The ARM Bare Metal Widget (arm-bmw) is an open hardware Cortex-M0 development board with a focus on battery power, non-volatile storage, and debuggability. It is suitable as a battery-powered data logger or a general purpose embedded controller.
The arm-bmw features a small 70 x 43mm footprint, lithium polymer battery and USB power selection, a lithium polymer battery charger, a 2-megabyte Flash memory for data storage, a basic user interface, an FTDI-cable compatible UART header, JTAG-SWD for flashing and debugging, and 16 assorted I/O for connectivity. Its BOM totals to under $15 USD. The arm-bmw is open hardware (CC-BY-4.0 licensed) and open source (MIT licensed).
Order 3 PCBs from OSH Park for $23.30 ($7.77 per board): https://oshpark.com/shared_projects/iBdyoHro
- NXP LPC1114FDH28 32-bit Cortex-M0 microcontroller
- Up to 50MHz CPU
- 12MHz on-chip RC oscillator
- 32kB Flash, 8kB SRAM
- 6-ch ADC, I2C, SPI, UART, PWM, Capture
- On-board 16-MBit (2-Mbyte) SPI Flash Memory (S25FL216K)
- Power
- USB (mini-B connector) or LiPo Battery powered
- 3-position power switch to select power between OFF, BAT, USB
- On-board LiPo Battery Charger (MCP73831T)
- Power LED, Charge LED
- User Interface
- On-board I2C I/O expander to save microcontroller I/Os (MCP23008)
- 4 LEDs
- 2 push buttons
- 2 DIP switches
- Input/Output
- 16-pin 0.1" pitch I/O header with I2C, SPI, Analog, Digital and Power pins
- JTAG Serial Wire Debug header for Flashing and Debug
- UART header, 6-pin TTL-232R-3V3 compatible
- Board
- Dangerous Prototypes SoB DP7043 (70x43mm / 2.756x1.693in) footprint
- 4 mounting holes
- Miscellaneous
- Optional external crystal and load capacitor pads
- Hand-solderable packages
See the datasheets section below for links to part datasheets.
Git: git clone https://github.com/vsergeev/arm-bmw-hw.git
GitHub: https://github.com/vsergeev/arm-bmw-hw
Git: git clone https://github.com/vsergeev/arm-bmw-sw.git
GitHub: https://github.com/vsergeev/arm-bmw-sw
The arm-bmw-sw project includes a testing suite to verify the correct operation of the UART, SPI, I2C, SPI Flash, I/O Expander, LEDs, and Buttons.
The arm-bmw provides a female JST-PH connector to accept a 3.7V lithium polymer battery, and a USB mini-B connector to accept 5V power from USB. The USB mini-B connector is only used for power and charging, not data.
A 3-position slide switch on the front selects between off, battery power, and USB power. The red Power LED indicates that 3.3V is present and that the arm-bmw is on. The orange Charge LED indicates that the lithium polymer battery is being charged from 5V USB power.
The onboard MCP1252 switched capacitor DC/DC converter regulates a 2V to 5.5V input to 3.3V, automatically switching between step down and step up operation as needed to provide 3.3V. This provides continuous power from a 3.7V lithium polymer battery as it drains to below 3.3V volts. The voltage regulator has a maximum output current of 120mA, so the arm-bmw should not be used to drive heavy loads alone.
The MCP73831T charge controller facilitates charging the connected lithium polymer battery. It operates whenever 5V power is present via the USB mini-B connector, regardless of the power slide switch state.
The arm-bmw can be programmed and interactively debugged through its 5-pin JTAG-SWD header, with a SWD dongle like the ST-LINK/V2. This dongle and the LPC1114 target are supported by OpenOCD. See arm-bmw-sw for configuration scripts for flashing and debugging over JTAG-SWD with openocd. See the JTAG-SWD header pinout below.
The arm-bmw also supports programming over UART with its on-chip ROM bootloader. The 2-pin bootloader header on the front can be jumpered to start the on-chip ROM bootloader on reset. Software like lpc21isp or Flash Magic can be used to program the LPC1114, over a UART-to-USB or UART-to-RS232 cable connected to the UART header. See the UART header pinout below.
The arm-bmw features a S25FL216K 16-MBit (2-MByte) SPI Flash for non-volatile storage in data logging applications. This SPI device is connected to the SPI0 controller of the microcontroller, sharing the MOSI, MISO, and SCK pins with the main I/O header. One microcontroller pin (PIO0_2/SSEL0) is dedicated to controlling its chip select.
The arm-bmw features a basic user interface, consisting of 4 LEDs, 2 push buttons, and 2 DIP switches. These 4 outputs and 4 inputs (8 I/Os total) are managed by an MCP23008 I2C I/O expander to conserve I/O pins on the microcontroller. The MCP23008 is connected to the I2C bus of the microcontroller, sharing the SDA and SCL pins with the main I/O header. In addition, one microcontroller pin (PIO0_3) is dedicated to the MCP23008 interrupt. The push buttons and DIP switches are debounced in hardware with an RC filter, to ensure that the MCP23008 interrupt is not spurious and to minimize the need for software debouncing.
