure it for your application. This will also allow you to become familiar with the way it works. First, connect +12V and 0V to the timer. Also connect a floating lead to the input, so that you can trigger the unit. Now place the Mode and Trigger links (LK1 & LK2 respectively) in their upper positions (as viewed with the PC board orientated as in Fig.2) and remove the multiplier link. Turn the upper BCD switch to “2” and set the lower switch to “0”. The timer is now configured for Alternating Mode, L/H (Low-to-High) Trigger and two seconds. When you connect the floating lead to +12V, the LED should light and the siliconchip.com.au New Logomatic Serial Data Logger Has a USB connection so it appears as a flash drive. Logged serial data is saved on micro-SD media as text files. Download to a PC over USB connection or remove microSD card and insert into a card reader. $89.95+GST Humidity Temperature Controller The N322RHT has 2 relay outputs which can be configured independently as control or alarm, either for temperature or relative humidity. A Relative Humidity and Temperature included. $195+GST USB-RS422/485 Converter Our popular isolated converter can be configured for four-wire RS422 and two-wire RS485 networks. Transmission rates to 1Mbps From $129+GST Signal Isolators and Converters TxIsoBlock and TxIsoRail are programmable isolated transmitters. Convert Pt100 and thermocouples to 4-20mA or 0-10V. TxIsoBlock is a head mount unit and TxIsoRail is a DIN rail mount unit. Non-isolated models also available From $89+GST Contact Ocean Controls Ph: 03 9782 5882 www.oceancontrols.com.au October 2008  65 +12V S1 1'S 1 8 0ra c 5 0 CN COM ON STD BOOT SWITCH C 1 23 901 NI 2 1 + NO C ON 10k DNG GND 23 901 1-SHOT INPUT S2 10'S CN s' 0 1 x10 CHASSIS (0V) + Fig.3: want to automatically switch a 12V lamp or some other load off after a preset time? This one-shot set-up will do the job. Note the position of link LK1. +12V PUSHBUTTON SWITCH CHASSIS (0V) DNG +12V INPUT S1 1'S ON C 23 901 NI 2 1 + 1 23 901 1-SHOT GND NO COM S2 10'S 1 8 0ra c 5 0 s'1 CN HIGH C ON + GOING 10k RE MIT OTUA + 78 ➡ 66  Silicon Chip s'1 78 ➡ Note: change the 2.2kW resistor in series with LED1 to 4.7kW for 24V operation or to 1kW for 6V operation. Also, change D1 to 1N5819 for 6V operation. HIGH 78 ➡ 24V & 6V Operation RE MIT OTUA + GOING + 456 Resistors (0.25W, 1%) 1 100kW 1 2.2kW 7 10kW 1 150W STD BOOT LAMP 456 Capacitors 2 100mF 16V PC electrolytic OR 2 100mF 35V PC electrolytic, for 24V operation 1 10mF 16V PC electrolytic 1 100nF MKT polyester (code 104 or 100n) 1 1nF MKT polyester (code 102 or 1n) 2 22pF ceramic (code 22 or 22p) CHASSIS (0V) 456 Semiconductors 1 PIC16F628A microcontroller programmed with 0511008A. hex (IC1) 1 LM2940T-5 low dropout regulator (REG1) 2 BC337 NPN transistors (Q1,Q2) 1 5mm red LED (LED1) 1 16V 1W zener diode (ZD1) 2 1N4004 1A diodes (D1,D2). Note: D1 should be 1N5819 for 6V operation +12V 456 1 PC board coded 05car081 or 05110081, 105 x 60mm 1 4MHz crystal (X1) 1 18-pin DIL socket for IC1 5 PC-mount 2-way screw terminals with 5mm pin spacing 2 BCD PC-mount rotary switches (S1,S2) 1 12V PC-mount DPDT 5A relay (Relay1) OR 1 6V PC-mount DPDT 5A relay (Relay1: Altronics Cat S4188C) for 6V operation OR 1 24V PC-mount DPDT 5A relay (Relay1: Altronics Cat S4195C) for 24V operation 1 70mm length of 0.8mm tinned copper wire 3 3-way headers, 2.54mm spacing 3 jumper shunts, 2.54mm spacing 2 PC stakes (for test points) +12V 78 ➡ Parts List LOAD CN s' 0 1 x1 + CHASSIS (0V) Fig.4: this is the set-up to use if you want to turn a load (eg, a lamp) on at the press of a button and then have it turn off at the end of a preset timing period. Link LK1 is again in the 1-shot position. relay should click in. Two seconds later, the LED should go out and the relay should turn off. This process should then keep repeating for as long as you have the signal wire connected to +12V. Setting the timing The rotary switches set the time duration. Set the upper switch to “7” and the cycling will slow to 7 seconds on, 7 seconds off. Now set the lower rotary switch