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How can an automotive instrument cluster function on bench?

 
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PostPosted: Fri May 30, 2008 10:14 pm    Post subject: How can an automotive instrument cluster function on bench? Reply with quote

I am trying to work on a late model car instrument panel. There are some fancy electronics on the cluster.
I want to do some repairs but I need a way of testing the device on the bench.

I was wondering what options I might have to get the cluster to function on the bench. I am sure there are many different ways depending on the design of the cluster but with good wiring diagram anybody have any idea's?
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Jun 02, 2008 8:08 am    Post subject: Reply with quote

If the car uses serial communication (CAN, RS-485 etc) between the instrument cluster and all other equipment, not much can be done without a CAN controller (or a PC with CAN interface and suitable software).
Otherwise, it should be relatively simple to make a test rig using information from the car's wiring diagram. Just connect ground and supply voltage (permanent and ignition) to the correct pins, and simulate the various sensors by switches, variable resistors etc.

The road speed sensor can usually be simulated by a tone generator provided that you know what kind of sensor it is, usually, either an inductive (variable reluctance) sensor producing a sine signal, or a hall sensor with open collector output, producing a square wave. In case of an input for a inductive sensor, set the tone generator to sine and connect it to the input via a suitable transformer (for example, a telephone line transformer from a scrapped modem, fax or answering machine). In case of an input for a hall sensor, use a NPN transistor and supply square wave from the tone generator between its emitter and base.

The RPM signal from the engine is often a 5Vpp or 12Vpp square wave. In some cases, particularly on older cars, it might be directly taken from the ignition coil primary and in such cases it might happen that the input needs the switching spikes of some hundred volts p-p for triggering.

Anyway, even if you can't hook up the instrument cluster to get all functions working, you should at least be able to check some internal supply voltages, clock oscillators, backlight and so on.
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