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Controller circuit checklist:
=============================
* Bypassing
- Vcc:
All Vcc/AVcc pins are bypassed properly. UVcc is the input to the
USB pads regulator and, while not very clear, doesn't seem to need
bypassing other than that of the VBus line feeding it.
Parts(C4, C6-8): 0.1uF 10%, X7R, 0603, EMK107B7104KA-T (buy 20)
- Ucap (C5): 1uF 10%, X7R, 0603, EMK107B7105KA-T (buy 10)
- Vbus:
The VBus pin 7 is not a power supply input, but instead a VBus
monitor input. Only the recommended 10uF capacitor (C1) is used
on the VBus line.
Parts(C1): 10uF 10%, X7R, 0805, EMK212BB7106KG-T (buy 10)
* Reset pin
- R3 value: AN2519 suggests "4.7k or more", Pro Micro uses 10k, Teensy uses nothing.
- R3 part no.: 10k, 100mW, 1%, CRCW060310K0FKEA (buy 10)
- Need filter cap?
AN2519 mentions it's not directly required; just added protection
for noisy environments. Could add pads, but since it would also
necessitate a further resistor between the reset switch, will
leave out for now.
* Clock crystal
- Crystal part no.: 16MHz, 10 pF, ABM3B-16.000MHZ-10-1-U-T (buy 4)
16MHz, 18 pF, ABM3B-16.000MHZ-B2-T (buy 4)
- Load capacitor part: 12pF 1%, 50V, C0G, 0603, GRM1885C1H120FA01D (buy 10)
15pF 1%, 50V, C0G, 0603, GRM1885C1H150FA01D (buy 10)
18pF 1%, 50V, C0G, 0603, GRM1885C1H180FA01D (buy 10)
22pF 1%, 50V, C0G, 0603, GRM1885C1H120FA01D (buy 10)
* USB comms
- R1/2 part no.: 22 Ohm, 100mW, 1%, CRCW060322R0FKEA (buy 10)
- DP/DM routing:
40mil/6mil trace width/spacing should give a differential
impedance of about 90Ohm, given 1oz/ft^2 copper (1.4mil) and a
60mil FR4 width. Skew phase has been tuned.
- Connector part no.: 5787834-1 (buy 4)
- Connector shield grounding:
Lots of conflicting information around. Best seems to be to
simply ground it, with the lowest impedance connection at the
quietest part of the board.
* USB programming
- pull-down on HWB sufficient?
The documentation says that with the HWB pin enabled (i.e. low),
the bootloader is executed after a "reset". It is not very clear
what may constitute a reset, i.e. whether a power-up is a reset as
well. But it seems that only a manual reset counts. It should
therefore be safe to tie the HWB pin permanently to ground,
through a current-limiting resistor. In case of problems, the
resistor can be omitted and the pads used as a jumper.
Also note that fuses cannot be programmed through the DFU, but we
shouldn't need to program any fuses. CKDIV8 divides the clock by
8, but QMK overrides it in software. As a last resort, it should
be possible to program via ISP, through the 6P6C connector.
* Split comms
- 6P6C part no.: 5520425-3 (buy 4)
- any easy way to isolate Vcc from USB port in slave?
Leave it for a possible second revision.
* PCB
- Manuf. service:
- Service design rules:
- DRC/ERC:
- Labels:
* BOM:
J1 (1 pcs, USB_B): 5787834-1 (buy 4)
Y1 (1 pcs, Crystal_GND24): 16MHz, 10 pF, ABM3B-16.000MHZ-10-1-U-T (buy 4)
16MHz, 18 pF, ABM3B-16.000MHZ-B2-T (buy 4)
C4,C7,C8,C6 (4 pcs, 100nF): 0.1uF 10%, X7R, 0603, EMK107B7104KA-T (buy 20)
C1 (1 pcs, 10uF): 10uF 10%, X7R, 0805, EMK212BB7106KG-T (buy 10)
J2,J3 (2 pcs, Conn_01x08): B8B-PH-K-S, PHR-8, SPH-002T-P0.5L (JST)
440054-8, 440129-8 (TE Connectivity) (buy 10)
J5 (1 pcs, Conn_01x06): B6B-PH-K-S, PHR-6, SPH-002T-P0.5L (JST)
440054-6, 440129-6 (TE Connectivity) (buy 5)
J4 (1 pcs, 6P6C): 5520425-3 (buy 4)
U1 (1 pcs, ATmega32U4-AU): ATMEGA32U4-AU (buy 3)
SW1 (1 pcs, SW_Push): TL3305AF160QG (buy 5)
R4 (1 pcs, 1k): RCA06031K00FKEA (buy 10)
C5 (1 pcs, 1uF 10%): EMK107B7105KA-T (buy 10)
C3,C2 (2 pcs, 22p): 12pF 1%, 50V, C0G, 0603, GRM1885C1H120FA01D (buy 10)
15pF 1%, 50V, C0G, 0603, GRM1885C1H150FA01D (buy 10)
18pF 1%, 50V, C0G, 0603, GRM1885C1H180FA01D (buy 10)
22pF 1%, 50V, C0G, 0603, GRM1885C1H220FA01D (buy 10)
R3 (1 pcs, 10K): CRCW060310K0FKEA (buy 10)
R2,R1 (2 pcs, 22 5%): CRCW060322R0FKEA (buy 10)