process of PHM1
I have not been documenting the design ´process of this prototype beside taking pictures. Now that I did a couple of changes to the pins in the prototype, and since there are so many details to keep track of, I decided to keep track of these changes to avoid confusions.
Changes to the first prototype
- redesigned the board completely, since I decided to integrate an atmega 2560 instead of an external arduino pro mini.
- changed the normal RGB LED’s with WS2812, allowing higher brigtness and a nice colour range.
- added more buttons, given the higher pin count of the new chip, and realizing that more direct access to functions was needed.
- integrated connectors for MIDI in and out, and for intercommunications between the similar units, using a presumed token bus protocol.
Changes to the second prototype
- was done using SeedStudio. One of the three boards was irrecuperably broken. Seeed responded with a voucher for next purchase. It’s something
- Sd card was wired wrongly, the accident happened due to the pin numbering on kicad library was not concordant to the pin numbering of the SeeedOpl SD card socket, and because the pin namings in the SD are quite confusing. I still need to check that the changes made to the schematic will effectively enable the SD card by desoldering and rewiring the current sd card according to the following table:
||arduino (IC) pin number
|| nominal/ SPI
||DAT2 / NC
||CD & DAT3/ Ch.Select
||DAT1 / Reserved
|| card detect
- The common bus system has not been tested because I only have two boards, and the critical point of the bus system is from 3 devices up. I have to test that it works with at least two anyways, before making a new run of prototypes.
- I will switch positions between 5V and BUS pins of the jack, because in their current order, plugging the wire sometimes induce a shortcircuit.
- There is one error in the midi output jack connector: I connected the 5V in the plug detector pin instead of the pin. In my current jack device, that is the pin 4 instead of the 8. This can be corrected easily with a jumper wire.
- Something is strange with the midi input: it is constantly detecting Serial in. I need to check what does this mean.
- changed the buttons because the ones used in this prototype had too short travel size, I need tact more similar to the classic through hole ones. I chose DTSM-62K-S-V-T/R(SN431)
- I switched the button detection from normal high to normal low. The first production relied on internal pullups, but this removed the possibility of making pressure measurement of the button, as it happened in the version zero