10 December 2009

PC Function Generator (Part 2)

I finished the PC Function Generator PCB this afternoon. You can see the finished module in the picture on the left. I was a bit scared it had a serious problem, because when I attached the power supply nothing happened. Not even the power led came on. I quickly checked if any parts were getting hot, but nothing got even warm. So I started looking at the PCB again and found no problems there either. Then I started to measure on the PCB and didn't see power everywhere. I was very confused about this. Then I thought it was time to read the manual. (Who ever does that? ;) ) And it turned out that this module switches itself on when it is activated by the accompanying software :) After this I attached it to the parallel port of my PC and started the software.

And guess what? It switched itself on :) So that mystery was solved. Here you see a picture I took from my screen. The software looks very basic, but there are some nice hidden features in it. But first things first. The function generator needs to be calibrated. Actually that process is quite simple. There is only one trimpotmeter on the PCB that adjusts the DC offset of the output. For this calibration you only have to attach a simple multimeter put on DC Volt measurement mode and adjust the trimmer until it reads exactly 0,00 Volts. So that is what I did.

After that I attached it to my oscilloscope to see the results of my freshly build apparatus :) And look a very nice sine wave! So it actually works :) After this I played a bit around with the software. You can load some freaky sound waves from a library and even design your own. I think this is very cool. You can also program it to cycle through different waves. So lets say 10 seconds of a 10 Volt Peak-Peak Sine wave at 200 Hz and then 10 seconds of a 5 Volt Peak-Peak Triangle etc. And also the Bode plot that I told you about that make a frequency response graph. I will try to show you all this functionality later on. Maybe also in a video.

After this it was time to put it in its enclosure. Here you see what it looks like with the lid of. I'm very happy that this project actually worked the very first time. Gave me my confidence back ;) Now I have to find a spot for this function generator and do some more testing. I want to see how accurate it is and compare it with my other function generator. Another cool thing I forgot to mention by the way is that is has a loop through connector for the parallel port. So the oscilloscope I build can be connected to this unit and operate both at the same time on the same parallel port. Very convinient. I think I'll fiddle around with it a bit more this evening. Well all in all a very productive day today :)

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