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https://www.sainsmart.com/products/4-channel-5v-usb-relay-module
The Relay Board is a Sainsmart 4 channel 5v USB relay module, which is simply a board that, when powered, allows computer control to open or close one of four circuit switches. The casing it is in can be removed, and was simply made for ease of use and protection. The only modification made to the relay board as it comes from the manufacturer is, two pins on the top of the board were soldered together to connect the USB-B port to the power supply and allow the board to be powered simply by being plugged into the computer, rather than needing an external power supply. The case itself simply contains two holes for each of the two switches needed for the shims, and one to plug the USB-B plug through. It also contains alligator clips connected to switch 1 and switch 2 for ease of use, which are run through the holes above said switches, and fiber optic cables, which run directly up from the on-board lights that indicate whether a switch is open or closed, to provide the same indication to an observer outside the casing.
If necessary to build up from scratch, a Sainsmart board linked above may be used from scratch with no modifications, though it may be desirable to solder together the 5V pin and the USB power pin as described above, so that no external power supply is needed. On a fresh board straight from the manufacturer, the software described below will control Slot 1 and Slot 2, which are the furthest switch from the USB port, and the second furthest, respectively.
Labview Control
The computer control for the power supply and shims is a labview VI that uses the library of functional subVI's provided by Oxford Instruments for use with the Mercury iPS. Once properly commissioned, the control works to prevent dangerous situations from occurring with respect to the power supply. It also contains several controls for the shim coils, and possible use as a level meter, which will be described below.
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