NI USB6008 and ULN2003A relay driver

[Intraframe]

Hello,

I know there are a few threads on this subject already, but I wanted to ask some questions regarding how to drive a solid state relay using my NI USB6008 and a ULN2003A. I am a student, but do not have much familiarity with these kind of electronics so bare with me.

Basically, I would have 2 relays (control voltage 3-32VDC, 28mA @ 32V) to drive. Since this is too much current for the USB6008, I would have to use another device such as the ULN2003A, and some external power supply, correct? I found this diagram on the forums:

But I am a little confused on how the 12V power supply is connected. Would the 12V go to both the COM of the 2003A and to the positive terminal of the relay? Is the negative terminal of the relay then connected to the 2003A? Finally, are all the grounds tied into the USB 6008?

I just want to verify this setup will work with my relays.

Thank you

[johnsold]

I suspect your confusion results from the use of the term "COM" in different ways. In many DAQ systems and many others COM is ground. In the ULN200x devices COM is short for "common free wheeling diodes" and is usually connected to the most positive power supply for the relay coils. The ULN200x devices do not have power supply connections because they are just arrays of transistors. The emitters are all connected to the ground (GND) terminal.

So the schematic you posted is correct. The GND (pin 32) of USB-6008, GND (pin 😎 of the ULN2003, and the negative lead of the battery or external power supply all connect together: This point is called Ground. The positive lead of the battery or external power supply, the positive terminal of the relay control input, and the COM (pin 9) of the ULN2003 are all connected together: This is the point called VCC or 12 VDC on your schematic.

Lynn

[Intraframe]

I see, thanks for clearing that up for me. And just to confirm, that means the negative terminal of the relay control input would be connected to the IC of the ULN2003  (pin 16)?

And if I had a second relay, its postive terminal would be connected to the same VCC point on the schematic?

[johnsold]

Yes.

Yes. And the second relay's negative terminal would go to a second output on the ULN2003.

Lynn

[Carmen92126]

Is pin 17 on the USB 6008 a digital ouput?

Is a relay driver usually or normally controlled with a digital control?

Thank you.

[Dennis_Knutson]

It's a digital input or output. Refer to the manual.

Yes.