Make Yourself an MSP430 LunchBox for 1$

Dhananjay V. Gadre,  Nikhilesh Prasannakumar and Divanshu Dodeja
NSIT
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Microcontroller Kits for the Masses

Arduino is one of the nicest things to happen to the DIY community in the last 10 years. It brought microcontroller usage within easy reach of non-specialists (from a technical viewpoint) such as artists, tinkerers, architects and musicians. It’s low threshold of learning, simple and reliable programming environment brought it to the workbench of high school students as well. Apart from being a great, low learning-curve platform, what has helped Arduino to gain such traction worldwide, in no small measure, is the relative low cost too! Although the original Arduino boards cost tens of dollars, variants and knockoffs cost as little as $4! No wonder we find them popular with high and middle school students, everywhere.

A large majority of Arduino variants feature microcontrollers from the AVR family of Atmel (now acquired by Microchip). Some variants using the ARM Cortex M0 microcontrollers as well as higher end Intel processors are also available. Although TI’s MSP430 is a strong competitor to AVR, boasting of superior features such as a 16-bit CPU, significantly lower power consumption and versatile peripherals, it doesn’t have a presence in the Arduino ecosystem. Even with significant software support in terms of the Energia (a fork of the Arduino IDE) which extends the simplicity of Arduino programming to TI microcontrollers, MSP430 has not been able to gain the same popularity as Arduino among enthusiasts. The relatively high cost of the MSP430 LaunchPad development kit ($10 and above) with no corresponding lower cost variants (as with Arduino family) is a likely deterrent.

What the MSP430 ecosystem needs to reach the masses is an extremely low cost entry-level platform which can stand up to the $3 Arduino variants. Such a platform is what we set about trying to design.

 

Microcontroller Essentials

Typically, a microcontroller system requires 4 support elements – power supply, clock, reset and code download ability. Let’s take the example of the Arduino: It is powered by a 5V supply, either provided directly through a USB port, or from an external DC source via an onboard voltage regulator. It uses a crystal oscillator (8/16 MHz depending on the variant) for the system clock. It has a push button switch as well as a clever mechanism attached to the USB to Serial converter chip to reset the microcontroller. The user program is downloaded on to the chip from the Arduino IDE using the above mentioned USB to Serial Bridge, aided by a bootloader program which has to be manually loaded into each fresh chip.

Inexpensive MSP430 Evaluation Kit: The MSP430 LunchBox

With the MSP430, the job is a whole lot easier. Turns out, the MSP430 already has a built-in bootloader on-chip. All that is required is a mechanism to invoke the bootloader and send serial data to it – both of which can quite easily be achieved by a USB to UART Bridge. One of the cheapest USB to UART Bridge chips available in the market today is the CH340G – a full speed USB device that emulates a standard serial interface with speeds up to 2 Mbps and support for all modem handshaking signals – which costs less than half a dollar! CH340 is also one of the major reasons for the 4$ Arduinos. 

All this brings us to this – A $1 (conditions apply) MSP430 LunchBox – a low cost, maker-friendly microcontroller development platform featuring the 20-pin MSP430G2553 Value Line controller. The board supports any 14-pin or 20-pin DIP package MSP430 G series microcontroller, which a hobbyist can obtain for free through Texas Instruments’ free sample programme. The entire bill of materials of the board, excluding the controller, is under $1. The PCB has been designed to be a single sided, toner transfer friendly one, allowing enthusiasts to fabricate one for themselves at little or no cost. The photograph in below shows the early lab prototype of the MSP430 LunchBox.

Figure 1: Lab prototype of the LunchBox

 

 

Comparing Various Variants of 'Apples'

The MSP430 LunchBox has a feature set comparable to that of TI’s own MSP430 LaunchPad Development Kit and can quite easily rival Arduino. Here’s a side by side comparison of the $1 MSP430 LunchBox, TI’s MSP430 LaunchPad and an Arduino Nano. 

