Part Re-usage

Many of the parts in RAND-E were picked because we either already had them or already knew how to use them. This includes all the pressure transducers, the solenoids, and the load cells. This did lead to situations where we had 2 different types of the same component, which had different power requirements and different (see, for example, transducer types). This is why the box takes 12V, 24V, and 5V.

The microcontroller (arduino mega) was chosen after we initially experimented with an arduino uno, but discovered it did not have enough pins for our use case.

Actuation Boards

The E-Box initially had a custom made actuation board that responded to the arduino over I2C, but that board burned out after an accidental mess up of the voltages. When replacing the board, we decided to go with a very simple COTS board that would essentially act as a ready-to-go set of 4 MOSFET actuated channels that could easily be wired up to the solenoids and to digital pins on the arduino. This is what prompted the switch from an arduino uno to a mega, as we now needed 8 pins to control the 8 channels, as opposed to only 2 for I2C.

ADC Boards

The ADC boards used on the box are based on the ADS1256 analog to digital converter chip from TI. These boards simplify the usage of the chip as they handle power and all the other analog requirements for us, and simply break out the digital interface used to communicate with the chips.

When using these boards, we did have trouble getting them to work properly. We faced issues ranging from non-responsiveness to incorrect readings to inconsistent behavior, so if in future projects these boards are used, be advised that it may be worthwhile to look for another option.

COTS Usage

Using COTS boards for actuation, sensing, and control means they are easily (and more cheaply) replaceable, and it takes the burden of design off of LRI members. For example, when the original actuation board burned out, we were unable to easily replace it since it was a custom board. However, since it did a lot more than it needed to, we switched to a COTS board which we could buy multiple of for backups, instead of having to place a custom order.