Posted inanalog2.0 tech notes

Noise Source Transistor — Conclusion

I have been working for a while to determine which transistor to use for noise source in noise generator.  I was using 2SC3311 which was obsoleted recently. I did several tests, mainly by listening, and chose BC547.  The reasons are: It has good taste as a noise source.  Easy to find sweet spots when using it with a filter and VCA. Noise level was close to 2SC3311, so my previous design works with simple replacement. Availability is good. Unlikely to get obsoleted soon. I started the test with listening "raw" noise without any modification and filtering.  However, it didn't work well.  Many of the candidates sounds similarly.  However, I found…
Posted intech notes

Reading Keypress with Python

This works for windows. http://stackoverflow.com/questions/12175964/python-method-for-reading-keypress However, you cannot use this feature from cygwin.  You need to invoke python script directly from Windows.  Double-clicking the python script works, but you need to catch exceptions in the case (otherwise, you don't know what happened when an exception was raised). Here is the sample program to read arrow keys. #!c:\Python32\python from msvcrt import getch import sys print("press ESC to exit") while True:     try:         key = ord(getch())         if key == 27: #ESC             break         elif key == 224: # special keys (arros, f keys, ins, del, etc.)             key = ord(getch())             if key == 75:                 print("left")             elif…
Posted intech notes

How to Play Sound with Python

This link helped http://stackoverflow.com/questions/307305/play-a-sound-with-python I'm working on Windows, so winsound worked.  It was as simple as #!/usr/bin/env python import winsound winsound.PlaySound("ex1.wav", winsound.SND_FILENAME)
Posted inanalog3

SPI / RX collision test

Done collision test between SPI and RX in the comm driver.  The driver would receive RX signal any time, even while the host processor is accessing the driver via SPI to send or retrieve data.  Currently, the serial RX is handled in external input interrupt handler, so any bug in RX handler may break registers (i.e., states) for SPI communication.  I actually saw those bugs several times.  The bugs are fixed now and load test has passed.  In the test, the load generator keeps sending data via serial channel.  I've changed the timing of data retrieval in the host of the receiver so that SPI / RX collisions frequently happen. …
Posted intech notes

Dragon’s Tail

dragons_tailAs mentioned in my previous post, AVI Dragon’s SPI pins in debugWire interface have to be disconnected during debug run in order to properly run an application that uses SPI / USI.  I also noticed that the Dragon dominates RESET pin, too.  In my project, I’m resetting target chip from Arduino.  The Dragon is killing this functionality as well.  This makes me quite uncomfortable with my development work, so I’ve enhanced the switch I made on bread board previously, and made a helper device.  It’s nicely working.  I named it “Dragon’s Tail”.

Posted intech notes

About AVR Dragon

Memo about AVR Dragon basics. What can be done with AVR Dragon: Run the program in the target device in debug mode. Stop at break points. Do step execution. Examine processor internals, such as memory and registers (capable only in stop mode). Program the target device. Tips The doc provided by Atmel worked best for me for "getting started" document. http://www.atmel.no/webdoc/avrdragon/index.html There are several ways to connect Dragon to the target device for debugging.  However, only debugWire is available for ATTiny* chips. debugWire commonly utilizes 6-pin header for ISP (In Circuit Programming). Dragon can be used both as OCD (On Chip Debugging) and ISP devices.  However, these modes cannot be…
Posted intech notes

Candidates for Noise Source Transistor

Typical analog noise generators make signal by amplifying AC component coming out from zener current of transistors reversely biased between emitter and base (here’s an example circuit).

Any bipolar transistor would work as such a noise source, but noise quality in listening is different from part numbers.  2SC828A is well known as good noise source, but it’s been obsolete for long.  So for Analog2.0, I have been recommending 2SC3311 instead.  But this part becomes obsolete as well.  Now I have to find another one.