Zero Cost Simple Function Generator
Every bench needs a function generator, even if you dont think so. Testing any circuit often requires you to inject a signal to see the results at the output. Using any PC computer (Intel/PC, Linux and possibly Mac) you can use the free Audacity Audio program to create sound files to play out the head phone or Line Out jacks to feed into your circuit under test (CUT). You can manipulate audio files you may have or download. Create Sine, Square, Noise and Triangle waves (using the Generate command). Set the amplitude and frequency. And you can save them to .wav files to output from the media player (of your choice). Even the oldest PC that works at all can output these files so you can allocate an old laptop or PC to this task. If you have a cheap "Oscope" that connects to the PC it can work at the same time as there is not much PC CPU power needed for either. If you use the Old PC as an 'Oscope' using a program that taps into the sound card inputs, it may or may not work together. Some old equipment had only In or Out but not both. You will have to experiment.
I just built several files on my laptop with Audacity of 6 min or so length and full amplitude (to get a large signal). I chose Sine, Square, Triangle and Noise. I set them at 440 hz (middle C for the musicians out there). I also made one with 1000hz (for the techie). To do that, I opened Audacity, clicked Generate in the menu, selected Tone and set the frequency, amplitude (relative to maximum), and length in seconds. The Waveform defaults to Sine but there are Square and Triangle too. The Noise is available under Generate.
Make them useful for what you are testing. I want to make a Times-10 amplifier to increase the sensitivity of my meters and 'junky' Oscope. I will do that by using a very accurate divide by 10 resister divider (with as accurate resisters as I can afford) and measure the signal in and signal out of the divider with several meters that I have. That way, I get a better chance of getting it accurate. I may borrow a 'good' meter to calibrate even more. Note that many times the meter is not as accurate as you want but if you measure on one scale, the relative accuracy is good so comparing 2 resistors comes out better than just looking at the absolute accuracy.
If this works out well, I may try to go for times-100, though the accuracy will not be very good on that, I would guess. I also need to use good, low noise parts and high impedance Op Amps. That will be another DIY for this website.
I just built several files on my laptop with Audacity of 6 min or so length and full amplitude (to get a large signal). I chose Sine, Square, Triangle and Noise. I set them at 440 hz (middle C for the musicians out there). I also made one with 1000hz (for the techie). To do that, I opened Audacity, clicked Generate in the menu, selected Tone and set the frequency, amplitude (relative to maximum), and length in seconds. The Waveform defaults to Sine but there are Square and Triangle too. The Noise is available under Generate.
Make them useful for what you are testing. I want to make a Times-10 amplifier to increase the sensitivity of my meters and 'junky' Oscope. I will do that by using a very accurate divide by 10 resister divider (with as accurate resisters as I can afford) and measure the signal in and signal out of the divider with several meters that I have. That way, I get a better chance of getting it accurate. I may borrow a 'good' meter to calibrate even more. Note that many times the meter is not as accurate as you want but if you measure on one scale, the relative accuracy is good so comparing 2 resistors comes out better than just looking at the absolute accuracy.
If this works out well, I may try to go for times-100, though the accuracy will not be very good on that, I would guess. I also need to use good, low noise parts and high impedance Op Amps. That will be another DIY for this website.