4 layers70 × 83.5 mm
2 layers54.5 × 73 mm
OS servo decoder-8
Open-Source-Model-Railway-Electronics/OS-Servo-DecoderThe OS-Servo-Decoder is a simple and robust DCC accessory decoder designed for driving up to 8 servo motors. It supports modern model railroads with flexible configuration options, external relay modules for polarity…
- Size
- 54.5 × 73 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 79
- Nets
- 85
- Pads
- 272
- Tracks, vias
- 608, 185
- Pours
- 1
- Routed
- Yes
- KiCad
- KiCad 8.0 (file 20240108)
- Created
- 13 Jun 2025
- Updated
- 24 May 2026
Overview
OS servo decoder-8 is an open-source printed circuit board by Open-Source-Model-Railway-Electronics, from the Open-Source-Model-Railway-Electronics/OS-Servo-Decoder repository on GitHub. It is a 2-layer board of 54.5 × 73 mm with 79 parts on 85 nets, routed with 608 tracks and 185 vias.
It is built around the ATMEGA328-AU, MT2499A and PCA9685PW, with the ULN2803A, SS53 and 1N4148WS among its other parts. Its parts include 34 resistors, 13 capacitors, 10 connectors, 8 diodes and 5 ICs. It belongs with the robots and motor control boards and the AVR (ATmega, ATtiny) boards of this library.
Main components
6
ATMEGA328-AU
TQFP-32(7x7)-40℃~+85℃ 1.8V~5.5V 10bit 1KB 20MHz 23 2KB 32KB 8 Bit AVR Built-in FLASH TQFP-32(7x7) Microcontrollers (MCU/MPU/SOC) ROHSMicrochip TechnologyMicrocontrollers (MCU/MPU/SOC)
MT2499A
ESOP-8-40℃~+85℃ 1 3.5A 340kHz 4.5V~21V 400uA Adjustable Buck Built-in Overcurrent Protection、Light load efficient mode、Cycle-by-cycle current limiting、Hiccup current limiting Step-down type Yes ESOP-8 DC-DC Converters ROHSXI'AN Aerosemi TechDC-DC Converters
PCA9685PW
TSSOP-28-40℃~+85℃ 100kHz~1MHz 16 2.3V~5.5V 25mA 5.5V Built-in PWM TSSOP-28 LED Drivers ROHSNXP SemiconductorsLED Drivers
ULN2803A
SOP-18-300mil-40℃~+85℃ 0.93mA 100uA 15pF 20uA 30V 500mA 50V 8 SOP-18-300mil Darlington Transistor Arrays ROHSUMWDarlington Transistor Arrays
SS53
SMA(DO-214AC)-55℃~+150℃ 1 Independent 100A 200uA@30V 30V 550mV@5A 5A SMA(DO-214AC) Schottky Diodes ROHSDIYI Elec TechSchottky Barrier Diodes (SBD)
1N4148WS
SOD-3231.25V@150mA 100V 150mA 1uA@75V 200mW 2A 4ns Independent SOD-323 Switching Diodes ROHSJiangsu Changjing Electronics Technology (CJ)Switching Diodes
README
README.mdOS-Servo-Decoder
The OS-Servo-Decoder is a simple and robust DCC accessory decoder designed for driving up to 8 servo motors. It supports modern model railroads with flexible configuration options, external relay modules for polarity switching (optional) and direct control using both input switches, DCC accessory commands and locomotive functions (F1–F8).