Feature	$1 MSP430 LunchBox	MSP430 LaunchPad	Arduino Nano
Microcontroller	MSP430G2553 & others	MSP430G2553 & others	ATMega 328
CPU Architecture	16-bit	16-bit	8-bit
Operating Voltage	3.3V	3.3V	5V
Operating Clock	10 kHz to 16 MHz	10 kHz to 16 MHz	10 kHz to 16 MHz
Operating Current	4.5 mA @ 16 MHz	4.5 mA @ 16 MHz	15 mA @ 16 MHz
Programming	Factory UART BSL	Onboard Spy-Bi-Wire	Custom Bootloader
Debugging	Not supported	Spy-Bi-Wire debugger	Not supported
Supported IDEs	CCS, Energia	CCS, Energia	Arduino, Atmel Studio
Available I/Os	14	16	20
Analog Inputs	8	8	6
PWM Outputs	6	6	6
Peripherals	1 LED, 1 Switch, UART	2 LEDs, 1 Switch, UART	1 LED, UART
Cost	$1	$10	$4

The LunchBox functionality as listed above, can be seen in a block diagram format here:

 

Figure 2: Block diagram of MSP430 LunchBox

The design of the MSP430 LunchBox was not without challenges. While the MSP430 has an in-built UART bootstrap loader (BSL), they are not brought out on the same pins as the standard UART interface of the MSP430. This meant that a provision for switching the CH340 USB to UART Bridge between the BSL UART and the MSP UART peripheral – implemented using a pair of shorting jumpers on board – had to be made. 

Another major challenge was on the software side – the UART BSL utility provided by Texas Instruments is quite outdated and contains a few bugs. One of the most critical is the issue with how the BSL Utility handles the flash memory. Graphics below shows the memory map of the MSP430 and it shows the flash memory on MSP 430 is divided into two parts – the code memory, which contains the user code and the information memory, which typically contains data such as calibration constants, Digitally Controlled Oscillator (DCO) settings etc. The calibrated DCO settings, which are required to generate accurate high speed clocks in the MSP are stored in Segment A of the Flash Information Memory (INFO-A).

 

 

Even though the BSL Software Utility provides an option to preserve the contents of the INFO-A segment, it does not seem to work properly and ends up erasing the entire information and code memory when invoked. Without the DCO constants, it is extremely difficult to implement UART communication due to errors in the system clock. As the bug fixes on an outdated software utility was quite a cumbersome task, we decided to implement a hardware solution to this issue – an external 32.768 kHz crystal oscillator which can be used as an accurate clock source for implementing UART communication. This ends up reducing the number of I/O pins available to the user by 2 pins, but also gives the advantage of having a crystal oscillator that can be easily used for real-time clock applications.

Here is the complete schematic diagram of the LunchBox. It shows the power supply for the MSP430 3.3V, derived from the 5V available on the USB connector and also available on the output headers. The clock for the microcontroller generated using an external crystal of 32.768 KHz frequency, connected to the Xin and Xout pins of the MSP430. The user interface peripherals are a simple pushbutton and an LED apart from the Reset switch. Jumpers J1 and J2 allow the user to switch the CH340 USB to UART bridge from the MSP’s UART peripheral pins to MSP’s BSL pins. These jumpers are manipulated manually. 

An image of the LunchBox PCB layout is seen below. As can be seen, the PCB can be fabricated as a single sided board with a few jumpers (represented in red color) or one can get the PCB fabricated as a double sided board through a suitable PCB manufacturer.

To enrich the learning experience, we also developed a simple and inexpensive I/O expansion board, the Mini-Voyager (a smaller version of the larger Voyager we have had for some time). As with the LunchBox, the Mini-Voyager is also a single sided PCB that can be fabricated at home or lab. The Mini-Voyager offers the user a 4-digit seven segment display, a set of charlieplexed LEDs, an RGB LED, a capacitive touch input, a potentiometer, an LDR and a thermistor as well as a navigation switch configuration. The picture here shows a Mini-Voyager in the company of a LunchBox, ready to be used.

The photograph below shows LunchBox and Mini-Voyager in action together. More than 50 experiments and small projects can be performed using this combination.

The MSP430 LunchBox and Mini-Voyager duo were recently used in a training program with 180 students of 5th semester of the Instrumentation and control division at NSIT and the experience with them was quite rewarding. See what they soldered and used!

We hope to use this platform as an inexpensive way to teach about the MSP430 family of microcontrollers in future and take this package to high school students as well. If you need further details and/or help with replicating the system at your end, we would be happy to hear from you.

 

Epilogue

How does one justify a BOM cost of 1$ for the LunchBox? The trick lies in ordering free samples from TI: the relevant MSP430 G series microcontroller and the LM1117 linear regulator. The only component you may need to purchase would be the CH340 USB to UART bridge and currently, this sells for 50 cents in volumes. The rest of the components are easily available in your, the electronics enthusiast's components box!