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The eLabtronics Timer

Add delays and extended 'on' periods to any electric car function

by Julian Edgar

Click on pics to view larger images

At a glance...

  • DIY module
  • Adjustable time period from 1 second to 1 hour
  • High power output
  • Automatic or manual trigger
  • Automatically trigger a timed period when a sensor voltage rises or falls past a preset value
  • One-shot timed period or a delayed 'on' time
  • Special manual mode counts the number of times you press a dashboard pushbutton!
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An electronic timer sounds like a pretty ho-hum kind of module, right? But that’s only until you try to come up with solutions to problems! Like, what sort of problems then?

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OK, how about adding a delayed ‘on’ time to a press-button? That’s so when you push the button and release it, the device stays operating for a pre-set time. That could be as useful as keeping your headlights illuminated after you’ve arrived home in the dark, giving you time to walk to your door.

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Or, how about adding an automatic ‘on’ time that keeps your electric windows working for 1 minute after you’ve turned off the ignition? Many modern cars already have this feature – but if you live in a household where there are two cars (one with and one without delayed electric window operation) you’re sure to be driven nuts whenever you’re in the ‘wrong’ car. I know I am...

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Or what about a timed turbo over-boost that lets you automatically run higher than normal boost for (say) 10 seconds? You put your foot down and the boost is allowed to rise to its new level – but only for a limited period. With such a short period of over-boost, even a factory intercooler will cope and yet in passing and short-term acceleration, you’ll have plenty more performance than normal.

Each of these scenarios needs a timer with a slightly different requirement – not only in the length of the timed period but also in the way the timer is triggered. In one of the above situations the timer triggered with a button push, in another it automatically turned on when the ignition turned off, and in another it needed to be triggered when a sensor (throttle position) exceeded a certain voltage level.

As you can see, when it’s required to perform lots of real world functions, what sounds like a no-brainer – a universal timer – actually requires a pretty sophisticated design. But with the eLabtronics Timer, all the work has been done for you.

The module is available fully built and costs only AUD$59 from the AutoSpeed Shop.

Let’s take a look at using the timer.

Using the eLabtronics Timer

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The Timer is based on the eLabtronics Multi-Purpose Module (see The eLabtronics Performance Modules). It has a high current output transistor called a MOSFET, a fuse, four wiring connections, an option switch and two user-adjustable multi-turn pots.

The eLabtronics Universal Timer’s wiring connections are:

  • Power - marked on the board as ‘+’. Power is nominally 12V.

  • Ground – marked as ‘-‘. You’d normally connect this to chassis earth or the negative terminal of battery.

  • Input – marked as ‘in’.

  • Output – marked as ‘out’.

When the eLabtronics Universal Timer output MOSFET is activated, battery power is available at the output terminal. So all you need to do is to wire your load (lights, buzzers, horns, solenoid, fans, pumps, etc) between the output terminal and chassis ground.

If the load has a polarity, the positive terminal goes to the Universal Timer. (Note that as with all MOSFETs, there is a slight voltage drop across it, so a little less than full battery voltage will be available at the output at high loads.)

Well come back to wiring in a moment, but that’s a general overview – just four module connections.

Controls

  • Pots

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The two on-board pots set the period the Timer runs for. One pot sets seconds (0-60) and the other sets minutes (0-60). Because these pots are multi-turn, you can accurately set a timed period from 1 second to just over 1 hour. And everything in between.

For example, if you want the timed period to be 5 seconds, set both pots fully anticlockwise. Then rotate the ‘seconds’ pot clockwise a little and test the timed period. (It’s easy to see what the timed period is because when the timer is activated, the on-board LED flashes twice per second.)

DIP Option Switch Positions

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The real smarts in the eLabtronics Universal Timer are in the four-position DIP Option Switch. Position the board so that the terminal strip is on the right and then the following switch positions give the listed behaviour.

Mode 1

X

X

X

X





In this mode, the output is switched on for the timed period when the input signal rises above 2.6V. After the timed period has elapsed, the timer switches off – even if the input signal is still above 2.6V. This means it’s a one-shot timer – the input signal needs to fall and then rise again to re-trigger.

This is the mode that would be used to run a timed turbo over-boost. The input would be connected to the throttle position sensor and the output would run a solenoid bleed allowing higher boost. When the throttle position sensor output rises above 2.6V, the output is triggered - but it won’t let boost remain high for more than the timed period, even if your foot stays flat to the floor.

If all that sounds complex, here’s another example of this mode’s use. Just connect the input to power via a normally-open push-button. When you press the button, the timer activates for the set period and then switches off – even if you leave your finger on the button!

Mode 2

X

X

X

X

This mode is the same as the one above, except the module triggers for its timed period when the input voltage falls below 2.6V. This mode is ideal for triggering things when the ignition is switched off – simply connect an ignition-switched power supply to the input and power the timer module from an always-on power source.

For example, the module can be used to feed power to the electric windows for a minute each time the ignition is switched off. Or, you could run a turbo cooling fan for 2 minutes every time the car is turned off. (The module will trigger when the Input voltage falls to zero, as is the case when the ignition is turned off.)

