DIY - Part 2

To do electronic work on your car you'll need...

by Julian Edgar

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Last week we covered the setting up of a DIY mechanical workshop - where to work and what tools to buy. However, if you're modifying any car of the last 15 years it's quite likely that you'll need a different breed of tools - because you'll be working with the electronics as much as you'll be twirling spanners. So are the tools that you need very expensive and the area where you work difficult to set up? No, and no.

When taking into account electronics you really need to consider a new working area - a 'clean' area if you like. Not as in a special clean room, but clean as in away from the grease and grime of your normal workbench. Electronics tends to require concentration, comfort and good lighting - rather than a cold/hot draughty workshop surrounded by car ramps, jacks and spiders!

But first, the equipment. We explain what to look for when buying multimeters, soldering irons, power supply, and more tech tips.


  • Multimeter

The key piece of equipment is a multimeter. A multimeter is a test tool which can measure a variety of different electrical factors - at minimum: volts, ohms and amps. In addition to these measurements, it helps if the meter can also display:

  • duty cycle
  • pulse width
  • rpm
  • temperature
  • continuity

Duty cycle indicates the proportion of time which a pulsed actuator is being excited for. Using an injector as an example, it shows what proportion of the time the injector is being held open. If the injectors in a modified car have a duty cycle of 100 per cent during full load measurement, then the max capability of the injectors has been reached - no more fuel can be supplied. 100 per cent duty cycle means that the injectors are constantly open.

Pulse width is a measurement which shows in milliseconds how long the injector (or any other pulsed actuator, like an idle air valve) is open for. This is useful if measurements are needed on one car to help set up programmable injection on another car, or to compare against manufacturers' specs - but generally the actual length of time which the device is open for doesn't matter very much so duty cycle is the more important parameter to have available.

Engine revs has obvious application in measurement - from accurately setting the idle speed to checking the accuracy of the tacho.

Temperature measurement (usually by a K-Type thermocouple) is very useful when working on cars - especially turbo ones. In addition to measuring the coolant temp (good for checking the gauge and measuring the temp at which the radiator fan switches on), it can also be used to check on engine, tranny and diff oil temps, and the temp of the induction air after the turbo. Intercooler efficiencies can then be measured, while the temp of the air in the induction air pick-up can be checked. In short, this function is extremely useful!

A continuity function simply means that an internal buzzer will sound when the meter's probes are connected together. If this happens it also means that the buzzer will sound if the probes are connected to either end of an unbroken wire - which is slightly more useful!

Multimeters are available in auto-ranging or manual-range types. An auto-ranging meter has much fewer selection positions on its main knob - just Amps, Volts, Ohms and Temp, for example. When the probes of the meter are connected to whatever is being measured, the meter will automatically select the right range to show the measurement. Meters with manual selection must be set to the right range first. On a manual meter, the 'Volts' settings might include 200 mV, 2 V, 20 V, 200 V and 500 V. When measuring battery voltage in a car, the correct setting would be '20 V', with anything up to 20 volts then able to be measured.

While an autoranging meter looks much simpler to use - just set the knob to 'volts' and the meter does the rest - the meter can be much slower to read the measured value, because it needs to first work out what range to operate in. If the number dances around for a long time before settling on the right one it can be a pain in the butt for quick measurements, and very difficult if the factor being measured is changing at the same time as well! Some autoranging meters also allow you the option of fixing the range, to speed up readings.

One very useful function of a multimeter is a 'peak hold' button. As the name suggests, the meter will retain on its display the max value measured. Especially when working by yourself on the road, this allows balls-to-the-wall testing without having to constantly glance down at the meter. All of the following have application when there's a peak hold facility:

  • max rpm used
  • peak output of any engine management sensor - for example, the airflow meter
  • max temps, including oils, induction air and post intercooler air
  • max duty cycle of injectors

The best place to buy a multimeter is from an electronics store. While automotive parts suppliers stock multimeters, they can be up to double the price for meters with just the same quality and features. Note that pretty much any digital multimeter will have sufficient accuracy for car use - buy on the criteria of price, features and warranty. Because of the huge decrease in prices over the years, it's not worth buying a multimeter secondhand - many used goods stores have them above new price!

  • Soldering Iron

Next on the list is a soldering iron. The sort that you pick depends very much on the type of soldering you expect to be doing most. A general purpose mains-powered iron (eg a 25 or 40 watt design) will perform most soldering tasks on a car - and also can be used to assemble electronic kits and work with individual components. An alternative to a mains-powered design is one that uses an inflammable gas cartridge - these save you have to drag along the power cord.

However, if you can stretch for the extra dollars, a temp-controlled iron is a better proposition. Not only do they - as the name suggests - allow you to dial up an appropriate temp for the job, but they usually are configured with a base station and a remote iron that's linked to it with a supple cord. The lighter iron makes it a lot easier to use, you get an inbuilt stand (good for safety! - see "From the Editor) and a tip-cleaning sponge is usually also provided. Variable temp soldering irons are available with digital displays showing the temp of the tip - but in all normal uses a simple knob that you set to (roughly) the desired temperature is fine - and cheaper than the digital display irons as well.

When you buy an iron it's a good idea to shell out for some extra tips - this saves you problems if later the supplier decides to drop that iron from the range. Soldering irons are usually very reliable - it's the tips that gradually erode away.

And don't forget to only use solder designed for electronics use.

