I recently used relays and the digital I/Os of the DP832 to control the polarity of the outputs. The circuit needs an external 24VDC supply to activate the relays. This makes it a bit impractical to use. I also plan to design a circuit that would automatically calibrate the DP832 also using relays.
The USB host port could be a possible solution. It would be interesting to see if it can supply enough power to activate the relays. Unfortunately the DP800 Series user manual does not provide enough information about the type of the USB port. I assume it is a normal USB 2.0 port capable of supplying 0.5A of current.
USB host port
I tested the port with 600mA for more than an hour without any interruptions. The voltage was 4.55V but I am not sure that it was not the voltage drop on the cable. In any case we should be able to get 2.5W out of the port continuously. That should be enough for at least 10 5V micro-relays.
At 1A the port shuts down after a few seconds.
Digital I/O host
The manual does not provide any information about the I/O ports (big surprise). They can either be used as inputs or outputs. They work at 3.3V but I suspect they are 5V compatible.
When used as an output a port cannot provide much current. I made a few measurements:
| Current | Voltage |
|---|---|
| 0 mA | 3.28V |
| 0.16 mA | 2.5V |
| 0.26 mA | 2.0V |
| 0.35 mA | 1.5V |
| 0.43 mA | 1.0V |
In any case the port can probably not even drive a BJT. I had success with load drivers though (e.g. the ITS4200SME).
I do not have time to reverse engineer the circuit but here are a couple of photos of the IO ports circuit.
