Thanks for the suggestions. I'll look into them. One thing is that I do not need to filter the output to get rid of the PWM. The output signal line can take PWM fine.

how "low" impedance? 500? 50 ? 1 Ohm? how "fast" voltage has to be set?

About 50 Ohms. Voltage does not have to be set quickly.

Thanks for the reply. I need to get the full 0 to 12 Volt range on the output line. Is there any way to do that?

I had a problem using a voltage divider to input a voltage (between 0 and 12 volts) to a low impedance signal line. I used a potentiometer as the voltage divider, and as I turned the pot the signal voltage would suddenly jump from around 1 volt to over 10 volts. So that did not work.

My new plan is to use a TIP120 transistor to send the voltage signal. I'll use an Arduino analog PWM output to the transistor's gate, and put ground and +12 volts through the transistor. By varying the output from the Arduino from 0 to 255, I hope to get the whole range between 0 and 12 volts. 

Will that give a good voltage signal on the low impedance signal line?

Thanks, MarkT. You are right. At Digikey I searched for USB receptacle, and there they were. It's nice to learn to be posher.

Oops, my mistake. I said RJ-45 female connectors, but what I was having trouble finding was USB female connectors. Jameco has them. Digikey and Mouser do not seem to.

And keep in mind some have integrated isolation transformers ("magnetics") that you'll want to avoid.

Thanks for the heads-up about the magnetics. I wondered what that meant.

Found them at Jameco. I knew that would happen. Whenever I give up and post, I find the answer shortly thereafter.

I'm working on a project where I use Cat5e cable to send four digital signals from an Arduino to some electronics about six feet away. I have the Cat5e cable that I need, with a male connector on one end.

What I need, though, is the RJ45 female connector to go with the electronics. I want to mount that connector on perfboard and run wires from the connector to some transistors and other components.

I thought those connectors would be easy to find, but can't find them anywhere. Any suggestions on where to look?

Let me second Coding Badly's suggestion of the Teensy. They cost $16 but they work really well if you need the serial over USB function. The other option I have used to buy a cheap USB programmer off of eBay and use it with an RBBB (Really Bare Bones Board) Arduino. That ended up costing about the same.

Adafruit sells a board for $20 that is similar to the Teensy. http://www.adafruit.com/products/296 But I could not get that board to work with serial over USB. (Plus I had a real tough time programming that board. The Teensy was much better.)

That's an interesting project. We converted an old pickup to an electric car, and replaced the wiring harness with a network-type setup. We use a Teensy (not an official Arduino, but like one) at each "corner," and connect the lights, horn and other accessories through a 4-relay board that is switched by the Teensy. It works well, replacing a complicated and heavy wiring harness with a simple network.

On a motorcycle, it might not work as well. Especially if you have all the wiring for the gasoline engine as well. You probably would not get the simplicity we can get, and since the distances are shorter on a motorcycle, the cost-benefit ration may not be in your favor.

Certainly it would take some effort. But it could be done, and you would learn a lot if nothing else. Whether you want to do it or not, only you can decide.

I can attach a YouTube video if this is still unclear.

A video would help.

The Teensy may work well for you. You can get one for $16 from www.pjrc.com. They also have a code library at that website for USB keyboards: http://www.pjrc.com/teensy/usb_keyboard.html

Good to hear that solved the problem. MarkT was right. I must admit I was wrong--I never thought that would be the cause. Always good to learn something new.

Although I cannot rule it out, I doubt that wire shielding is the problem. Certainly, as suggested, you may want to getting a better cable. Even a USB cable would work.

You said that if you unhook up the 12 Volt supply to the motor controller, things work. If you do hook up the 12 Volt supply, things do not work. Is that even when no current is flowing to the motor controller? In other words, when the motor is not on?

The reason I ask about the pot input pins is that I think that is where the problem lies. I don't think your Arduino is reading the correct value from the steering pot. If you could confirm that by testing, that might help. You could hook your computer up to the first Arduino, have it read the pot input pins, and then have print out the values to the serial monitor.

That is a tricky problem. As I understand it, when you connect up a 12 Volt supply to a motor controller, that affects only one pot reading on an Arduino where the pot is connected to a separate 5 Volt supply. Is that right?

What connection is there between the 12 Volt and 5 Volt supplies?

Are all grounds connected?

Where is the code that reads the pots? Did you set the analogRead input pins to be INPUT?