Last week in
The eLabtronics Pulser, Part
1 we introduced the eLabtronics Pulser, a cheap and easy to connect pre-built
electronic module that allows you to pulse lights, horns, pumps, etc. It’s ideal
for alarm applications, flashing high-powered LEDs and a host of
applications.
Briefly mentioned in that introductory story was
that while the Pulser is normally switched on by connecting its Input terminal
to power, the Pulser actually turns on when the voltage on the Input rises above
about 2.6V.
This seemingly minor point is very important, as
it allows the Pulser to be automatically triggered by changing light levels,
temperature or even the output of an engine management sensor.
For example, the Pulser can be configured to
automatically start flashing lights when it gets dark, pulse an intercooler
water spray (eg for 5 seconds every 15 seconds) when the intercooler gets hot or
engine load is high, or even pulse a warning lamp when the outside temp drops to
near zero (eg to warn of black ice on the road).
It can even be triggered when the
difference between two temperatures exceeds a certain amount!
Some soldering and component recognition skills
are required when configuring the Pulser for automatic switch-on, so the
electronic skills needed are a little higher than when wiring-in the Pulser for
normal manual use. However, the wiring is still very straightforward.
5V supply
To automatically trigger the Pulser on the basis
of temperature or light intensity, use is made of a regulated 5V supply sourced
from the module. This is available on the pin shown here.
Note that while a regulated 5V is available on
this pin, the amount of current that can be drawn is strictly limited. There is
sufficient current available to operate the temperature and light sensor
circuits described here, but there is not enough current available to run
other sensors (eg automotive MAP sensors). In fact, the output current rating of this source is only 2 milliamps.
Effectively, the 5V pin supplies a fixed voltage
that is them modified by the action of the specific sensor (temp or light) and
adjustment pot before being fed to the Input.
So how is the Pulser wired for auto operation?
Let’s look at temperature first.
Temperature
By using one or two low cost temperature sensors
(thermistors) and a few other components, the Pulser can be configured to switch
itself on the basis of temperature. The switching point is adjustable and a
number of different configurations can be used.
This is the approach to go for when things need to
be pulsed once the temperature rises above a certain point. One example
use is to sound an over-temp alarm – eg pulse a buzzer or light.
Here is the wiring diagram. Note that for the sake
of simplicity, the power and load connections for the Pulser are not shown here
(or in most of the wiring diagrams in this story).
However, as a special once-off, here is a full
working system, complete with ground, +12V and the load connections.
To trigger the Pulser on the basis of temperature,
the required additional components are:
The circuit is wired as shown here. Note that the
pot is shown from the front view (if you wire the pot in reverse, the adjustment
will just work in the opposite direction). You can use any type of 1 meg-ohm
pot, including a multi-turn design that will allow finer adjustment of the
temperature set-point. The thermistor and resistor have no polarity so they can
go into the circuit either way around.
In this circuit, turning the pot clockwise
increases the temp at which the Pulser turns on. With the depicted
components, the selectable temp range is from about 0 degrees C to about 100
degrees C.
This is the approach to go for when things need to
be pulsed once the temperature falls below a certain point.
For example, to be warned of the potential
presence of black ice on the road, you’d set the system to pulse a dashboard
light when the outside temp falls below about 3 degrees C.
Another way of looking at this is to say that the
output will be on when it is cold, and off when it is hot. An additional example
use is a warning light that stays on when the engine oil temp is still cold.
Place the sensor so that it can detect engine oil temp and as soon as the cold
car is started, the light will flash. Once the oil temp reaches your pre-set
value, the light will stop flashing.
The required components are again:
The circuit is wired as shown here. Note that the
pot is shown from the front view (if you wire the pot in reverse, the adjustment
will just work in the opposite direction). As before, you can use any type of 1
meg-ohm pot, including a multi-turn design. The thermistor and resistor have no
polarity so they can go into the circuit either way around.
In this circuit, turning the pot anti-clockwise
decreases the temp at which the Pulser turns on. With the depicted
components, the selectable temp range is from about 0 degrees C to about 100
degrees C.
This is the approach to go for when things need to
be pulsed once the temperature difference between two sensors
increases above a certain point.
The benefit of using two sensors is that it takes
into account different ambient temp levels that might exist. An example makes it
clearer.
