Everything on this project was going flawlessly, and I am embarrassed something so simple has halted me in my tracks! I am using the arduino to produce a 5V signal, I am trying to connect it to a 12V relay that will break an 24V DC circuit. Essentially the code works, and when the photo-eye sees a problem it will trigger the 12V to open the 24V to stop the motor in its place. My problem is amplifying the 5V signal. I have tried the TIP-102, MOSFET and 2N3904 transistors in this arrangement: http://www.arduino.cc/playground/upload … driver.pdf and http://blog.lib.umn.edu/ali/2010ema8600 … mosfet.jpg
At best, my 12V/24V relay will buzz. I know the relay is wired correctly as I have worked with these many times before; the codes is also correct as the LED’s and buzzers are doing their job.
I feel like the problem is obvious, however I can’t see it by myself. Can anyone point it out for me??? Thanks!
Sounds like the transistor is not fully conducting and the voltage on the relay coils is not great enough.
First, are you sure the relay coil works at 12V? Try connecting 12V direct to the coil to be sure it pulls in and your power supply sources enough current.
What is the current required by the relay coil? or coil resistance?
Measure the processor output pin voltage and the voltage at the transistor base. The difference is the voltage drop on the base resistor and Ohm’s Law gives the transistors base current. Is the base current times the transistor’s beta large enough the power the relay coil?
Yep, sometimes these simple circuits are the ones that cause trouble.
For some reason the transistor that the manufacturer recommended would not work. I got my replacement from Radio Shack.
I have the digital output pin from the Arduino go into one side of the RR coil, then the other to the Arduino ground. I hooked up my Negative end of my power supply to the N.O. pin of the RR, the COM side was wired to my PR, then the other pin on the PR went to my Positive end of the power supply.
Very simple, as I expected, just the parts wouldn’t work with my PLC. Hope that might help someone’s future frustrations.
I am doing a relay controler with arduino, and i am asking my self why are you using this reed relay …? i am not so good at electronic, i am learning day after day.
I was about to do Arduino > 5v com > relay 12V (with 12v power supplie) > 24V passing through relay (with 24V power supplie)
Basically the Reed Relay responds to the 5V signal, and can open/close a 12V circuit. I like to use the Reed Relays because they are very fast in responding, cheap, and easy to use. You can then take a 12V power supply and run them through the Reed Relay to basically amplify your Arduino signal.
Using the 12V signal, I then use a more robust relay (I often control 110AC or High Amp DC motors) with that 12V signal that we just previously amplified. Relays are generally really easy to work with because they are just switches, you rarely need to worry about the electricity flowing through them.
I am sure a MOSFET would work for your application as well. I just had an issue with one once, then found the Reed Relay to work perfectly, from there have had no desire to try it again.
BJMarsh:
I am sure a MOSFET would work for your application as well.
You bet. The key to success (well, aside from knowing which terminal to connect to which device) is looking for a threshold voltage that’s compatible with your microcontroller’s Voh (with some margin). Using a MOSFET as a switch is easy-peasy, as long as the gate voltage actually makes it switch. Relays are swell if you need to switch AC (though triacs work for that, just saying) or really crufty loads.
