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Project Features
- Automatically resets a crashed, frozen Linux PC
- Simple
- Uses a cheap USB-to-serial adapter
Introduction
For several years I have been using a MythTV Linux server to record television shows. It works very well and I like it a lot. It has one major problem though: Sometimes it locks up. I suspect that this happens when it changes channels and signals are weak (e.g. due to bad weather). It seems the drivers for my DVB-S receiver cards don't like that.
This is annoying, because it remains in that state until the PC is reset manually. No recordings are made in that state. It gets particularly annoying when I am on holiday, because then the recordings of a week or more can be lost. The box needs to be reset via the reset button. Not even ctrl-alt-del will work.
The aim of this project was to automate the process with an external watchdog. The idea was that the PC had to send a "heartbeat signal", i.e. a fixed character via a USB-to-serial adapter regularly. If it doesn't do so, the watchdog resets the PC after five minutes.
Since this is a Linux box, a simple cron job can be used to create such a heartbeat signal. If the signal is there, this means that the operating system is alive, the cron daemon is working and the USB driver is good.
Introduction
Halloween is a rather new tradition in our part of the world, but my family is very enthusiastic about it. Tombstones are built, bones are scattered in our front garden and a fog machine is kept in the basement for just this one day of the year. This time I thought that I could contribute a little LED effect. My idea was to use a couple of red LEDs to create a red-glowing eye effect, like some evil little monsters lurking in the dark.
Features
- Low cost and low part count
- Four different flashing patterns, easily modifyable
- Speed control and pattern switching via pot
Introduction
This is nothing special, really. "Knight Rider lights" or "Larson Scanners" seem to be very popular microcontroller projects. I guess they are the next step right after the blinking LED (a.k.a. the "Hello World" program for microcontrollers).
I was recently asked if I could draw a schematic for such a device and in the end I decided to actually build the circuit. That way I could turn it into a blog post and make it available to a wider audience. The other point was that I could get my kids involved in building this.
This version is not exactly a beginner's project, because the charlieplexing is quite complex and turning the schematic into wiring can be a little confusing. So perhaps it is a good project to improve your soldering skills.
Project Features
- 27 LEDs in a 3x3x3 configuration
- Controller is a AVR tiny13 with 1 kByte of program memory
- Programmed in C
Introduction
The idea is not new. You can find loads and loads of LED cubes on the net. Some are small, some are insanely large and some even use RGB LEDs. And I must say I like them all. One LED-cube caught my eye because it mentions that it uses charlieplexing to control the LEDs. Its size is 5x4x4. But the instructable also says that with the 14 ports used it could have controlled 182 LEDs instead of the 80 it actually uses.
This got me thinking. How would you go about if you wanted to make a charlieplexed LED cube with efficient use of the available ports? Basically, with charlieplexing you get a multiplexed 2D matrix. How do you fit that into a 3D cube? (For the rest of this post I assume that you know what charlieplexing is.)
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