MyRaspberryAndMe

Tinkering with Raspberry (and other things)


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GPRS/GSM via Serial (again)

I recently stumbled over a cheap GPRS/GSM shield made for the Arduino platform, of course on ebay, of course from China. As it was priced at a very reasonable 20 EUR (25 USD), I thought I’d go with the risk and order from China. Several weeks later it finally arrived and, I couldn’t believe that at first, worked out of the box.

This is how it looks. If you get interested in one of these gadgets, just search for “GSM Arduino” on ebay, that should do the trick.

P1010427

It’s a SIM900 based design and has a real time clock (plus buffer battery) on the back. A full description of all the possible AT-commands can be found here. It is basically the same shield that can be bought from Seedstudio, but much cheaper. A description with some sample sourcecode (that is working!) can be found at the Geeetech-Wiki pages. Continue reading


Pi-Hicle final – motor-control and autonomous driving

So this is going to be the final part of the “Pi-Hicle” series (here are Part 1, Part 2, Part 3, Part 4). There is some good news and some bad news… But first a video of the vehicle moving:

The good news is that the BigTrak is in fact runnning on its own, avoiding obstacles with its three IR sensors. The bad news is that I have discarded the Raspberry Pi for this project. The vehicle is controlled by an Arduino mini now and there won’t be a Raspberry Pi in it in the near future. Now why this?

  1. I fell in love with the BigTrak and I simply can’t make any more holes in it, let alone ripping the keyboard off
  2. My plan to decrease the speed gradually as obstacles are detected does not work. There is not enough torque to move the wheels when the speed goes below 60% (and that is still too fast indoors, at least at my home)
  3. With the vehicle moving that fast a video camera is obsolete, one wouldn’t get a clear picture of anything (and I don’t have pets to annoy…)

So I am going to share the last steps in making this project. This involves mounting the sensors and putting everything together and the simple, yet working, code for making the BigTrak drive. Continue reading


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Pi-Hicle part 4 – Sensor Phalanx

I finally had the time to do some more work on my Raspberry Pi controlled Big Trak. So this is all about sensing the environment, well, avoiding obstacles, that is.

My idea is to have the vehicle measure the distance to any obstacles in front and to both sides. If it can’t move any further in forward direction, it will be turned in the direction (left or right) where there is the biggest distance to any obstacles. Very simple but that should be very effective. And it gives the impression of “real autonomy”, because the vehicle will turn in different directions to avoid a collision.

To get this done I ordered three Sharp GP2Y0A02YK0F distance sensors. They are well documented and used by many people out there, so I thought they should do for me, too. The sensors translate the distance into a voltage, so there is an analog value to be mapped to the distance. There is a data sheet with a nice graph showing the expected output voltage oder distance. According to the specifications the sensor has a range of 20 to 150 cm. That quickly proved to be a little too optimistic… Continue reading


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AM03127 LED marquee + Arduino + Bluetooth = RaspberryPi remote control

After some days of soldering, testing and coding I am now able to control my LED marquee remotely via bluetooth from my Raspberry Pi. Using an Arduino Pro Mini (5V model) and the HC-05 module mentioned in my last blog post, I was able to mount all components inside the sign’s housing.

Some features of the bluetooth enabled display:

  • send messages to display (up to two messages with a length of 360 characters each are possible)
  • select display mode (message – time – off)
  • set time from and to Real Time Clock
  • set display intervals
  • increase/decrease speed of marquee

The sourcecode consists of the Arduino sketch to control the sign and a Python class that encapsulates the communication and message handling to the LED sign. As always, the sources will be available in my GitHub repository (direct link to sources). In this post I will describe the hardware and software developed to accomplish this. Some soldering skills may be required… Continue reading