12-08-2008 01:51 AM
Hello Board,
I need to drive a 24V relay coil with the open collector digital output of the USB-6008. Is there a preferred way of doing this? I have already blown one output. I think it was from tieing the grounds of my 24V supply and the DAQ 5V supply? The 6008 output can only drive 8.5 mA, so I was thinking of using a low If optocoupler. I found one that takes only 5mA to drive the LED. I would have to drive another Darlington transistor with its output, though. Is there an easier way? Thanks for your help!
Best regards,
Mike
12-08-2008 04:44 AM
12-08-2008 06:09 AM
The cheap version is a resistor (10k?), a PNP Transistor (connected to 24V) AND A (free runnning) DIODE (!) across the solenoid to protect the pnp.
Your 24V GND will connect to the PC GND, so think about ground loops and if that is a good idea... (No problem if you have a exclusive clean 24V source)
There are a lot of interface schematics in the net, however a good book like "The Art Of Electronics" (Horowitz/Hill) help to understand (nice gift!! HINT HINT).
Optocouplers are a good idea to protect your USB device 😉 That was learning by BDOING
12-08-2008 06:53 AM
I too have had good success using Opto22 products.
Just used an Opto22 OAC5 and a USB 6008 to drive four
120v AC solenoid coils for a test plate setup. Was very simple.
Have also used the Opto22 DC version in other applications.
Crydom's solid state devices are also very simple to use.