I am looking for an example of a day-light sensing LED light, similar to https://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/ but instead of turning on when dark, I want it to turn on when light. Could anyone point me to an example, or lead me down the right path?


closed as too broad by Andy aka, brhans, Voltage Spike, Dwayne Reid, Dmitry Grigoryev Jun 18 '18 at 8:11

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Welcome to EE.SE - in general, don't make people click through links. Draw the circuit using the built in circuit editor and have it in the question :) \$\endgroup\$ – awjlogan Jun 14 '18 at 16:03
  • \$\begingroup\$ Good suggestion, I'll be sure to do that in future posts! \$\endgroup\$ – ts1111 Jun 14 '18 at 16:55
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    \$\begingroup\$ He's suggesting you do it in this one. Your question becomes useless to anyone else when that link dies. \$\endgroup\$ – Transistor Jun 14 '18 at 16:56
  • \$\begingroup\$ What you are looking for is called an ambient light sensor, e.g. OPT3001 www.ti.com/lit/ds/symlink/opt3001.pdf \$\endgroup\$ – Misunderstood Jun 15 '18 at 20:35

You have two simple possibilities:

  1. Switch the position of the resistor and the phototransistor. This way the resistor will pull down the base of the NPN when it's dark and the phototransistor will pull it up when it detects light.
  2. Use a PNP instead of the NPN transistor and keep the resistor and the phototransistor where they are.
  • \$\begingroup\$ Great, thanks for the quick response! I'll give this a try. \$\endgroup\$ – ts1111 Jun 14 '18 at 16:55

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