I am a newbie. My fist post. I have a Uno R3. I want to connect to a rs232 that has +- 15v. I believe this needs to be reduced to a 0-5v. This is a single wire (not USB) sending temperature data. What is the best way to safely connect this to either the analog pins or the Rx/Dx can either take the full rs232 voltage? Most rs232 to TTL converters are all USB connections? Can I just use a voltage reducer like a 7805?
Thank you.
A MAX232 will do the job, though it's a bit of overkill for just receiving a single signal. You can use the bare IC (and a handful of capacitors) or a breakout board like below:
Edit: and there's always the ancient MC1489AN.
Yeah, where I work we have several boards (not Arduinos) that use the MAX232 (or similar) for interfacing between RS-232 and 5V logic.
But you could probably use something "simpler". These chips work both ways (transmit and receive) and they can generate the higher positive & negative voltages from 5V.
No! Those are voltage regulators for power supplies (to get constant 5V from a higher voltage) and they don't work with signals.
True RS232 signals need to be inverted, as well as converted to 0-5V for the Uno R3.
The schematic below is for bidirectional transmissions. Transistor Q1 and resistors R1 and R2 should be enough for your single line conversion.
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RS-232 also requires a data-ground wire. So at least two wires are necessary.
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I have used 74C914 as a receiver with a 27K resistor in series with the incoming wire. I drove the TX with the HC chip directly and it worked. I beleive a 74HC14 would work as well.
Thank you. That is very helpful. This makes sense.
That would be an easy choice, thank you. I also found this, that seems like to me would work, Here is the link.
and a screenshot.
Use the MAX232. It's the right tool for the job and it doesn't require any tinkering or adjustment. It should just work
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