Quick electronics question

[cropwell]

m_c,

I would do it all with a 4066 quad analogue switch. Presuming the '12-24v line' is actually the logic input on the controller for the touch probe, which is resistor strapped high and the probe output is +5v when triggered.
You would use 1/4 of the 4066 to convert the probe output. 1/4 to switch the LED and you have 2 spare to use for other things, like inhibiting the spindle.

The 4066 has an 'on' resistance of about 80ohm (if my memory serves me).

Cheers,

Rob

[Doddy]

m_c,

I would do it all with a 4066 quad analogue switch.

Might work but not at 24V... or at least without spilling some smoke. Also CMOS tends to have a high switching voltage at high VSS - the 5V sensor voltage wouldn't cut it at 12V. Max current through a single channel is 10mA so rate the LED resistor accordingly.

Sorry!, not a dig!

OP: Why not use a common ground as a sense input, rather than a 5V input? (if you have 5V handy then ignore)

[cropwell]

Might work but not at 24V... or at least without spilling some smoke. Also CMOS tends to have a high switching voltage at high VSS - the 5V sensor voltage wouldn't cut it at 12V. Max current through a single channel is 10mA so rate the LED resistor accordingly.

Sorry!, not a dig!

OP: Why not use a common ground as a sense input, rather than a 5V input? (if you have 5V handy then ignore)

No - you are right, 15v abs max and 10mA. But I still can't see how the original circuit would work. I would need some resistor values then I could simulate it or even bread board it. Also it would be useful to know the impedance on the 12-24v.