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Distance Protocols

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AtomSoft

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I need a protocol that will go the distance... Im talking anywhere from 30 - 150 ft...

Im looking for more of a hardware solution. Where little software (coding) if any is needed.

Power should be no more than 12v

Any Thoughts?

This is for a intercom system I am developing... i would just like opinions and stuff.

Thanks :)
 
Any Thoughts?

This is for a intercom system I am developing... i would just like opinions and stuff.

Thanks :)

hi J,
What data rates do you have in mind.?

Type of cable you want to use.? or is it an RF link.??

E.
 
30 to 150 feet is pretty trivial. I have a 40ft piece of crappy thin coax, running 115200 baud direct from a PC RS232 serial port, and at the other end a machine with a single NPN transistor inverter into a PIC USART RX pin. The signal at the other end is pretty much flawless, I'm sure it would run 200-400 kbaud over that crappy 40ft coax and still work perfectly but the PC serial port is limited to 115 kbaud.

But if you are talking RF comms then I'm off-topic so I'll shut up now. ;)
 
NO RF :)

Just plain wired. So you are telling me i can use a COAX cable for simple UART? Would it be possible for me to simply use a RS232 Chip to pump it to the +/- 12v ? Nothing else is needed?

Dont play with my emotions here :)
 
Check out RS485. RS232 will often do longer distances without a problem, but RS485 is designed for long distance. It's probably overkill for 30' but at 150' I would prefer it over 232.
 
I'll agree with RS485. Single 5V (or 3.3V) power supply. The differential signal makes it much more imune to noise and differences in ground potentials. You can go full duplex on 2 pair ( one pair TX, one pair RX), or half duplex with a single pair that alternates direction.

RS485 also supports having multiple talker/listeners along the bus, so that can daisy chain a single cable through all your intercom stations.
 
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Hey Jason! I use a slightly different approach..... I take the normal RS232 software and change the hardware..... I get over 150 meters.... I change my line drivers for current converters... 5v = 6mA. I receive on the other side with a 680Ω resistor... I have tested with over 100Ω resistance in the cable length and it still works fine.
 
Can i just use Ethernet wire? This way i can have

2x GND
2x VCC
RX
TX
2x CUSTOM SIGNAL....

Remember that Ethernet CATx cable uses 4 twisted pairs and is designed to work with differential signalling.

You would want to send the RX and TX down different pairs with the other wire in each pair to Gnd to avoid interference.

I have used CAT5 cable in much this way myself with one wire in each of the four pairs grounded and the signal or power in the other and it has worked fine at 10M/30ft.

Be careful if your have a microcontroller I/O pin connected directly to the cable though. Fast rising edges into an unterminated cable can glitch the microcontroller - I have found :)
 
Agreeing with roman on this, I have a half roll 50m or so length of unscreened alarm cable from my office to the workshop carrying 19k baud without issues and its both directions, one end is just a max 232 to a pic.
 
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Yeah, you can get quite a distance even at 115200 baud, this is not like an RF frequency.

I forgot to say my setup uses 0v-5v serial BACK to the PC, so it's +/-12v RS232 one way and 0-5v back the other way. No problems at all with the 0-5v serial comms at 115200 baud and 40 feet of stereo coax.

CATx cable using a twisted "pair" would probably work even better still.

Re the cable termination I do the opposite; put a series resistor before the cable (at the transmitter end). That gives you a little bit of RC and smooths the transistions, and asynch serial handles sloping transitions really well (but can have a problem with ringing if your transitions are too fast). From memory my existing setup uses a 220 or 270 ohm series resistor on the transmitter side(s), which is also good insurance if you get a cable short.
 
I think its a 1458 rs232 transmitter chip, they tell you about the series resistor and line loading in the datasheet, they reccomend 100r, you can increase baud to an extent as the driver doesnt have to charge and discharge the capacitance as quick.
I dont think the max232 gives you full spec rs232, I wouldnt really know as I only read the datasheet till I got it working.
If you use catx then if stp connect the drain wire to ground at one end.
 
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