This article was first published in 2009. Some of the kits mentioned in this story are no longer available from AutoSpeed but are available from Jaycar Electronics.
Last week in How to Electronically Modify Your Car, Part 8 we looked at using a prebuilt electronic module – the
eLabtronics Voltage Switch. As we saw, this allowed a range of interesting
modifications, especially through utilising the car’s standard
That module was prebuilt – but how about using an
electronic kit, something that’s usually cheaper to buy than a prebuilt module?
I have been involved in building electronic kits
for most of my adult life. I’ve built plenty of kits, and have helped design and
develop them as well. But, I have to say: I think that kits are the reason that
many people abandon the DIY electronic modification of cars.
Huh? Why so?
Well, the trouble with electronic kits is that it
is so easy to make a mistake in their construction, resulting in a product that
simply doesn’t work. The skills needed to fault-find a kit are vastly
higher than the skills needed to build a kit, so in nearly all cases, if
the kit doesn’t work when you’ve finished building it, then you’re stuck with a
pile of useless junk. And junk that’s cost you money, time and enthusiasm.
I don’t have any figures to back this up, but it
wouldn’t surprise me if as many as one-third of all electronic kits that get
sold never end up working.
I think it’s vastly better to pay more and (1) buy
a prebuilt module, or (2) buy a kit that has been constructed and tested. Now I
might be accused of bias – the AutoSpeed shop sells prebuilt modules and
prebuilt kits, and the latter are a lot more expensive than just the bare kit.
But it’s simply so easy to spend say $50 buying a kit, work really hard for
three or four hours making it – and then find it doesn’t work.
So if you’re a beginner to electronics – and this
series is aimed at just such people – don’t embrace the buying and building of
electronic kits as a natural extension of your DIY electronic car modification.
To build a kit, not only do you need to develop a whole swag of component
recognition skills, you also need to be meticulous in construction and be very
good at soldering. Furthermore, you need to be able to interpret instructions
that assume quite a lot of background knowledge.
However, kits allow you to do modifications that
would otherwise be difficult, and certainly to do them at a low price. So let’s
look at what is involved in building a kit, starting with what’s probably the
simplest kit you can buy.
Car Modification - Voltage Monitor kit
kit comprises just a tiny printed circuit board (PCB), a dual-colour LED, a
trim-pot (ie a small pot designed only for screwdriver adjustment) and a handful
of other components. What it does is monitor to the voltage of its power supply,
lighting the LED green when the voltage is above the set level, and changing the
LED to red when it falls below the set level.
what use is this?
of the best uses is as a battery monitor. That might be the car battery, or in
portable battery-powered gear, it might be the voltage of the replaceable
batteries. You can even use it to monitor the battery of an electric bike. It
can be used with voltages ranging from 6 – 30V. (Note that because the device is
powered by the voltage it is measuring, it’s not suitable for use with sensor
available from the Autospeed store for AUD$8.95
first step is to solder into place the five resistors. To solder components to
the board, you poke the wire leads through the right holes and then solder the
leads to the pads on the back of the board. You then snip off the excess lead
a multimeter to sort out which resistor is which, and then use both the overlay
diagram in the instructions and this diagram to put them each into their right
installed resistors should look like this.
you have done that, place the trimpot on the board and solder it into place.
capacitor is next. It is a polarised component, which means that it must be
soldered into place with the right orientation. (The resistors, on the other
hand, can go either way around.)
capacitor's polarity is indicated by a 'minus' symbol near one lead. This lead
goes closest to the edge of the PCB, ie the positive lead is nearer the
integrated circuit (IC).
next step is to solder the LED onto the board. Note that again the instructions
are slightly deceptive - better to follow this diagram. As can be seen here, the
LED has three leads, each of different lengths. Orientate the LED and PCB so
that the shortest lead goes into the top hole, the longest into the middle and
the other lead into the bottom hole.
that if you get this around the wrong way all that will happen is that the LED
will start off red and then turn green as the voltage falls, rather than the
other way around.
in the component assembly there's the three-legged voltage reference and the
8-legged IC. The voltage ref is assembled with the orientation shown here - the
flat facing away from the edge of the board, while the 8-legged IC goes with the
notch (sometimes shown on the IC as a dot) facing in the direction shown
solder into place the two wiring pins and the finished PCB should then look like
best way to set up the monitor is on the actual car. Grab your multimeter and
connect the module to power and earth, making sure that you don't get these
connections reversed. Depending on where the trimpot is set, the LED will then
glow red or green. Turn the pot until the LED is green, and then back the other
way until it just turns red. Then start the car. With the increase in battery
voltage from the running alternator, the LED should immediately go green.
that you've shown it works, use your multimeter to measure the voltage feeding
the module. On my car, the running-engine battery voltage is no less than 14.4
volts, while when the engine is switched off, the battery voltage immediately
drops to about 12.4V. If I have the lights and ignition on (but the engine still
off) the battery voltage plummets, dropping to the high elevens in a minute or
so. However, if I leave the lights off and just play the sound system loudly,
the battery voltage drops only very slowly.
looking at all these voltages, I made the decision that I wanted the LED to
change from green to red at about 12.0V.
turning the adjustment trimpot very carefully, it's possible to set the module
so that the LED changes to red very close to 12V - just what's wanted in this
case. And of course, if you want the LED to change colour at, say, 11.5V, just
adjust the pot a little further.
A couple of other simple kits are:
This kit allows you to display the raw voltage
output of a traditional narrow band oxygen sensor, as fitted to most cars of the
last 25 or so years. This allows you to see when the air/fuel ratio is rich,
lean or stoichiometric (“normal”). It also allows you to see when the engine
management system is in open and closed loop. See Cheaply Monitoring Air/Fuel Ratios
for more. The kit costs
This is a very useful kit, able to do far more
than its name suggests. Uses include running an injector, dimming lights, motor
speed control (eg of a water/air intercooler pump), pulsing a light or horn, and
pulsing a solenoid to control flow. We covered the kit in detail at The Nitrous Fuel
Controller - That's Also a Lot More!. The kit costs AUD$24.95
Don’t get me wrong – successfully constructing
kits can be a fun and rewarding part of electronically modifying cars. However,
if you are a beginner to electronics, don’t assume that making a kit must be
easy and that success will inevitably follow. In many cases, that’s not the
However, on the other side of the ledger, starting
with simple kits will develop skills, and then more complex kits can follow.
Next week we’ll change pace and look at the
different types of signals you’ll find in car electronic systems.
The parts in this series:
Part 1 - background and tools
Part 2 - understanding electrical circuits.
Part 3 - volts, amps and ohms
Part 4 - using a multimeter
Part 5 - modifying car systems with resistors and pots
Part 6 - shifting input signals using pots
Part 7 - using relays
Part 8 - using pre-built electronic modules
Part 9 - building electronic kits
Part 10 - understanding analog and digital signals
Part 11 - measuring analog and digital signals
Part 12 - intercepting analog and digital signals
Part 13 - the best approaches to modifying car electronics ? and the series conclusion