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Race Technology DASH2 wiki


Frosty

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Owing to an increasing number of questions in the tech forum, I thought a page in the FAQ section was needed as a central store for information relating to the Race Technology DASH2. As information gets suggested (and no doubt corrected) within this thread, I'll update the front page accordingly.

If you find this topic helpful then please do let me know  ;)

I keep reading about pull-up resistors - what are they and why do I need them?

The DASH2 is capable of reading sensor values for things like fuel level, oil pressure, and engine temperature etc. For each of these sensors, the DASH2 expects a mapped voltage input for given values. e.g. 100c = 2.54V. The problem is, Westfield supply VDO sensors with their kits which give varying resistance instead of varying voltage to indicate values.

This is no problem though, because the Westfield loom that is supplied with the DASH2 has 4 neat little circuits (potential dividers - one per sensor channel) which already contains the pull-up resistor. All you need to do is connect the sensor to the loom as per the instructions.

What are the pull-up resistors rated at?

The pull-up resistors are 910 ohms each. This is the basis of your calculations to convert resistance to voltage (more on this later).

Which sensors are connected to which input?

On the Westfield DASH2 loom they are as follows:

Analog 1: Not used (but circuit is there ready for a connection for a sensor of your own).

Analog 2: Water temp

Analog 3: Fuel level

Analog 4: Oil pressure

Ok so my DASH2 is plugged in, and my sensors are all connected, so how do I configure them?

The DASH2 will now see a voltage from each of the sensors that you have plugged in, and you need to tell the DASH2 what these voltages mean. We'll start with the fuel sender...

1) Download the Race Technology software from the website, install, and then open DASH2 software.

2) On the input scaling tab, select "Analog 3" from the dropdown list - this is the analog input connected to the fuel level sender in our loom.

3) Select "Generate an equation from table" and you will see a new window. This window references voltage to a value. So if you put in 1.0 as the voltage, and 50 as the value, the fuel level would display "50" when there is 1.0V from the fuel tank sender. So you add the full voltage as 100, and the empty voltage as 0. Pretty simple huh? (Details on how to find these voltages follow below...)

4) Name the channel - this is what will appear on the DASH2 display whilst driving. "Fuel" will do in this case.

5) Save your configuration file, and then send it to the DASH2 unit.

How do I calculate the voltage values from the resistance that the sensors output?

It might help to read up here on how a potential divider works to help you understand what's going on. This site is very easy to understand: http://www.electronics2000.co.uk/data/itemsmr/potdiv.php

If you do not care though, then all you need are 3 things. The voltage of the circuit (this is always exactly 5V because each of the circuits are powered from the DASH2 regulated 5v reference feed), the fixed pull-up resistor value (910 ohms - see above), and the resistance from the sensor you are calibrating.

The calculation is as follows: Voltage = (Sensor_ohms / (910 + Sensor_ohms)) * 5v

As a sample, let's do the fuel sender at empty (3 ohms) and full (180 ohms).

So the voltage the fuel sensor will output at 3 ohms = (3ohms / (910 + 3 ohms)) * 5 = 0.016429V

Now full fuel (180 ohms) = (180ohms / (910 + 180ohms)) * 5 = 0.825688

Hopefully this has explained exactly how the potential divider is used, and how to calculate voltage from sensor resistance for various values. An Excel spreadsheet will save you masses of time here.

What are the resistance values for each of the VDO sensors?

The data can be found in the following PDF's.

Temperature Sensors:

http://www.ljf-design.com/westfield/vdo_pressure_sensors.pdf

Water temp (marked 801/5/1) = curve table 92-027-004.

Oil temp (marked 801/9/3) = curve table 92-027-006.

Pressure Sensors:

http://www.ljf-design.com/westfield/vdo_temp_sensors.pdf

Fuel Level Sensors:

3 ohms = empty

180 ohms = full

Is there a Spreadsheet I can use for easy calibration and pasting into the DASH2 software?

You can either write one yourself, or just download the one I created which has full resistance values for oil pressure, oil temperature, fuel level, and water temperature, as well as the ability to specify different pull-up resistor and reference feed values. This will save you a lot of typing :)

Download the spreadsheet here:

http://www.ljf-design.com/westfield/vdo_sensors.xls

Speedo sensor Issues:

If you have upgraded to the DASH2 after building your car, the chances are you have a VDO speedo transducer at the rear of your car working from the 6 driveshaft bolts. Unfortunately, this sensor is NOT compatible with the DASH2 (something to do with the sensor frequency). Westfield supply a slightly different sensor which works using the front wheel hub bolts instead.

