Voltage sharing? - Page 1
Forum section: electronics / beginners

author: brownt
author_rank: Regular Contributor
timestamp: July 01, 2021, 09:16:26 am
content: Hi,Can these two circuits be placed safely in parallel via their expression jacks to an external potentiometer?What happens if one of these 5v circuits was placed in parallel with a 3.3v circuit. The configuration of the 3.3-volt circuit is not known?thanks

author: gcewing
author_rank: Regular Contributor
timestamp: July 01, 2021, 10:23:16 am
content: It might not work very well, because the resistors from AVDD in each unit would get paralleled and change the range of adjustment. You could try it, but be prepared for things to be a bit wonky.You would be better off using a ganged potentiometer, so that each unit has its own electrically independent pot.As for the 3.3V unit, without knowing anything about what's inside, nothing can be said about what would happen if you paralleled it with one of these. In the worst case it might be damaged by having its 3.3V supply raised up.

author: brownt
author_rank: Regular Contributor
timestamp: July 05, 2021, 09:12:43 am
content: OK thanks.What if there were only two device possibilities. Devices with 5v and devices with 3.3 volts.And what if 3.3 volts was actually enough amplitude for the 5v devices. That is to say that the full 5volts is not actually required anyway.Could I use a 3.3 volt zener as shown in the attachment, and hence it wouldn't matter which two, or more, devices I attached to the one potentiometer?

author: Zero999
author_rank: Super Contributor
timestamp: July 06, 2021, 02:31:12 pm
content: Quote from: brownt on July 05, 2021, 09:12:43 amYou might get more replies if you cut all that white space, off the schematic. It just looks like a smudge to me. Many people here are busy and don't have time to mess around with big arse images, which contain as much data as a sanely sized one.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 06, 2021, 02:58:05 pm
content: Dont join the two Vdd lines, shown in red. And similarly, dont join the two Vss, shown in black. You only need the pot supplies once.If you want the two ctrl inputs to track, use one pot. If use two pots, one for reach ctrl. The ctrl inpiut have an impedance of 10k. Your pot needs to be 1k or lower.It would be less probelmatic if you buffered the wiper of a higher value pot, say 10k, with an opamp: single supply rail to rail 5V.If this is a CV input for pitch you need a very stable referrence to provide the pot supply. A zenner just wont cut it.

author: Zero999
author_rank: Super Contributor
timestamp: July 06, 2021, 09:09:37 pm
content: I've finally found the time to sort out the schematic for you.No, don't connect the supply lines in parallel. Connect the potentiometer to one power supply and the wiper to both inputs. You might need a unity gain op-amp buffer on each input. If there's a 5V rail handy, use the cheap and easy to get LM358, otherwise a rail-to-rail input & output op-amp such as the LMC6482, TSV792, LM7301, TSV621 etc.

author: brownt
author_rank: Regular Contributor
timestamp: July 10, 2021, 06:08:46 am
content: Ok, so that's like that attachment, correct?Why might buffering be required?What does the section of the circuit in red do? Protection of something?thanks