Originally I've designed a wireless node for monitoring temperatre,humidity and pressure,
power and sized as CR2032, and a gateway using nRF24L01, then upload to Xively per minute.
But after a while, I figure out that most of the time, I'm too lazy to check out current T&H by clicking Xively website, I want to know the data straight from the device.
So I've try to build a sensor node with a display that shows the current T&H.
Most project I've seen is using tiny OLED display, which is definitely wayyyy too much power,
other might use EPD, but the cost of EPD module often quite high, also the refresh rate isn't that fast for update per one second device.
But most product that has slimier function uses traditional LCD display, which is reflective like EPD so it don't consume much power, but also cheap.
I can see why most people didn't build one using this, because it is highly customize and high volume display, factory won't sell one unit for customize display. But there is some catch, since it is high volume product, factory will have some spare part on sell, after searching couple factory, I found a display that fit my need.
And the next step is trying to use this raw LCD display, eevblog recently produce a wonderful video about it :EEVBLOG
basically I've two choice, integrated LCD controller MCU or external LCD controller, If I gonna use GPIO to modulate LCD signal, I have no confidence that I can control the power consumption. Most LCD controller I've seen consumption quite a lot power, between couple mA to hundreds of uA, which is unacceptable, since the previous no-display node average current is 17uA only, couple hundreds uA will shorten the battery life a lot.
And I turn to integrated LCD controller MCU, there is a lot MCU that have LCD controller build-in, but Ti stands out in my view. Ti MSP430FR4133 have a excellence development board, which have a power meter on board! also the power consumption really stands out.
So I've build around MSP430FR4133, adding SHT21 as T&H sensor, BMP180 as pressure sensor, also since it will be place on somewhere I can see it, I also put a light sensor OPT3001.
And since the display is kinda thin, I decided to build a card size and make it as thin as possible. I've cut a hole on PCB to place CR2032, and using two CR2032 holder to clamp the battery.
Since MSP430FR4133 have energia support, I can easily move the original code from Arduino to MSP430, the only thing I have to do is setup LCD controller.