Fuel level pull up resistor.

evel
Posts: 2
Joined: Sat Dec 17, 2016 3:09 am

Fuel level pull up resistor.

Postby evel » Wed Dec 21, 2016 9:10 am

Hello all,

Iv been having some problems with getting my RT Dash 2 Pro to correctly read my fuel level sensor in my '94 MX5.
At empty it reads 3ohm and full is 110ohm (according to the book) Iv wired it up with a 100ohm pull up resistor but when i attach a multimeter I read 5V at the 5V source and 5V at the analogue input and 60ohms from the sensor (tank must be ~half full). Now I dont 100% understand how/what a pull up resistor does, should the difference between the two points be very small ie millivolts, or am I on the wrong track? Also do i need a slightly larger resistor so the dash can correctly read the fuel level?

In the attached image, the little boxes with the lines are multimeters.

Thanks all and Merry Christmas!!
Attachments
Fuelsensor.png
Fuellevel
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Support (D)
Posts: 78
Joined: Mon Aug 17, 2015 9:36 am

Re: Fuel level pull up resistor.

Postby Support (D) » Wed Dec 21, 2016 11:42 am

Hello,

The pull up resistor is implimented to create a potential divider circuit. This converts the resistance output of the sender to voltage, this is what the DASH2PRO expects to see on its analogue inputs. With a 100ohm resistor attached you should get around 1.875V, firstly I would configure the dash to display the analogue voltage on screen, to ensure the voltage read from the multi-meter is indeed correct.

To do this, simply read the configuration back from the unit. Set the analogue channel, where the sender is connected, to display on screen one in the "Set up LCD data areas" section of the software. Set the smoothing to "Update display instantly (eg: RPM)", the decimal places to "3" & finally take note of the display label or make one yourself. Now send the new configuration into the dash & check what voltage the dash is displaying.

Best regards,
Support(D)


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