Using Flexostat with eVOLVER Framework?

Gotten this questions a couple times and just wanted to start a thread on this:

For folks interested in the flexostat or other existing systems, could they just plug them in to the eVOLVER motherboard?

eVOLVER is a hardware and software framework for continuous culture and can very much integrate Flexostat hardware into the system. This post is an analysis on how this might happen. Firstly, I’ll explain why integration of eVOLVER is advantageous. Secondly, I’ll go into a bit more detail about the architecture of the Flexostat device. Finally, I will discuss how one might approach integration into eVOLVER. My hope is inspire generalizable insight for designing continuous culture systems and integration into eVOLVER.

1) Why would one try to integrate Flexostat into eVOLVER?
Flexostat is a pioneering turbidostat system invented by Chris Takahashi from the Klavins Lab at University of Washington. Because it only consists of two simple electronic boards and 3D printed parts, it is one of the easiest turbidostat systems to build, thus has a low activation energy, and is very affordable. Unfortunately, the same benefits make it difficult to scale to higher throughput or re-engineer. Changing sensors or how parameters are measured might require a drastic redesign of the two PCBs. Additionally, USB connection is lightweight but might be difficult to seamlessly scale to ~100s of vessels.

On the contrary, eVOLVER offers the ability to scale to higher throughput due to the networking architecture, streamlined power and wire management, and plug and play PCBs, amenable to quick redesign. A big disadvantage is the startup cost of setting up an entire system. One great option would be to get introduced to tinkering with continuous culture systems, with a system like Flexostat but scale that with eVOLVER.

2) How does the Flexostat work and how is it different than eVOLVER?

Here’s a quick schematic I put together diagraming the Flexostat control architecture.


Some key things of note that are different than eVOLVER:

  • An Arduino on Each Sleeve: Both the Main Board and OD Board have Arduino Mega micro-controllers on them (whereas eVOLVER primarily has the micro-controller on the Motherboards only). eVOLVER was initially designed like this to keep the experimental parameters modular and keep the Smart Sleeves simple (and not requiring an additional layer of programming).

  • Ethernet Connectors instead Ribbon Cables: The eVOLVER system uses common .1" pitch, two row, 16 pin connectors. To plug the Flexostat in its current state into eVOLVER, one would have to make an appropriate adaptor or switch out the connector on the Flexostat.

3) How would one make these modifications?

  • SA Board for Serial Communication: Sensor/ Actuator (SA) boards are PCBs that plug into the 70-pin-footprint on the MotherBoard. For example, to control temperature, the PWM board and the ADC boards are plugged into the SA slots, heating the culture and detecting the temperature respectively. To integrate the Flexostat without any redesign, the simplest way is to recapitulate the communication to the main board. This would require the SA boards to (1) provide a serial connection between the SAMD21 Arduino on the Motherboard to the OD Board, and (2) provide 5V and 12V to power the logic, sensor, and motor components.


Great summary. But if it requires designing a board for serial communication/routing, it seems like it’d be better/easier to just redesign the flexostat vial board?
That way you could separate the parameters, but use the flexostat 3D printed part and sensors in order to do traditional OD600 absorbance and/or fluorescence using the sensor layout they used. It’d also keep the arduino away from the growth vessel in case of overflow.

Yea I think thats a great point. One caveat is that if you were to redesign the Flexostat vial board, then it would not work with the old Flexostat Main Board. One might use the Flexostat (or any DIY other continuous culture system) as a quick starter kit and if it requires any redesign, it would be an extra barrier for integration into eVOLVER. But maybe moving forward, that would be a great suggestion for engineering new DIY culture systems, if there’s any desire to integrate into eVOLVER.

Great write up. So in this proposed setup, the serial comm SA board would also have an arduino on the motherboard to actually do the interfacing between the eVOLVER server and the flexostat vial board. And that would also mean that none of the other slots on the motherboard would really be necessary since everything is on the flexostat vial board. The single arduino could process all incoming commands, translate them to flexostat expected input, and route it to the correct vial. It would also read data in a similar manner, translating back to the expected eVOLVER server format. Is this what you’re thinking?

So the connector as is requires 6 different wires, beyond just serial communication (see below for picture of OD board connector). So, you would actually be able to control and power 2 Flexostat devices with one 16 pin ribbon cable (if you make the right breakout adaptors to the Ethernet plugs). So you’re right. Most of the pins aren’t super useful (e.g. providing a constant voltage source) but the design as is requires these pins.