making digital fuel/temp gauges ?????

[sleek]

hi
the analouge ones in my car are a bit dodgey and id like to make new ones with a digital readout with a common anode display i dont really have any expierience making circuits but i can solder and use a multimeter and i have programmed pcs before in vb and qbasic
how i wanna do it is get the inputs from the back of the gauges and thats about all ive thought up ..... can someone oint me in the right direction? ive searched the forum and cant find anything

thanx alot

 

[k7elp60]

digital temperature and fuel guages

It seems to me that both the sending units are resistors and the analogue
guages are in reality current meters. So as the temperature changes or as the fuel level changes there is a difference in voltage across the sensors. I'll bet if you connect a digital voltmeter between frame or ground of the vehicle and the sensors you will measure a voltage that changes with temperature or fuel level. There was an article a number of years ago in a Popular Electronics magazine(no longer published), that addressed this exact subject. I saved the article. I will see If I can find it
perhaps it will help.

 

[gerty]

You may have to add/subtract resistance from the sensors to calibrate the
gauges, otherwise I think K7 is right on track... 8)

 

[weegee]

I am doing this exact thing at the moment - you need a potential divider using a preset and the signal from the sender.

Use the preset to calibrate and feed the voltage into effectivly a voltmeter circuit or one of them chips for doing the bargraph displays (they are commonely used is AUDIO VU meters)

 

[absolution]

do like the other guy said and take measurements. u can do a variety of things for digital output. if you want a number output you can use a 7107 if i remember right i think thats a dvm not sure at the moment or you can do a bar output and use a series of op amps or a specialty chip designed to do the job. :twisted: