General improvements for flight models

[brunofalmeida]

• [x] For unused PEX pins, put a current limiting resistor (e.g. 100 ohms) to ground
  • Only do this if you're tying it to ground, otherwise can leave floating
• [x] Fix ADC (ADS7952) circuit - op amp connected to it (AD8613) does not have V+ connected to VA (analog power) - op amp power floating
  • Fixed in pcbs-common

[brunofalmeida]

• [x] Fix translucency problem of the PAY-Optical PCB
  • Update - fixed

[brunofalmeida]

• [x] Fix systems PCB DSUB25 header pinout

[brunofalmeida]

• [x] Implement 3-way heartbeat resets on all boards so any MCU can reset either of the other 2 MCUs (OBC and EPS have it but need minor fixes, PAY doesn't have it yet)
• [x] Use 100 ohm resistors in series with reset outputs for current limiting
• [x] Use a 0 ohm resistor in series with the reset input for optional disconnecting
• [x] Already have 30k pullups on RSTn inputs in micro-ATMEGA32M1.SchDoc

The current OBC has most of this implemented except the 0 ohm on the input - see Sheet 1 of https://github.com/HeronMkII/pcbs/blob/master/bus/obc-comm/Project%20Outputs%20for%20obc-comm/Schematic%20Prints/obc-comm.pdf

Here is the proper schematic:

Update (2019-08-18): Should NOT have the 0 ohm resistor in the top of the photo. In any case, we need the reset input of each MCU to be connected to the systems PCB for programming, so there's no point in having the 0 ohm resistor.

[brunofalmeida]

GPIO pins for antenna deployment

• [x] Substitute 2 GND pins on the EPS-OBC butterfly connector for GPIO pins controlled by OBC
• [x] Might need to add a gate drive buffer, either on EPS or OBC?
• [x] Route to 6 pin molex connector on EPS

[brunofalmeida]

Change 6-pin programming headers so they don't have tall male pins that interfere mechanically:

• [x] On the board, use low-profile female headers (the same type as the debugging headers on OBC and PAY-SSM)
• [x] Buy and use 6-pin male-to-male adapters (almost the same as the programming headers currently on OBC and PAY-SSM) that interface with the programmer's female header

[brunofalmeida]

• [x] Are we at risk of the PGM <-> RUN switches being switched during vibe?
• [x] Might need to add a 4-pin header (2 pairs of 2 pins) to each PCB - solder or short together (with 2-pin caps) the RST and SCK_A/RX to the RUN equivalents
• [x] Maybe permanently short to RUN side and only program through the systems PCB?
• [x] Decision - connect systems debugging header nets directly to MCU to bypass PGM <-> RUN switches on each board

[brunofalmeida]

• [x] Look at programming headers, possibly shorter pins or facing outwards to the side (#38)
  • Using low-profile female headers, no right-angled headers to the side
• [x] Check UART labels (#42), label TX and RX
• [x] Revisit programming setup of microcontrollers between PAY-SSM and PAY-Optical (#43) - might not be an issue with the new architecture but look into it
• [x] Physical stacking of PAY-SSM and PAY-Optical (#44)

[brunofalmeida]

• [x] Consider fire code - separate hardware device (probably on OBC) that would listen for UART coming out of the transceiver, see a special code, and reset OBC
• [x] Consider external flash memory hardware on EPS/PAY to store programs for re-programming

[brunofalmeida]

• [x] Consider using ATmegaS64M1 rad-hardened microcontrollers - see Rad-hardened microcontrollers page on OneNote - common footprint is TQFP32 so should use that footprint
• [x] Everyone use the TQFP32 footprints for the 64M1 - footprint and size are exactly the same (are directly swappable)

Is this the correct one?

Yes it's correct - Bruno

[brunofalmeida]

• [x] Connect systems debugging header nets directly to MCU to bypass PGM <-> RUN switches on each board

[brunofalmeida]

Implement a system between EPS and OBC that will tell us when the deployment algorithm is about to be run on the antenna. This is a preventative measure if it is activated accidentally so we can monitor the LED closely and kill the power if necessary to not deploy the real antenna. The idea is to add two LEDs (preferably red) that OBC will blink furiously when it is about to deploy the antenna.

• [x] Add a new GPIO output from the OBC microcontroller to an LED on OBC (anywhere on the top side).
• [x] The signal should also go through the butterfly connector to an LED on EPS. The LED must be placed near the systems debugging connector on the edge of the board such that it is easily visible from the outside when the satellite is fully assembled, even when the solar panels/solar PCBs are mounted.

[brunofalmeida]

• [x] Revisit RTC battery ground on EPS - RTC ground is connected/disconnected to main ground through deployment switch, protection circuit, diode in MOSFET
  • Way to get correct RTC battery voltage is to connect the main power so the protection circuit is active (conducting)
  • Nominal RTC battery voltage is ~3.2V - if ground not properly connected, measure ~2V - if grounds are properly connected, measure ~3.2V
• [x] Should we get rid of the RTC battery? Is it not really useful? Need to examine use cases and failure modes where it would have a purpose
  • Current decision is to keep it, applies when battery voltage is low
• [x] Need to do test where the battery voltage drops to become too low, but the grounds stay connected so the RTC battery should be powering the RTC properly
  • Result - seems to work, supplying a 2V battery current (do not need to first supply a proper higher battery voltage) allows the RTC GND to be connected to the main GND

[brunofalmeida]

Not sure if this is the best place, but note for @vogeldylan:

• [x] Need to update EPS MICD with connector placements for antenna 6-pin connector, battery, and deployment switches

[brunofalmeida]

- [ ] Need to put 5V back on the EPS-OBC connector, add two up translation buffers (3V3 to 5V) with input pulldown resistors on OBC

@jadenreimer EDIT (2019-08-06): Not changing anything on EPS-OBC connector nor OBC, just adding two up translation buffers (3V3 to 5V) with input pulldown resistors on EPS near the antenna 6-pin connector. The 3V3 versions of the release signals will be sent to SYS for easier routing.

• [x] Implement buffers on EPS
• [ ] Update systems wiring diagram, rename ANT_REL_A -> ANT_REL_A_3V3, ANT_REL_B -> ANT_REL_B_3V3, rename versions going to the antenna 6-pin connector to ANT_REL_A_5V, ANT_REL_B_5V