RS232 to TTL (newbie question)

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pisabe;;
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RS232 to TTL (newbie question)

#1 Post by pisabe;; » 04 Apr 2022, 17:42

Hi,

I am trying to control an amplifier (Devialet brand, which provides for a serial command interface) from my home automation system (Openhab running on Windows). I want to use a D1 mini that will be connected directly to the amp, and commands will be sent to the D1 mini through MQTT. I believe that I have already nailed down the software part correctly. For example, if I bypass completely the amplifier by connecting together the RX and TX pins of the D1 mini, I can see that any amplifier command issued by Openhab does get published on MQTT and is then published back by the D1 mini (in place of the amplifier response).

Assuming that the software is OK, what remains to be clarified and executed is the hardwired connection between the D1 mini and the amp. The Devialet serial connection uses a 3.5mm minijack with TX, RX and GND signals. According to Devialet the spec is as follows:
  • +5V to +12V for positive signals
  • -5V to -12V for negative signals
I tried connecting the D1 mini pins directly to the Devialet 3.5 mm minijack but that did not work (I don't think it damaged the D1 mini, though), presumably because the 3.3 volts odf the D1 mini are insufficient.

What I think I understand. but I need to check with you, is whether or not I can simply use the following "RS232 to TTL Adapter MAX232":

https://www.amazon.ca/-/fr/adaptateurs- ... uage=en_CA

And if so, whether or not you think it will be OK to simply send the 3 Devialet signals (RX, TX, and GND -- no VCC) to the female DB9 on one end and connect 4 D1 pins on the other end of the adapter: TX, RX, GND and 3.3 VCC.

Thanks in advance.

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ThomasB
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Re: RS232 to TTL (newbie question)

#2 Post by ThomasB » 05 Apr 2022, 00:51

According to Devialet the spec is as follows:
+5V to +12V for positive signals
-5V to -12V for negative signals
That confirms your device has a traditional RS-232 interface and is not an Arduino type "Logic Level" RS-232. So you are correct, you'll need the MAX232 chip.
... you think it will be OK to simply send the 3 Devialet signals (RX, TX, and GND -- no VCC)
The MAX chip will need 3.3V for power. So that suggests that its VCC pin should connect to the D1 Mini's 3.3V.

- Thomas

pisabe;;
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Posts: 21
Joined: 21 Apr 2021, 20:50

Re: RS232 to TTL (newbie question)

#3 Post by pisabe;; » 05 Apr 2022, 01:44

@Thomas: thanks a lot for your feedback! I will try that route as soon as I can get hold of a MAX232 chip.

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