So I have had this pile of Ebay sitting on my desk for sometime and today I have gotten excited enough to actually start taking a look at it all and seeing how it works. I got these frequency generator chips for like a buck and after setting them up with the test circuit, i could not get them to work, it happens, now and again you get Ebay’d in the butt.
So I figured next i should test out the TDA2822 audio amps. I for 50 for 2 bucks which is a lifetimes supply. Do they work, well, yes they do and here are the results.
Here is the test circuit straight out of the PDF. As you can see parts count is low. So I put the IC on the breadboard and used just 1 1/2 for a mono amp. I also used just 2 caps, pin8 to ground, 470uf as it was already on the breadboard and the input cap on pin 1. Powered with 8v as its a handy voltage i have on my breadboard. 12v would probably be a better option to allow for a larger voltage swing.
As you can see, nothing fancy here, just the IC and 2 caps and my signal gen and oscilloscope probes doing there thing allowing the pixies to in and out and display them in the screen.
So we stick in 0.1v 600hz sinewave and see what happens.
Well, we actually hit the voltage rails and clip somewhat. 0.1v in almost 8v out, that is the voltage gain there. And when i do some da finger poken, the IC itself is cool to the touch, not warm, not hot, but about the same as ambient temperature of the room. So i am thinking Bye Bye LM386, and hello life time supply of TDA2822. And being a stereo IC, I can also bridge the left and right for even greater output. Not that I think i would need it.
So i have been busy laying out some boards for my receiver project. Bandpass and Lowpass filter boards, DDS and AF Amp board and a shield board for stacking these things together with other bits of circuits. Got them sent off the the fabricobblers in China and will have them back in a few days and will start to assembling them
3 Band Filter Board
DDS VFO and Audio Amp board with TX and RX switching.
A shield board that stacks under the DDS board.
So i was looking for a way to make a negative voltage. Did a bunch of google and came up with a number of different ways. One that was kind of catchy was to use a 555 timer as an arsetable vibrator with a couple of caps and diodes to invert a signal voltage.
So in the above schematic, everything on the right of the 555 timer just sets up the chip to make a square wave which is then fed into C3. C3 and D1 invert the signal and D2 and C4 act as a filter.
So i built this on the breadboard as it gets very little love in this house. The cap on the right is the input and the output is taken from the junction of D2 and C2.
Using my signal generator rather than a 555 timer, I fed an 8v 50khz signal into the circuit. Yes my RedPotato scope has loss from the input protection diodes on its input and i am not using any compensation. So the yellow trace in the scope output is the input signal and the 2nd probe was used to measure the output voltage, 8v in -7v out, which is about right accounting for all the diode losses on the scope input and in the circuit under test. All in all i learned something out of this, which i am happy about and now actually understand what its doing and how it works.