Cheapest way to communicate

[Jumper]

There are plenty of 433 Mhz modules you can use for this. Pick the right one and you can have up to 500m.

One way or 2 way communication?

Cable? fiber optics...

Usually the communication part is not the problem, it is to provide power to all units without having to change batteries every day.

/me

[koossa]

Is wireless cheaper than RS485?

[ScaleRobotics]

Depends on what type of cable you run...........

[koossa]

So, If I'm going for a cheap cable then RS485 is cheaper than wireless.
Is there anything cheaper than RS485?

[ScaleRobotics]

From what I have read, RS-422 or RS-485 can handle about 4000 feet on cat-5 network cable, which is pretty cheap. Sounds like even RS-232 will get close to the distance you want, but you would need good cable, and a low com rate, (and very low noise in your environment). So cheapest sounds like RS-485 or RS-422.

[Ioannis]

This a philosophic discussion.

If you want to find the cost of each solution, you have to mke a market research based on the distance and speed of your connection.

Then choose the one that is right from the possible solution (either RF, IR, cable, fiber etc) and compare the cost for your case.

You have to do your homework. No other way.... sorry.

Ioannis

[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.

[Melanie]

If it's just two PICs, Point-to-Point, proper RS232 will easilly work down 100m of junk Telephone or Burglar Alarm cable. It should have a range of about 1km without Repeaters (using decent screened Cable).