The newly published book High Performance Electronics for Cars
contains a number of ‘building block’ projects. The electronic kits, which are
all available from the AutoSpeed shop or Jaycar Electronics, include a Frequency
Switch, Temperature Switch and the one covered here – a Voltage Switch.
The Simple Voltage Switch (SVS) is a brilliant device because it allows you
to trigger outcomes from any voltage outputting sensor on the car. That includes
throttle position sensors, most airflow meters, most oxygen sensors, fuel level
senders, temperature senders (both for the dashboard gauge and ECU), oil
pressure senders and others.
Don’t see any uses?
Well, whatever variable is already being sensed (whether that’s engine load,
engine temperature, oil pressure, etc) can now be used to additionally switch
something on and off. So you can trigger radiator cooling fans from the ECU or
dashboard temp sensor, turn on intercooler water sprays at high loads, switch on
intercooler fans when the engine load is very low (ie the engine is idling),
sound a low oil pressure alarm if the oil pressure drops, and so on.
Straight away, you can forget using add-on pressure switches, throttle
position micro-switches or temp switches. No more trying to fit a sensor that
was never designed to be there – you just make use of the existing factory
sensor!
The SVS uses an on-board double pole, double throw (DPDT) relay so you can
operate most devices directly from the module. The use of the DPDT relay also
allows you to operate two completely separate circuits, even letting you turn
off one device as the other turns on! And it gets even better. The switch-on
voltage is set by a multi-turn pot, allowing very fine adjustment. Furthermore,
the hysteresis (the difference between the turn-on and turn-off levels) can be
adjusted so you’ll never have a problem with on/off chattering.
Whew! You can see why – especially at a kit price of AUD$29.95 – we think
that this is a damn good thing!
The Background Story
So how did this kit come about?
The Simple Voltage Switch was developed and designed by Silicon Chip
(www.siliconchip.com.au)
electronics
magazine. The kit, along with many others, is covered in the Silicon Chip
publication, High Performance Electronics for Cars. The book is a
must-have for DIY modifiers. The kit for the Simple Voltage Switch is available
from Jaycar Electronics
(www.jaycar.com.au
)
or
through the
AutoSpeed shop.
The electronics design and development of the Simple Voltage Switch was
carried out by electronics engineer John Clarke, while I came up with the
concept and did all the on-car development. (During this period I wore a
different hat to an AutoSpeed contributor, working for Silicon Chip Publications
as a freelance contributor to High Performance Electronics for Cars.)
So by no means should the Simple Voltage Switch be seen as an
AutoSpeed-developed project, but at the same time I am happy that AutoSpeed
endorses it and promotes it. Julian Edgar
|
Making the Kit
The kit uses a screen-printed Printed Circuit Board (PCB) which shows which
components go where. This makes it easy to construct – that is, if you have
experience with making electronic kits. If you’re a beginner or don’t
particularly want to learn how to assemble kits, the SVS is available completely
built and tested from the AutoSpeed shop. However, you’ll pay quite a lot more
so keep that in mind when making your constructional decision.
Most of the construction is quite easy – the only tricky bits are the diodes
which require a magnifying glass to read their part numbers. Of course, you must
get the polarity right on the diodes, electrolytic capacitors, the IC and the
transistor. Also don’t forget when soldering the connecting terminals in place
to have their openings facing out from the centre of the board – otherwise,
getting wires into them will be tricky...
The kit can be used to sense voltages that rise to the trip-point (called
low/high, as in "low voltage to high voltage switching") or the opposite. In
most applications you’ll want low-to-high switching - for example, when the
airflow meter voltage rises to a certain level, an intercooler water spray
switches on. However, when sensing the output of a temperature sensor, it’s
likely you’ll want a high-to-low setting, as the voltage output of these sensors
usually falls with rising temp.
So it’s best to use a multimeter to measure the output of the sensor in
question so you’ll know which way to configure the kit.
Testing the Kit
Always test the kit on the bench before installing it in a car. The relevant
chapter in the book (a B&W photocopy is included with the kit) shows how to
use a 10K pot as a variable voltage source, allowing you to test the operation
of the SVS. Make sure that the when the setpoint is exceeded, the relay clicks
over and the LED comes on. Try adjusting the hysteresis (the single turn pot)
and checking that you can vary how much the signal input voltage has to drop
before the switch clicks off.
The SVS can be adjusted to operate when the input signal voltage is anywhere
in the range from 0-16V. In addition, the device uses a high input impedance so
it won’t load sensors down – not even oxygen sensors. This means the sensor can
keep on performing its original function and at the same time also work with the
SVS.
Kit Uses
So what are some uses? They’re almost unlimited but here’s a selection:
Triggers from...
|
To achieve...
|
Throttle position sensor |
Nitrous activation
Auto trans kickdown |
Airflow meter |
Intercooler water spray trigger
Intercooler fan trigger
Engine management modification trigger
Turbo wastegate anti-creep control |
Fuel level sender |
Low fuel warning light |
Oil pressure sender |
Low oil pressure alarm |
Oxygen sensor |
Engine management modification trigger
Closed loop indication |
Coolant temperature sensor |
Trigger radiator fans |
Intake temperature sensor |
Engine management modification trigger |
Accelerometer |
Active four wheel drive modification trigger |
Battery |
Low battery voltage warning |
MAP sensor |
Intercooler water spray trigger
Intercooler fan trigger
Engine management modification trigger
Boost light |
We’ll be using the SVS in lots of projects, so expect to see a lot more of
this versatile module!