OptoElectronic Meter Reader
This project had a goal of reading a watt-hour meter over
the telephone line.
It had 2 major challenges:
- Don't connect the telephone line electrically to the
- 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
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