The I2C address of the MCP23008 is configured by populating three 0-ohm jumpers on the back of the board, in either a 0 or 1 position, which pull down or up the MCP23008's A0, A1, A2 address pins. By default, these three jumpers are in the 0 position, so the MCP23008 has an address of 0x20 on the I2C bus.
Free software to drive the I2C bus, MCP23008 chip, and manage the UI is avaiable in the arm-bmw-sw library.
The LPC1114 microcontroller has an on-chip 12MHz RC oscillator, which can be configured with the internal PLL to provide a 48MHz system clock using no external parts -- this is the default configuration. The arm-bmw also provides pads for an external HC49UP crystal and 0805 load capacitors for cases where a more accurate oscillator or a different multiple is required.
The I/O header exposes one I2C bus (SDA, SCL), one SPI bus (MISO, MOSI, SCK), and 11 additional pins that may be used as digital I/O, ADC inputs, timer capture inputs, or PWM outputs, depending on the pin's supported functions.
| BMW Pin | uC Pin | uC Pin Functions | Notes |
|---|---|---|---|
SDA |
PIO0_5 |
PIO0_5/SDA |
I/O Expander shares this I2C bus. Pulled up with 10K. |
SCL |
PIO0_4 |
PIO0_4/SCL |
I/O Expander shares this I2C bus. Pulled up with 10K. |
MISO |
PIO0_8 |
PIO0_8/MISO0/CT16B0_MAT0 |
SPI Flash shares this SPI bus. |
MOSI |
PIO0_9 |
PIO0_9/MOSI0/CT16B0_MAT1 |
SPI Flash shares this SPI bus. |
SCK |
PIO0_6 |
PIO0_6/SCK0 |
SPI Flash shares this SPI bus. |
A0 |
PIO0_11 |
PIO0_11/AD0/CT32B0_MAT3 |
|
A1 |
PIO1_0 |
PIO1_0/AD1/CT32B1_CAP0 |
|
A2 |
PIO1_1 |
PIO1_1/AD2/CT32B1_MAT0 |
|
A3 |
PIO1_2 |
PIO1_2/AD3/CT32B1_MAT1 |
|
A4 |
PIO1_3 |
SWDIO/PIO1_3/AD4/CT32B1_MAT2 |
JTAG-SWD header shares this pin. |
A5 |
PIO1_4 |
PIO1_4/AD5/CT32B1_MAT3/WAKEUP |
|
P0 |
PIO0_7 |
PIO0_7/CTS |
|
P1 |
PIO0_10 |
SWCLK/PIO0_10/SCK0/CT16B0_MAT2 |
JTAG-SWD header shares this pin. |
P2 |
PIO1_5 |
PIO1_5/RTS/CT32B0_CAP0 |
|
P3 |
PIO1_8 |
PIO1_8/CT16B1_CAP0 |
|
P4 |
PIO1_9 |
PIO1_9/CT16B1_MAT0 |
|
3V3 |
- | - | |
GND |
- | - |
Compatible with ST-LINK/V2 and other JTAG-SWD dongles.
| BMW Pin | uC Pin | uC Pin Functions | Notes |
|---|---|---|---|
!RST |
PIO0_0 |
!RESET/PIO0_0 |
Pulled up with 10K. |
SWDIO |
PIO1_3 |
SWDIO/PIO1_3/AD4/CT32B1_MAT2 |
|
SWDCLK |
PIO0_10 |
SWCLK/PIO0_10/SCK0/CT16B0_MAT2 |
|
GND |
- | - | |
3V3 |
- | - |
Compatible with the FTDI TTL-232R-3V3 cable.
