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| UART single direction long cable |
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| veryevil:
Hi, I'm looking to have two boards connected via about a meter of cable (unshielded) and I have a common gnd and a single data connection. I only want to send data one direction and was going to be using UART @ 115200 baud (maybe faster but I doubt it). I was looking for an alternative to using a full RS232 driver at both ends to give me some immunity, for cost and size reasons using a whole rs232 driver bothers me, but I haven't found any good driver ICs. I do have 12V on board so was wondering about just putting the 3v3 Tx side into a fet and boosting it to 12V and then having a window comparator on the other end to receive the 12v and make it 3v3 out again? Any thoughts or gotchas? Cheers |
| NiHaoMike:
That should work fine. |
| Siwastaja:
Without a schematic, hard to say. Talking about a single MOSFET, you'll need a pull-up, and a lot depends on the value of this pull-up. Use a small one, combined with a properly chosen series termination, and it's likely to be fairly good, but then you may have a power consumption issue. Too high, and this is worse than not using anything, as your line is high impedance in the '1' state! Your existing 3V3 signal is, at least, a proper push-pull signal with around 20-30 ohms of transmitter impedance. Terminate it with a series 47 ohm resistor at the source, and off you go. If this somehow isn't robust enough, then consider a proper RS422 transceiver IC - they are widely available and will get you proper margin using differential pair. |
| Benta:
How do you manage flow control with only one wire? How do you know the receiver is ready to accept data? |
| ajb:
You shouldn't have any trouble in most environments. You might have trouble if this is inside of a system with a lot of motors and heavy loads flipping on and off or something, but 112k over a meter is not a big deal. |
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