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A hand-held twist-to-set countdown timer for your kitchen.

Recently I built an Attiny85 Twist-to-Set Kitchen Timer by bobson.h. After finishing the build, I found that the optical rotary encoder had a number of problems which I won’t go into here. Instead I decided to start over and redesign the mechanism to use a mechanical rotary encoder.

The circuit is designed around a ATtiny3216 microprocessor. This 20pin device has enough IO pins for the 4-Digit 7-Segment clock display, the rotary encoder output, a push button switch and speaker. It also uses very little power in sleep mode. The rotary encoder contacts are debounced using an RC network and Schmitt trigger (74HC14).

3D printing
The STL files are included. Either take these to a 3D print shop or if you have your own printer, run them through your slicing software. I used a 0.1mm layer height for “Twist - Button.stl” and 0.2mm layer height for the rest of the pieces.

Twist - Bottom.stl” and “Twist - Ring.stl” require supports touching the build plate only.

Twist - Rim.stl” should be printing using a contrasting color.

For “Twist - Top.stl”, drill out the two PCB mounting holes with a 2.5mm drill and create a thread with a 3mm tap.

Glue “Twist - Ring.stl” to one end of “Twist - Rim.stl” using super glue. Make sure you orientate “Twist - Rim.stl” correctly. Test it on “Twist - Bottom.stl” first, it will only turn correctly if orientated correctly on the base. The Rim is glued to the open side.”

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