| Electronics > Projects, Designs, and Technical Stuff |
| How to measure the voltage across a potentiometer ratiometrically |
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| Rerouter:
Bit of an odd implementation, but a RC curve for the PWM reference gets the multiplier within 1-2% error over the range that I am after, If I understood the math better I could probably expand that range, but for now this more than suits, Right now 10-30V is the stable range, anything less is not, but if used with a 5V supply it would be a stable supply anyway, If anyone knows any other methods I'm willing to give them a try, or any criticism to my weird circuit. edit: technically only 1 input is constrained, the other could be bipolar if the mosfet right most mostfet was replaced with an analog switch. |
| SiliconWizard:
--- Quote from: Rerouter on May 10, 2020, 01:25:24 am ---SiliconWizard, The exciter voltage could be external, e.g. tapping in to another system currently using the resistive sensor, Its an edge case that is not that common, If I can keep the option, then means I don't have to compromise on it. --- End quote --- That doesn't change anything much. I already figured the input voltage may not be fixed. Whatever you do, the main thing to consider is the possible range of this voltage. Almost no solution will work for an arbitrarily low or high voltage, for instance. You absolutely *need* to have a clear requirement on the acceptable voltage range, from which we can work out a solution. If the min "exciter" voltage is guaranteed to be 5V (as your schematic would suggest), then an LDO should be appropriate. If it can be lower than 5V, how low? |
| David Hess:
--- Quote from: Rerouter on May 10, 2020, 01:16:33 am ---Going to play around with seeing if I can make it with a PWM multiplier, as I'm already using one elsewhere in the circuit. Triangle wave vs divided supply voltage, double the supply voltage means half the on time, means half the voltage on the output on average, sounds like it should work in theory. --- End quote --- That could work. I have also seen it done with charge pump type circuits where the frequency varies with the excitation voltage. |
| jbb:
I think you can do something a bit cleaner. To check I’m on the right track, is this what you want? - Vin 5V to 30V - Sense resistor Rx 0 to 5 kOhm - Vout = Vin * Rx / 5 kOhm (ratiometric) If so, that wide voltage range will be a bit of a challenge... Questions: Will Vout need to provide any current? How fast does it need to be? |
| Rerouter:
- Vin 5V and 10.8-28V (I revised this a little when trying to make my own multiplier) - sense resistor 3 - 1000 Ohm - Vout = Vin * some constant, main thing is that it is consistant when the supply voltage changes lets say no output current, as I can buffer the output response time within 1 second. |
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