LEAP#186 Asynchronous Counters with JK Flip-Flops
A quick demonstration using four JK flip-flops set up in "toggle" mode to implement an asynchronous 4-bit binary counter. This is the classic circuit, straight out of a text book. It's implemented with:
- two 74LS73 for the flip-flops
- a 555 Timer astable oscillator providing the clock pulse
Why "asynchronous"? This refers to the fact that the output of each flip-flip cascades to trigger the next in series. Although instantaneous to the eye, there is none-the-less a propagation delay as the changes ripple through the flip flops. It's clearly seen in an analog scope trace. Here is the falling edge of 0xF transitioning to 0x0, which ripples over about a 42ns period:
Here's a quick video of the circuit in action ... though definitely not the most exciting thing you'll see on YouTube today:
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LEAP#185 Building the Böhm Stirling-Technik HB13 Small Bonsai
What has this to do with electronics? Well, nothing (yet), but there's ample scope later;-)
A Stirling engine is a closed-cycle regenerative heat engine with a permanently gaseous working fluid. They are named after Robert Stirling who invented the first practical example in 1816.
Böhm is a small(?) specialist manufacturer from Germany that's taken up a side-line in producing Stirling engine kits. When I first discovered them, I couldn't resist. So here's my build of the Small Bonsai (HB-13).
As always, all my notes and schematics are in the Little Arduino Projects repo on GitHub.
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LEAP#184 Adjustable Pulse Generator
Yet another variation on the basic 555 timer astable oscillator to allow a wide range of frequency and duty cycle adjustments. It's similar to the circuit used in kits like this.
As you can see from the schematic, it's the combination of pot and capacitor selector that produce the wide range of oscillator control:
But the challenge with the classic 555 astable circuit is trying to hold frequency or duty cycle constant while adjusting the other. This circuit doesn't solve that problem, but for something different, I plotted the functions with WolframAlpha. If you correlate the two graphs below, you can see the severe penalty you pay in terms of duty cycle when attempting to push for maximum frequency. It definitely is a case of trying to find the best compromise for your application.
As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub, including live links to WolframAlpha to reproduce these plots.
Frequency for all values of R1, R2 (C=1µF)
Duty Cycle for all values of R1, R2 (C=1µF)
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LEAP#183 Polarity Testing
A simple polarity test for uses a series of inverters. The input signal is pumped into two parallel inverter chains:
- a single inverter
- a series of two inverters
I used a venerable CD4069 for a quick test, although any inverter (matched to the voltage of the signal) will do. The result of the polarity test is displayed with a pair of LEDs reversed in parallel.
As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.
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