3

I currently can't buy an optoisolator, so I was wondering if I could wrap a optointerrupter in tape to shield it from light and use that as an optoisolator. Is this possible?

Bram Wyllie
  • 43
  • 1
  • 1
  • 5
  • I gave +1 to the question because you used imagination to try to find a substitute. Also because you confessed (under Olin's answer) to to using your ingenuity due to lack of funds. – Marla Jan 02 '16 at 23:53

3 Answers3

2

Don't have an opto-isolator? Make one.

All transistors are photo-electric until put in a can or some opaque plastic. If you have a small signal metal can transistor you can cut or file the top off and super-glue it to an LED.

LED superglued to transistor.

LED superglued to 'photo-transistor'.

Heatshrink cover.

The finished article with heatshrink sleeving.

The transistor is a 35-year old BC108. LED is a generic red - probably same vintage.

Watch out for light getting in the back of the LED. Current transfer may not be very good so you may need to 'Darlington' the output.

Community
  • 1
Transistor
  • 175,532
  • 13
  • 190
  • 404
  • I don't have a metal can transistor, but I found something like it. Will this work? I think it's a diode: Thing – Bram Wyllie Jan 02 '16 at 23:12
  • @BramWyllie, I think not. Have a look at using LEDs as photodiodes. There is a little hope there but I'd say the current out of it is very weak and would need amplification. Your question doesn't specify what frequency you hope to operate at. Post the details in your question (and not here in the comments). – Transistor Jan 02 '16 at 23:38
1

Sure, it's possible, but opto-isolators are intended to provide isolation and usually have isolation levels and common-mode rejection levels specified. An opto-interruptor has a different purpose and may not specify those things. If isolation and/or common mode rejection are important in your application you may get into trouble if they are unknowns. Also, your tape may not be opaque to all frequencies that the receiver is sensitive to, so you may get interference from some light/radiation sources. Digi-Key has lots of opto-isolators and they ship almost anywhere so not sure why you can't buy an optoisolator, but depending on your application you may want to.

John D
  • 23,824
  • 1
  • 41
  • 61
1

Yes. Most opto-interruptors have poor characteristics as opto-isolators, but it is possible. Also keep in mind that they may be using IR, not visible, and most black electrical tape is quite transparent in near IR.

Also, "can't buy optoisolator" doesn't make sense. These things are readily available from the other end of the internet, and cheaper than opto-interruptors too. It seems you are only saying this because you want the answer to be to use a interruptor.

Olin Lathrop
  • 313,258
  • 36
  • 434
  • 925