Use your spare Raspberry Pi to measure soil moisture

One thing about successful plant growing it to keep proper moisture level of soil. This is even more important when plant is pot where it has no way reach water source. To avoid drying out or over-watering – a simple electronics can help. Of course this can be achieved with simple 555 timer based buzzer sensor. But why bother if there is a spare Raspberry Pi. Jeremy Blythe shared his build where his raspberry Pi successfully monitors his plants.


He used soil moisture sensor brick which gives analog signal. Raspberry Pi cannot read analog, so there is an external ADC (MCP3008) used which interfaces via SPI. Jeremy put external circuit on a sticky breadboard which stuck nicely to plexiglass. On top of RasPi he placed Adafruit RGB negative 16×2 LCD with keypad. As all good things in Raspberry Pi this one is also controlled with help of Python script. With his project he also wanted to show various ways of displaying sensor information. So he covered LCD, console, and even remote with ControlMyPi service.


Multipurpose Raspberry Pi driven VFD display

There are so many things you would like to check once you enter your room. This can be weather, time, or even Bitcoin price. Lostengineer was working on something similar. He attachedc VFD display to Raspberry Pi which connects to internet with USB wireless adapter. He wanted that display would activate itself once he enters the room, so he connected PIR motion sensor. If nobody is home, display enters sleep mode.


The display he had accepts serial data, what makes it even easier to interface. Operation is controlled by Python script which pulls required and sends to display. Project is still in progress, but it is promised to be open source.


Learning about accelerometers and gyroscopes

Accelerometers and gyroscopes are commonly used sensors where some sort of balance is needed. Combination of both in one board is called IMU (Inertial Measurement Unit). You will find one on flight controllers, balance modules and in many other areas. If you are going to build something from scratch then you should know some background information on how to interpret readings and how to use them in control. Gadget Gangster have shared pretty good instructable where he explains how to interface IMU device to microcontroller and how to use this data to get desired results.


As example he uses Acc_Gyro board with LIS331AL triple axis accelerometer and LPR550AL dual axis gyroscope. He goes through some math while explaining how to determine orientation of IMU using either only accelerometer data or combination with gyroscope readings. Plus gyroscope gives some clue about rotation around one or another axis. SO if you are thinking of building inertial system, you should do your homework and understand hos things work.


Raspberry Pi Compute module

Raspberry Pi has been very popular small computer board. It’s initial layout is quite flexible that allows it to use as standalone computer or embedded device with controllable I/Os. Probably standard Raspberry Pi is more oriented to be small single board computer, where you can connect peripherals like keyboard, mouse, display, Ethernet. The I/O part seemed to be left on a side. Eventually extension boards started to appear to fill the need of functionality like ADC, DAC, more digital I/Os. Eventually you end up stacking stuff on top like Arduino. But we like elegant things don’t we? So Raspberry Pi team has been working on different Raspberry Pi concept – Compute module. This is smaller module which have same BCM2835 processor, same RAM. Instead of SD flash there is a 4Gbyte flash memory. Practically this is it. Module is traced on DDR2 SODIMM sized PCB which actually fits this connector.

It has no external connectors like Ethernet, USB or audio but there are way more GPIOs. Module can be snapped in to any custom made I/O board that can have more controllable I/Os or interfaces like found on standard Raspberry Pi. So definitely module will have to go along with custom I/O board. It will give even more freedom to community. They’ve also taken care of example I/O board to get started.