Home Switch Problem

[Kev2960]

Hi John the bob looks like this. I have tried both normally open and normally closed

[john swift]

looking at the breakout boards inputs



when the limit switch is closed, the EL817 opto isolator's NPN transistor will ground the printer ports input pin

the breakout board does not have any pull up resistors to ensure a printer port input is at a valid logic high when the limit switch is open

this can be a problem with PC's or laptops with 3.3V printer ports

John

[m_c]

looking at the breakout boards inputs



when the limit switch is closed, the EL817 opto isolator's NPN transistor will ground the printer ports input pin

Going back to this photo, my calcs based on the 1k resistor, means the opto should have 24V on the pin you've marked as 5V. At 5V, the 1k resistor would limit the current to roughly 3mA, whereas 24V would give roughly 22mA. Having had a look at the datasheet for the opto, it's expecting 20mA with a forward voltage of 1.2V.

Kev, have you measured the voltage at the top left pins on the optos?
Try using the bottom pin on the connector for gnd, and also the main power in gnd for the voltage measurements, just in case it's a gnd fault, not a positive supply fault.

If there is no voltage showing, is there power at the fan connector/is the fan working?
Would it be possible to get a photo of the underside of the board, so we can see where the power supply feed to the opto comes from?
Given the layout, I'd think the optos would take a feed from the same supply going to the fan connector, but without seeing the underside of the board, that is purely a guess.