Suppose you want to turn on an intercooler water
spray when the core temp exceeds 50 degrees C. Trouble is, if the intercooler is
under the bonnet, that will happen most times you’re stopped in traffic and the
day is hot! The result is an empty water tank.
Now change that set-up to using two sensors – one
positioned in the general area of the intercooler core and the other actually
buried in the fins of the intercooler core. If the spray is set to trip when the
intercooler core sensor is (say) 15 degrees C hotter than the other sensor, the
spray will come on only when the core is not working sufficiently well – in
fact, when it is working as a pre-heater! Tricky, eh?
The wiring is carried out as shown here. The
‘reference sensor’ is placed so that it will be the cooler of the two sensors.
When the ‘active sensor’ is (say) 15 degrees C higher in temp than the
reference, the Pulser will be switched on. This temp difference can be set by
the pot.
The required components are:
-
1 x 200 kilo-ohm resistor
-
2 x 100 kilo-ohm thermistors
-
1 x 500 kilo-ohm potentiometer (“pot”)
In this circuit, turning the pot clockwise
increases the temp difference at which the Pulser turns on. With the
depicted components, the selectable temp range is from about 0 degrees C to
about 100 degrees C.
Light Intensity
Wired in this form, the Pulser switches itself
on when it gets dark.
An example use is to automatically turn on an
in-cabin ‘alarm armed’ flasher LED whenever it’s dark. (If the sensor is placed
near the dashboard lights, the flashing LED will stay off until it is dark
and the dash lights are off!)
The wiring requires a Light Dependent Resistor
(LDR) with a nominal 48 – 140 kilo-ohm response and a 1 meg-ohm pot. Turning the
pot clockwise increases the level of darkness needed to trigger the Pulser.
Mounting
the Sensors
Both
the thermistors and LDR come as bare electronic components. To wire them into
place, you’ll need to do two things: solder them to extension wiring and mount
them.
Here’s
a bare thermistor
Shorten
the leads and then solder two insulted wires to the leads.
Use
insulation tape (when working with relatively low temps) or good quality
heatshrink (high temp sensing) to insulate the connections. Insulate them from each other as well as enclosing them.
The
Light Dependent Resistor (LDR) can be handled in the same way.
If
the sensor is detecting just ambient conditions (eg in-cabin temperature or
light intensity), the sensor can simply be positioned appropriately and held in
place with a cable tie. However, if the sensor is working in a much tougher
environment, use high-temp epoxy to mount the sensor in a threaded brass fitting
so that it can be securely mounted.
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Triggering from Engine Management
Sensors
The Pulser can also be triggered by engine
management sensors that output a voltage. That includes most MAP sensors, most
airflow meters, and nearly all throttle position sensors.
Typically, these sensors output a voltage of about
1-4.5V over their operating range. For example, an airflow meter might have an
output of 1.2V at idle, rising to 4.1V at full power.
The Pulser turns on when the voltage on its Input
exceeds about 2.6V. If in your application, you want the Pulser to turn on at
2.6V, you’re laughing. You just connect the Input of the Pulser to the engine
management sensor. But what if you want the Pulser to trip when the airflow
meter is at say 2.9V output?
It’s easy – and here’s how you do it. For
triggering when the output of the sensor is at more than 2.6V, a 1
meg-ohm pot is wired between the signal and ground of the sensor. The wiper
(middle terminal on most pots) is then connected to the input of the Pulser.
Adjustment of the pot sets the turn-on point of the Pulser. Simple as that!
If the voltage at which you want the Pulser to
trip is less that 2.6V, wire the 1 meg-ohm pot as shown here. Again,
adjustment of the pot sets the turn-on point of the Pulser.
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If
you’re triggering the Pulser on the basis of temperature, light intensity or the
output of an engine management sensor, you’ll need the Accessories Pack. It comprises:
1
x 1 meg-ohm pot
1
x 500 kilo-ohm pot
1
x 200 kilo-ohm resistor
2
x 100 kilo-ohm thermistors
1
light dependent resistor (LDR)
A
box is also available for the Pulser – see
Performance Modules Box - Bulkhead - Black
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Conclusion
The automatic turn-on facility of the Pulser
increases its versatility, allowing it to react to changing temperature and
light levels, and parameters sensed by the engine management system like load or
throttle position. Best of all, the extra components are cheap and the wiring
and set-up easy!
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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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