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DASH2PRO-HowDoI / ConnectA1Or2WireSensor

How do I connect a 1 or 2 wire sensor to the DASH2 PRO.

The DASH2 PRO requires a voltage input on it's sensor inputs that goes from a minimum of 0v to 12v maximum.

For sensors with 3 wires, typically you have:

  • voltage supply
  • 0v or ground
  • signal out

Note that in some cases the ground connection maybe via the body of the sensor in which case there will only be 2 wires coming out of the actual sensor - however this is relatively unusual.

In this case the signal out can be connected directly to the one of the analogue inputs on the DASH2 PRO.

For sensors with 1 or 2 wires, it is slightly more complicated.

For a sensor with 2 wires it is typically a variable resistor with both ends of the resistor available:

In this case we need to use a "pull up" resistor to convert the changing resistance to a changing voltage:

1 wire sensors are the same, but in this case the 2nd wire on the sensor is ground and made via the sensor body earthing to the engine casting etc.

Once the sensor is connected to the DASH2 PRO with the pull up resistor then it can be calibrated in the normal way. For more information on this, please refer to this section.

Choosing a value for the pull up resistor

Please note that it is the installer responsibility to choose the correct value of “pull up” resistor when using 1 or 2 wire sensors with Race Technology products. For a particular sensor type there is no “correct” value of resistor however it must be selected to be “somewhere near” to ensure:

  • There is a reasonable voltage swing, ideally this wants to be a “few volts” rather than a few “milli volts”. A small signal can get easily lost in “noise”.

You cannot take too much current from the 5v reference output, depending on the product typically this cannot be more than a total of 100mA.

The table below gives a indication of suitable pull up resistor values:

Sensor Pull up resistor Notes
100 Ohms or lower (typical for low cost/quality VDO sensors) 100 Ohms With such a low pull up resistor you will only be able to have a maximum of 2 sensors before you use 100mA
Between about 100 Ohms to 500 Ohms Between about 100 Ohms to 500 Ohms 500 Ohms  
Between about 500 Ohms to “a few” kiloOhms 1 kiloOhm (1k) This is the normal setup for Race Technology Supplied sensors
Between “a few” kilohms and “a few” 10’s kilohms 10 kiloOhm (10k)  
Page last modified on January 22, 2015, at 10:53 AM