While repairing a Tek TDS 520 I used a somewhat unconventional debug interface. I didn’t have the good uart at the time, so this interface consisted of a cPLD and a FT245RL. The scope does write information to the debug port, even when there’s no uart-chip connected. So fetching the information written to the address of the TX-buffer is possible.
The scope is now working fine again, but I want a real bidirectional debug interface. So I did a little reverse engineering…
The Tektronix TDS 520 is a digitizing oscilloscope from the early 90s. It offers 500 MHz analog bandwidth, 500 MS/s sampling rate, 2 full-featured channels and 2 auxiliary channels with a limited vertical sensivity. Although being at age nowadays, this oscilloscope has perfect properties for a prominent place in the shack at home.
Every (home)lab needs a good variable powersupply and so does mine. I wanted to design something with a microcontroller to set the voltage and current limit. Using a microcontroller also brings the possibility to use an LCD and fancy rotary encoders for control. The control loops themselves are pure analog.
I made this powersupply mostly from components I already had.
When I wanted to gently interface an incremental rotary encoder with an 8-bit Atmel AVR microcontroller, I couldn’t find a nice example. That’s why I wrote this little text. Many other howtos, manuals and descriptions are fuzzy, incomplete or too complicated to do the (easy) job.
This article describes three things: the hardware (just the minimal hardware) and two pieces of code. The first is just a simple interrupt based program and the other uses timers to make bigger steps when you turn faster.
The idea to build a tube amp arose at a party, where all good ideas start. It stayed just an idea for about two years, due to other important things. This winter (2008/2009) the amp got my attention again. So I bought some books, googled for examples, searched explanations and gathered other info. Arnova and I then developed the first drafts for the amp. Later we visited some electronics fairs to get tubes and sockets. I have to be honest, eventually I bought new transformers and tubes. At the fairs I couldn’t find any proper power or output transformers, suitable chokes and half of my EL84 were bad. Reconsider buying old(er) parts.