Cheapest way to communicate

[koossa]

Good day Picers

What is the cheapest way to communicate between pics at a distance of 100 meters?

Thank you!

[dhouston]

Smoke signals?

[tenaja]

Pics get pretty expensive once they let out a puff or two of smoke...

[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.

[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.

[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).

[dhouston]

Pics get pretty expensive once they let out a puff or two of smoke...But that might be a one-time expense. The OP really hasn't provided sufficient detail. Even Melanie's educated string probably cannot hazard an educated guess. What's the duration of the communications link? Is it one-to-one or one-to-many? What type of messages? What's the terrain? Is the path horizontal or vertical? Is it level or does it span a canyon? How can a wire be routed? Stapled to tree trunks or utility poles, buried in a trench? Must it be taut or can it sag? Etc., etc.,...

[koossa]

What's the duration of the communications link?

it is a 24/7 communication link, every second.



Is it one-to-one or one-to-many?

one-to-many



What type of messages?

short, status monitoring



What's the terrain?

Horizontal, maximum of 1 meter difference in elevation



Stapled to tree trunks or utility poles, buried in a trench?

Buried in a trench



Must it be taut or can it sag?

Can be sag

Thank you!!

[Luckyborg]

Probably the cheapest solution would be a 20 ma current loop circuit. 1 transistor (PN2222A), 1 opto-coupler (we use a 4n26) and a few resistors and you are set. I think I remember something about that being good for around 2000 feet, especially if you can go with a lower baud rate. Having said that, I would probably still go with RS422/485 just because it is more of a standard these days.

David

[joseph]

Good day Picers

What is the cheapest way to communicate between pics at a distance of 100 meters?

Thank you!

laser pointers might work :D

[dhouston]

one-to-manyIf you have to have a two-way communication with more than one node, I think RS-485 is the best choice. Two way wireless gets complcated and expensive rather quickly. Also, most jurisdictions have limts on how often a wireless node can transmit. B&B Electronics has an excellent whitepaper on RS-485.http://www.bb-elec.com/tech_articles/rs422_485_app_note/table_of_contents.asp

[dhouston]

Here's another helpful article on RS-485.http://www.embeddedsys.com/subpages/resources/images/documents/microsys_art_RS485.pdfAlso, even if buried in a trench, you will need to protect against lightning by opto-isolating the nodes. See the ISOLATED LINK section of the Axelson article. You can use direct burial CAT5 cable to avoid the need for conduit.

If you can provide more detail about the number of nodes and the nature of the messages we might be able to suggest less costly methods. It might be less costly to use WiFi which can be done for under $60 per node. It's inherently isolated and you can use serial communications. http://www.ewiznet.com/goods_detail.php?goodsIdx=135

[dhouston]

One caveat on the WiFi module. Its range is specified as up to 200m. That is in a straight, unobstructed line. YMWV

[koossa]

Hi Dave

Thank you very much for the info and links!!!

[imjames407]

i think Walkie talkie is the best option.