|Thread take-up lever up -- optimal position to sense (and later stop the machine in)||The needle shaft is up but the thread take-up lever is down -- so even if we could sense this position, it wouldn't help us much.|
For the firs experiment, we just connected an LED that will light up whenever the lever is "up".
|A little bit of scrap PCB, a bit of soldering lead, an LED, a resistor, a power source....
The lever is down, it doesn't touch the board, and the LED is off.
|The lever is up and touches the board, closes a circuit and... voilà ! The LED is on!|
And this is the entire set-up in motion:
Simple circuit for the very first
machine rotation sensing solution.
The machine itself constitutes the switch.
- At maximum speed, the signals occur 75 ms apart. This means the maximum speed of the machine is 13.333 Hz (not 10 as I had estimated), so it can do 800 stitches per minute.
- We get vibration effects which get worse at high speeds: As the lever hits the board, it bounces off a few times. This, e.g., distorted the frequency estimated by the oscilloscope and will be a problem for any electronic equipment we will want to connect. Bernd suggested using a capacitor to alleviate this problem, but I will have to learn how...