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As part of a class about designing for the plastic injection molding process, I designed, cut molds and shot some napkin rings called the Impaled Napkin Rings series. Process below.
I first 3D printed some prototypes to see how they worked. I learned that living hinges do not work with our printer material. I cut the molds using a HAAS Office Mill OM1. I had to recut one side as the living hinge at the neck was so small on the first iteration that when the molds separated after shooting they would decapitate the napkin ring (if that makes sense). I widened the neck and they shot perfectly.
I’ve been inspired by many chairs over the last week or so and spent far too much time in my head and on paper sketching ideas. Last night I cut and assembled the chair I designed in six hours using 2 2x4x8’s and a 4 foot by 4 foot piece of 1/2″ plywood. Here is some process documentation and some photos of the final project. I was pleased with amount of time it took to cut and assemble but not so happy with the bulkiness and lack of personal expression in the piece. It was a great exercise in making a functional and comfortable chair, which I have never attempted or done before and I’m excited for the next 7 weeks to fully design and explore my next chair.
Today we’re building a simple voltage divider where the output is read using an analog input on an Arduino Nano. I’m following a similar project that uses a thermistor instead of conductive cord.
We use the equation Vo = R / (R + 10K) * Vcc to measure the expected voltage output at various resistances. The conductive, resistive rubber cord has a resistance of 350-400 Ohms per inch (not very exact but fine for our prototyping needs). My fixed Resistor is a 10k (already in the equation above) and Vcc is 5v from my laptop to the Arduino.
Here is the simplified math:
ADC value = Vi * 1023 / Vcc
ADC value = R / (R + 10K) * Vcc * 1023 / Vcc
ADC value = R / (R + 10K) * 1023
R = 10K / (1023/ADC – 1)
We will test using the following code from the tutorial linked above.
We now want to measure two things:
We can measure this by measuring the amount of time it takes to reach a peak (maximum value) from the baseline resistance.
We can measure this by measuring the peak-to-peak time.
So far I’ve slightly modified the code so that it will tell me when the cord is measuring breath in and breath out or holding breath.