<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Bwired</i>
<br />Hi Ame
How does your photo transistor react when you open the door of the fuse box and some bright light comes in?
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That is a good question. I have found that the heatshrink tubing around the phototransistor is very good at rejecting external light, and the phototranstor itself seems to be very focused (perhaps this is due to the shape of the clear plastic housing). Also, the meter cupboard is in a dim corridor in the house, and the light nearby has a lampshade that casts a shadow over the meter.
The worst case would be that the bright light would prevent the phototransistor from sensing the black bar, so when the cupboard was open, pulses would be missed. However, with low load the pulses are about 1 minute apart, and with high load about 20s apart, so if you are quick (don't leave the cupboard open) you won't miss many pulses. If I use cheap laser pointers then they are so bright that I can turn the gain of the circuit way down so that external light is unlikely to affect it.
I have attached a picture of the prototype sensor. The legs of the components have been bent to make the light reflect properly, and the board is stuck to the meter with blu-tak. I will make a bracket for the sensor later when I have finalised the design.