Monthly Archives: October 2016

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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How to configure RealVNC on a Pi with 3.5” LCD

With the release of a new Raspbian version (2016-09-23) RealVNC have ported their VNC server and viewer applications to Pi, and they are now integrated with the system and PIXEL desktop. With raspi-config, one can enable start of RealVNC at boot time. This is particularly useful, if you’re running your Pi headless a (without monitor), but still want to access the LXDE desktop. RealVNC usually works out of the box, but …

35lcdtft… it doesn’t, when you connect a non-standard display. I recently upgraded one of my Raspberry Pi’s with a 3.5” LCD touch screen, which connects through the GPIO header and has a resolution of 320×480 pixels. Unfortunately, with the display attached, VNCviewer’s desktop size also shrinks to 340×480 pixels which is very inconvenient to read when it is displayed on a 1920×1080 HDMI monitor. Scaling of the window makes its contents very blurry.

However, with some special settings, one can circumvent this problem:

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How to enable USB OTG mode on a Pi Zero

Thanks to the Maker Faire Berlin on 1st and 2nd of October, I was able to purchase a Pi Zero board, which currently is out of stock  at most distributors. Indeed, it is a nice little board for experimenting with the GPIO header.


In contrast to other Pi versions, it features a micro USB port, which is capable to connect in USB OTG mode (On-The-Go) to a host-PC. Thus, there is no need for a power supply and WiFi dongle, since communication with the host-PC is established through USB networking. This is especially useful if you want to use the Pi Zero in headless mode, for example in a classroom environment already equipped with desktop PCs and/or notebooks.

There are already  other tutorials which describe how to enable USB OTG mode on a Pi Zero. However, I’ve been struggling with configuration of a fixed IP and internet/ network connection through USB on the Pi Zero. So here are some helpful instructions on how to achieve this:

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