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Topic: Question about long wires and ardino (Read 2427 times) previous topic - next topic

Hi guys,
I want to connect 20+ pcs of my sensors ( Ultrasonic sensors(HC-04)  and 2x 10mm LED) to my arduino.
My problem is that each sensor(Ultrasonic sensors(HC-04)  and 2x 10mm LED)  is far way from my Arduino board.Lets say 20-40m.
I want to use FTP cat5e cable to conect all my sensors to my Arduino board.No network cards ot TCP/IP communication-direct wire but cat5.
I want to set cat5 cable because its cheap,good and easy to support.
What problems should I expet if I connect my sensors with cat5e at long distance 20-40meters.
Will I have problems with the voltage drop accros the cable or with noices caused by other cables?

Thanks in Advance
Anton

CrossRoads

That's a long way to go. I would suggest a line driver, like RS484 on both ends, to redrive the signals.
Maxim-ic.com carries quad for sure and and maybe hex or even octal drivers and receivers.
If you want to cut down on wires, put a processor on the remote end and send the sensor data and the LED on/off data serially back & forth.
Supply over 4 of the lines, 2 for twisted pair Rx, 2 for twisted pair Tx.
If the sensors only have 1 wire output, then bump up to a '1284 family part for 32 IO - 2 for serial data, 30 for the sensors & LEDs.

I sell this bare board for $5 mailed to US locations, populate as you wish. Plug on a RS485  driver card instead of FTDI for serial.

Here's a tyoical PL.
http://www.crossroadsfencing.com/BobuinoRev17/1284_Duemilanove_PL.pdf
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Hi,
Thanks for the replay.
I am investigating your suggestion.
I am not 100% procent sure that I understand you solution.
I will search the web for more info about RS485 and hope I will understand your post better.
Sorry I am newbie :)

Cheers
Anton

fungus


Hi,
Thanks for the replay.
I am investigating your suggestion.
I am not 100% procent sure that I understand you solution.
I will search the web for more info about RS485 and hope I will understand your post better.


RS485 is sort of like RS232 for long wires.

These days people tend to use wireless connections for this sort of thing though.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#4
Oct 10, 2012, 04:39 pm Last Edit: Oct 10, 2012, 04:47 pm by tonko_lonko Reason: 1
I was hoping that the cat5e FTP cable will protect me from most of the noices but it seems I am wrong.
I need to find cheap solution to transfer the data trought so long wires becasue may sensors should be very very cheap-becase someday I hope I will need a lot of them(1000+).
If each sensor has its own arduino with enc28j60 network module or some kind of wireless module I will not have problems with the wires but I will produce too expensive sensor that I can't afford.(1pcs-ok 1000pcs-not ok)
So you dont have any ideas about cheap solution?

Now i Will investigate this MAX485-how it works and what I should do with this.

CrossRoads

Here's a nice application note about wiring up RS485
http://www.maximintegrated.com/app-notes/index.mvp/id/763

What I am suggesting is using 8 conductor CAT5 wiring.
Use 1 twisted pair for +5/Gnd
Use 2nd twisted pair for +5/Gnd
Use 1 twisted pair for data from near end to far end.
Use 1 twisted pair for data from far end to near end.

At the far end, receive a message from the near for switching the LEDs on/pff.
At the far end, sample the sensors and send messages to the near end with whatever they are telling you.
Use a board with some IO so you can connect everything.


You can use this board too
https://www.sparkfun.com/products/10124
Only does half-duplex vs full duplex.
The app note explains about that. Connect up the unused pins to bring power down the line.

Your next post = 1000's of sensors.
These will all go back to the same 'master node' ?
So 50+ slave nodes with 20+ sendors on each one?
I think you might want a custom board for the remote nodes for that.
Maybe use inexpensive 434 MHz RF transceivers (nRFL2401+ based) at each end. Have the master poll each remote sequentially to get their data and send LED commands.

Post a link to the HC04 sensor, lets see what's involved to use it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

fungus


I was hoping that the cat5e FTP cable will protect me from most of the noices but it seems I am wrong.
I need to find cheap solution to transfer the data trought so long wires becasue may sensors should be very very cheap-becase someday I hope I will need a lot of them(1000+).
If each sensor has its own arduino with enc28j60 network module or some kind of wireless module I will not have problems with the wires but I will produce too expensive sensor that I can't afford.(1pcs-ok 1000pcs-not ok)
So you dont have any ideas about cheap solution?

Now i Will investigate this MAX485-how it works and what I should do with this.


The only real problem with long wires is data transfer rate. If you're not sending much information then simple twisted-pair wire could be enough. Use one wire for data and another for clock ... a bit of software to control it ... might be all you need. Higher voltages usually help because at that length you start to notice that wire has a resistance and voltages drop along it, but 5V might work if you get the line impedences right. 40m isn't really all that long.

First things first though...how much data do you need to send?
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Thanks All for you comments.They are very helpful.



