V measurment across a switch can? interfere with the circuit?

greets

Can the Arduino interfere with the functioning of a circuit if you use the Arduino to measure voltage drops across switches (i.e. see if this or that switch is open/closed)? I have a device and I want to use an Arduino to detect open/closing of multiple switches. Also could shift registers be used to increase the amount of switch detectors?

naut: greets

Can the Arduino interfere with the functioning of a circuit if you use the Arduino to measure voltage drops across switches (i.e. see if this or that switch is open/closed)? I have a device and I want to use an Arduino to detect open/closing of multiple switches. Also could shift registers be used to increase the amount of switch detectors?

If the maximum voltage across switch is 5.5vdc or less there is no problem reading it on a arduino as arduino input pins have very high input impedance so will have little or no effect on the signal. Whether to read it as a digital or analog voltage depends on the nature of the signal going through the switch. However for it to work there must be a common ground wire also run from the circuit to be measured to an arduino ground pin. You can't do it with just one wire.

Lefty

The switch terminal voltage needs to be between 0V and 5V if directly connected, but its much more robust to connect to the Arduino via 10k resistors, then small over or under-voltages won't be instantly damaging and accidently setting the pins as outputs won't risk burning them out.

If there is any risk of mains voltages being present then don't even think of doing this!

MarkT: If there is any risk of mains voltages being present then don't even think of doing this!

Nope, the device runs at IC voltage levels. I have not measured the levels but if they are over 5V I'll just use resistors to get them down to within the 0 to 5v range.

What I'm more interested in is if I could use muultiplexers or shift registers to detect the engagement of the momentary switches...?