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Forum Index : Electronics : Switching + or - ?
| Author | Message | ||||
Poppy Guru  Joined: 25/07/2019 Location: GermanyPosts: 486 |
Hi everyone,  if you install a switch to any circuit what do you switch, the positive or the negative terminal? Theoretically the electrons are said to be coming from the PLUS but physically they are supposed to come from the MINUS, does it make any practical difference which side to cut off? So how do you manage this and particularly why?  Andre ... such a GURU? | ||||
CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2075 |
Depends entirely on the application. Power I switch the +ve, signals I switch -ve For signals I always like to pull down with the switch - it limits the current capability of what's going on... i.e. pull up resistor (10K+) down through the switch, this way the current is limited by the resistor to an un-conditioned GND, whereas if you switch the +ve, the current at the sense point is potentially Icc unless you take steps to limit it. I can't think of an instance where I have installed a remote switch unit for sensing and gave it Vcc... it's always pulled up by the sense inputs and all I do at the switch is ground whichever wire... In the event a cable gets cut through, the most current you can get out of the thing is Vcc/10K or about 330uA, maybe a bit more if you short several sense inputs (and this parallel the pull-ups) but it is still tiny. Horses for courses though. I think it comes from my years ago work with TTL which always liked to be pulled low... kind of "stuck"...not a bad habit. Edited 2019-10-29 21:08 by CaptainBoing |
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