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Just a quick update, I've uploaded a driver for HD44780 LCD modules (common on eBay and elsewhere) for the STM32F4 line of microcontrollers.
LCD commands are added to a queue and executed on a timer interrupt, freeing up the processor in-between. Communication to the LCD is in 4 bit mode and the busy flag is polled so 7 GPIOs are used. I've implemented commands to control the display, print characters and set the CGRAM, yet to come is scrolling support.
I've tested it using an STM32F4 Discovery and a few 1, 2 and 4 line displays.
It's about time for some hardware, so here is the DDS Sine Sweeper, a sine source which outputs a sine wave from 1Hz-40MHz. It's cheap and easy to build and all the plans and software are freely available.
From time to time I found myself needing a separate signal generator. In the back of my head I was thinking of just something simple but I also wanted to play about with DDS (Direct Digital Synthesis), a method of creating a waveform digitally. This allows precise control over the frequency from a microcontroller, allowing you to set the frequency and even jump to another very quickly. Although it does have drawbacks the simplicity was a winner for me.
Last year while developing Linux drivers for digital TV, Antti Palosaar noticed a hidden debug mode, which allowed you to sample relatively large chunks of radio spectrum. Thanks to this the RTL-SDR library was born and Software Defined Radio was available on the cheap, after all these dongles tend to cost less than £20.
A little while ago I uploaded my contribution to this, a GUI called RTLSDR Scanner, to GitHub.
GPX Logger is now available on Google Play for Android, it's a simple app to log GPS location data to a memory card. I've designed it as a data logger but it will also show your location on a map and display information about satellite signal strength.
If you use this app for anything out of the ordinary I would be interested to hear about it.
