Published January 20, 2014 © CC BY-SA

Magic Mote Wireless Sensor Node

Compact PCB for MSP430G2553 and NRF24L01+.

IntermediateFull instructions provided2 hours2,576

Story

About

This compact PCB interfaces a low power MSP430G2553 microcontroller with a Nordic NRF24L01+ 2.4 GHz radio frequency transceiver module. It's well adapted to serve as a wireless sensor node, but has enough I/O options to be put to use wherever a small microcontroller is required.

I set out to design a wireless sensor PCB that could be inexpensively prototyped in quantities of 10. NRF24L01+ modules are exceedingly cheap (~$10 for 10), use very little power, and have sufficient range for most indoor projects. Low power MSP430 microcontrollers make an ideal partner for battery powered applications. I settled on the MSP430G2553, but the MSP430G2452 can be substituted whenever hardware UART is not required.

The layout of this board is derived from the Spirillis boosterpack for easy compatibility with the Spirillis msprf24 library. I/O options include a 3.5 mm jack socket or 3-pin header, a 4-pin header with an analogue input, and a 6-pin programming/serial header. The dimensions of the board are suitable for panelizing (2 per 5x5 cm prototype).

Members of the 43oh forum came forward with design tips. J.P. Norair suggested LED indicators for the TX and RX processes controlled by firmware. I originally designed the board to be powered by a Lithium coin cell, but Spirillis showed the way forward so I added pin holes for a 2xAA battery holder. Power can also be supplied to any of the pin headers. I also figured out how to measure the battery voltage without using a voltage divider and broke out the pin I had earmarked for that as an analogue input with RC low pass filter. Finally, I put 220 Ω resistors on the power and data wires to the jack socket to ameliorate momentary shorts when plugging in.

New version

An updated design is now available with a reduced part count, ribbon connector compatible serial/programming header, and improved switch position. See the Github repository for a preview.