In The evolution of FlexSEA prototypes I’m showing the first 3 generations of FlexSEA-Execute designs. While the 3rd generation, FlexSEA-Execute 0.1 (I know, it’s the third one but I named it 0.1 because I changed the naming convention and it felt wrong to start with 0.3!) is stable and functional, nothing is ever perfect. In my thesis I wrote down:

List of modifications that do not require circuit modifications (only BOM changes):

• Lower the I²C resistor pull-ups (R45, R46) to 1.8kΩ (currently 4.7kΩ)
• Change the IO protection resistors (R10-R13, R64, R65) to 120Ω (currently 100Ω)
• Less resistive PTCs (F1, F2)
• Lower the Gate resistor values by at least half. More calculations and testing is required to find the optimal value.

List of modifications requiring circuit modifications:

• The 400kHz I²C limit on the MPU-6500 is slowing down the bus. If a new IMU has to be selected a 1MHz version should be considered.
• RGB LED: poor color balance. The next design should use 243/249/412Ω.
• Add a second green LED to unify the user interface with Manage.
• Add an external filtering capacitor for the Delta Sigma converter (0.1 to 1.0µF, see component datasheet).
• Add SWD (P1[3]) to the PSoC 5 SWD connector (J9). The Serial Viewer isn’t supported yet but will be convenient in the future.
• The ‘+5V’ supply should be measured.
• The RS-485 transceivers (U4, U10, U11) should use the 8-SON package to save board space and unify the BOM with Manage.
• The position of the SWD connectors (J5, J9) is not convenient. They should be on the top side. Swapping their position with the RS-485 transceivers would be convenient.
• Many expansion pins are on port 12. They are SIO and not GPIO (no analog features). Most of the expansion signals should support analog inputs.

Of course, since then I had many improvement ideas. But first, I need to run a series of experiment to confirm/infirm some parts of the design:

• Test the triple channel RS-485
• Test RGB resistor values
• Gate resistor values
• Reliability test with the lower gate resistors
• Thermal/load test with the lower gate resistors
• How should I interface a wireless module?
• Test the shorted lead protection
• Single stage SG amplifier?
• Test with external SPI circuits
• How can I use a Manage board with minimal wires? Or directly connect Plan?
• Evaluate LM510x chips to get smaller drivers
• Is there a better PSoC 5 available?
• PSoC 4 with Bluetooth to replace the co-processor???
• Shorted leads: better MOSFETs?
• How can I support higher voltages? Currently limited by the LM25011 (42V). 48V would be great.
• Can I add memory to log experiments?

Other than minor technical fixes, the biggest improvements will be the wireless communication and the high supply voltage. Once I’m done with that list (spoiler alert, I already found answers for some of the questions!) I’ll implement all the changes in Altium and roll-out a new batch of Execute boards. This should keep me busy for the next few weeks!

Do you see something missing? What feature would you integrate?