Need Help On Ac Voltmeter !!

[boboco]

Hi Uludere,

I forgot the week-end, I got round to trying to get the data over to you but using Eagle CAD, I can't get a file under 200K, so now I'll try it in little bits. First of all the simple input for chunking AC attached.

Using a 2.4 volt zener diode D1 and R1- 1.0K, generate 2.4V as offset for the PIC input, decouple with C1, C2 from Vdd against Vss. This is also connection for one of the meter probes. Remember that both Vdd and Vss must float, the probes may not come into contact with Vss or Vdd.

The resistors R2 and R3 must be calculated as divider for the max. voltage you want to measure. If e.g. you want to measure max. 100 VAC RMS then calculate 100 x 1.42 = 142V say 150 V peak each node and select the resistors accordingly to allow not more than +/- 2.5V at the PIC input. I've put a 100nF capacitor over the PIC input to reduce noise, if you keep the frequency under ca. 100-150 Hz it won't affect the input materialy.

If you now put the probes over the voltage you want to measure, the reduced signal divided by R2 and R3 2 will appear over the ADC input offset at 2.4 V.

Let me know when or if you want to try this type, I'll send you software or the next circuit if you want to try the RMS method.

Greetings,

Rob

[uludere72]

thx for your kind response..
i want to try the RMS method, would you mind sending about it ?

if the file is big , you can send to my email adresss.. [email protected]

[onur]

Hi
Can we see rms method?

[leisryan]

Sir:
Good day to you sir

To measure low AC voltages (< ca. 10V) accurately by rectification it is necessary to use ideal diodes. Normal diodes will have a forward drop voltage of ca. 0.6V (silicon) or ca. 0.3V (germanium). Best here is to use two OPs with diodes in the feedback, trimmed to 0V. For those who wish, I will be happy to supply circuits etc.

Sir, I would be grateful if you would provide me the schematics

Yours trully,
Ryan