Mode 3

X

X

X

X

This mode is easiest thought of as adding an extended ‘on’ time. The output switches on when the input rises above 2.6V, and then stays on for the timed period after the input drops below 2.6V.

For example, you might have a radiator fan triggered by a temp switch. You’d like the fan to say running for two minutes after the temp switch has turned off, so you use the temp switch to feed power to the input terminal of the timer. The timer’s output powers the fan. When the temp switch says ‘run that fan’ the timer will do just that. But when the temp switch says ‘stop that fan’ the timer will keep it running for the selected period.

Mode 4

X

X

X

X

This mode is the same as the one above but the timer triggers when the input falls below 2.6V and then stays on for the timed period after the input rises above 2.6V.

It’s ideal for triggering from sensors that have an output voltage that decreases when the variable (eg temp or airflow) is increasing. For example, you could use this mode to trigger an intercooler water spray, using the output of an airflow meter that falls with increasing load. At high loads the water spray pump turns on, then its stays on for the preset time after the load falls.

Mode 5

X

X

X

X

This mode is different to the others in that it is designed to be used with a normally-open pushbutton that connects the input to power. In short, it makes the module a manually-controlled timer. But there’s a trick in it – and it’s a damn’ good trick.

What the timer does is count the number of times you press the button. Let’s say you use the on-board pots to set the timer for a 1-minute period. If you press the external pushbutton once, the timer will turn on for a minute. But if you press the button twice, it will turn on for 2 minutes! And so on – the number of button presses multiplied by the timed period sets the total output time.

This is the perfect mode when you want for manual control over when the timer operates, and for how long it operates. Almost anything requiring a manually timed period can be run in this way. One example is a manually controlled intercooler spray – all you need is a pushbutton on the dash and you can give the ‘cooler a short squirt, a medium squirt or a long squirt – even with your hands back on the steering wheel.

Incidentally, you can also cancel the output at any time, just by keeping your finger on the button for a few seconds.

This mode (and mode #1) are also useful when setting the timed period. After setting the DIP switches correctly, trigger the timer by momentarily connecting the input terminal to power.

Mode Summary

OK, so let’s take a summary look at the five different timer modes.

Mode

Output

Input Trigger

Mode 1

One shot then off

Activates when input rises above 2.6V

Mode 2

One shot then off

Activates when input falls below 2.6V

Mode 3

Extended ‘on’ time

Activates when input rises above 2.6V

Mode 4

Extended ‘on’ time

Activates when input falls below 2.6V

Mode 5

One shot then off

Number of press-button pushes

Conclusion

That’s probably enough to chew on for this week – next week we’ll look in detail at a use of the Timer.

Universal Timer Specifications

Operating Power: 10 – 40 V DC

Output power: up to 10 amps continuous with appropriate heatsink, up to 15 amps short pulsed with appropriate heatsink, up to 100 amps with appropriately heatsinked external solid state relay

Timed period: User-selectable from 1 second to 61 minutes

Timed outputs: one shot, delayed ‘on’ or manual pushbutton

Timer trigger: User-selectable from rising input voltage, falling input voltage or push-button

Fuse: 15 amps

The Universal Timer is available fully built and tested from the AutoSpeed Shop.

Output Power

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The output MOSFET (transistor) on the Timer is rated to handle a continuous 10 amps – but that’s when it is fitted with a big heatsink. How hot the MOSFET (and the circuit board) get depends not only on the output current but also whether or not the output is being pulsed or held continuously on.

For short pulses, the heatsinked MOSFET will handle up to 15 amps.

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As a rule of thumb, no heat sink at all will be needed if you’re operating warning lights or LEDs – even high powered ones.

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If you are switching on a string of low power filament lamps, a small heatsink will be needed.

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If you’re turning on a large pump or small fan, a medium sized heatsink will usually be needed.

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Finally, if you’re switching loads like multiple car horns or multiple headlights, a large heatsink will be needed.

The heatsink needs to be isolated from ground and positive supplies, so either mount it so it fits inside a box (and can’t touch anything metallic!) or mount the heatsink to the MOSFET using an insulating spacer and nylon nut and bolt. In either case a smear of heatsink compound will be needed between the MOSFET and the heatsink.

Don’t forget that in most uses of the Timer, no heatsink – or only a small heatsink – will be needed.

Ultra High Currents

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But what if you want to operate really big electrical loads – like multiple radiator fans, high-powered sirens or the like? There’s no problem – you’ll just need to buy a solid state DC relay. These relays are fully electronic, so have no moving parts.

In addition to being very durable, an electronic relay can switch very large currents. When equipped with a suitable heatsink, the relay shown here can handle 100 amps continuously and cope with a very short term switch-on current gulp of 240 amps.

When using an external sold state relay, the Timer doesn’t need to use a heatsink, so packaging becomes easier – the Timer can easily fit into a box and the solid state relay can mount remotely.

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This diagram shows how the relay is wired to the module. The electronic relay is available from the AutoSpeed shop for AUD$40 – see Solid State Relay.

Note: if the load is not going to be turned on and off a lot, a conventional relay can be used.

The eLabtronics modules are engineered and manufactured by eLabtronics. The modules are based on concepts and specifications developed by Julian Edgar, with the aim being to provide cost-effective and useful modules for car modification (and also industrial and educational uses).

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