Signaling over a long UTP cable

Using Arduino Project Guidance
1

Im trying to figure out what will happen if I send a HIGH signal over a UTP (Ethernet) cable that is 100 meters long. (Two wires are actually used, the other being the ground).

I suppose this depends on the resistance of this length of cable (doubled ? Because of the ground cable?)
Ok I can Google the resistance of the cable, just someone verify that this is the correct way to do it ?

And second, suppose I use a pwm signal, of 2 millisecond slots. Apart from voltage drop, will this be attenuated or otherwise distorted over 100 meters of UTP cable ?

EDIT: I can not test this because I dont have an Ethernet Shield yet.

2

Are you wanting to send network traffic, IE, Ethernet signals, or just send other signals? Ethernet will be fine.

If you are simply using the wire to switch things on and off, it depends on what you want to operate at the far end. Small current switching such as operating an optoisolator will be ok. Turning on LED strings would probably fail.

If the PWM is controlling a MOSFET, it would probably work but the frequency may have to be lower.

Weedpharma

3

Hundred meters cable means capacitance, and signal bouncing at the end, and picking up electric noise and all kind of bad things.

I think that a 2ms PWM signal will not work.

An Ethernet or RS-485 uses a signal that is made for a long cable. It is a combination of volt and current and impedance. They have also protection for electric spikes that the cable might pick up.
If you connect an Arduino output to a 100 meter cable, it might damage the Arduino, and at the end of the cable, the signal doesn't even look like the original signal.

4

In short, you need RS-485 transmitters and receivers to do it properly.

Research on that.

5

Hello,
thanks for your answers,

there are only four different "toggle" commands to send to an Arduino.

The sender need not be an Arduino, it could just be switches driving transistors or simply closing the circuit.

But the receiver must be an Arduino and be able to clearly distinguish between HIGH and LOW.

Since there are only four commands to send, I think an Ethernet shield is overkill ? (or RJ-485 for that matter).

6

Switches? OK, switches go to ground (not 5V) at the source end and at the other end, you have a pull-up to 5V - 1k should be OK - and from that point, a series resistor of 22k to the Arduino input pin with a 0.1μF capacitor from that input to ground to reject transients.

7

If you already have the cable, get two arduinos and give it a try. What does google say about the maximum range for ethernet?

8

Maximum Ethernet distance is 100 meters.
Beyond that, the signal becomes distorted and requires a repeater, switch, or other active device.

But I want to use the cable in another way (just turn it HIGH or LOW).
Like "breadboard wiring".

Ok I ll give it a try. But I need to buy 100 meters of wire first. Thought to ask first.

9

Only HIGH and LOW is okay. I would protect both the output (with 100 ohm resistor) and the input (RC-filter of 4k7 100nF).
When there are mains wires near the cable I would also use diode clamps at the input with an extra 1k resistor.
Perhaps even 10 ohm in the ground to the cable to prevent ground current, but that depends on how both Arduino boards are powered.

10

I'm not a specialist in the theory but in fact I dealt with the same issue and I solved it using a proper shielded S-FTP (double shielded) cable. It's about 50 meters in my case approx. 10cm in the ground around my house. It's connected to Arduino digital inputs. At the other end there are some basic sensors like a tilt switch, PIR sensor. At the Arduino end there is a Schmitt-Trigger and a Resistor-Cap. combination to "filter" and "smooth" the signals.

I started the project with cheaper UTP cables and I got a lot of false-signals on the cables. As soon as I switched to properly shielded (but expensive) cables the false-alarms are totally gone. The Arduino is running for more than 6 months without interruption, still 100% accurate signals.