The sensor data sheet shows an internal resistor in series with the LED and op amp. It would be unclear where that resistor is, until we study the photograph carefully and compare it to the data sheet electrical and mechanical drawing.

After some study, some of us decided that the unmarked resistor in the data sheet is the 3.3k resistor that's visible on the underside of the sensor assembly. I, (and apparently kchriste) felt that matching the current consumption into the V+ pin was the best way to choose the new resistor value.

Since this resistor is internal to the sensor, choosing its value does require careful study of the sensor data sheet. I think that suggesting a change to the part without looking at the data sheet was hasty.

If you had some other resistor in mind, (external to the sensor?), I was confused and please accept my apology. Actually I still am confused.

This is another part that I have. Its number is S7275-1 and I did not found any datasheet for it.

The circuit being more complex I just tried it without modification at 5 volts and to my surprise It is working. I then tried an unmodified one like the first one and it is working too at 5 volts. Same crisp and clean trigger.

For the usage of this part, as I understand it now, the CNC software keep the photointerrupter dedicated parallel port pin high. Since its output (of the part) is floatting when not trigered, the port pin stay high. When triggered, It connect the ground to the port pin forcing a low witch indicate to the software to stop everything. Does it make sense?

Alain

I'm seeing four devices. Are they marked "303", "122", "221", and "PA" ?

"303","122","122" and "PA"

I suppose that because of the PA being there this part has a much higher output capacity then the other one??

What is that PA? Is it a PNP transistor?

PA is probably either a Toshiba 2SC4666A or 2SC3295A (which probably doesn't matter since I don't see any difference between them anyways). It would be a high gain (600-1200) NPN transistor, 150 mA, 50V. [edit] Actually it appears that it's probably the 2SC4666A because it's the narrower one.[/edit]

Although the collector is rated at 150 mA, it's not wise not to push it because it could make the crisp operation much softer.

Originally Posted by Mr RB

I had no way of knowing that without reading the datasheet which was not necessary or relevant to the good advice I gave re measuring the device and choosing a specific resistor value.

Here I disagree, and that's all I have to say, about that, at this point

Originally Posted by Mr RB

If you think I'm worng then just say so, I'm wrong as often as the next guy. But don't explain what my words "mean" as if I was too stupid to choose the right words myself.

I apologize for typing on your behalf or appearing to be condescending towards you. That was not my intent.

Since there was different voltages present on the donnor machine, some parts working at 12 volts, some other at 24 volts and some other at other voltages and since the first device showed here is designed for 24 volts with a 3K3Ω resistor, could we deduce that this second one, with 2 - 1K2Ω resistors in serie is probably designed for 12 volts operation?

If so then could we deduce that the resistor of the first device should be changed to something like 1K2Ω to work at 5 volts instead of the 330Ω mentioned previously ?

Is this too simplistic?

I am more concerned about the first device that can be easily modified. The second one, specially if it is effectively designed to work at 12 volts, I will keep it as it is.

If you want 'OEM' operation but on 5V, I would try to determine what the original supply current was (if you only know the voltage, set it and measure the current on the bench). Then change one or both of the 122 resistors until that current is achieved at 5V.

This sensor is a little more versatile, too. If you have minor problems with stray light, you can reduce the 303 resistor (maybe as low as 4k7) to desensitize it.