| BMW Pin | uC Pin | uC Pin Functions | Notes |
|---|---|---|---|
GND |
- | - | |
NC |
- | - | |
NC |
- | - | |
uC RX |
PIO1_6 |
PIO1_6/RXD/CT32B0_MAT0 |
|
uC TX |
PIO1_7 |
PIO1_7/TXD/CT32B0_MAT1 |
|
NC |
- | - |
| Qty | Part | Description | Part Number | Order Qty | Total Price |
|---|---|---|---|---|---|
| 1 | U1 | ARM Cortex-M0 MCU | Arrow LPC1114FDH28/102:5 | 1 | 3.07 |
| 1 | U2 | SPI Flash Memory | Digi-key 1274-1052-ND | 1 | 0.32 |
| 1 | U3 | I2C I/O Expander | Digi-key MCP23008-E/SO-ND | 1 | 1.22 |
| 1 | U4 | 3.3V Regulator | Digi-key MCP1252-33X50I/MS-ND | 1 | 1.64 |
| 1 | U5 | LiPo Charger | Digi-key MCP73831T-2ACI/OTCT-ND | 1 | 0.67 |
| 8 | C3, C4, C5, C6, C10, C11, C13, C14 | C 0805 0.1uF | Digi-key 1276-1099-1-ND | 10 | 0.44 |
| 2 | C9, C12 | C 0805 1uF | Digi-key 1276-1066-1-ND | 5 | 0.50 |
| 2 | C15, C16 | C 0805 4.7uF | Digi-key 1276-1244-1-ND | 5 | 0.75 |
| 2 | C7, C8 | C 1206 10uF | Digi-key 1276-1075-1-ND | 5 | 1.15 |
| 8 | R1, R7, R8, R9, R14, R15, R16, R17, R18, R19, R27 | R 0805 10k | Digi-key 1276-5332-1-ND | 15 | 0.30 |
| 4 | R10, R11, R12, R13 | R 0805 100k | Digi-key 1276-3512-1-ND | 10 | 0.20 |
| 6 | R20, R21, R22, R23, R24, R25 | R 0603 0 jumper | Digi-key RHM0.0CGCT-ND | 10 | 0.10 |
| 4 | LED1, LED2, LED3, LED4 | Green LED | Digi-key 475-1410-1-ND | 5 | 0.40 |
| 1 | LED_PWR | Red LED | Digi-key 475-1415-1-ND | 2 | 0.16 |
| 1 | LED_CHG | Orange LED | Digi-key 754-1130-1-ND | 2 | 0.40 |
| 5 | R2, R3, R4, R5, R6, R26 | R 0805 for LED 1.5k | Digi-key 1276-5533-1-ND | 10 | 0.18 |
| 1 | CON_BAT | JST-PH Connector | Digi-key 455-1749-1-ND | 1 | 0.56 |
| 1 | CON_USB | USB Mini-B Connector | Digi-key 151-1206-1-ND | 1 | 0.41 |
| 1 | JP_,TP_ | 40p header break-away | Digi-key S1012EC-30-ND | 1 | 0.48 |
| 1 | JP_UART | 6p header right angle | Digi-key S1112EC-06-ND | 1 | 0.23 |
| 1 | SW_PWR | Slide switch | Digi-key 563-1095-1-ND | 1 | 0.63 |
| 2 | SW_B0, SW_B1 | Tactile switch | Digi-key 450-1792-1-ND | 2 | 0.40 |
| 1 | SW_DIP | 2-pos DIP switch | Digi-key 450-2045-ND | 1 | 0.81 |
| 1 OPT | BATTERY | 3.7V LiPo Battery | SparkFun PRT-00731 | 1 | 4.95 |
| 4 OPT | STANDOFF | 10mm Nylon Standoff | Digi-key 25510K-ND | 4 | 2.36 |
| 4 OPT | STANDOFF SCREW | 7mm Nylon Screw | Digi-key 29341K-ND | 4 | 0.76 |
| DNP | C1, C2 | C 0805 xtal load caps | - | - | - |
| DNP | Q1 | Crystal | - | - | - |
| Parts Total | $15.02 |
The parts total does not include the PCB, LiPo battery, or standoffs.
Order 3 PCBs from OSH Park for $23.30 ($7.77 per board): https://oshpark.com/shared_projects/iBdyoHro
The unit price of a complete arm-bmw comes out to $22.79, with the BOM parts above and PCBs from OSH Park.
- U1, ARM Cortex-M0 MCU, LPC1114FDH28: site, datasheet, user manual
- U2, SPI Flash Memory, S25FL216K: datasheet
- U3, I2C I/O Expander, MCP23008: site, datasheet
- U4, 3.3V DC/DC Converter, MCP1252: site, datasheet
- U5, LiPo Charge Controller, MCP73831T: site, datasheet
- Revision 2 - 06/06/2014
- Schematic
- Add Dangerous Prototypes DP7043 pcb footprint and mounting holes
- Add lipo battery charger and charge status led
- Add mini-b usb connector for charging or usb power
- Add capacitors for hardware debouncing for 2 pos dip switch
- Change all 0603 size components to 0805 size
- Change C12 size to 0805 (same as C9)
- Change 0402 size for I2C IO expander address jumpers to 0603 size
- Change I2C pull-ups to 10k
- Change BL bootloader switch to a pin header jumper
- Change test points to single pin headers
- Layout
- Change to longer pads on io expander
- Change to longer pads on voltage regulator
- Change test point pin headers to 0.1" pitch apart
- Move passives away from I2C IO expander for easier soldering
- Move passives away from voltage regulator for easier soldering
- Label the UART header pins
- BOM
- Change power switch from mom-on-mom to on-on-on
- Change spi flash size from 8mbit to 16mbit (same price)
- Change to taller 2-pos DIP switch
- Schematic
- Revision 1 - 09/16/2013
- Initial release
arm-bmw-hw is CC-BY-4.0 licensed.