Low voltage rectification/measurement

[bmwm3edward]

I'm trying to measure a low A/C voltage with a Microcontroller (varies from 0-1 volt p-p).  I realize this is not the 0-5 Volt DC range MC's like to see, but to start, I attached a FW rectifer with a 10uf cap to see if I could get a near DC equivalent (less the RMS value, of course), then send to the MC input analog input pin. 

I get no voltage on the output of my rectifier with a 0.8vac p-p.  What's the deal?   Is this too low voltage for a rectifier to rectify?

Do I need an op/amp or something to boost the voltage, then rectify, then send to the MC?

The larger scope of the project is current measurement - I'm using a current transformer that produces .1 mv per amp of current draw on the secondary winding given a specific burden resistor.  That part of the circuit works.

[jlcstrat]

It could be you're dropping all your voltage in the rectifier...Blog 38 talks about using an AD8036 as a full-wave rectifier...check it out.

[EEVblog]

You'll likely need a "precision rectifier", Google will give oyu plenty of example circuits.
Or else use a True RMS converter chip which gives you a nice DC output relative to actual RMS value. They use these in Multimeters.
Analog Devices make a range of them.

Dave.

[bmwm3edward]

Good info.  I've ordered a few chips, I'll see how they work out.  One from Silicon Labs, one from Microchip.   The silicon labs one is interesting because it's in series with the load.  Whoa.

Oh, and Dave - thanks to your magnanamous review of the Rigol, I ordered one.  Got mine on ebay for $385 USD shipped from Hong Kong.  Arrived in 7 days.  My first digital scope (My dad's hand me down 15 MHz BK Precision was my first). 

But you can't go with an analog scope anymore with these kinds of projects.

Now we need a newbie tutorial for the digital features on these DSOs.  I'm a fast study, but I'm new.

Cheers.