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So currently I am using a phototranssitor to detect light from several IR LEDS; however, I am having some trouble. I am currently using the right side of the circuit in the picture half way down the page on this website (http://www.nerdkits.com/videos/theremin_with_ir_distance_sensor/) should be under the heading The Electronics. Anyway I have been trying for ages. I have a 5V supply, connected to the collector of the phototransistor (BPV11) in series with a 10K ohm resistor to increase the sensitivity to light, then to ground (as shown in the picture). My problem is when testing I am getting changes of MAX 100mV (milli) which is no were near my friends change of 1V to 5V with the same set up. I have tried every orientation to no prevail. Any help? And yes the LEDS are working!

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  • \$\begingroup\$ Phototransistors have large sensitivity variations. And how much light of the LEDs does reach the PT? \$\endgroup\$ – CL. Oct 20 '15 at 12:00
  • \$\begingroup\$ the bpv11 brings the base lead out, check that you've got it hooked up correctly. vishay.com/docs/81504/bpv11.pdf \$\endgroup\$ – George Herold Oct 20 '15 at 14:41
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Have you got the phototransistor the correct way round.

It will probably work (but not very well) if you have the leads reversed.

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