Westfield Megabusa Build Diary

10 Mar 2008
Additional sensors for the DASH2 digital dash

I wanted to use an oil temperature display with the DASH2, and I thought it would be very easy to use the sensor that Westfield sell. Looking at the software, asks for the input voltage of the sensor at various intervals. The problem is that the Westfield VDO sender gives a varied level or resistance and not voltage.

There is a way around this though. In order to use a thermistor with the DASH2, you must create a potential divider. What this does is uses a known voltage output, then applies two levels of resistance to the circuit - one fixed, and the other variable (the output of the oil temperature sender). This in turn gives a variable voltage, and this voltage can be used in the DASH2. You are effectively converting resistance into voltage.

What you need to do is get the resistance levels for the various temperature points, convert them using the potential divider formula, and then use that voltage in the dash.

This link was very useful to me: http://electronics2000.co.uk/data/itemsmr/potdiv.php

The DASH2 unit has a 5v reference output, so you use this.

I used a 1k resistor for the oil temperature, so if for example my resistor gave out 300ohms when the oil temperature was 10C, you would do V2 = (R2 / (R1 + R2)) * V1

V1 would be 5v, R1 would be whatever resistor you fitted inline with the 5v feed (1k in my case), and R2 would be the resistance that the sensor gives at 10C.

This would give you 1.154V, so you would set your channel output in the DASH2 to read 10C at 1.154V, then do the same for 20, 30, and so on.

Look at the images below which should show you how to create the complete circuit.

Laurence

My diagram - use the 5v feed from the DASH2 to splice into to begin the circuit, then add a resistor (1k is ideal), then connect your sensor, then feed the circuit into the desired DASH2 channel. My 1k resistor soldered in line. Heat shrink used to protect it.

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