Electronics > Beginners
Using TIMM pot with 2 pins
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anishkgt:
Thank you. I am not sure how to go about it with am opamp. So it would compare the voltage from the electrodes at the invtering and non-inverting pins when the electrodes are open. So how would the output look like from the opamp when the electrodes are open and closed ? I don't have any at the moment. Which one would i need to test this on a bread board and what other components would i require ?
anishkgt:
I was thinking of getting this Diff amp (https://www.digikey.com/product-detail/en/on-semiconductor/LM393N/LM393NFS-ND/458695) Would any resistors be required ? i've got couple of 1k, 10k 39R, 360R bunch of 0.1uf ceramic caps.
JS:
Ok, I see where this go. Build a non inverting stage, I don't know the voltage at the point where you measure, but that dividing the reference voltage would be the desired gain and define resistance values.

Now, 393 aren't differential amplifiers, are comparators.

If you don't really know what you are doing this isn't a good project, high energy and low knowledge are a bad mix, some of the questions seems like that. To starts, it's always recomended to use an insulation transformer while working at mains projects, you are not using one for what I've seen, there are a ton of safety issues with this and I can't make them into a post, you should learn that starting with small projects and build up confidence and experience befor going to something like this... Sory dude, but that's the way it is.

JS

anishkgt:
Well thanks for the heads-up. I am pretty sure about what am doing but just don't how to use opamps. Comparators are something i can understand. I tried using a configuration at the primary to set a dc reference and compared it against the voltage at the primary when the secondary are shorted. Well it did not work actually they were beyond my knowledge about comparators.

If you could quide me i could get it done or suggest me an opamp to test on a bread board and i will try learn as i go building it. Would a general pupose opamp like MCP6002-I/P (http://ww1.microchip.com/downloads/en/DeviceDoc/21733j.pdf) or the LM358 (http://www.ti.com/lit/ds/symlink/lm358.pdf)help me begin with ?
JS:
I would say the lm358 should do, they are quite situable for working ih micro cobtrollers projects. What micro are you using? In particular... What adc? What voltage range?

From a single rail you should ac coupke your signal to an inverting stage and feed 0.5 Vcc to the non inverting input. The gain will depend on other factors. What voltage do you see on the secondary for the 3 states you are interested?

JS

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