Electronics > Beginners
Use transistors to switch between two signals
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hirada:
A reply from a beginner: My (simplified) version of yours to turn on the relay would look like this. The need of a base resistor could propbably be argued and you only have ~4.3V for the relay as opposed to 5V.

Edit: Assuming of course, the MCU output delivers enough current and is 5V as well, so you have 5Vb.

tron9000:

--- Quote from: hirada on April 24, 2018, 11:58:43 am ---A reply from a beginner: My (simplified) version of yours to turn on the relay would look like this. The need of a base resistor could propbably be argued and you only have ~4.3V for the relay as opposed to 5V.

Edit: Assuming of course, the MCU output delivers enough current and is 5V as well, so you have 5Vb.

--- End quote ---

The beauty about relays is that even if you switch it low side, leaving one end "flapping in the breeze" its not going to float and/or accidentally turn on.
Lt_Flash:
You can use LTC4412 to switch between two power sources and also can control it from MCU

http://www.analog.com/media/en/technical-documentation/data-sheets/4412fb.pdf

If that's not a power signals - then why just not use a multiplexer? There's a lot of 2-channel ones available.
gbuilder:
Thank-you all for the input, some very interesting comments and I have learned a lot!
I've enjoyed following the different approaches to solve this very simple problem, I guess that's what makes electronics design interesting.
Sorry for the error in my initial schematic, I've uploaded a correction to the OP.

I've decided to order a bunch of 4053 multiplexer ICs. Of all the 405x series, this seems particularly versatile and might come in handy in many other situations. Also I could get 10 for £2  ;D


IanMacdonald:
A CD4016 is similar to the 4053 but gives you four single switches.  Another arrangement that works well where small signal handling with low noise and distortion is needed, is a pair of JFETs such as 2N3819's.
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