$10 logic analyzer
March 5, 2009
After a lot of umming and ahhing and general procrastination I decided to dig this out of the cupboard to give it a whirl again.
I replaced the 74LS00 with a max232 but it still didn`t work. A little bit of fiddling later and I found that I had forgotten to write the fuse bits which is why it didn`t work. Being an impatient sort and eager to get this thing working I accidentally wrote the wrong fuses and somehow locked myself out of the chip. DOH! I tried a few different crystals and also an external clock but just can`t bring the chip back. And to cap it all off the new shuttle PC I got doesn`t have any serial or parallel ports. I can see the purchase of an STK500 and usb to serial cable in the near future.
I`m not sure what I could have done wrong but this project is on indefinite hold until I get a new IC or a HV programmer to reset the fuses.
Lesson learnt.. triple check fuses before programming.
So lacking a scope and the money to buy one but wanting to see what was happening to the I2C bus for Ozzy, I thought I would give this cheap DIY logic analyzer a go.
Most of the parts I already had on hand, but I did buy some IC hooks from sparkfun to use. They are small and fairly cheap feeling but should do the trick fine.
It`s finished, as per the circuit diagram on the original site, but something is up with my serial port. It doesnt output a positive voltage until it finds a proper device (or something I dont understand). I found a small program called pwon to run which forces power out of the serial port, and that works OK but then when I run the program it can`t connect to the device.
I don`t know if running this pwon program makesthe PC think that the serial port is busy, or if it`s a problem somewhere else. I`ve got to try using external power first, and if that doesn`t work swap the 74LS00 for a real rs232 IC.