USB-6008 Relay Drive Interface

[Cburg]

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

[Brian_Beal]

I have used OPTO22 G4 modules with the USB DAQ before, even though they technically exceed the current rating of the output.  I have applications that have been running for 2+years with these.

[Henrik_Volkers]

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

[anengineer]

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.