Saturday, 17 February 2018

Pre-Meeting, February 17, 2018 - Arduino Shift Register Control of R-2R 8-bit DAC to Astable Multi-vibrator (1/2 556 Timer)

Hi Y'all!
We hope to see y'all tomorrow at the RPUG Meeting at the library. I have been working on getting a shift register to control the frequency played by an astable 555 timer. Two shift registers are connected to LEDs at this point so it is pretty close. I am building the astable multi-vibrator right now.
The idea is to test the breadboarded device with one shift register. That will give it 8 bits to work with: 5V / 255 = 19.6 mV per bit.
Once I get that running, I will expand the DAC to more than 8 bits, giving more resolution to the frequency. Blah, blah, blah, until you realize that with more bits, you get greater control over the tones you can play. One of the interesting possibilities of using shift registers to control R-2R DACs is that you control the bit resolution. You can pick and choose how many bits are used to control each device. A web search on R-2R DACs will give you the idea that I am talking about. I can take 4 bits from one shift register to add to the first shift register and then use the remaining 4 bits to control something else.
An Arduino Nano is the brains at the moment but it should work with any other Arduino, even a 3V one, such as an Arduino Due. A 3V signal still registers with 5V logic ICs as a high signal so all that stuff will work. Watch out trying to go the other way, sending 5V signals to a 3V device. Many 3V devices will be damaged by 5V signals.
See you tomorrow!

Look for the next post with schematics and equations for all that technical stuff.

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