Cheapest way to communicate

[Jumper]

My vote goes to RS-485 using a CAT-5 network cable. In this cable we have 8 wires so we can use 3 for GND, 3 for 12V and one for 'A' and one for 'B'. Or if you want to have a full duplex you can get that too and still have 2 wires each for + and -. Cheap standard connectors and a very common cable.

And because it is RS-485 you can hook up a PC to the system using a USB-RS485 converter which also is a very standard component.

Now we have power and communication. Just slap on a suitable max chip and a power-regulator on each slave and off you go. MAX3072E is one but there are plenty more...

Stable, quite cheap and very very standard. This combined with a PIC having a hardware usart and some DT instant interupts and you are up and running in notime.

[koossa]

Hi Jumper!

Thank you very much for your reply, I will go for the RS 485 then!!!

[Melanie]

Duh... so RS-485 is cheaper (Post #1) than good old RS-232 running in junk Telephone or Burglar Alarm cable? Two tin cans and a bit of taught string does 100m...

[Jumper]

Why not use TTL levels and connect the pic and hope for the best.

Since TTL might be a bad idea we can probably assume that we need to use a communication chip and here we can choose MAX232 (the old favorite) or a 422/485 chip. RS-232 in a CAT-5 cable at 19200 will give you the maximum length according to the standard of 147 feet (44.8m) but we all know that standards are for the weak, sick and cowardly.

The thing that makes me choose RS-422/485 is that is supports multiple slaves on the same bus. It is possible to have up to 256 units connected to the same 2 bus lines. How many units per bus is stated in the datasheet for the RS-422/485 chip.

RS-232, RS-423, RS-422, RS-485 they are all relatives but some of them are the poor cousin from the contryside. RS-422 and RS-485 is electrically the same they just have a different protocol to allow for multiple drivers for the 485.

read the links below and you can compare the different standards.

http://www.rs485.com/rs485spec.html

http://www.lammertbies.nl/comm/info/RS-232_specs.html


But Melanie is right as always, what ever that can be found in the trash-pile will probably do the job best now now now and the cable will probably be the biggest cost anyway.