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Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 AM

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More details found in DC Magazine

Coin Operated Telescope
designed by David A. Johnson, P.E.

My client owns several coin operated telescopes.  Their problem is that the battery needs to be replaced every few months. I needed to design a new circuit to control the shutter.  The solenoid used was too power-hungry.

Once the coin was accepted and fell into the coin box, a motor would open the shutter for 2 minutes.  After those minutes had elapsed, the motor would reverse direction and close the shutter.  The timer would allow only one coin at a time.   

The circuit that controls the electronic timing sequence is fairly simple.  I designed the control system using some standard logic devices.  The coin acceptance mechanism provides a switch closure when a quarter fell into the coin box.  This starts a timer.  Power is routed to the flapper motor.  When the flapper was fully open, a motor stall current sensor turns off power to the motor.  This leaves the shutter in the fully open position.  When the timer timed out, the polarity of the motor drive reverses.  When the shutter flapper is fully closed, the motor again stalls and power is turned off power to the motor. 

http://www.micromo.com/ miniature gear motors

 
Click on Drawing Below to view PDF version of Schematic
Coin Operated Telescope Circuit Designed by Dave Johnson

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