# Switching of RS485 differential line. Two sources, one output

I'm looking for a solution for my project.

I have two signal sources (primary source and secondary source) on the RS485 (A/B) differential line. When/if something goes wrong on the primary, then I switch over the button switches to the secondary source.

Which electric component could I use for switching the differential line (other than a relay)?

• If you're going to do it manually use a double pole switch. Why not a relay? – Finbarr Apr 20 at 19:06

As you don't wish to use a relay, you could possibly use a CD4066, CMOS Quad Bilateral Switch (datasheet):

Although as suggested in Finbarr's comment, as you might want to use a double pole switch, you would want to use all four switches within the IC package.

See image below taken from How to Build a 4066 Quad Bilateral Switch Circuit

Just modify the schematic to use the other two input and output pins as well as Control C and Control D

• I don't want an electromagnetic relay. Analog switch is a super variant. Can I use this TS3A44159? Switching will be handled by the processor. – PetrTN Apr 21 at 7:09
• Could you edit and update your question to state why you don't want to use an electromagnetic relay? It might help in answering your question more precisely. WRT to the TS3A44159, I'm afraid that I'm not familiar with that device - although after a brief glance at the datasheet I can't see why not. – Greenonline Apr 21 at 7:13

The appropriate component here would be a relay – either in its electromagnetic form, or in the form of an analog switch.

There's dedicated bus switch ICs.

• I don't want to use an electromagnetic relay. Can you recommend an analog switch? For this line? – PetrTN Apr 20 at 13:13
• @PetrTN: Seems worth looking at NX3L2467. However in your diagram you have the switch in the wrong place -- it should be between the driver IC and the TVS protection, to avoid exposing the switch to ESD or coupled transients. – Ben Voigt Apr 21 at 15:56