background

ANSI has a standard for a "Type 2 Optical Port" which is adopted by some smart power meters in the USA (and Australia?). It is a half-duplex infrared optical serial link. The standard has been around since 1996. I've seen the horseshoe shaped interface on power meters for commercial buildings for some time now, but they've also started to appear on some domestic buildings.

I've been interested in the possibility of logging real-time power usage, but not enough to spend the $300+ for a commercial reader.

Without a local interface for the consumer, these "smart" power meters are limited to infrequent polling by the power company over a UHF link, which doesn't seem very "smart" to me.

design

The micro is a PIC16F1459 leveraging my open-source bootloader. This particular PIC costs a bit more than the '1454, but has a software-configurable comparator. I've seen some other projects on the web that rely on various manually adjusted trimpots, but the advantage of my design is that the micro's comparator (used as a data-slicer) has its threshold set in software.

The entire project (schematics, firmware, etc.) is available via Sourceforge. The individual files are here.

latest status

Initial testing was very positive. As of 20140125, I was able to use a pair of devices to form an optical bridge between two PCs.

However, try as I might, I have not been able to talk to a power meter. This could mean that my implementation is not conformant to the standard, although I've read everything I can find in detail. It could also be that the optical ports are disabled by the local power company (as they poll the meters remotely over a wireless link and have no need for the ports).

As of 20140208, I modified the implementation slightly by changing the bias resistor on the photodiode from 10kohms to 47kohms. This greatly increased the receive sensitivity (and in turn the maximum distance of the link), and was still usable at the 9600bps rate ostensibly used by ANSI meters. However, this didn't make any difference in talking to the power meter.

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