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controlling the frequency of 555 timer

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dinesh401

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is there any chance to control the freq of 555 timer by using a microcontroller... i.e. if 555 timer is designed to certain freq..it works according to it. but i want to change the freq of 555 timer by using a 8051 mc( ON and OFF the 555 ic) and not by changing anything in 555 timer circuit.
is there any chance to get the desired output?
 

i don't think 89c51 can generate -ve pulse as required by trigger pin of 555 if there is any other controller which can provide negative pulse then it can work

---------- Post added at 22:23 ---------- Previous post was at 22:20 ----------

check the data sheet for for the triggering current of the 555 and the controller to be used they must be same
 

Voltage controlled oscillators based on the 555 series are well known. One way to do that with your MCU would be to generate a PWM output, then pass that through a low-pass D/A filter, say 10K and 10 uF (just a guess). Use that voltage output at the Control Voltage pin (pin5) of the 555.

Why would you want to do that, if you already have an MCU?

John
 

Likely there is a chance... till you (actually we) know what you really need from the 555 IC and MCU to do :)
 
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    FvM

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actually. i am building a six legged robot. each leg consists of 3 servo motors. the servo motor is controlled by using pwm signal.
so if we generate pwm signal from our 89s52 controller the processor time will be wasted. so i thought of using 555 timer. it can generate pwm signal.
so if we on the 555 timer by our mc. the processor time will be saved. but 555 timer generates only specific time..... but i want 1 ms, 1.25 ms, 1.5.ms, 2 ms(ON Period only). these signals are needed for me . so other than 555 timer . is there any ic which generates pwm signals just by ONing the ic to get the different pwm signals ? . or by selection of inputs the ouput of that ic changes it frequncy automaticaly depending upon my requiremnt.
 

Hi,
In general the answer yes,
All you need a is PWM signal, the 89s52 is not too far off from a pic or a 8051 instruction set, so you can try these links i) 8051 PWM with software code ii) Pic based.
One thing to be wary of considering your driving servo motors is the load on controller. Try and buffer out the controller from the motor circuitry.

The 555 timer IC can also generate PWM signals:
Assuming you have fixed trigger and control voltages applied, your frequency \[\propto\] K/R1*C1
Now, K is a constant which is rather circuit dependent and can be foudn in your data sheet.
R1 just use a potentiometer to change the corresponding duty cycle you require.

If you want to use the 555 timer still, you have 4 times available, use 4 switches connected to 4 resistance values each one corresponding to the required duty cycle. Other options include using a mux, etc.

On a side note: the microcontroller option is very more practical solution as it gives you more option wrt to control e.g. derivative gains etc..

Have fun
 

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