I'm trying to find a sensor that is similar to the ones used in floppy drives to determine the track 0.

It's an optical sensor with about 3-4mm of space between the emitter and the receiver so that it can detect if the beam is interrupted.

All parts I can find are pretty large elements but I am looking for something small and I don't know what name they may have

An example of such sensor is on the photo here, the black part:

Track 0 sensor on a floppy drive

Additional question: I have a box moving on rails and it has 5 positions; the range is about 1m, precision about 0.5cm. Are these sensors the best way to go?

  • 3
    \$\begingroup\$ You'll want to search for "photointerrupter". There are different types, but the one shown in the picture is fairly common. \$\endgroup\$
    – DerStrom8
    Commented Apr 4, 2017 at 11:12
  • 1
    \$\begingroup\$ thomas, unrelated, but a heads up, in case you forgot to pay your registrar: tried to click on the link in your profile, and wdindustries.net is not a registered domain \$\endgroup\$ Commented Apr 4, 2017 at 11:56
  • \$\begingroup\$ @Markus, yes, it's an old company we created; it made pc/xbox game ports, but it's defunct now; I had no idea it was still attached to the profile. thanks! \$\endgroup\$
    – Thomas
    Commented Apr 4, 2017 at 13:35
  • \$\begingroup\$ For your actual use case, look into Digital Readouts used for milling machines, lathes etc. Some can be had quite inexpensively and if anything would be overkill for your application. \$\endgroup\$ Commented Apr 4, 2017 at 21:59
  • \$\begingroup\$ a forked light barrier? \$\endgroup\$
    – dlatikay
    Commented Apr 5, 2017 at 7:20

2 Answers 2


To add to what Olin said, the sensors are also known as "photointerrupters" when searching some of the distributors.

There are at least two major types of these sensors: Logic output and transistor output. Logic being the type that drives it's own output signal, and the transistor type acting more like a switch.

photointerrupter sensor

As for:

I have a box moving on rails and it has 5 positions; the range is about 1m, precision about 0.5cm. Are these sensors the best way to go?

I don't see how you're going to use these sensors to detect a box's position if you want a "small" sensor. The beams are between two appendages about 1cm apart. So unless your box will fit in a 1cm space, you may want a different approach.

Note that you can use the same concept over a larger area, you just need separated emitters and "receivers". The kind used in the floppy disk drives combine the two into a small package. Instead, you'll probably want an emitter on one side of the box, and the receiver on the other.

  • 1
    \$\begingroup\$ I would have a small tab running outside of the box, like the floppy has on its head assembly \$\endgroup\$
    – Thomas
    Commented Apr 4, 2017 at 13:34

Try "opto-interrupter" or "optical interrupter".


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.