Hey Sam,
There is no canned solution that we offer. The digital outputs are 3.3 volt compatible and can only source about 1mA. They work well when interfaced to 3.3 volt logic.
You could try using the output as a switch to ground. Connect the SSR (+) control line to (+) Power (external power supply) and the (-) to the USB-1616HS-4 output. Connect (-) Power to the USB-1616HS-4 ground. When the output is set high, the SSR will be off but when it is set low current will flow from (+) Power down through the output to ground, which is (-) Power and this turns on the SSR. Test the output with a load on the SSR output because they need some current to flow to stay on.
Best regards,
John
