The World's Lowest Cost Arm Cortex-M0+ Development Board

The STM32G031 Core Module was designed to be one of the lowest cost Cortex-M0+ development boards on the market.

The STM32G031 is part of the ST Value series of microcontrollers and is the simplest microcontroller to work with as it comes with a very easy to solder SO8N footprint. It also is one of the cheapest, if not the cheapest Arm Cortex-M0+ microcontroller.

Features

• STM32G031J6M6 8 pin microcontroller. 32-bits @ 64Mhz. 32k flash, 8k SRAM. I2C, UART, SPI, ADC, DMA, timers, RTC, and more.
• Ultra small size.5 x 1 inch, incorporate into any project.
• Fits into any breadboard, standard 2 x 4 pin 100 mil headers.
• Easy to power via USB extension cable, or directly in a USB plug.
• Onboard 3.3V regulator, power from 5V, li-ion battery, portable USB charger.
• PureModules compatible connector, used for programming and expansion options.

Development

We started with the STMicroelectronics development board for the same part, a $10 board. A great price for what you get, including programming and more. Although at $10 its still too expensive to put it anywhere. We wanted to make something for under $1, yet still remain useful. Since we wanted to use it in many places, we wanted a small form factor, but not so small you can't hand solder or breadboard with it. We settled on a 0.5 x 1 inch form factor. Also the smaller the PCB the cheaper it is to make.

With a budget of under $1 (in prototype quantity's, not mass production) we had to make some choices on what are must have, vs nice to have. After brainstorming we came to two main parts only, a regulator and the microcontroller.

We wanted to maximize the PCB real estate so we ended up settling on 3 PCB features. 1: USB PCB connector for 5V power. 2: 2x 100 mil headers to access all the CPU IO, and 3: a PUREmodules edge connector for IO and programming.

The USB connector we wired only the GND and 5V pads to minimize interfering with anything on the USB side. This should allow for 100mA at 5V in most situations.

The 2x 100 mil headers were spaced to fit exactly in the center of a breadboard allowing access to all the pins for any breadboard needs. Also an interesting use case for using this board for only its 3.3V regulator, allowing a breadboard to have 3.3V power with only a USB extension cable.

The PUREmodules edge connector was selected since we use this for almost everything we do, and it cost $0 to add. This connector actually works out nicely as it have 10 total pads to work with, so we have access to 5V, 3.3V, all the GPIO and GND. We kept the pinout compatible with the PUREmodules i2c based connector and SWD programming adapters. So now we have a very low cost and simple way to program it, as well as connect to a wide range of sensors, as well as easily expand the functionality of this board to almost anything else.

Pricing

So in single units the parts costs about 1.40 for the micro, and about 40 cents for the regulator. The caps are pennies each. PCBs from OSH park are 3 for $2.40. So under $5 all in for ordering single quantities. Not that bad, but our goal is under $1. What volume do we need for $1. At about 1000 boards, there is a nice price point were the micro costs around 50 cents and 15 cents for the regulator, the PCB and assembly eats up the rest of $1. So there you go, at 1000 volume it's a $1 development board.

In order to get the price for assembled boards closer to the $1 goal, we are looking to build a higher volume run. Check out the project on GroupGets if you are interested.

Building

Now if you want to build your own, The files are pre-uploaded to OSH Park for easy ordering. Just buy the micro and regulator, and a few 0402 1uF caps. Just put the parts where they fit, no need for an assembly drawing or anything.