Wednesday, July 1, 2015
@MAKE #Electronics Experiment 29: Filtering Frequencies Part II
Note: first, apologies to +Eric Buijs who noted that the TEA2025B runs hot at 9V. I either did not notice or did not perceive that in part 1. However, in part 2 I experienced the same thing. Using an adjustable wall wart, I was able to apply different voltages. 9V works best, but it runs at safer temps at 7,5V and 6V. Besides the heat, the biggest difference is the volume coming out of the speaker (see video at link below).
Part 2 of this experiment involves adding a 555 timer in astable mode (with resistors and capacitors) and two pots: a 500 Ohm for volume control (between output pin 3 of the 555 and the input of the TEA2025B) and a 100K to manipulate the waveform (between 555 discharge pin 7 and threshold pin 6). I skipped the buttons for this exercise, and connected it with each filter and with no filter at all. The differences are discernible.
I did not have a 500Ohm pot, so I used a 1K. It really only worked as a volume control at 9V.
Charles says to disconnect the audio source and use the timer as input to the amp. I also added my cell phone playing Pandora back in. It works for that, too.
A very worthwhile experiment. I'm looking forward to doing more with audio.
Here's the video.