The sensor is available from Westfield, or from RS Components. The part number is XS1N08PA349. It's around £40 for the unit.

Speedo Sensor Wiring:

If you have the Westfield loom for the DASH2 then you need to find the speedo block connector, and then solder the 3 speedo sensor wires into this block in the following way:

Sender                         Speedo Loom

BROWN            to         GREEN (+12v)

BLUE                to         BLACK (GND)

BLACK              to         YELLOW/WHITE (Pulse signal)

All you are doing here is re-routing the wires that would normally plug into the speedo unit, and instead using them to power the sensor, and then return the pulse to the block connector.

If you do not have the Westfield loom, you need to use any 12v signal that is live with ignition (nearly always a green cable), and use this to power the sensor (brown cable as above). You must also earth the sensor (blue cable).

Lastly, you need to return the pulse signal to the DASH2. All you need to do here is connect the black cable from the sensor to the brown wire that goes into the DASH2 unit on the CONN1 block. See your DASH2 manual if you are not sure where to find this.

This connects the speedo pulse from your sensor directly into the DASH2 speedo input. Job done!

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I think the read-out in litres is better so I have come up with the following equation for a long range tank: Fuel level in litres y = 51.9x + 0.853 I called Westfield today and they gave me the fo

excellent find

makes sorting out resistor values easy cheers

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cast iron
excellent find

makes sorting out resistor values easy cheers

I dont think it is a find. Its more a pulling together of his own hard work. well done Frosty

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Cheers guys I'm glad you like it. I have spent a great deal of time with the DASH2 and over time I'll extend the topic further to explain how you can make the sensor readings much more accurate.

In the meantime, if there is anything that doesn't make sense then please let me know so I can amend the post and explain it a little better.

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Great thread thanks for posting it has been a great help.

I have an additional question. I am using the standard Westfield DASH 2 setup which is working fine. I would like to add an oil temp sensor. If I use a VDO Oil temp sender and connect to Analog 1 (The spare) will it overload the DASH2, as I understand there is a limit . :durr:

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Great thread thanks for posting it has been a great help.

I have an additional question. I am using the standard Westfield DASH 2 setup which is working fine. I would like to add an oil temp sensor. If I use a VDO Oil temp sender and connect to Analog 1 (The spare) will it overload the DASH2, as I understand there is a limit . :durr:

There is indeed a limit, but with the Westfield loom you do not have to worry and I'll explain why...

The 5v reference feed that powers the 4 analog sensor potential dividers is connected to a 5v voltage regulator (divided 4 ways), and this voltage regulator is limited to 50mA, so total load on this must not exceed 50mA.

To work out the total load in worst case scenario, assume there could be an occasion where all of your sensors give 0 ohms - this is the maximum current flowing.

So let's work out what one of our sensors is drawing in terms of current.

5v / 910ohms = 0.0055A (or 5.5mA)

Now we have 4 of these sensors, and each has the same resistor in place, so just multiply by 4.

So the worst case load for all 4 sensors is 22mA, so you'll be absolutely fine.

Thanks Luapno I'll add this to the first post at some point.

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Believe it or not the only thing I knew about electronics before owning the DASH2 was what I learnt in science back at school in the mid 90's (most of which was forgotten)!

Everything else has come from trial and error with the DASH2  :D

Glad I could help.

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This is all very interesting, my sensors all work but my rpm does not.  It worked from about 0-3000 but I was at full revs at 3000 so I changed the numbers in the boxes to read 1to9 with 1 being the lowest but now there is no bar going up and down what am i doing wrong?
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This is all very interesting, my sensors all work but my rpm does not.  It worked from about 0-3000 but I was at full revs at 3000 so I changed the numbers in the boxes to read 1to9 with 1 being the lowest but now there is no bar going up and down what am i doing wrong?

Hmm a few questions for you.

1) which engine are you running?

2) What do you have in the pulses per rev box on your dash config?

3) Do you know where the RPM feed is read from on the engine?

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It is an xe running an old alpha ignition only system this is where the feed is taken as you can not take it directly off the coil.  I went through a lot of hassle to find out which wire it was as I bought it second hand.  Troy from Northampton Motorsport made some phone calls and not even webcon were sure but it is the only one I get a reading off so must be right.  The pulses per rev is set at 2 all help appreciated as at a loss with this
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So you have taken the feed from the ignition system? Have you taken it from one single cylinder, so when the spark is fired, you will get a pulse down your rpm feed?

If so, you will be getting 0.5 pulses per rpm. In other words, the engine needs to rotate twice for one ignition pulse to occur.

If the above is true, place 0.5 in your pulses per rpm box.

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