to “1” while leaving the upper switch at “7”. The time period will now be 17 seconds on, 17 seconds off. If you leave the rotary switches set to 17 (top one on 7 and bottom one on 1) and place the multiplier link in its uppermost position, the time shown on the rotary switches will be divided by 10, giving a 1.7 second on and off time. Move the multiplier link to its bottom position and the rotary switch time will be multiplied by 10, ie, giving 170 second (2 minutes and 50 seconds) on and off times. In summary, the upper rotary switch shows units and the lower switch shows tens. The multiplier can be set in three positions: (1) Link LK3 removed, so the time dissiliconchip.com.au +12V HEAVY DUTY RELAY CHASSIS (0V) RE MIT OTUA s'1 DNG +12V CN 901 COM S1 1'S CHASSIS (0V) ON C 1 901 23 INPUT 456 NI 2 1 + 23 78 ➡ GND 1-SHOT 456 GOING LOW NO 1 8 0ra c 5 0 10k + C ON + IGNITION SWITCH S2 10'S CN LOAD 78 ➡ s' 0 1 x10 + CHASSIS (0V) Fig.5: this 1-shot set-up will continue to supply power to a load (eg, a car radio or the headlights) after the car’s ignition has been turned off. The heavy-duty relay is included to ensure reliable operation with high-current loads. Note the location of link LK2 compared to the other set-ups (ie, it’s fitted in the H/L position). +12V SWITCH CHASSIS (0V) 901 456 23 78 ➡ DNG GND +12V S1 1'S ON 23 901 INPUT COM C 456 NI 2 1 + 1 NO S2 10'S 1 8 0ra c 5 0 s'1 C ON PULSE HIGH CN +GOING 10k RE MIT OTUA + LOAD CN 78 ➡ s' 0 1 x10 + CHASSIS (0V) Fig.6: in this set-up, LK1 is in the “ALT” (or pulse) position and so the load (eg, a lamp or a siren) pulses on and off according to the period set by the BCD switches (and link LK3). The switch simply turn the circuit on or off. played on the rotary switches equals seconds; (2) Link LK3 at top position, so the time displayed on the rotary switches equals seconds divided by 10; and (3) Link LK3 at bottom position, so the time displayed on the rotary switches equals seconds multiplied by 10. Now try the one-shot mode by moving LK1 to its bottom (1-shot) position. Then remove the multiplier link and set the rotary switches to give a 5-second timing period (ie, bottom switch on “0” and top switch on “5”). Now when you connect the signal input lead to 12V, the relay will click siliconchip.com.au in for five seconds and then switch off. If you disconnect and then reconnect the signal input within the timed period, the timer will start counting again – so the timing period is from the last sensing connection. In practice, you can set the positions of the rotary switches and multiplier link to give any time period you want from 0.1 seconds to 990 seconds (16.5 minutes). Variable alternating mode Once you’re familiar with the oneshot and alternating modes, you can try out the variable on/off alternating mode. This gives you the option of different “on” and “off” times. This mode is activated as follows: (1). Set the timer to alternating mode (link LK1 in upper position). (2). Set the top rotary switch (S1) to the number 7. (3). Temporarily connect TP1 to TP GND (these are the two test pins near the top rotary switch). Note: this needs to done for a least 2s before the change occurs. In this mode, the bottom rotary switch sets the length of time the relay is closed and the top rotary switch sets the length of time the relay is open. For example, if you set the top switch to “3” and the bottom switch to “1”, with the multiplier link (LK3) removed, the relay and its accompanying LED will cycle on for 1 second, off for 3 seconds, on for 1 second, etc. If you want to change back to standard alternating mode, set S1 to the number 7 and again temporarily connect TP1 to TP GND for at least 2s. High to low triggering Up until now, you have been triggering the timer by connecting the floating lead to +12V. Now let’s configure it to trigger when the floating input lead is disconnected from +12V. To do this, move the Trigger Mode link (LK2) to its lower position (H/L) and then check that the timer starts when the floating input lead is disconSC nected from +12V. October 2008  67