  • Hand Tools

You'll also need a pair of small side (diagonal) cutters, small pointy nose pliers, some small files and drill-bits, and a good magnifier. The latter can be a stand-alone device that waves about on an arm, or magnifying goggles that you wear on your head to make you look like something from Mars.

  • Power Supply

This one's an option - but you'll be damn glad that you bought it. Especially useful if you're building something and want to test it before it gets into the car, a variable power supply can churn out variable voltages and in some cases, variably limit the current flow as well. It would be nice to have a power supply sitting on the bench that can produce 0-30 volts at currents up to 50 amps - but unless your pockets are very deep indeed, it isn't going to happen. Instead, at realistic prices you're more likely to find power supplies that do currents up to 3 amps or so.

Most important is to have a power supply that has built-in digital meters to show the current being drawn and the voltage being supplied. Having this information instantly available (sure, you can measure it with your multimeter - but then that ties up the meter) is extremely useful. For example, imagine that you've just whipped up a circuit that should draw about 100 milliamps and as soon as you connect it, the power supply meter immediately shows there's a current draw of an amp! Ouch - time to do a rapid disconnect and find what's wrong...

A power supply that has extra outputs available (eg fixed 12 and 5 volt outputs) can also be useful, even if these ancillary outputs are only low in max current capability. Many electronic circuits work off 5 volts and if you can power the circuit with this supply - and still have another variable power source available - it gives better flexibility. Look also for fine and coarse supply voltage adjustments (so much easier to get that voltage right!) and that variable current output. The latter allows you to set the max current very low, so that if anything goes wrong the current can't skyrocket. The power supply should also be completely protected against overload, high temperature and dead shorts.

  • Breadboard

Finally, if you're going to be constructing circuits from scratch (eg building an IC-based circuit from a diagram), use a breadboard to build the prototype. I must confess that it took me a very long time to discover just how useful these things are. So what are they in fact? Just a board with lots of holes electrically joined in a certain pattern underneath that allows you to plug in components and then link them with additional external wires. It's easy to make changes (f-a-r easier than by soldering and unsoldering), but even better is that the circuit is constructed from the same on-top view as the diagram is drawn, making the chances of wiring errors much less than if you're working upside-down. Once everything is up and running you can transfer the components and wiring to perforated board for the final build.

Work Space

As indicated earlier, you need a clean, comfortable working area with excellent lighting and good ventilation. The latter's due to the fact that soldering releases poisonous fumes - best to have a fan or dedicated sucker drawing that air away from your face. You need room on the working surface for the power supply, multimeter and soldering iron - so by the time that you add it up, despite the fact that the actual device that you are working on is small, you'll still need at minimum a large kitchen table.

Small clear lid plastic boxes that have multiple compartments are an excellent way of storing components - and it's a good idea to buy some 'mixed bags' of capacitors, resistors, pots and so on so that you have alternative value components readily at hand.

When you fit the device to the car you'll also need to be able to get power to the soldering iron, have good lighting and access, and so on. (For more on this, see last week's article.) However, making sure that something works on the bench before you start sorting ECU pin-outs while lying contorted under the dash is a far better way of doings things - more comfortable as well...


If you organise the right tools and space for both mechanical and electronic work on your car there'll be nothing holding you back! As we've shown in this and last week's article, it doesn't have to be an expensive process if you start off with the basics and buy carefully. And there's nothing like being comfortable and having the right tools available to increase your enjoyment in the modifications that you're undertaking...

  • Often when you're testing something on the bench you'll want to power the device (eg by a running car voltage level of 13.8) but also have a variable voltage available, for example to simulate an engine management sensor output voltage. But how do you generate the sensor output? The simple way is to wire a 10 k-ohm potentiometer across the 13.8 volt supply, with each furthest connection going to the power and earth respectively. On the middle terminal will then be a variable 0-13.8 volts variable supply. It won't be good for much current, but it's perfect to simulate a sensor output.
  • Some multimeters have a PC connection, usually by a serial port connection. If you also own a laptop, you can use this to log and display data from the meter, eg injector duty cycle during a hard drive. However, the downside is that most multimeters won't talk to the PC fast enough to get real-time data - where you'd like 10 times a second sampling, you're more likely to get once per second. However, that's still fast enough to log post intercooler temps, for example.
  • When working your bench power supply hard, make sure that its ventilation holes and external heatsink are free to breathe. Many power supplies push out quite a lot of heat when supplying current near to their max, and you don't want to start a fire or have the power supply shut down half way through that fuel pump flow test...
  • Multimeters are now so cheap that every car modifier should have one. I can remember (here you need to adopt quavering, ancient tones) when a decent multimeter would set you back at least AUD$200... ahhhh, those were the days... Now they're seventy bucks for a better meter.
  • Don't tell the purists but a temp-controlled soldering iron is also excellent for welding plastics. Either by using a filler rod or simply fusing the plastic together, the small tip of a soldering iron makes a good job. Just make sure that you have plenty of ventilation and clean the tip while it's still hot. For more on plastic welding, see "Melting It Together - Plastic Welding".
  • We believe that all enthusiasts should have the workshop manual for the car that they're modifying - if that's at all possible. But it's when you come to modifying the electronics of a car that the manual becomes even more important. At minimum, beg borrow or steal a circuit diagram (complete with colour codes!) for the car.
  • If you are better versed in mechanical modifications than electronics, the best way to start the learning process is to build a simple electronic kit. Jaycar Electronics ( has a range of automotive kits.

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