# 1963 Gas Gauge Project

Discussion in 'The Projects Forum' started by bbowles, Jun 6, 2011.

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1. ### bbowles Thread Starter New Member

Jun 6, 2011
2
0
Hello everyone, I am a bit stuck on a project and need some tips. My skill level is only hobbyist.

The problem:
The vehicle has a gas gauge from 1963 that moves based on a coil of wire wrapped around a flexible metal strip. As the coil warms the gauge increases. The gauge registers 0 ohms as full and 70 ohms as empty. A new tank and sending unit was installed at some point in it's history. The new sending unit is 200 ohms full and 60 ohms empty.

My proposed solution:
Use ATTiny13 built in ADC to read the sender and PWM to drive an NPN transistor going to the gauge. I've figured out the ATTiny13 well enough to read a potentiometer with the ADC and control an LED based on the ADC reading with the PWM.

Where I need help:
The ADC reads the voltage as reference to Vcc (5v), 1024 = 5v and 0=0v. The gauge runs off 5v too. I want to use a voltage divider to read the sending unit's resistance but can't figure out what I need to do to limit the current enough and still have a wide enough range with 60-200ohms.

I imagine the circuit resembling:
??? ohms
|
_ --/\/\/\(sender)----
60-200 ohms

I can't figure out any resistance configuration that gives me more of a range than 30 on the ADC. Am I on the right track or do I need to figure out a different way to measure the voltage coming from the sender to correspond to the resistance?

Thanks in advance for any help!

2. ### #12 Expert

Nov 30, 2010
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Car projects are forbidden on this site.

3. ### bbowles Thread Starter New Member

Jun 6, 2011
2
0
The forum seemed to remove my leading spaces on the |. It is supposed to be on the ADC side.

Apr 20, 2004
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