Extending Serial Distance

[neon_kenny]

I want to assure that I will be able to run serial lines a distance of about 40 feet. I understand that I can optimize with wider wires, shielding, slower baud rate, and terminating resistor.  I'm wondering if I couldn't just use a MAX232 on the PROP-2 output and if that will be enough to communicate with four DC-16's over this distance. Assuming I take the same precautions for a PC port i.e. 22k resistor etc., will that work? Or would I need to receive with another MAX232 to return to TTL levels? 

Thanks in advance.

[JonnyMac]

This is dangerous stuff, trying to run RS-232 more than a few feet -- don't do it.   And RS-232 isn't designed to be multi-dropped, anyway.

If you're going to go through the trouble to make adapters I suggest you add an RS-485 (which IS designed to be multi-dropped) circuit to both ends; this will let you use the max baud rate of the DC-16 and extend to distances WAY beyond 40 feet without worrying about noise (so long as you use twisted cable).  You'll only be able to talk to the DC-16s (not get status from) but I suspect that all you want, anyway.

Below is a circuit using a component that we've done some work with; it's easy to use.  The top part is a TTL serial to RS-485 converter and the bottom circuit is an RS-485 to TTL serial converter.  Note that the ends of the line need termination so that's built into the transmit side and optional on the receive side (connect the jumper on the last node).

I hope this helps.

[neon_kenny]

All I can say is thank you, thank you, thank you.

[JonnyMac]

You're welcome.

Notes:
  1) Use twisted cable (CAT-5 is fine)
  2) Use True (not Open True) baud mode on the Prop-2 side if you're not using one of the pins with a pull-up and the ULN influence removed

[bsnut]

Jon,

Will this work with a Prop1?

Thanks,
William "BSnut "

[JonnyMac]

Yes.

[bsnut]

Thanks Jon for the quick service ;D.