Thursday, December 22, 2016

Thinking more about the energy monitor...

I had kind of given up on the energy monitor project for the simple reason that getting data into some useful form would be beyond what I have available to me at the moment.

However, opportunities present themselves in odd places. My employer needed something similar to monitor the lines of an air compressor to determine when the compressors are on or off. They didn't want to break the lines, so a non-invasive method of collecting data was needed.

Well, I had these clip-on current sensors from Seeed Studios left from my attempt, so I brought them in and measured the output to see if it would work. Yes, but the output of the clip is AC, and every device we have only measures a DC input.

Easy enough to solve, I pulled out an old design I had from the audio days, a precision full-wave rectifier circuit located on Page 234 of a book called "Encyclopedia of Electronic Circuits, Vol. 1" by Rudolf Graf. While some of the circuits in the book are less than useful due to age, incompleteness, or simply by being reference block diagrams instead of circuits, there are a few gems.

(This image is presented as a reference only.)

While I've made some changes to the circuit, using TL08x Op-Amps and germanium point contact diodes, output buffers and some minor output filtering, the circuit presented is doing the dirty work.

Since I have access to circuit board tools, I've decided to lay it out on a new board, give it it's own filtered power supplies, and add some easy-to-use connectors to it. What's amazing is how much bigger the diodes are as compared to almost everything else on the board, save the input connectors.

Then again, what's cooler than a 1N34A point-contact germanium diode in a glass case?

(image from

The board layout is the same form factor as my power supply and alarm monitor board, a size I've adopted for a lot of different things. Right now, I've completed the schematic (save the power converter, which I have not chosen yet) and am getting ready to see how well everything fits. Here's hoping I can get everything on this board!

Once it's all done, I'm going to work the design a little and begin the energy monitor project again.