Development of a 48 pin breakout box and implementation of an automated prototype.

While working in the nano-electronics lab, I had the opportunity develop a breakout box that interfaces our measurement instruments with the sample probe. The breakout box (Fig1) consists of 88 toggle switches that activate 44 BNC pins in a make-before-break (MBB) contact configuration. The MBB configuration ensures the sample is grounded while activating the measurement instruments, protecting the sample from electrostatic discharge.

I further devised a conceptual design of an automated breakout box that would replace the toggle switches with micro controllers and micro latching relays. First, I developed a 3D model in AutoCAD (Fig.1) to visualize the box and its key features. The 88 toggles switches would be replaced by one 3-position rotary switch. When in the first position, the power is off. The second position would activate the first set of relays, connecting the sample probe to the measurement instruments, but leaving the sample grounded. The third position would then activate the second series of relays, disconnecting the ground to the sample. Implementation of such a design would allow us to integrate the breakout box with our automated Python routines and eliminate yet one more operation involving human interaction.

I’ve since had the opportunity to practice my skills in SPICE, AutoDesk Eagle, and PCB etching. To demonstrate how a latching relay circuit would work, I developed the circuit in Fig.3 in Spice with Eagle. Fig. 4 is the actual circuit I built using PCB etching techniques. The latching relays need a reverse current to reset the magnetic coil. However, Arduino micro controllers are capable of producing a forward bias only. Therefore, it was necessary to produce a circuit that could produce a reverse bias when the forward bias is shut off. Fig. 5 is the Spice simulation output of Fig.3 and was successfully reproduced in the physical prototype.