Need help measuring 120VAC main

please provide the full schematic, there is no rectifier in this diagram nor the values of the components

We will be better able to help if you provide the full diagram with details

Thanks

As requested....

The zener (ZD6) is just a 3.3v to keep the Pi's GPIO's safe.

First I must give you the quick lecture on mains safety:

USE AN ISOLATING TRANSFORMER !!!

If your circuit is connected to the mains supply it is not safe.

Now to filtering some safe 60Hz AC to measure it:

You don't really need a bridge rectifier - a single diode will do.

Use LTSpice to simulate this kind of stuff - it's free and easy to use.

This is about what you've got but I'm running AC into it just to see the response of the filter - as you can see its not really working at the right sort of frequency at all - you need a filter which lets through almost nothing at 60 or 120 Hz (half or full wave rectifier)

The second circuit is a simplification of yours (but remember you shouldn't build this - if the 1M resistor fails you DIE !!)

I think this is what you are seeing on your design the problem is that there is almost no filtering going on.

This third go is with some better component values and some simplification:

Now it works - its taking a while to settle and there is some ripple. If you were to use a small transformer to give you a nice safe 10V to work with you could have this design where we can reduce some impedances without risk of death !

You can get a faster response at the expense of ripple by reducing the capacitor values or the resistor values. The input impedance of the ADC must be high (> 100k). If  you use  a transformer you may live to improve it.

Have fun, use simulation.

MK

First I must give you the quick lecture on mains safety:

USE AN ISOLATING TRANSFORMER !!!

If your circuit is connected to the mains supply it is not safe.

Now to filtering some safe 60Hz AC to measure it:

You don't really need a bridge rectifier - a single diode will do.

Use LTSpice to simulate this kind of stuff - it's free and easy to use.

This is about what you've got but I'm running AC into it just to see the response of the filter - as you can see its not really working at the right sort of frequency at all - you need a filter which lets through almost nothing at 60 or 120 Hz (half or full wave rectifier)

The second circuit is a simplification of yours (but remember you shouldn't build this - if the 1M resistor fails you DIE !!)

I think this is what you are seeing on your design the problem is that there is almost no filtering going on.

This third go is with some better component values and some simplification:

Now it works - its taking a while to settle and there is some ripple. If you were to use a small transformer to give you a nice safe 10V to work with you could have this design where we can reduce some impedances without risk of death !

You can get a faster response at the expense of ripple by reducing the capacitor values or the resistor values. The input impedance of the ADC must be high (> 100k). If  you use  a transformer you may live to improve it.

Have fun, use simulation.

MK