Wireless modules

Since playing around with arduino and HopeRF modules showed promising results I just ordered a bunch of RFM69HC modules to build more nodes and run an actual mesh network..

Today they finally arrived 🙂

20150429_003After some amount of soldering I should be able to test the mesh network functionality properly.

Wireless modules

Building a wireless network node

Since half a year i have laying around some arduino mini pros and some rfm23bp radio modules and this week I have the opportunity to do some hacking and i decided to see if I could come up with some mesh network nodes build from these components. A picture of that rfm23bp module:


Today I started checking if the hardware actually works and set everything up – which to my surprise took way less time than anticipated. So here is the first breadboard setup:

20150413_015In the middle you can see the Arduino Pro Mini running with 3,3V / 8Mhz, the big thing on the right is the power supply and the rf module is connected on the left. On top of the whole setup you can see the serial/usb adaptor to program the controller from a laptop.

After connecting everything i tried running a sample program for the RadioHead library I’m going to use. After programming and monitoring the serial output of the setup I was able to see the debug messages telling me that the rf module is transmitting. So far – so good, but to actually see if it is working I need to build another node that then could receive the messages from the first one to confirm it actually is working – which i could not do today as I never expected to have it up and running in such a short time.

To not be bored and actually see if something comes out of that rf module i asked a colleague to borrow me his rtlsdr DVB-T dongle and installed gnuradio-sdr along with the gr-osmosdr package which then gave me a nice specturm analyzer like tool that would show any radio activity in the defined wavelength. So, after setting that up and starting the tool I hit the reset button on the network node module and instantly had a visible peak showing that it actually transmitted something:

spectrum_analyze_ism_bandTonight I’ll solder some connectors to the second rf module and then will start hacking on some application making use of the nodes. Eventually I’ll create a third node and then could start testing the mesh functionality.


I finished basic communication between two Arduinos using both a RFM23BP module. The result is some simple application that let’s you chat between Arduinos using their serial port as interface. Code and basic documentation are available at  https://github.com/greygoo/rfchat and https://github.com/greygoo/rfmesh.

Here the connection layout between the Arduino Pro and the RFM23BP module:


Building a wireless network node

Building my own head mounted displays

Finally I found some time to snap pictures of my latest hack, a hmd build from parts bought cheap on amazon. It is currently a protoype I want to gather experience with and will eventually become a complete eyetap device – steampunk style 🙂

As parts I use mostly brass and acrylic plastic for the frame and a display salvaged from cheap chinese videoglasses I got for around 80 Euro from amazon. The electronics of the videoglasses are small enough to fit inside a small box on the frame and the lenses from the original videoglasses are reused as well. The only additional part I obtained is a beamsplitter plate for the transparent display. In the currently pictured version this beamsplitter is not yet attached but I use a cheaper plastic version I took out of a laser board game. The plastic beam splitter is not good enough for actual use of the display but it is sufficient for adjusting distance of the lense and testing the overall setup.

The microdisplay inside the videoglasses are Kopin 320C display units, it comes with two – one for each eye.

When I think I reached a satisfying state I also add some more detailed instructions on how to built it.

Some pictures to get a impression:


The unit from front.


from the side



The unit connected to a n900 mobile phone. The small silver box is from the chinese videoglasses and contains some rechargable battery for powering the display.


The attempt of taking a picture of the actual displayed screen.20150113_014

The unit how it is used in combination with my glasses. At the moment I attach them using some velcro.20150113_019

Again with glasses.20150113_020

And once more from the front.20150113_023

Building my own head mounted displays