Category Archives: Shields

Voice-control RC sockets with Google’s AIY Project Kit

Issue 57 of the official MagPi magazine contains a Do-It-Yourself Artificial Intelligence kit made by Google. The build instructions inside issue 57 are straightforward, so that you can talk to an intelligent device within minutes.

However, the installation walk-through in the MagPi57 did not work without problems, therefore I recommend to follow the instructions on Google’s AIY Project Page.

Speech recognition is an amazing feature for the Pi and if you ever wanted to know what “the answer to life, the universe and everything ” is, you should go for it!

The kit turned out to be very popular and it is currently difficult to get hold on it. It is sold out at many places :-(.

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A Raspberry Pi Moisture Sensor to Monitor Your Plants

For quite a while I am monitoring temperature and humidity in each single room of my apartment. I was inspired by several Raspberry projects, featuring a “Garden Pi“, to monitor my house plants as well, using a probe to measure moisture level of soil.

On the net, one can find many low-cost sensors which are compatible with Arduino or Raspberry Pi. They usually consist of simple PCBs with two electrodes which are pushed into the earth. Moisture is determined by measuring conductivity of the soil which isn’t very reliable for long-term measurements. Cheap sensors are often affected by heavy corrosion, so that  Copper ions will leach out and might poison your plants.

moisture-sensorIn contrast, sensors measuring soil moisture levels by capacitive sensing rather than resistive sensing are much more suitable, because they are made of corrosion resistant material which gives them an excellent service life.

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Home-Automation using 433Mhz RC-Sockets

The small 35 liters fish tank in my living room is illuminated with a 6400 K energy-saving bulb. The light is controlled by a power outlet with a build-in digital timer. Unfortunately, the timer is somewhat complicated to program. Since it is not backed with a battery, one is losing all settings each time it is being disconnected. Therefore I wanted to control the light in a more convenient manner.


Recently, I stumbled upon a kit of cheap (less than 10 €) 433 MHz RC power sockets. I soon had in mind to let my RasPi server take care about the fish tank illumination by connecting one of these sockets to the aquarium.G550694Each socket has a row of ten dip switches on its backside, in order to set a system code and to assign it to one out of four buttons on the remote control (A – D). The socket communicates at a frequency of 433 MHz, using ASK modulation. Although it would be possible to solder some wires to the remote buttons, directly connecting them with RasPi’s GPIO header, it is much more safe and convenient (and consuming less GPIO pins) to control the sockets using a 433 MHz transmitter.

433 MHz transmitter

PDR_0195It is important to chose a transmitter capable to communicate by ASK-, rather than FSK modulation (such as the HOPERF RFM12B). It requires only one GPIO pin to talk to Raspberry and can be safely wired to +5 V, since we’re not reading anything from the GPIO pin.

Download and install rcswitch-pi

For transmitting signals to the rc-switches, I downloaded the following code to my Pi:

$ git clone

in send.cpp I changed the line reading int PIN = 0; to the GPIO pin connected to the transmitter. GPIO numbering is done according to the WiringPi library:

gpio1Then, I typed “make”, chmod 755 and moved the “send” program into my binary PATH (e.g. /usr/local/bin).