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I am using the AEDR-8300 as a simple optical encoder solution. The part seems simple enough:

  1. An LED emitter
  2. Photodiodes that pick up the light that is reflected from a codewheel or black/white strip

The current part I have is the AEDR-8300-P, which has a minimum and maximum LPI of 150. I can understand why there is a maximum LPI but why is there a minimum LPI?

PS: I am not getting any output on either output channel on my test circuit and I am trying to understand if I need an improved black/white strip or if my circuit is not right. I've also tried using pull ups/pull downs but there was no difference.

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Simply put, the geometries of the devices are designed for a specific spacing between light and dark in order to maintain a true quadrature output.

If you don't match the device to the target lines per inch (and also spacing, and light/dark ratio's), the device cannot generate an accurate quadrature output.

Not getting any output could also depend on your setup. Try to eliminate any ambient light hitting the sensor. Or your gap from the sensor to the reflective strip may be incorrect.

If just the line density is incorrect, that could cause no output, but there is a 75% chance that you should see at least one output on (Quadrature signals only have one state out of 4 with a 0,0 output).

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  • \$\begingroup\$ An engineer from Avago got back to me and mentioned that the resolution mismatch can at most be 5%. I guess your argument makes sense too. The device has multiple photodiodes and I assume that the LPI rating varies the distance between the photodiodes. \$\endgroup\$ – rith87 May 11 '15 at 1:25

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