Wheel Encoders - Part number, max current


I am trying to use the Wheel Encoders for a custom wheel on a plane designed at our college. The encoders work well as is, but the detection range could be a tad longer. I would like to bump up the current to the emitters.

I do not know the part number for the devices on the board, so I do not know the Vf of the diodes (I could figure that out easily enough), nor do I know the max current specification. I wold like to find out if I can bump this up maybe 20% or 30% without damaging anything.

I did some measuring. Vf of the emitter diodes, with the standard 100ohm resistors and 5V is 1.17V. The current through them is about 13.3ma. They are in series, so its the same current through both.

I think I am going to try and boost the current to 17.8ma by replacing one of the resistors with a 50ohm.

It would be great to know that this is still well in spec.

Also, perhaps I could just adjust the detection range with the pots???


The part is a Fairchild QRE1113, for which 20 mA should be fine. In our tests, more brightness didn’t really get us much. I’m not sure about your application, but I’m concerned about reliability if you’re going to use this outside. In that case, more brightness on the LEDs might help compensate for more ambient light.

- Jan