====== 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). * Package: Checked. * Optimized routing for VCC. * Missing decouple C: Added C5 (100nF). ==== 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. * I2C Pullups are missing: Added R4 and R5. * VDD and capacitor not optimal: Optimized. * Antenna: Ok * Pinnings: Checked ==== 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. * Traces are ok, values must be checked in prototyping phase ===== 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 ==== * C3 is far away from H-Bridge, bring it nearer ==== DCC Track input ==== * Decoupling capacitor at IC1 is missing (100nF) ==== 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