Help please. Dip switches and mach 3 settings

[john swift]

there must be a detail we don't have to explain why you measure 26V on input P13

which terminal did you connect the volt meters negative probe ?



the printer port ground is connected to the mains supply earth / ground

on the other side of the BOB's opto-isolated circuit

the 5 inputs can not be more than +10V more than
the 12-24V supply ground , input ground & analogue output ground
(which are all connected together on the BOB)

depending on the 12V power supply your using the 3 grounds may be at a different potential to the mains supply ground

small switch mode power supplies such as the ones used with laptops and other IT equipment don't have the negative output terminal connected to earth like PC AT or ATX supplies
they have a small capacitor bridging the mains input & DC output !!!!
( the capacitor is a backwards step just to comply with EMI requirements)

the leakage from a couple of devices is OK but several power supplies can add up to give you a shock

John

PS