So a few months back I made a PCB board for testing some higher voltages with my teensy. (9 voltages from +/- 0-36V in ~4v increments with a voltage divider for the final 4v output into a teensy analog input.)
I got the idea from a forum member to do this via flying/floating capacitor measurements even longer ago:
Original Thread:
Explicitly about flying cap thread (2nd thread):
I finally got to populate my board, write some code, and test out the circuit...but after some basic initial problems, and testing the SSRs to make sure they opened fully, I think I realized I made a grave mistake...
It looks to me that I set up a situation where I properly float my capacitor and connect it to the voltages I want to measure, but when I go to measure the voltage (after disconnecting from my sources) I put one leg of my cap at the analogInput, and the next leg........floating!!
So, I think that is why I'm not successfully measuring anything.
I can't attest to why I made my original schematic as I did, but I think I did it completely foolishly. [edit:I looked at the thread from before! It looks like originally in my proto-schematic I posted there, I was not stupidly floating the capacitor. So somewhere along the line I broke the plan and forgot to question the logic.]
finally, purpose of this thread / TL;DR I was hoping I could show two partial schematics, (1) what I made . And (2) what I think I should have made. Any comment on the idea that the 1st is wrong, or the 2nd improved, would be greatly appreciated.
[ADDENDUM Just some opamp questions, not too important compared to the first part.]
I've spent several hours trying to read about op-amps type devices, but I'm not entirely sure what I'm doing. The final voltage from my capacitors will be ~4V, a bit too high for the teensy. At the moment I'm using a 6k:10k ladder/divider, but that will quickly discharge my 3uF flying storage cap and I don't really know if I can read the voltage fast enough (I also have to give some time to ensure the SSR is opened fully.) If I slow the discharge with a higher resistance ladder/divider, I increase the impedance, which is another topic I don't fully know much about with respect to how it'll affect the ADC.
I think this means I need a buffer amplifier. But from what I read there are alot of opamps and I'm not clear on what will skew my data since usually the op-amps seem to be used for amplifying applications. SO, erm, are there go-to high-accuracy (<0.5% distortion from the signal) buffer amps that I should be looking at? I don't expect my hours of non ECE reading to get me to understand them so well, but I'm hoping I might get a practical idea of how to implement one without massive error. And I guess since I'll need a >4V power source for the amplifier, anything fancy I need to do for the power source? Does it have to be a linear regulator or can I just use a 5V step-down switching regulator from Pololu or somewhere?
Many thanks, [seriously, many thanks. i am looking around a lot and hoping to learn more, but sometimes reach a roadblock on what I can read about without just asking.]
-Tomek
I got the idea from a forum member to do this via flying/floating capacitor measurements even longer ago:
Original Thread:
Explicitly about flying cap thread (2nd thread):
I finally got to populate my board, write some code, and test out the circuit...but after some basic initial problems, and testing the SSRs to make sure they opened fully, I think I realized I made a grave mistake...
It looks to me that I set up a situation where I properly float my capacitor and connect it to the voltages I want to measure, but when I go to measure the voltage (after disconnecting from my sources) I put one leg of my cap at the analogInput, and the next leg........floating!!
So, I think that is why I'm not successfully measuring anything.
I can't attest to why I made my original schematic as I did, but I think I did it completely foolishly. [edit:I looked at the thread from before! It looks like originally in my proto-schematic I posted there, I was not stupidly floating the capacitor. So somewhere along the line I broke the plan and forgot to question the logic.]
finally, purpose of this thread / TL;DR I was hoping I could show two partial schematics, (1) what I made . And (2) what I think I should have made. Any comment on the idea that the 1st is wrong, or the 2nd improved, would be greatly appreciated.
[ADDENDUM Just some opamp questions, not too important compared to the first part.]
I've spent several hours trying to read about op-amps type devices, but I'm not entirely sure what I'm doing. The final voltage from my capacitors will be ~4V, a bit too high for the teensy. At the moment I'm using a 6k:10k ladder/divider, but that will quickly discharge my 3uF flying storage cap and I don't really know if I can read the voltage fast enough (I also have to give some time to ensure the SSR is opened fully.) If I slow the discharge with a higher resistance ladder/divider, I increase the impedance, which is another topic I don't fully know much about with respect to how it'll affect the ADC.
I think this means I need a buffer amplifier. But from what I read there are alot of opamps and I'm not clear on what will skew my data since usually the op-amps seem to be used for amplifying applications. SO, erm, are there go-to high-accuracy (<0.5% distortion from the signal) buffer amps that I should be looking at? I don't expect my hours of non ECE reading to get me to understand them so well, but I'm hoping I might get a practical idea of how to implement one without massive error. And I guess since I'll need a >4V power source for the amplifier, anything fancy I need to do for the power source? Does it have to be a linear regulator or can I just use a 5V step-down switching regulator from Pololu or somewhere?
Many thanks, [seriously, many thanks. i am looking around a lot and hoping to learn more, but sometimes reach a roadblock on what I can read about without just asking.]
-Tomek