[Jeri] shows off a delta sigma ADC

[Jeri] has had a bear of a time moving up to Valve Software, but electron microscope is safely in her garage (!) and her electronics lab is slowly taking shape. Since she can’t bring out the real-life gravity gun she’s working on, she decided to show off a one-bit ADC that uses just a flip-flop to sample an analog waveform  into digital data.

By toggling the clock input of a 74xx74 (or any flip-flop, really) and feeding the complimentary output to back into the data input, [Jeri] can get an output that is a 50% duty cycle feeding into the input of the chip. Adding an audio input to this data input with 10k pot to this feedback loop will cause the duty cycle to change in relation to the analog input, making a one-bit ADC.

As with any electronic shortcut, there are a few drawbacks: the clock cycle feeding into the flip-flop has to be pretty fast; at least a few dozen kilohertz if you’re sampling audio. Still, if you don’t have a free ADC pin, or you’d just like to build a bitcrushing guitar pedal, it’s a very simple (and cheap) way to get analog into a digital micro.

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A one-bit processor

Put on that abstract thinking cap, get out the pen and paper, and spend some time figuring out how this one-bit processor works. [Strawdog] came up with the concept one day during his commute to work (don’t worry, he takes the train… much safer than [Dave Jones’] frightening drive-time podcasts). He sketched it out on paper to make sure he knew where he was going with the project, then collaborated with Legion Labs to implement it in processing as an easier way to visualize its functionality. Since it’s one-bit there’s only room for one instruction. That instruction is a copy, then branch-if instruction. It copies the current bit to one address, and if that bit was one, it branches to a second address.

Going a bit fast for you? We think the description is fairly good, but if you can’t quite put it together from the article’s description, you may want to build this 2-bit paper processor and learn how it works first. It should teach you the basic concepts you need to understand the 1-bit version. As you can see in the image above, there’s also a single-step feature in the processing example that lets you analyze the effects of each instruction during program execution.