Power meter (Part 2)

I have been tumbling through the net, looking for interfaces to the TIC. So far, I found two types of reference designs:

  • The quick, dirty, safe but questionable design
  • The academic design

Most of the interfaces described on the web are very basic. They feature a single optocoupler and a biasing resistor.
The other option is much sophisticated and features a signal shaping stage. The design is far better, but requires TTL components and their power supply.

Credit

Once again, I decided to design one of mine, with my own constants: state of the art, compact, cheap and safe. This one features features a few cheap analog components arranged in these sections: power supply, demodulator and opto-switch.

Power supply: here we use a simple half wave rectifier (D1 and D3) biased through R2. The rectified signal is dampened by C1 and optionally regulated by D5. The output is a stable DC voltage.

Demodulator: once again we use a simple half wave rectifier (D4 and D2) biased through R1. The rectified signal is moderately dampened by C2 and applied through R3 to the base of Q1 acting as a switch. R3 discharges C2 in order to prevent tailing pulses.

Opto-switch: this is the easy part of the schematics ! The internal LED is biased through R5 and switched by Q1. Tx is switched to ground when a wave hits the input of the demodulator.

Warning: As you can see on the schematics, the interface has a separate ground from the Arduino, which is probably connected to your PC and thus to the mains ground. At all times the interface GND (labelled GNDA) must be floating versus GROUND.

Note: During the development satge, is used a reference signal generated with my RIGOL DG1022U DDS function generator, using the burst mode applied to a 50 kHz, 6 Vpp, 0V offset signal.

And the plots are screen shots from my good’ol RIGOL DS1052E tweeked to 100 Mhz

Both are electronic’s enthusiasts best friends ! Affordable, compact, reliable (except the encoders from the scope), accurate and pretty powerful.

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