Reverse Engineering an Automobile Fuel Gauge using MSP430 Launchpad

I have been keeping my hands off the blog for a while after the previous post.. I had exams at university. But in the meantime i had some time to get my car`s faulty petrol/gasoline Gauge Indicator Changed. I got the old one and as usual i tried to reverse engineer the gauge with all the simple tools i had. Technically, Its a ” Floating type Liquid Level Resistive Transducer’ (You can trust me on that..I am a student of Electrical Engineering 😀 ). So basically its a variable resistor much like the LDR or a Potentiometer. The one that i have is a pricol make for Maruti Suzuki Cars. You can have a look at the pictures below. DSC05612


Using the TI MSP430 Launchpad i decided to sort of simulate how the Indicator would actually work in real situations. So i pulled up the ADC Pin on the MSP430G2231 using a 220 ohm resistor and connected the fuel gauge indicator as in the set-up picture you can see below.You can use any platform you like arduino,stellaris etc. all you need to do is read the ADC value and produce a corresponding brightness for the LED and when at a low level raise a low fuel alarm which in my case is the RED led. I used Launchpad as it has Two on-board LED`s while my arduino has only one ; additionally i was lazy enough not to wire another led to arduino 😛 .


On measuring the resistance across the fuel gauge i found that when at the lowest position it has a resistance of about 112 ohms and at the maximum it was about 7.2 ohms. On the sticker pasted on the top its mentioned-” Do not connect direct 12 volts”.Which is pretty obvious because since the resistance is low, the current will be pretty high.


but on full scale its about 12/7.2 ohms=1.67amps

This current is pretty high and will surely burn the coil.

So we now know why the sticker is there! 😀

The program simply blinks the red led when there is low fuel. Rest of the time the intensity of the Green LED is proportional to the amount of fuel thereby producing a variable DC voltage which can be sensed using a voltmeter quite similar to the one fitted in the car console.


Watch this video:

Thanks and Regards,

IndianTinker 😀