Multiplexing 6 RS232 slaves to a single RS232 master using a single supply - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: December 21, 2024, 07:53:09 pm
content: Hi,I need to multiplex 6 RS232 (from 6 slave PCBs) into one RS232 master PCB and I am looking at switches like these ones:-https://dir.heisener.com/DatasheetDownload/MAX335EWG.pdf-https://www.vishay.com/docs/70062/dg408.pdfBut, like many others similar ones, they require negative voltages which I am trying to avoid adding. Are there any other multiplexing solutions/ICs that can work from a single supply (I could not find any)?If not, any other solutions or suggestions (preferably using a single supply)?Thank you

author: ch_scr
author_rank: Frequent Contributor
timestamp: December 21, 2024, 08:01:13 pm
content: Use MAX232 (or similar) single-supply IC that convert RS232 to UART (and back), multiplex at the UART side.No need for analog switch IC, could use e.g. 74HC151.

author: ricko_uk
author_rank: Super Contributor
timestamp: December 23, 2024, 02:45:13 am
content: Thank you ch_scr,that was the initial thought but because of how the system is split the client requires the switching of the RS232 levels.Thank you

author: Smokey
author_rank: Super Contributor
timestamp: December 23, 2024, 03:04:02 am
content: +----------+ +--------+ +----------------+| RS232-1 | -> | UART-1 |----+ |+----------+ +--------+ | |+----------+ +--------+ | || RS232-2 | -> | UART-2 |----+ |+----------+ +--------+ | |+----------+ +--------+ | | +--------+ +--------+| RS232-3 | -> | UART-3 |----+6:1 Multiplexer | -> | UART | -> | RS232 |+----------+ +--------+ | | +--------+ +--------++----------+ +--------+ | || RS232-4 | -> | UART-4 |----+ |+----------+ +--------+ | |+----------+ +--------+ | || RS232-5 | -> | UART-5 |----+ |+----------+ +--------+ | |+----------+ +--------+ | || RS232-6 | -> | UART-6 |----+ |+----------+ +--------+ +----------------+(GG Claude.ai ascii art)2, 4 channel MAX232 type transceivers and a mux. All single supply (not counting the max232 charge pumps)

author: ricko_uk
author_rank: Super Contributor
timestamp: December 23, 2024, 04:14:11 am
content: Thank you Smokey,yes that's another possible/interesting solution. Although it would, more or less, balance out (actually have more components / space) than having a charge pump to generate the negative voltage and use analog switch that requires negative voltage my original solution).I guess there aren't other "simple" low component count alternatives.I was hoping there might be perhaps some single supply switches that I might have missed in my search that can handle the negative 12V of the RS232.Thank you all as usual!

author: oPossum
author_rank: Super Contributor
timestamp: December 23, 2024, 04:19:16 am
content: https://www.littelfuse.com/products/power-semiconductors-control-ics/solid-state-relays/optomos-relays/normally-open-relays

author: PCB.Wiz
author_rank: Super Contributor
timestamp: December 23, 2024, 05:02:24 am
content: Quote from: ricko_uk on December 21, 2024, 07:53:09 pmThere are SSR and Opto-FET solutions, but they are not low cost or small.The closest looks to be parts like TI’s TMUX4051 - that is +/-12V rated and does 8:1For the negative rail, you could apply 6x small stky diodes, which can come in triples per package, to phantom power off the idling low RS232 rails.

author: m k
author_rank: Super Contributor
timestamp: December 23, 2024, 08:13:28 am
content: Quote from: ricko_uk on December 23, 2024, 02:45:13 amHow many signals, are they always active, are they sending simultaneously?