# motor timer

Posted on Feb 6, 2014

The basic idea is to turn the motor just a little bit every 15 seconds or so. A monofilament line transmits the motion to the ornament. It gets wound by the motor and slowly unwinds by turning the ornament. The charging path has a 1 megohm resistor in it, which combined with the 22 microfarad capacitor, yields a time constant of about 22 seconds.

The formula for the 555 timer has a factor of about 0. 5 on the time, so it comes out to around 11 seconds. The discharge path is through a 10 kilohm resistor, so its time constant is around a fifth of a second. During the discharge portion of the cycle, the 555 output pin is low; this is used to activate the motor. Doing it this way takes advantage of the fact that the 555 can sink quite a bit more current than it can source (but read on, this didn`t work as we expected). In addition, it takes fewer components to implement a < 50 percent duty cycle. Use Google to search for 555 timer. We suggest using a TLC555 - it`s a low power version of the classic 555 and it runs reliably at 3 volts. It also doesn`t glitch the power supply as badly as other kinds of 555 chips, which can happen when the internal flip-flop triggers. We tried skipping the bypass capacitor, but it didn`t work, so you`ll still need that. This circuit can be used with two AA batteries, or a 9 volt battery. It depends on the motor`s specifications. The 555 will accept anything from 3 to 18 volts; the timing won`t change. (But don`t panic! We found an answer. Read on. ) The weight of the ornament was probably increasing the friction. The theory is that the low power 555 was limiting the current to the motor, resulting in a loss of torque: completely shorting out the output to ground would let the motor work. A simple fix might be to skip the diode or add...

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