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Recommended RS232 "shield"?

Posted: 08 Aug 2018 01:19
by ondrej_bajer
Hi guys,

I'm looking for the best RS232 "shield" for Z-Uno. As of today, I'm using this one: ... 3286469667

For shame, I'm experiencing couple of issues with this one:
1) Despite the description, it needs +5V for propper operation. When powered from 3.3V pin, it transmits just a garbage. Based on that, I'm not sure whether the RX/TX pins work as 5V TTL or 3.3V logic.

2) Talking to a PC works great, but when connected to a Solar Inverter, Z-Uno board is fried from time to time. Namely the TX pin. Found that a physical connect/disconnect is a critical operation. Once it's connected and starts working, it won't die. So, I've put 660R resistor on the TX pin, which is still okay for a communication to work, while it prolonged life of the Z-Uno board a lot.... but couple of days later, RX pin was fried during reconnect operation. And the trick with a resistor does not work for RX.

So, I'd really like to have a good alternative. Maybe something with a galvanic isolation, to avoid ground loops too.
Is there something you can recommend, please?

Thanks beforehand,