Here is a PIC16F628 microcontroller clocked at 20MHz generating an analog RGB video signal with composite sync.
This project was inspired by Rickard Gunee’s PIC Video Howto which gave me a big headstart in writing the code. Thanks Rickard! I have been wanting to work on this project since reading the tutorial several years ago, and finally got a chance to start it last week.
There are few fundamental differences in my approach compared to Rickard’s and others I have seen in the past. His tutorial was written a few years ago before 20MHz PICs were commonly available (it uses an overclocked PIC16F84.) He also focuses on generating composite video to drive a standard television (using the AV inputs). I am generating RGB video which will interface with the Sharp LCD I had sitting on the shelf. RGB is a little different in that it uses a separate sync signal (composite horizontal and vertical sync on one inverted TTL line) and each color is brought out as a separate 0.7Vpp signal. These two differences make the RGB interface considerably easier (in my opinon) to work with, especially since the approach to composite video Rickard uses is limited to black and white.
So far the biggest challenges have been with getting the video timing right. I am writing the whole program in PIC assembly and every clock cycle counts.
More on this project soon, but until then, there are a few more photos on flickr.
Andrew Milmoe of Make:SF recommended Charles Petzold’s book Code to me several months ago to help me refresh my knowledge of computer architecture as I dive into embedded systems development. I finally finished reading it this week and thoroughly enjoyed it. Code is both a history of the computer as well as a tutorial illustrating how to build one from the ground up using switches and gates. Some chapters are slow reading due to the complicated subject matter, but the way he brings everything together at the end makes it a great read. Although the book is in some ways dated (written in 1999, it talks about 128MB of memory being novel and Apple having problems in the desktop market) I found that it is still relevant. This is particularly true for microcontrollers and embedded systems which have more in common with the 8 bit computer that is the subject of the book than a Pentium 4 in today’s desktop PC’s.
Code: The Hidden Language of Computer Hardware and Software
Charles Petzold’s latest book, Code: The Hidden Language of Computer Hardware and Software, crosses over into general-interest nonfiction from his usual programming genre. It’s a carefully written, carefully researched gem that will appeal to anyone who wants to understand computer technology at its essence. Readers learn about number systems (decimal, octal, binary, and all that) through Petzold’s patient (and frequently entertaining) prose and then discover the logical systems that are used to process them. There’s loads of historical information too. From Louis Braille’s development of his eponymous raised-dot code to Intel Corporation’s release of its early microprocessors, Petzold presents stories of people trying to communicate with (and by means of) mechanical and electrical devices. It’s a fascinating progression of technologies, and Petzold presents a clear statement of how they fit together.
The real value of Code is in its explanation of technologies that have been obscured for years behind fancy user interfaces and programming environments, which, in the name of rapid application development, insulate the programmer from the machine. In a section on machine language, Petzold dissects the instruction sets of the genre-defining Intel 8080 and Motorola 6800 processors. He walks the reader through the process of performing various operations with each chip, explaining which opcodes poke which values into which registers along the way. Petzold knows that the hidden language of computers exhibits real beauty. In Code, he helps readers appreciate it. –David Wall
Meet Charlie Chip, the Fry’s Electronics mascot. This cute little guy was found on, get ready for this, a Fry’s Electronics pocket protector (pictured below) that I found for sale at the register while shopping at the Sunnyvale location. How awesome is that?
Thank you, Fry’s.
I have always struggled to take decent macro photos of small objects to document my hobbies. I finally got fed up with poor lighting and blurry shots and decided to build my own light tent to solve the problem. There are lots and lots of examples on the web showing how to build a DIY light tent. I wanted something cheap, small, and portable, so I merged ideas from a couple existing designs and used some scrap materials I had in the garage. In the end I managed to make a light tent for about $35.
The major components are:
- Light. I bought two desk lamps at Target for $9.99 ea. I bought 100W CFL lights from Home Depot to avoid the unwanted heat and energy usage of conventional light bulbs, $9 for two. I bought the color balanced type (3500K) which cost a little more but help accurate color reproduction in the photos.
- Frame. I used an old shoe rack, but almost anything can be made to work.
- Light diffuser. I tried bedsheets, which attenuated too much of the light. Instead I used tracing paper (vellum) that I had left over from another project.
- Background. I used poster board from Target. I bought one sheet each of 6 colors, for about $5.
- Tripod – I didn’t have one so I bought the cheapest one Best Buy had, around $30. Since I needed this for general use anyway, it’s not included in the total.
The results are really spectacular. Now I can take macro shots of small objects without the glare and lighting problems I have experienced in the past. For an example check out the photo below or see the complete set on flickr.