555 timer

 

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Will Wyatt (Willtech)
Member
Username: Willtech

Post Number: 3
Registered: 10-2007
Posted on Sunday, November 4, 2007 - 2:36 pm:    Edit Post    Move Post (Moderator/Admin Only)

Ive decided to go for the trigger theory in line with the 555 timer. However i have worked out with the gearing system i have it will take 8 seconds for the model to fully open with my motor (Tamiya 70168 Double Gearbox) . What resistors and capacitor specs will i need to include with the timer, Is there an equation which i can follow? Will
Admin (Admin)
Board Administrator
Username: Admin

Post Number: 618
Registered: 10-2004
Posted on Monday, November 5, 2007 - 8:49 pm:    Edit Post    Move Post (Moderator/Admin Only)

Will,

I assume your message relates to your earlier thread http://www.technobots.co.uk/discus/messages/4/884.html?1193780411

I also assume that once the mechanism fully opens the motor will be stopped by means of a limit switch or are you going to have two timers, one timer drives the motor to the open position, another timer times our before the motor is reversed and closes the mechanism (check out the 556).

What you are asking is outside of our normal support but as it happens, I played around with 555's 20 years ago so I can answer your query.

With the 555 in monostable mode, a momentary trigger on pin 2 (negative going) will give an output pulse on pin 3. The length of the pulse is 1.1xRxC (R in ohms, C in Farads) For 8 seconds, use 100uF and 75k. You can always use a variable resistor for fine tuning, i.e. a 51k resistor in series with a 47k pot.