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Chapter 11 Under-bonnet intercoolers suffer from heat soak, making the use of water sprays obligatory in hi-po applications. The Auto Timer can be configured to operate a high-pressure pump with 2-second spurts every five seconds, allowing full use to be made of the evaporating water, without wastage. Versatile Auto Timer A multipurpose adjustable timer with lots of uses and external triggering. T HIS AUTO TIMER has a wide range of applications in a car. It can keep something running for a 2-minute period at the push of a button or it can cycle a device on and off. It Main Features •  Triggered on rising or falling voltage (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 at 5A •  LED indicator for timing 66 PERFORMANCE ELECTRONICS FOR CARS can be triggered when a 12V signal is applied or when it is removed. It can even pulse something for a short burst every 5 or 10 seconds. Some real life uses? Well, how many times after getting out of the car have you realised that you’ve left a window down slightly and have had to go through the process of re-inserting the key and turning on the ignition so that you can wind the power window up? With this timer, it’s easy to keep the windows working for a minute or so after you’ve turned off the ignition – enough time to take care of situations like that. How about an intercooler water spray? Factory cars fitted with an intercooler spray usually trigger it for only a short period; otherwise water tends to be wasted. With this timer you can have it squirt for three seconds every nine seconds when you’re on boost – maximising the evaporative cooling effect and minimising the water usage. Or what if you want to run a turbo cooling fan for five minutes after you switch off the car? Maybe you want to do the same with the radiator fan? Perhaps you’d like the boot light to automatically switch off after five minutes, even with the boot still open? Or be able to press a button so that the headlights stay on for 30 seconds to give you light to walk to your front door? Any of these things are possible with this timer – as well as a stack more uses. In short, it’s a fantastic building block. Construction When assembling the PC board, make sure that you insert the polarised components the right way around. siliconchip.com.au These parts include the rotary switches, diodes, IC, LED, transistors, the voltage regulator and the electrolytic capacitors. During construction, you should also look closely at the photos, overlay diagram (Fig.1) and the parts list to avoid making any mistakes. Testing The timer should be tested on the bench before being installed in a car. In addition to making sure that all the functions work, bench-testing the timer also allows you to become familiar with its operation. The first step is to connect +12V and earth connections to the timer. Also connect a floating wire to the input, allowing you to trigger the timer. That done, place the Mode and Trigger links (LK1 & LK2 respectively) in their upper positions (as viewed with the PC board orientated as in Fig.1) and remove the Multiplier link. Turn the upper 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 2 seconds. When you connect the signal input wire to +12V, the LED should light and the relay should click in. Then, 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 time duration is easily changed by altering the positions of the rotary switches. Set the upper switch to “8” and the cycling will slow to 8 seconds on, 8 seconds off. Now set the lower rotary switch to “1” while leaving the upper switch at “8”. The time period will now be 18 seconds on, 18 seconds off. Easy, huh? If you leave the rotary switches set to 18 (top one on 8 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 1.8 second on and off time. Move the Multiplier link to its bottom position and the rotary switch time will be multiplied by 10; ie, in this case giving 180 seconds (3 minutes) on and off times. As you can see, setting the timing period is easy. In summary, the upper rotary switch shows units and the lower switch shows tens. The Mulsiliconchip.com.au Fig.1: follow this parts layout diagram closely when building your Auto Timer. Just how you install the various links will depend on your application – see text and Figs.3-6. When constructed, your circuit board should look like this. When assembling the PC board, make sure that you insert the polarised components the correct way around. These parts include the rotary switches, diodes, IC, LED, transistor, voltage regulator and the electrolytic capacitors. tiplier can be set in three