Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: polar bear6 on April 24, 2006, 08:25:50 PM

Title: 555 timer IC
Post by: polar bear6 on April 24, 2006, 08:25:50 PM
i just bought 50 555timer IC's for about 3$, and the only thing i know i can use em for is photovore.
i found a neat schemetic.
in Junkbots, bugbots and bots on weels (a BEAM robotics book)  it said that it could be use to shitloads of things, but i only found the photovore...
anyone know any other neat stuff I can use them for?

damn, im gonna make me one of theese:
Title: Re: 555 timer IC
Post by: Admin on April 25, 2006, 01:37:20 PM
The 555 timer
has a billion uses . . .

The best use for robotics I can think of is for PWM (which also has hundreds of uses).

I always wanted to try and figure out how to use a 555 to control a servo without a microcontroller, but have been too busy/lazy to bother with it.
Title: Re: 555 timer IC
Post by: polar bear6 on April 26, 2006, 10:00:20 AM
i kindah forgot what PWM was, can you plz explain?
Title: Re: 555 timer IC
Post by: Admin on April 26, 2006, 10:19:07 AM
Pulse Width Modulation

Basically a square wave, scroll down to the last picture:

You basically turn something off and on really really fast, so instead of being fully on or fully off, you get something in between. This way you can get analog control through pure binary control.

Its like turning a motor on and off really fast by hand so that it isnt running full speed, but it is still moving. That is PWM. Of course it is better with millisecond control, like with a microcontroller, or a 555 timer  :P

And of course, the ratio of on to off pulse widths determines the speed of your motor, or brightness of your lightbulb, and so on.  8)

Oh and just to not confuse you, servo's are not powered by PWM (at least not by the user). Instead you send PWM just as a control signal that its own internal circuitry interprets. A particular width instead determines the angle the servo is at, or speed at which it rotates if modified, through its own internal feedback control system thingy.
Title: Re: 555 timer IC
Post by: bibinjohn on August 01, 2006, 02:08:43 PM
555 cannot source enough current to drive a motor. IF you want pwm using 555 then use astable circuit, instead of Ra and Rb use one pot with one end on Vcc, other end on pin6 and the variable end on pin7. Use one diode with one end on pin6 and other on pin7. Use H-bridge to drive the motor.

Bibin John