Parts
79| Qty | Value | Footprint | References |
|---|---|---|---|
| 16 | 220R | Resistor_SMD:R_0402_1005Metric | R1602, R1603, R1604, R1605, R1606, R1607, R1608, R1609, R1610, R1611, R1612, R1613, R1614, R1615, R1616, R1617 |
| 11 | 10k | custom_kicad_lib_sk:R_0603_smalltext | R701, R702, R801, R802, R904, R905, R1002, R1003, R1004, R1005, R1601 |
| 4 | 100nF | Capacitor_SMD:C_0402_1005Metric | C202, C902, C906, C1601 |
| 4 | 22uF | Capacitor_SMD:C_0603_1608Metric | C402, C901, C904, C905 |
| 4 | Conn_02x03_Odd_Even | Connector_PinHeader_2.54mm:PinHeader_2x03_P2.54mm_Vertical | J701, J801, J901, J1001 |
| 4 | SS53 | Diode_SMD:D_SMA | D501, D502, D503, D504 |
| 4 | Screw_Terminal_01x03 | Connector_Phoenix_MC:PhoenixContact_MC_1,5_3-G-3.5_1x03_P3.50mm_Horizontal | J401, J1301, J1401, J1501 |
| 2 | 12pF | Capacitor_SMD:C_0603_1608Metric | C201, C203 |
| 2 | 1N4148WS | Diode_SMD:D_SOD-323 | D401, D1001 |
| 2 | 6k2 | Resistor_SMD:R_0603_1608Metric_Pad0.98x0.95mm_HandSolder | R201, R203 |
| 2 | LED | LED_SMD:LED_0805_2012Metric_Pad1.15x1.40mm_HandSolder | D201, D202 |
| 2 | SW_Push | custom_kicad_lib_sk:tactile_SMD_6mm | SW601, SW602 |
| 1 | 1000uF | Capacitor_SMD:CP_Elec_8x10.5 | C401 |
| 1 | 100nF | Capacitor_SMD:C_0603_1608Metric | C501 |
| 1 | 10k | Resistor_SMD:R_0402_1005Metric_Pad0.72x0.64mm_HandSolder | R202 |
| 1 | 150k | Resistor_SMD:R_0603_1608Metric | R903 |
| 1 | 1k | custom_kicad_lib_sk:R_0603_smalltext | R1001 |
| 1 | 20k | Resistor_SMD:R_0603_1608Metric | R902 |
| 1 | 220k | Resistor_SMD:R_0603_1608Metric | R901 |
| 1 | 22nF | Capacitor_SMD:C_0402_1005Metric | C903 |
| 1 | 6N137 | Package_SO:SOP-8_6.62x9.15mm_P2.54mm | U1001 |
| 1 | ATmega328-A | Package_QFP:TQFP-32_7x7mm_P0.8mm | U202 |
| 1 | Crystal_GND2 | custom_kicad_lib_sk:crystal_arduino | Y201 |
| 1 | FEMALE | Connector_Phoenix_MC:PhoenixContact_MC_1,5_4-G-3.5_1x04_P3.50mm_Horizontal | J101 |
| 1 | ICSP | Connector_PinHeader_2.54mm:PinHeader_1x06_P2.54mm_Vertical | J201 |
| 1 | L | Inductor_SMD:L_Bourns-SRN8040_8x8.15mm | L901 |
| 1 | LOGO | custom_kicad_lib_sk:OS-model-railway-electronics-30mm | G*** |
| 1 | MT2499A | Package_SO:TI_SO-PowerPAD-8 | U901 |
| 1 | PCA9685PW | Package_SO:TSSOP-28_4.4x9.7mm_P0.65mm | U1601 |
| 1 | ULN2803A | Package_SO:SOIC-18W_7.5x11.6mm_P1.27mm | U1101 |
The 75 most common of 79 parts.
Questions
How big is the OS servo decoder-8 PCB?
It measures 54.5 × 73 mm and has 2 copper layers, 1.6 mm thick.
What parts does the OS servo decoder-8 use?
79 parts, built around the ATMEGA328-AU, MT2499A, PCA9685PW and ULN2803A. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the OS servo decoder-8 KiCad files?
From the Open-Source-Model-Railway-Electronics/OS-Servo-Decoder repository on GitHub, at the commit this page was made from: the board is hardware/OS-servo-decoder-8.kicad_pcb and its schematic hardware/Buck.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the OS servo decoder-8 design in my own project?
Its repository states no licence, so its author keeps all rights: ask Open-Source-Model-Railway-Electronics before reusing the design.
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