positions: (1) Link LK3 removed, where the time displayed on the rotary switches equals seconds; (2) Link LK3 at top position, where the time displayed on the rotary switches equals seconds divided by 10; and (3) Link LK3 at bottom position, where the time displayed on the rotary switches equals seconds multiplied by 10. Now that you know how to set the timing periods, move the Mode link (LK1) to its bottom 1-shot position. That done, remove the Multiplier link and set the rotary switches to give a 5-second timing period (bottom switch 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 PERFORMANCE ELECTRONICS FOR CARS 67 How It Works The circuit for the timer is based on IC1, a PIC16F84 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 to indicate the timing duration. The time duration is set using two 10-position BCD rotary switches that provide changes from 1-99 in steps of 1. A separate jumper connection (link LK3) selects either x 0.1, x1 or x10 multipliers of the set time duration. In the standard x1 position (LK3 open), the time duration is in seconds and the switches provide a 1-99 second timing period, selectable in 1-second steps. The 0.1 multiplier provides 0.1s to 9.9s timing periods, selectable in 0.1s steps. The x10 multiplier 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 closed for the set period after triggering. (2). The second alternating mode switches the relay on and off at the rate set by the time selection rotary switches. (3). The third mode is an optional extra on the alternating mode. The variable on/off alternating mode allows you to set the length of the on and off periods when the timer is alternating. Triggering options are a rising edge or falling edge trigger for the one-shot mode, or a low-to-high (L/H) or highto-low (H/L) signal for the alternating mode. These options are set using links LK1 and LK2. The trigger signal is applied via a 10kΩ resistor and 16V zener diode ZD1 to limit transient voltages. This effectively clamps the signal at a maximum of +16V and -0.6V above and below ground. This signal then drives transistor Q1 via another 10kΩ resistor Q1’s collector inverts the input signal and drives pin 6 of IC1 via a 10kΩ pull-up resistor and a 150Ω 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 switches S1 and 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 10kΩ pullup resistor to ensure it is high unless pulled low via S2. The switches provide a unique BCD code on these inputs for each setting and these are monitored by the program within IC1 to determine the timing period. The RA1 and RA0 inputs 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 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. Diode D2 prevents damage to Q2 from any back-EMF spikes produced when the relay coil is switched off. IC2 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. IC1 is operated at 4MHz using crystal X1. The two 22pF capacitors provide the correct loading for the crystal, so that the clock circuit starts reliably. Power Supply The PC board fits straight into a 130 x 68 x 42mm jiffy box, so when the timer is adjusted correctly, the board can be inserted into the box and tucked out of sight. 68 PERFORMANCE ELECTRONICS FOR CARS Power for the circuit is derived via the vehicle’s fusebox and is fed via diode D1 which provides reverse polarity protection. A +5V rail is then derived from an LM2940CT-5 regulator which is designed specifically for automotive applications and includes transient voltage protection. The 100µF capacitor at REG1’s input provides further transient voltage suppression. siliconchip.com.au D1 +11.4V REG1 1N4004 LM2940-5 +12V A K IN ZENER, 1N4004 +5V OUT GND 100 µF 16V 10 µF 100nF 16V 2 GND IN GND 4 10k Q1 BC337 10k K ZD1 16V 1W A RB4 B 6 RB5 RB0 RB7 1nF IC1 PIC16F84 100k RB1 RA4 RA3 16 X1 4MHz 15 OSC1 RA2 OSC2 RA1 B E SC C AUTO TIMER 10 22pF 2 11 COM 4 13 22pF Vss 5 RA0 8 7 3 9 +11.4V BCD SWITCH 0–9 (1's) 1 A 8 TP1 RB2 RB3 BC327, BC337 S1 12 C E A 1 2 3 RB6 150Ω LED K MCLR 10k OUT K MC34064 1 +5V 14 Vdd 2004 A 10k IC2 3 MC34064 LM2940CT-5 SIGNAL INPUT 10k λ LED1 D2 1N4004 S2 BCD SWITCH 0–9 (10's) 2.2k 1 2 K COM 4 K A 8 Q2 BC337 10k 2 B +5V 1 NO COM NC C NO COM NC E 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.2: a PIC microcontroller takes care of most of the circuit functions. The two BCD switches (S1 & S2) set the timing period. Worried that the turbo might cook, even after a good idle-down period? The Auto Timer can be used to run a turbo cooling fan that can stop the oil coking. Just press a button, walk away and the fan will run for a pre-determined period. siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 