How to scale to 150 volts for LCD

[sayzer]

Some notes from me:


In DT's schematic in that link, use 100K for R1 and 2K2 Trimpot for R2.

Apply 150V to your probes.

WHILE you are adjusting trimpot have your eyes looking at LCD for your ADC reading. Just use the raw reading. Do not scale it to anything.


Main reason for using trimpot: to drop from 150V down to 5V level, you use a resistor value around 100K or 150K. But say that you are using metal film resistor with %1 tolerance.
That means, your R1 can be 101K or 99K. You never know the actual resistance value in mass production. This difference of "1K" will give you a large deviation in your ADC reading. Thus, you need a fine tune, lets call it calibration by using a trimpot.

[wildbilly]

Thanks Darrel. I had a look at the link and that has been very helpful. Thanks a lot. Thank you too Sayzer for your input, most valuable. Even though it has been challlenging at times, it still is fun learning this stuff, especially when the forum is off such great help. Thanks again.

Wild...

[CocaColaKid]

Would it not make more sense to use a 1M and a 33K trimmer? This would allow you to achieve the optimum ration of 30:1 (150V/5V) would it not. With a 100K and 2.2K trimmer you'll have a ratio of 45:1 which will output only 3.33V at the full 150V.

[wildbilly]

Yes. Sounds and looks logical. Thanks for your input

[sayzer]

Would it not make more sense to use a 1M and a 33K trimmer? This would allow you to achieve the optimum ration of 30:1 (150V/5V) would it not. With a 100K and 2.2K trimmer you'll have a ratio of 45:1 which will output only 3.33V at the full 150V.

It was an example.

But, %1 of 1M is 100K.

That means, the resistor says 1M but it may actually be somewhere between 900K and 1100K.

That also means a lot more you know.
Using 33K trimpot is not going to be helpful in fixing the tolerance deviance.



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