First of all you really are planning to use transformers for isolation, right? Current transformer in this sense: https://en.wikipedia.org/wiki/Current_transformer
<https://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Stromwandler_Zeichnung.svg/220px-Stromwandler_Zeichnung.svg.png> There are also clamp-on ones, but you don't need to make any physical connection to the 220 volts AC you're trying to measure. It needs to be just one wire though, not a pair, because the second one has current flowing the opposite direction which will cancel the first one. So you'd probably need an electrician to get into the electrical panel and hook it up for you. I think it's possible to flip the reference voltage around so negative would be the default. If you look at the pinouts there are 2 pins for voltage reference, just ground the positive one instead of the negative. I've mostly only used dual slope integrating A/Ds and those would read negative just fine, but this is a successive approximation one. A wacky idea, if you've got a sound input, would be to feed the AC out of the current transformer into a sound input and monitor the amplitude of the waveform. You'd probably want to do a bunch of averaging to smooth it out. These A/Ds are much faster than you need so you'll probably want to average out some noise anyway. I dunno, I just got my Beagle in the mail yesterday, but I bought it because of the A/D inputs which I want to use to monitor solar panel outputs. I think the reason they're there is for touchpad X,Y inputs but there are 6 at least, you could borrow one for something else. On Wednesday, October 30, 2013 at 2:57:53 PM UTC-4, [email protected] wrote: > > I'd like to use my BeagleBone Black to build a small power efficiency > station for my school. For that I plan to measure power consumption using a > current transformer and a voltage transformer, feed the data into a small & > fast database and show it through a web interface to the school staff. > I see that 50 Hz are not a problem for BB ADCs, but I'm not sure at all > using them is a good idea. > Intially I planned to use the same voltage I must measure to power the BB. > I'm starting from a circuit like the attached one (replacing the UA78M33 by > a UA7805CKCT which provides up to 1.5 A output) > > > <https://lh4.googleusercontent.com/-Rh9IrbXEzAU/UnFV0UcdTSI/AAAAAAAAEAM/TduMV2A5CT4/s1600/adc.jpg> > > Changing the R1/R2 divisor I can make the 220V signal lower , but I'd > always get a signal with a negative side (-0.9V - +0.9V) in the best case. > Same for the current transformer, after applying its output to a 100 ohms > resistor. So, first, is it an awful idea to use BB for this purpose? If > not, how can I avoid the negative part of the signal before feeding the BB > ADCs? > > Thanks in advance > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/ce774959-18f4-446a-a435-fc771eed1948%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