69 Fitting The Timer For Your Application How you fit the timer depends almost totally on what it is that you are triggering. Let’s take four basic scenarios: •  Time limiting something that would otherwise stay on forever (or until the battery went flat!) – see Fig.3 •  Starting a timing period with a pushbutton – see Fig.4 •  Auto-timed period after ignition- Fig.3: Time Limiting – want the boot light to switch off after 10 minutes, even if the boot is still open? This is how you do it for this and other similar applications. off – see Fig.5 •  Pulsing a device – see Fig.6 Suggested Uses •  Allow ignition-off items to work for a period after the key is removed •  Pulse intercooler water spray pumps •  Keep water/air intercooler pump and fan running for a period after ignition key switch-off •  Pulse horn and/or headlights for alarm indication •  Run a turbo cooling fan after shut-down Fig.4: Pushbutton Timed Period – this is when you want to start something operating at the press of a button and then keep it going for the timed period. An example is a headlights-on system that allows you time to walk to your front door before the lights go off. •  Limit boot light “on time” when boot is open •  Allow delayed headlight-on time after parking from 0.1 seconds to 990 seconds (16.5 minutes). Alternating Mode on “0” and top switch on “5”). Now when you connect the signal input wire to 12V, the timer will stay on for 5 seconds. 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 70 PERFORMANCE ELECTRONICS FOR CARS Once you’re familiar with one-shot and alternating modes, you can try out the special variable on/off alternating mode. So what’s this one then? Well, when you tested the timer in alternating mode, you would have noticed that the “on” and “off” times were of the same length. So, if you had the timer set to 5 seconds, the relay would have been on for 5 seconds, then off for 5 seconds, on for 5 seconds, off for 5 seconds, etc. Sometimes, however, you might want the “on” and “off” times to be different from one another. If you enter the variable on/off alternating mode, this timer can also do that. This mode is activated by the following procedure: (1). Set the timer to alternating mode (link LK1 in upper position). (2). Set the top rotary switch to the number 7. (3). Temporarily connect TP1 to TP GND (these are the two test pins near the top rotary switch). In this mode, the length of time the relay is closed is set by the bottom rosiliconchip.com.au +12V HEAVY DUTY RELAY CHASSIS (0V) AUTO TIMER PC BOARD RE MIT OTUA DNG +12V 901 S1 1'S ON CHASSIS (0V) 23 901 INPUT COM C 456 NI 2 1 + 1 23 78 ➡ GND 1-SHOT 456 GOING LOW NO 1 8 0ra c 5 0 s'1 CN 10k + C ON + IGNITION SWITCH S2 10'S CN 78 ➡ s' 0 1 LOAD x10 + CHASSIS (0V) Fig.5: Ignition-Off Auto Timed Period – this is one to go for if you’d like your sound system to stay working for awhile after the ignition key is out. Because the load could be quite high (ie, it could draw lots of current), a heavy-duty automotive relay has also been wired into the circuit. Note the location of link LK2 in this set-up. Parts List 1 PC board coded 05car081, 105 x 60mm 1 4MHz crystal (X1) 1 DIP18 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) 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 Semiconductors Fig.6: Pulsing A Device – used in this way, the Auto Timer can pulse a device; eg, a siren or lights. To switch big loads, use an external automotive relay (see Fig.5). tary switch and the length of time the relay is open is set by the top rotary switch. 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. There’s just one final function of the timer to check out. You’ll have noticed that the timer has been triggering when you have connected the siliconchip.com.au signal wire to +12V. You can also configure the timer to trigger when the signal drops from +12V to 0V – in other words, when the signal wire is disconnected from +12V. To do this, move the Trigger Mode link (LK2) from its upper position to its lower position and then check that the timer starts when the signal input wire is disconnected from +12V. Conclusion The cliche that the uses are limited only by your imagination really applies here. Go and find some automotive uses we haven’t even thought of! n 1 PIC16F84-04P microcontroller programmed with oneshott.hex (IC1) 1 MC34064 5V supply supervisor (IC2) 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) Capacitors 2 100µF 16V PC electrolytic 1 10µF 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) Resistors (0.25W, 1%) 1 100kΩ 7 10kΩ 1 2.2kΩ 1 150Ω PERFORMANCE ELECTRONICS FOR CARS 71