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all. I know enough about soldering and circuits to be dangerous, meaning I can follow instructions, but I could not design my way through an open door.

I am interested in using an IR Break Beam Sensor (3.3v 20ma to power it--details https://www.adafruit.com/products/2167 ) to cause an LED to turn ON when the beam is detected, not when the beam is broken. Basically, I want to detect when a roll of paper is NOT between the two sensors and then have an LED stay on (or blink would be better). I should be able to do this simply, no? It needs to run 24/7 but the beam most of the time will not be broken. Any circuit guidance would be appreciated and then I will try to figure out what kind of battery power i would need. Oh, when the paper is replaced, I would want the circuit to turn off the LED. The paper is definitely thick enough to block the beam. Thanks for any guidance/resources. -Bob

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closed as too broad by Michael Karas, laptop2d, Autistic, brhans, ThreePhaseEel Jan 10 '17 at 1:45

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\$ Adafruit is helpful in that they have handy application guides for a lot of their products, including yours \$\endgroup\$ – Cheibriados Aug 12 '16 at 17:21
  • \$\begingroup\$ @user2665119 you should do research BEFORE you ask questions here. electronics.stackexchange.com/help/how-to-ask \$\endgroup\$ – laptop2d Aug 12 '16 at 18:29
  • \$\begingroup\$ I read adafruit's material. NONE of that material was helpful, so maybe you might want to read it as well before you comment. Thanks for your help. \$\endgroup\$ – user2665119 Aug 12 '16 at 20:09
  • \$\begingroup\$ laptop2d, and how exactly do you know what research I did? You don't. If you have a suggestion, fine. But otherwise I fail to see any helpfulness from your contribution. \$\endgroup\$ – user2665119 Aug 12 '16 at 20:12
  • \$\begingroup\$ VTC - This site is not a free consulting site from which to solicit designs. \$\endgroup\$ – Michael Karas Jan 9 '17 at 9:38
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Put the breakbeam modules on each side. The module with the white wire will generate the signal to control the LED.

In fact there is a sample circuit showing exactly how to set it up in the datasheet. The resistor values are 5.1k and 1k.

The 5.1k pullup resistor is needed because the output is open-collector.

The 1k resistor sets the current through the LED (brightness). The current will be $$ \frac{5V- V_{LED}}{R_{1k}}$$

datasheet picture

If you want to invert the sensors output, you can accomplish that with a PMOS. Make sure the turn on voltage of the PMOS is not too high. ~2V should be fine. When the output is high, the PMOS turns off and prevents the LED from getting any current. When the output is low, the PMOS turns on and so does the LED.

for active low

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  • \$\begingroup\$ Thank you. with this I can get started. I looked at the stuff on Adafruit, but I did not see this. I looked at their tutorial stuff and it all seemed to involve interfacing with Arduino. Again, thank you for your assistance. Much appreciated. Oh, wait. Is the LED on when the beam is broken? I need to reverse that behavior so that the LED is on when the beam is connected. I need some kind of way to invert the behavior. Any ideas on how I could do that? \$\endgroup\$ – user2665119 Aug 12 '16 at 20:14
  • \$\begingroup\$ @user2665119: I updated with one way which could work for you, using a PMOS. A PNP would probably work too. \$\endgroup\$ – jbord39 Aug 12 '16 at 22:01

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