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[on:]

I've recently put together a project to monitor the IR pulses emitted by my smart meter.

Everything works great, except I'm having problems with ambient light.  I'm using a Radio Shack IR photo transistor to fire an external interrupt on digital pin 2.

Right now I have some black vinyl floor runner material wrapped around the meter underneath the hose clamp that holds the bracket for the photo transistor.  I had to put another piece on the front face today.  My meter is on the south side of the house, and the face of the meter gets a good tan at noon.

I'm wondering if using a qrd1114 might be a better choice--not driving the emitter.  The datasheet says it has a "daylight filter".  Anyone have suggestions?  It's a good thing my meter is wireless, if the electric company sees what I've done they would threaten to disconnect service.  I was already planning on getting a qrd for my gas meter.

The black and decker energy monitor, and front probe mount of wattvision (http://www.wattvision.com/info/products) do not have any of the shading I'm using.

Please do not suggest using analog!  It maxes out as soon as I go outside, and the pulses are way to short to detect.

I would rather not have to put together a preamp/detector if I don't have to.  I'm hoping I can fix this with a better photo-transistor. 

This hacked up mounting threatens the long term viability of the project.

[Reply #1 on:]

With a little more research I've found:

http://www.futurel.bg/datasheets/6/AN_651X_008%20-%20rev%201-1.pdf

The spec for the IR port should be covered by ANSI C12.18.

They suggest an OP804SL.  Ironically the ansi spec says ambient light shouldn't be a factor. 

[Reply #2 on:]

Initial test of OP804SL mounted on the smart meter was a failure, I buggered up and wired up base instead of collector.  After tearing my sensor apart and realizing my error, I began playing with the base pin to adjust bias.  Ended up with a 22K resistor to GND.  Very unscientific test, I used a remote control and cigarette lighter.  Adjusted the bias resistor until the phototransistor driving an LED did not respond to the lighter, but reliably responded to remote control.  The OP804SL is very directional.  IR source has to be almost perfectly on axis at close range.  My smart meter mount consists of an L bracket with an extra hole drilled to line up with the IR LED, and a Radio Shack LED threaded panel mount.  The TO18 package does not seat very well.  I had to bend over the tab, and shim the photo-t with some tape.

Right now it's working in evening sunshine, I will know for sure tomorrow afternoon.  Hopefully the electric company doesn't give me crap about the sensor.  At least now it doesn't look so obvious.

Anyhow, the OP804SL might be a good choice for anyone trying to do outdoor IR stuff.

[Reply #3 on:]

Why don't you use wireless if the meter already has wireless? There should be a protocol. Does your meter have IRDA and/or data terminals?

[Reply #4 on:]

Wireless stuff is beyond me.  It appears the wireless interface is added on by http://www.tantalus.com/ on top of the GE meter. 

I've found a blog post of someone who was able to sniff the wireless output of his smart meter.

The IR interface is too convient.  The new IR photo-transistor is proving to be reliable.  The installation is cleaner, not as obvious. 

My only real complaint is the 2 Whr pulses.  Wish it was 1.  Time between pulses gets a little long when there is little load.

[Reply #5 on:]

Oh BTW, the IR is probably pulsed at 38,400 Hz like a TV remote. Steady IR doesn't effect the readers except if they wash the signal out.

I have IR detectors that look like black leds with 2 leads, the light is the bias. The black in the bulb filters regular light very well but not reflected IR.

If I put the bulb in even a short tube, it won't 'see' much more than a signal led, get less scattered interference. You won't have to modify the meter.

[Reply #6 on:]

Is it more efficient to declare frequently used variables in the global scope, rather than declaring them over and over again locally?

[Reply #7 on:]

Oh BTW, the IR is probably pulsed at 38,400 Hz like a TV remote. Steady IR doesn't effect the readers except if they wash the signal out.

I have IR detectors that look like black leds with 2 leads, the light is the bias. The black in the bulb filters regular light very well but not reflected IR.

If I put the bulb in even a short tube, it won't 'see' much more than a signal led, get less scattered interference. You won't have to modify the meter.

Found the manual for the meter.  It specs a 25ms pulse, no mention of modulation.  Looking at it with a cell phone doesn't reveal any flicker like a remote control.  The stupid RS photo-transistor was clear with no filtering, part of my original problem.  The 804 has functioned correctly with full on daylight.  Alignment was fairly critical, it's crazy directional.  The LED in the meter is slightly off axis, and the hole I drilled in the bracket was slightly off.  A shim of weather-striping made up the difference.  I used http://www.radioshack.com/product/index.jsp?productId=2062559, it sits flush on the face of the meter.  Need to get a pic posted.