Railflyer PCB review
Truck PCB (2012-10-23)
Revisited 30.11.
No current limiting resistor on the LEDs but LED22 and LED23.
If no external resistor is used there might be a problem with to high current through the LEDs which reduces lifetime or can destroys several LEDs
Christopher states, that maximum of 10 LEDs per truck are switched on, but 20 mA each. This means a total current of 200 mA per truck. This is to much for the 3.3V regulator.
Suggestions to solve this:
Use the regulated 5V instead of the 3.3V here.
Use current sources instead the transistor/resistor combination.
Connect the LEDs in series instead of parallel: i.e. if the LEDs need less than 2.5V voltage drop.
Further problem: +5V is not available at the moment.
Use the free contacts 2 and 3 for this OR if each truck PCB gets its own motor driver the Motor N and P signals.
General problems and suggestions
Wires go through parts on schematic: cleaned up.
Logo and text: Removed.
Checked package of 2SC4617 (Q1-Q11): Ok
Check the used LEDs, particularly LED9-LED16. Transistor can only drive up to 150 mA!!!
Processor PCB (2012-10-22)
General problems and suggestions
As send by Christopher board and schematics are not consistent: That is bad :(
Following steps to solve this: Renamed J2 to FRONT_TRUCK (rotated and mirrored for correct pinning), renamed J1 to REAR_TRUCK, Rotated and mirrored J7 for correct pinning (Pin 1 is low battery, P20 is 3,3V now)
Layer 2 and Layer 3 in board removed as not needed.
Board: Some vias are to close together: Shorts possible while soldering.
Board: For current wires the distance inbetween is too low
Keep the connections to the truck PCBs as short as possible to prevent EMI issues!
Renamed DCC_P to DCC_R for consistence with Power PCB
Resized the smallest vias to standard 0.25 mm drill
Resized motor and DCC wires to 0.4 mm drill
Sound chip IC3 (SGTL5000)
This IC converts a I2S stream into an audio stream.
The package is QFN-20 (SGTL5000XNLA3/R2), checked.
I2C: Address is 0x14/0x15, up to 400 kHz are supported
C3 is too far away from VDDA pin: Fixed.
Ground connection is suboptimal, resized ground layer.
Capacitors are 0201: Ok.
Serial flash IC2 (MT29F4G01)
This IC stores the wav-Files for sound generation. Altough a Flash with parallel bus access, only the SPI pins are used (as a common SPI flash/eeprom SO8).
Accelerometer IC4 (MMA7361LC)
This IC measures 3 axes acceleration (as analog signals).
Package: LGA. Checked.
0g-Detect is open: ok.
Sleep pin is open: not ok, connected to controller with pulldown (for saving battery power).
g-Select pin is open: ok, internal pulldown resistor enables 1.5g operation.
Three outputs (X,Y and Z) go to ADC inputs of controller: ok, decoupling/filter is installed (C1-C3).
Microcontroller IC1 (MC13224V)
This controller controls the locomotive and is connected via wireless or DCC to the command station.
BEMF circuit
This circuit can be used to measure the back EMF of the connected motors. It is a simple voltage divider with hold element.
Power PCB (2012-10-12)
Battery monitor IC6 (MAX17059)
This part is for monitoring the battery voltage and has an I2C interface.
correct: version for 2 cell monitor
Not correct: C36, bypass VDD and GND with 100nF NOT Cell and GND
Not correct: Connect CTG to GND!
Recommendation: ALRT is open drain, pullup needed (better do not use the internal MC ones, so the board works stand alone)
I2C: Address is 0x6C/0x6D, up to 400 kHz are supported
Package: TDFN-8, mark pin 1 on ground plane, pinning is correct.
Bypass-C is not optimal routed
Routing of SDA/SCL to connector J2 is okay
Battery charger IC5 (MAX1873)
This part is for loading the battery.
D7 can be omitted, VDCC is sourced by a bridge rectifier which prevents back source.
Shunt R17 with 0.04 Ohms limits load current to 2.5 A from rails
Shunt R15 with 0.08 Ohms limits load current to 2.5 A
Voltage regulator IC4 (TL1963ADCQ)
This part regulates voltage to 5V from input voltage which can be up to 20V DC. Current can be up to 1.5A.
Input capacitance is missing (10 uf)
Correct: Calculated output voltage due resistor ratio: 5.0336
Output capacitance C1 is ok
Voltage regulator IC3 (MIC5205-3.3)
This part regulates voltage to 3.3V from input voltage 5V. Current can be up to 150 mA.
* No errors but the ouput current might be a show stopper
H-Bridge interface and H-Bridge
General suggestions
Circuit around D9, C38 and R42 is not considered in BOM, maybe it is a smoother for VDCC voltage, leave it for now.
Bad: All schematics one one Eagle sheet, better use two (for printing and reading)
Bad: I would avoid using P$ as prefix for pin assignments
Board: For current wires the distance inbetween is too low
Board: Remove old logos as ordered