The only real problem with long wires is data transfer rate. If you're not sending much information then simple twisted-pair wire could be enough. Use one wire for data and another for clock ... a bit of software to control it ... might be all you need. Higher voltages usually help because at that length you start to notice that wire has a resistance and voltages drop along it, but 5V might work if you get the line impedences right. 40m isn't really all that long.

First things first though...how much data do you need to send?


I dont know how much data it is but I dont need speed.

I will explain my case in more details:
My "sensor" box contains: HC-SR04 and two leds.
When my range distance sensor detect change in the distance I need to get this information in arduino process the information about the distance change and turn on the led located on the sensor.
I dont need performance and speed.If I turn on the led after 1 second delay its not a problem.
So I dont need speed

What you think?

MichaelMeissner

Now, I don't have the electronic chops to calculate likely noise levels, but I imagine at those distances, you want something that does checksums, and if the data didn't arrive correctly formatted, ask for it to be resent.  Something like RS484 should work.

However, if you are using ethernet cables, you might want to think about encoding the information into one or more packets, and sending them out via TCP/IP (which handles resending the information for you) or UDP/IP (where you take care of retransmission).  If nothing else, you can put a store and forward router in between if the wires are too long.  It also opens up the possibility of using wifi to send packets wirelessly, or maybe ethernet over power lines.  I imagine it is more cost, and more complex code.

fungus

#9
Oct 11, 2012, 08:48 am Last Edit: Oct 11, 2012, 08:53 am by fungus Reason: 1

I dont know how much data it is but I dont need speed.

I will explain my case in more details:
My "sensor" box contains: HC-SR04 and two leds.
What you think?


I think that changes everything...

You're not sending any data at all, you're just sending a pulse and seeing how long it takes to return. Twisted pairs and stuff isn't going to help at all for that, it's all about line impedances and stuff.

You'll need shielded cable, ordinary audio/video cable should be good enough for this. Whether it will work as-is will depend on the electronics of the sensor board. The best thing to do is get yourself 40m of cable and try it. If you have access to an oscilloscope, have a look at the pulse at the sensor end and see how many volts it is. If it's dropped down a lot you either have to raise the impedance of the receiver or raise the voltage of the transmitter.

Basically: With long wires you start to notice that copper has a resistance. The transmission wire and the receiver are two resistors connected in series, call then R1 (wire) and R2 (receiver). The voltage will obviously drop across R1. How much it drops depends on the resistance R2. To compensate you either have to raise the transmission voltage or raise the resistance of R2.

(For the engineers: Yeah, there's capacitances and stuff as well...but we're only sending a single pulse so I think we can ignore them).
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

michael_x

Quote
You'll need shielded cable, ordinary audio/video cable should be good enough for this
...
For the engineers: Yeah, there's capacitances and stuff as well...but we're only sending a single pulse so I think we can ignore them


Rising speed of a signal is no issue here, agreed.
LED signals also do not matter.

But as a wannabe engineer without real hardware knowledge, tonko lonko's approach of twisted pairs cable seems nice to me.
I think 40m is not really a distance, but I fear noise on the trigger and echo pin.
How would you wire these signals? Does having GND as one of the twisted wires do the noise cancelling trick ? 

fungus


How would you wire these signals? Does having GND as one of the twisted wires do the noise cancelling trick ? 


Twisting the outgoing pulse with GND and the return pulse with 5V might help with noise... but I don't think noise will be your problem.

Your main problem will be getting enough volts to appear at the end of the wire if your input has a low impedance.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

michael_x

Quote
Your main problem will be getting enough volts to appear at the end of the wire

I googled the DC resistance of Cat5 cable and got results of 95 Ohm / km ( or 50 Ohm / km )
40 m is less than 5 Ohm. A 10..20 mA current sees a hardly measurable voltage drop  less than 0.1V

No need to adjust the LED resistors, nor any other stuff, IMO. 

CrossRoads

Lets move on, check out this Ping Library
http://code.google.com/p/arduino-new-ping/

Simple sketch is shown - takes a dozen lines of code & 2 pins per sensor.
A standalone '1284 type processor connected to 13 sensors and 6 pins connected to an RF transceiver
http://arduino-direct.com/sunshop/index.php?l=product_detail&p=188

or maybe a 100-pin 640/1280/2560 type processor to have more IO pins without needing to add mux/demux chips to drive more ping sensors.

Really depends on how the ping sensors (1000+ still) are to be distributed.

If its more like 500+ sensors boxes with 2 ping sensors and 2 LEDs, then a much less expensive uC that can suport SPI for a transceiver can be used.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

MichaelMeissner

It occurs to me, that if you need a really long distance, that a fiber optic cable would probably be better than copper wire.  According to wikipedia, you can get single mode fiber optic cable in lengths up to 12km (7.4 miles).  However, that is probably overkill.  8) :smiley-roll:

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