Multiple VGA / RS232 Connections, Relayed device power supply

Thread Starter

givemetheafd

Joined Jun 20, 2018
8
Hello Gentlemen,

I'm looking for a way to have 10 devices connected to the same serial port, while only having one transmit/be powered at any one time. Essentially, I'm looking at having a switch box for the power supply but some way to have multiple rs232 connections that don't have to be manually switched at the same time as the power supply switch box (although i'm open to that as well).

Ive seen a lot of devices where one transmitter can be connected to multiple receivers but not the other way around.

Thanks in advance
 

Papabravo

Joined Feb 24, 2006
19,592
Hello Gentlemen,

I'm looking for a way to have 10 devices connected to the same serial port, while only having one transmit/be powered at any one time. Essentially, I'm looking at having a switch box for the power supply but some way to have multiple rs232 connections that don't have to be manually switched at the same time as the power supply switch box (although i'm open to that as well).

Ive seen a lot of devices where one transmitter can be connected to multiple receivers but not the other way around.

Thanks in advance
Do you know what the characteristics of the un-powered transmitters will do to the transmitter that is powered? The complexity of this scheme makes it unlikely you will ever receive any benefit from doing this. Just use RS-485 an the comms problem is solved
 

ericgibbs

Joined Jan 29, 2010
16,793
hi,
If I understand your app correctly.
You could use low power reed/coil relays that select the desired incoming RXDin line.
Power the selected reed-coil from the power select switch.
Likewise for the outgoing TXDout line.
There are various DIP style reed relays.
E
 

Thread Starter

givemetheafd

Joined Jun 20, 2018
8
Do you know what the characteristics of the un-powered transmitters will do to the transmitter that is powered? The complexity of this scheme makes it unlikely you will ever receive any benefit from doing this. Just use RS-485 an the comms problem is solved
Doing some research, it appears rs485 is for one way communication?
 

Thread Starter

givemetheafd

Joined Jun 20, 2018
8
hi,
If I understand your app correctly.
You could use low power reed/coil relays that select the desired incoming RXDin line.
Power the selected reed-coil from the power select switch.
Likewise for the outgoing TXDout line.
There are various DIP style reed relays.
E
By switching the RXD line and outgoing TXDout line using reed relays would I would be able to avoid converting to 422?
 

ericgibbs

Joined Jan 29, 2010
16,793
hi,
No problem, upto 100ft is possible with RS232, using the correct cabling.
E

EDIT:
Wire the PC 9Way serial input connector as a null modem, so the PC will not require any handshaking, you can then use Half Duplex. ie two way comms.
 
Last edited:

Papabravo

Joined Feb 24, 2006
19,592
looked at 2 wire systems i suppose. So I can use 4 wire duplex 485 for my purposes?
You can use either one.
Full duplex meas you can transmit and receive at the same time.
Half duplex means you transmit and then you listen, or you listen and then transmit, but you don't do both at the same time.
 

Thread Starter

givemetheafd

Joined Jun 20, 2018
8
You can use either one.
Full duplex meas you can transmit and receive at the same time.
Half duplex means you transmit and then you listen, or you listen and then transmit, but you don't do both at the same time.
that's what i meant by one way communication, and i do want duplex. Thanks for your help
 

olphart

Joined Sep 22, 2012
113
Simple question first:
> Do you have control over the comm protocol?
If so, make each unit addressable
> Else, I'd use a set of 1488s to select the TTL Tx output stream.
3 of the 4 are NAND gated. Since you select, you'll know who's responding.
> Shouldn't be too hard to wire-OR the Rx streams.
This presumes a poll / respond to each selectable unit.
 
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