|A partly assembled PianoForte pcb before adding the wireless modules.|
In a couple of previous posts I commented how many modern electronic products are built from a series of building blocks - generally consisting of a microcontroller, a power supply and a communications interface - these days, usually wireless.
If you put these three subsystems together onto a pcb you will then have the basis for creating some interesting devices.
Unfortunately, most dev boards don't tend to give you all these elements, sometimes you just get the microcontroller and power supply, but little or no thought has been given to the communications interface - which is of course how you get the data in and out.
So in early March, I tried to address these shortfalls, and come up with a dev board that delivers more in all three areas.
The STM32F373 was the obvious choice. It's a 32bit ARM M4 Cortex part running at 72MHz. One of the attractive features is that it has three separate 16 bit ADCs which are ideal for analogue sensing or energy monitoring applications.
The micro is in a 64 pin quad flatpack, making it relatively easy to use, and providing about 48 lines of GPIO and peripherals.
Some of the features:
3 USARTS - up to 3Mbaud datarate
3 SPI interfaces
2 I2C Intefaces
13 Timers for PWM generation and quadrature decoding
Real Time Clock
Floating Point Unit
72MHz maximum clock frequency
48 lines of general purpose I/O
12 12bit ADC multiplexed channels
3 16 bit Sigma-Delta ADCs for high resolution analogue signal measurement
2 DAC channels
Full speed USB
micro SD card holder
Battery powered either from LiPo or alkaline cells
Three different wireless interfaces to pick and choose from, WiFi, BLE and 433MHz FSK
The GPIO is 5V tolerant - so there is little risk of damaging anything in a mixed voltage environment.
The PianoForte board uses a low cost boost converter at the heart of its power supply circuit. It allows very flexible powering of the circuit, Not only can it accept a 5V supply - from USB or FTDI cable, but it can be battery powered from a 3.7V LiPo cell or even a couple of AAA alkaline cells. The boost converter will actually run off a single 1.5V alkaline cell, and run all the way down to 0.6V. This gives the freedom run any of the wireless module options, from battery power.
There are a variety of wireless communication options available today - and these generally take the form of small modules. PianoForte is designed to accept three of the currently most popular wireless options - depending on application.
WiFi - we have a connector onboard to accept the popular ESP8266 WiFi module. This can act both as an access point (AP) or station (STA). It communicates with the microcontroller using an AT-command set over a USART serial connection.
Bluetooth 4.0. Bluetooth Low Energy (BLE)
This is used on all smartphones, both iPhone and Android. It provides a direct way for a smartphone to communicate with the PianoForte, with the possibility of uploading new firmware over the air. Many BLE modules are available cheaply from China - and PianoForte uses the popular HM-11 module.
Low Power Wireless - this is for longer distance communication - up to 250m outdoors, 30m indoors.
PianoForte uses the popular RFM69CW device. Using either 433MHz or 868MHz ISM band, this has the capability of better propagation through buildings at lower power than any of the 2.4GHz devices. It is included to make the PianoForte compatible with popular open source energy monitoring devices.
PianoForte has two intended modes of operation.
1. As an analogue and digital I/O co-processor for the Raspberry Pi.
Let PianoForte handle all the real world acquisition and control stuff whist the Pi runs the high level apps. The Pi communicates with the PianoForte via it's serial UART, using simple serial commands. Set PianoForte running with, for example a 16 bit, 3 channel analogue data acquisition task, and poll the data from it when convenient.
2. As a battery powered, stand alone wireless node.
Pianoforte is capable in its own right of running some fairly sophisticated measurement and control applications, and being battery powered and wireless is not tied to a conventional USB lead or 5V power supply. It can run on dc voltages down to 0.6V, as a result of it's on board high efficiency boost converter.
As this is the start of a series of posts, more details will follow in future posts.