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?
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.
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...
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
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:
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
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
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
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
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
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
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
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
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The
Universal Timer is available fully built and tested from the AutoSpeed Shop.
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Output
Power
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.
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.
If
you are switching on a string of low power filament lamps, a small heatsink will
be needed.
If
you’re turning on a large pump or small fan, a medium sized heatsink will
usually be needed.
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
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.
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.
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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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