Opto circuit design

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jwax
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Opto circuit design

Post by jwax »

Starting with a NTE3105 Opto Interrupter, I'm trying to build a circuit that outputs 5 volts when the opto device is in the dark, but zero when illuminated.
In other words, when a reflective surface is close to the device, the detector is illuminated, so zero out. If the reflective surface is removed, the detector is now dark, then it outputs 5 VDC.
Here's the device:
http://www.radioshack.com/nte3105-opto- ... 05&start=1

Would another npn transistor be all that's needed?

Any circuit design suggestions appreciated!

John
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CeaSaR
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Re: Opto circuit design

Post by CeaSaR »

I do believe this is what you want.

http://www.electronics-tutorials.ws/logic/logic_4.html

For further research, Google "one transistor state inverter"

CesSaR
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dyarker
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Re: Opto circuit design

Post by dyarker »

Disagree about external invertor being needed. Here is spec sheet for the NTE3105:
http://www.nteinc.com/specs/3100to3199/pdf/nte3105.pdf
A current limit resistor for LED.
A resistor from collector to Vcc. Emitter to common. Output from collector resistor junction.

When internal NPN transistor base is dark, the transistor is OFF; output is high. Actual voltage depends on load current.

When internal NPN transistor is lit, the transistor is ON; the output is low. Actual voltage is Vce(sat) of the transistor.

Cheers,
Dale Y
sghioto
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Re: Opto circuit design

Post by sghioto »

Agree with dyarker.

Steve G.
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jwax
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Re: Opto circuit design

Post by jwax »

Thanks guys!
dyarker's got it. Simpler than I thought!
At first, only had 2.2K of collector resistor, kind of shaky results, but 27K ohms gives enough gain to assure positive ON-OFF switching. :grin:
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