Dual OP-Amp (DOPA), Lol. Thanks eric, I'll be waiting.
hi bb,
Reply to your results. Please confirm what type of OPA you are now using.
#1.
Measuring VS, I can also get 0.07v to 0.77v and beyond (200 Ohm pot) from Full to empty tank.
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The reading should be as you have posted ie: 70mV thru 770mV
#2 Measuring the voltages on vo1, it reads (from full tank to empty) 0.63v to 3.1v and beyond but I can't get below 0.63v.
You should be able to get down to vo1 = +0.35v
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Note that I can go beyond 3.1v (Since I'm using a 200 Ohm trimpot to emulate the sender) but not below 0.63v (0 resistance already).
The vo1 = +3.1v is what I would expect.
Note: some pots have 'end' resistance and not go down to a 'complete zero R'
#3 Measuring the voltages on vo2, it reads (from full tank to empty) 2.40v to 0.64v but I can't get below 0.64v.
The +0.64v minimum is making the LM3914 to light LED's #1 and 2
The above measurements were taken at the standard SPAN and ZERO pot settings (14.5K and 19K).
Increasing the ZERO pot's resistance will light the 2 upper LEDs (Making it an 8 functioning LEDs), but can't get to turn off the 2 lower LEDs even by tweaking both trim pots.
This is what I would expect the ZERO pot to do.
As a result, Only 6 LEDs are functioning on the full fuel sender range. The last 2 LEDs stays on forever, while the upper 2 leds don't light forever the (0.64v to 2.40v range) at the standard pot settings.
This error is due to the +0.64v offset error.
If the OPA is causing these problems , there is a solution, adding a resistor to the LM3914, I will explain how to do that, if required.