Electronics Laboratory



Bob Glusick

OptoElectronic Meter Reader


This project had a goal of reading a watt-hour meter over the telephone line.

It had 2 major challenges: 

  1. Don't connect the telephone line electrically to the power lines
  2. Don't impede the motion of the meter device, and cause errors in the reading.

Of course, this was well before the integrated circuit, so the logic elements had to be constructed from scratch to answer the telephone, sequence through the individual data bits, and hang up at the end. 

Optoelectronic elements were used to achieve all these goals. Only light traveled from the phone line to the power line circuitry (over a short but safe distance) and back, and only light beams were interrupted by code wheels on the readout dials (so there was virtually no error from drag). Since the technology involved only opto-electronics, it made sense to extend the devices to perform the switching and sequencing logic functions. 

The overview photo shows the  working meter which ran in our lab and could be dialed up remotely to listen to it's codes. The 2 terminals at the top of the meter were the bi-directional optically isolated telephone line. The sensing and sequencing logic was in the box behind the dials, which had shaft extenders to reach through the logic. 

The EL array photo shows several electroluminescent cells manufactured for us by GE NELA park. The technology was commercialized as "Night Lites".  The meter reader used the 3 EL elements at the lower right of the picture labeled "10 stage ring counter", "Power switch", and Multiple star wheel decoder". 

The PC (Photoconductor) picture shows the matching photo sensors. There are only 3, but each is shown with the conductor pattern and no photo sensor, and then the complete array with the photo sensor in place. Elma Littebrant was responsible for fabricating these photo arrays for us at the E Lab.

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This page last updated on 11/06/2007