Are electronic devices really in a very low power mode when on stand-by ?
Also, how much energy am I wasting for powering devices when not in use ?
I wanted to check it out and decided to build a device capable to detect stand-by mode of my electronic devices and start metering energy used. All this had to be done automatically without my intervention. Metering would start upon entering stand-by and stopped upon exiting.
To do so I needed an energy meter and a current gauge to monitor the current of mains supplied devices and start/stop metering.
For the meter I first looked for silicon, of course. Energy metering is a hot issue with a lot of chip makers and many of them supply cheap solutions.
The project was proceeding when recently I was lucky enough to find two electromechanical meters at a local special trash collecting center (electrical, white goods, furniture).
Actually there should be a plenty of these scrap meters available here as the local electric company is replacing these meters with remotely controlled electronic meters.
I took them along with two VCRs and a printer. The first meter I opened and dismantled to satisfy my inner primary need. The second meter I decided to use in place of the silicon-based one; also, the ready made electromechanical meter solved the calibration issue.
This PopSci contest made me hurry and change priorities in my to-do-list, so here is my design.
Schematic V0.2 is an improved version of the electronic control box over the previous one. I added a potentiometer to set the hysteresis level. This helps discriminate power on vs. stand-by for noisy power supplies like some switchers are. This also helps get firmer metering on/off states.
The schematic shows in red the differences with respect to previuos version.
Step 1: Caution, safety first !
Before starting, you must be absolutely aware that this thing is powered from the mains and
as such it could kill you, cause damage or injuries. If you are not really skilled at mains
powered electronics and related safety building practice and are not well aware of the risk related, you are suggested to have a friend help you with this project.
Also, as a general rule, when you are working on dangerous things always have someone next to you instructed on what to do if something goes unexpectedly.
Most parts of the circuit should not be considered safe to touch when the circuit is powered on.
Keep low voltage and high voltage wiring as separate as possible. The relay is the point where the two worlds are closer. Choose a good relay and have the wires soldered firmly. Tape well and possibly use heat-shrink tube.
These notes are not just to scare or bother anyone, but I absolutely want that fun does not turn