Full Design Review - 12/15/09 M Chip Pin-by-pin schematic compared to datasheet and package: 1 pd3 DIO3 2 pd4 dio4 3 GND DISCONNECTED! FIXED! 4 VCC OK 5 GND OK 6 VCC DISCONNECTED! FIXED! 7 xtal1 ok 8 xtal2 ok 9 pd5 dio5 10 pd6 dio6 11 pd7 dio7 12 pb0 dio8 13 pb1 dio9 14 pb2 ss 15 pb3 mosi 16 pb4 miso 17 pb5/sck sck 18 avcc connected to vcc, ok (datasheet p4) 19 ADC6 DISCONNECTED! NC OK 20 aref aref header 21 gnd agnd (not ref in datasheet to AGND, only GND) OK 22 ADC7 DISCONNECTED NC OK 23 pc0/adc0 24 pc1/adc1 25 pc2/adc2 26 pc3/adc3 27 pc4/adc4 28 pc5/adc5 29 pc6/RESET 30 pd0/rx 31 pd1/tx 32 pd2 ? MCHIP: 16MHz Xtal or 20MHz? Go 20Mhz! Should not be a problem. Maybe some baud rate misalignment with the other chips. ? MCHIP: Xtal capacitor size justification? ? Xtal package pin check to datasheet? V Chip ? 16MHz Xtal or 20MHz or other? ? Xtal capacitor size justification? Pin-by-pin schematic compared to datasheet and package: 1 pd3 DIO3 2 pd4 dio4 3 GND DISCONNECTED! FIXED! 4 VCC OK 5 GND OK 6 VCC DISCONNECTED! FIXED! 7 xtal1 ok 8 xtal2 ok 9 pd5 dio5 10 pd6 dio6 11 pd7 dio7 12 pb0 dio1 (as per tellymate) 13 pb1 into V DAC 14 NC 15 dac 16 17 18 19 ADC6 DISCONNECTED! NC OK 20 NC 21 22 23 24 25 26 27 28 29 30 31 32 P Chip Pin-by-pin schematic compared to datasheet and package: 1 pd3 DIO3 2 pd4 dio4 3 GND DISCONNECTED! FIXED! 4 VCC OK 5 GND OK 6 VCC DISCONNECTED! FIXED! 7 xtal1 ok 8 xtal2 ok 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 ? Pin 1 marked? OK ? Crystal capacitor value justification? OK Atmega328 datasheet recommends 12 - 22 pF Video DAC ? Diode Requirements? OK. Diodes make low outputs look like a disconnect - ie, they won't sink any current. ? Voltage levels expected? OK - taken from tellymate. video device supplies 75 ohm termination. MOSI=0V, PB1=0, OUT=0V (Sync level) MOSI=5V, PB1=0, OUT=5V*75/(330 + 75) = .93V (unused??) MOSI=0V, PB1=5V, OUT=5V*75/(1000 + 75)= .35V (black level) MOSI=5V, PB1=5V, OUT=5V*75/(248 + 75)= 1.16V (white level, slightly high) ? Do I need termination resistor? OK - No. some tellymate versions don't even have the option. VICSP ? Pin 1 marked? OK ? Schematic vs ICSP pinout? ? No buffer resistor on V RESET/DIO9? OK - possible but unlikely contention with M Chip if software error. ? Should/can KBCLK be on an interrupt line? PICSP ? Pin 1 marked? OK ?Schematic vs ICSP pinout? ? No buffer resistor on P RESET/DIO8? OK - possible but unlikely contention with M Chip if software error. ? Buffer resistor sizing R30, R31 and R32? OK ? L1 LED silkscreen marking? USB IF ? Justification for 2.2k pullup on D-? If P Chip output is high impedence, then this will pull D- to 3.6V, expected by spec (opposite of D+). ? USB clamping diode spec? OK ? Current through R50 and R51 during clamped operation? OK. (5V - 3.6V)/68 = 20 mA ? Main board power supply bypass capacitor sizes? OK. Shotgun, but can be changed later if really needed. ? Are Calibration marks appropriate? OK - adjusted according to web sources ? USB connector grounding? FIXED - For shielded USB 2 cables, the shell must be connected to ground. Intel recommends an optional ferrite bead on ground, power, and shell as well. I'm skipping the ferrite. ? Verify USB pinout to datasheets? OK ? L2 power LED current calculation? OK - 5V/1000ohm = 5mA - low but used in Arduino ? Keyboard connector pinout? OK ? Arduino Power Expansion Header pinout? ? Arduino Expansion Header orientations? Power - Analog - DIO1 - DIO2 ? SD Card power requirements? 27 - 90 mA? http://forum.brighthand.com/showthread.php?t=187443 -"The normal cards have a peak current of about 40mA when doing a write and the high-speed cards are about 60mA." - -"the spec allows an SDHC card to draw up to 200 mA. Although, we've found measured some high speed SDHC cards draw up to 450 mA." http://www.embeddedrelated.com/usenet/embedded/show/112554-1.php FIXED - Switched to 100mA regulator in same SOT89 package almost same price. (can go much higher if needed in same package and price) ? Do I need 3.3V regulator bypass cap? FIXED - Uzebox had a 10uF cap, so I've added one. ? Audio out value justification? ? Is fuse too fussy? OK - Intel recommends a 500mA fuse. ?IR2 recv pinout verification? OK ? SD Card pinout verification? OK ? SD Card connector grounding? FIXED - grounded ? IR LED current calculation? FIXED - Reduced to 13 mA, transistor remove. ? IR LED PNP transistor selection and spec? FIXED - removed. ? Full schematic CRC check? FIXED PCB ? Silkscreen on via? OK - Mostly harmless except for legibility. FreeDRM doesn't complain. Will clean up as I see them. ? Silkscreen clearances? ? Via near bypass cap verification? OK ? Trace clearance? ? Board edge clearance? ? Board thickness? ? What other Atmega chips are compatible? BOM - Digikey order formation - Mouser order formation - Update BOM DONE ? Crystal footprint verification? OK ? switch footprint verification? ? RCA footprint verification? ? RCA tip/shield orientation? OK ? 0603 resistor footprint? ? fuse footprint? ? 0603 cap footprint? ? Regulator footprint? ? LED footprints? ----