Monday, November 06, 2006


Testing the limits...

Quite some time ago I acquired half a dozen Hamamatsu P5587 reflective IR detector chips. They include both a IR source (~0.9 microns) and detector on the front face of the chip. The detectors look like little red spider eyes.

While you can use the company's PDF to size the resistors and capacitors that the chip needs, Acroname helpfully provides you with a schematic for the chip in their on-line parts catalog.

I built a test board for this chip quite some time ago and found that for the detection speeds we require for a RepRap the Acroname parts sizings works quite acceptably.

To get the chip onto the RepRap y-axis I did a quick lashup onto a thin wafer of poplar and attached it to the z-axis frame with one of my ubiquitous c-clamps.

Currently, the detector floats about 1.5 mm above the work surface edge. I am not sure at this point whether I should just make IR opaque marks on the tempered float glass work surface or glue a strip of paper onto that edge of the glass with something a bit more baroque in terms of a detector scheme. You can see that that remote power board at the bottom of the picture is getting a bit workout.

Here are two detail pictures of the lashup. One side ...

... and the other.

Now the big task will to be to get all the sensors and actuators to work together in the 16F877A. I expect that I will be toying with that job through this weeked. :-D

Tested the circuit. It works. It gives 5v for IR opaque surfaces and 0.1v for transparent ones.

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