Setting up threading on a Boxford 160TCL lathe

If the disc exists, then I would use it.

The original sensors were probably something fairly standard.

I think I would use something like uk.rs-online.com/web/p/slotted-optical-switches/6666473/ which has logic output so save messing about with pull-ups etc.

As there are 5 in the pack, you might as well do the full ABZ set for rigid-tapping support.

rider-83 wrote:

What would be my wiring requirements?
+5v & GND on two legs, and the others would connect direct to the LPT?

With the ones I linked to, yes.

rider-83 wrote:

I have the emitter LED connected to +5DC & GND to an external power supply.

You probably didn't want to do that without a resistor to limit the current. The data sheet does not show any current limiting resistor and says that the LED has a max current limit of 50mA. I would suggest aiming for 5mA, at which point the LED forward voltage is 1,1V.

5V - 1.1V = 3.9V at the LED, V=IR suggests that a 680R resistor would be about right.

If you have already switched it on like that then the LED might well be dead now. You might be able to see if it is lit up in infra-red with your mobile phone camera.

The three other legs, I'm a little lost. My thoughts were the GND to a GND pin on the LPT, but I'm unsure of the other two. It looks from the wiring diagram that I apply a further 5v and collect the signal from the middle pin?

Yes, that's right. You can connect the 5V to the same 5V as the LED (not via the resistor). And check that the output varies between 0V and 5V with a multimeter before connecting to the parallel port.
You could consider stealing the 5V from a USB port, then you can be sure that the port and the sensor share a power supply reference.
(just cut an end off of a USB cable, the red and black cores will be 5V and 0V.

andypugh wrote:

rider-83 wrote:

I have the emitter LED connected to +5DC & GND to an external power supply.

You probably didn't want to do that without a resistor to limit the current. The data sheet does not show any current limiting resistor and says that the LED has a max current limit of 50mA. I would suggest aiming for 5mA, at which point the LED forward voltage is 1,1V.

5V - 1.1V = 3.9V at the LED, V=IR suggests that a 680R resistor would be about right.

If you have already switched it on like that then the LED might well be dead now. You might be able to see if it is lit up in infra-red with your mobile phone camera.

The three other legs, I'm a little lost. My thoughts were the GND to a GND pin on the LPT, but I'm unsure of the other two. It looks from the wiring diagram that I apply a further 5v and collect the signal from the middle pin?

Yes, that's right. You can connect the 5V to the same 5V as the LED (not via the resistor). And check that the output varies between 0V and 5V with a multimeter before connecting to the parallel port.
You could consider stealing the 5V from a USB port, then you can be sure that the port and the sensor share a power supply reference.
(just cut an end off of a USB cable, the red and black cores will be 5V and 0V.

rider-83 wrote:

I've just found on the internet a separate data sheet from 'Sharp'. They are suggesting a 47ohm resistor. How does that sound?

It sounds low. V/R = 3.9 / 47 = 82Ma.

Are you sure it wasn't 470 ohms?