- Tue Feb 28, 2012 1:33 am
#140410
If the curves look OK to you, I'd say just about any general purpose op-amp will do, the LM358 SF sells is fine. Look up inverting op-amp circuits w/offset adjustment. One thing I've not thought through is what voltage you'll need to run it off of. It might be you need a simple voltage regulator as well.
hassmaschine wrote:my EE friend had this to say:The graph below indicates the input (stock curve) and output (from an op-amp) and the desired output (what a new gauge+new sender would do). The gain of this circuit was ~ -0.41 and allowed for an offset voltage of 3.4 V. Given your stock sender has a bit of a curve to it (vs being a straight line), and the new gauge wants more of a straight line, You can see there's some error btw the op-amp output and the desired curve. Some of this error may be the eyeball estimation of gauge/fuel level that went into your measured data. I'd make the gain and offset of the op-amp circuit somewhat adjustable to mitigate any error.I think you're focusing on the potential difference with 5v too much. You should care about what the potential difference with ground is, which is equal to the pontential. You're trying to make 5v the ground, which it's not. Ground is the ground...so, I'm going to target an inverting circuit, with 5v-0.5v inputs, and .9v-2.75v outputs.
If the curves look OK to you, I'd say just about any general purpose op-amp will do, the LM358 SF sells is fine. Look up inverting op-amp circuits w/offset adjustment. One thing I've not thought through is what voltage you'll need to run it off of. It might be you need a simple voltage regulator as well.
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