I am trying to use Arduino UNOs with 5 volt relays to operate model train accessories. The relays switch @14v AC. Things seem to work well for a while in testing and then after a while, the computer no longer recognizes the UNO. I am using Windows 7 Home Premium.
Specifically what happens is that the serial port associated with the USB port is not found. I try switching USB ports on the computer and changing USB cables and nothing happens. On the first UNO that had the problem, I get a Windows message "One of the USB devices attached to this computer has malfunctioned and Windows does not recognize it." The green power light on he UNO is lit and the L LED is solid.
So I bought a new UNO. It worked fine for a while. Now Windows does not even see it. I get no Windows message at all. The green power light in on and the L LED is solid. Pressing Reset on the Arduino doesn't make a difference. Again tried different USB ports and cables to no avail.
Have I fried 2 UNO Boards? Or did I scramble some code in the UNO. May I have touched a wrong wire to the wrong place? I have one more UNO that works and I am reluctant to put it back in the circuit.
Any suggestions would be welcome. My knowledge level is just a little beyond neophyte.
How are you driving the relays? directly off the pins or using a transistor to provide additional current?
Do you have a diode across the relay coil to prevent reverse voltage damage to the UNO?
I am not using diodes or transistors. (Because I didn't know that I should.) The relays are being driven by the UNO - I write a digital pin HIGH (6 for one relay, 7 for the other). The digital pin is connected to one side of the relay coil; arduino ground to the other side.
Analog pins A0 and A1 are connected to ambient light sensors using a voltage divider. When a trolley passes over the light sensor in the track, the Arduino sees the change in voltage and triggers a routine which sends pin 6 (or 7) high, activating the relay.
About 10 volts AC run into the common of the relay and out the normally closed side of the relay. When the relay is activated, the NC side of the relay is switched off and track power is cut off.
The other relay controls an Accessory. When one wire is connected to the accessory ground a solenoid in the accessory is activated to raise a group of people; when the other wire is connected to ground another solenoid is activated to lower the people.
The second relay handles about 14v AC.
The arduino itself is powered by a Vellman variable power supply I built from a kit. It puts out 9v dc.
Am I trying to do too much? I am a learner (at least I hope to!) and welcome any suggestions.
I got the same error message a while back, though i fried my uno, tried my seccond, same message. Turns out my USB driver decided it wanted to throw a hissy fit. still does it every once in a while but updating the drivers worked for me.