Amplifier circuit, need more sensitivity or gain?

Ron H

Joined Apr 14, 2005
7,014
Hey Ron,

The Vout won't go lower than 5mV when G=5, no resistor, is that normal?
The minimum Vout can NEVER go below the negative power supply rail, which in your case is ground (zero volts). 5mV is pretty close to zero. The minimum possible output should be independent of the gain.
You have to adjust the offset as follows:
With no strain on the gage, adjust the output offset beginning at some positive voltage, then reduce it toward zero until it just barely stops changing, i.e., just to the point where you can see that it will go no lower. If you turn the pot farther, with no change in the output, you have effectively added a negative offset to the input, which is not what you want.
 

Thread Starter

Nevalite

Joined Feb 20, 2012
45
Hello everyone,

I am having a problem with this circuit. The problem is that after having installed this on the car I believe the vibrations of the car changed the adjustment on the trim pot I'm using to adjust the offset and the offset got ruined. I need a hard wired solution for this. Could I just measure the resistance on each side of the wiper once I have it set where I want it and replace the trim pot with resistors? 2 resistors wired together with a lead in between the two going to ground?

Any advice with this would be much appreciated.

Thanks!
 

wayneh

Joined Sep 9, 2010
17,163
A trim pot can always be replaced with a fixed resistor, but it's often frustrating when you discover you need a bit of tweaking afterwards. You can choose the next higher value, and then plan to test add-on resistors in parallel with it, allowing you to tweak-in-place. Don't forget that resistors (and semiconductors) change value with temperature, ie. drift.
 
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