Discussion in "Project Doubts" started by    LAMBO    Apr 12, 2018.
Thu Jun 21 2018, 10:13 AM
hi sir
can we change the frequency on pin no 39 of IC at89s52 in oder to get desire frequency in output
i have a link related with mine project down below


Thu Jun 21 2018, 06:49 PM
The frequency of the pulses has to be the same as mains, that is 50Hz.
What you want to change is the time between the start of the new cycle
and the pulse from pin 39.

From what I see the timing is way out.
I suspect the problem is with the signal on pin 12 ( P3.2.)
Without an oscilloscope it will be hard to test.

Connect a 1K resistor in series with a small loudspeaker. (transistor radio sized)
With long leads and crocodile clips it is a useful tester.

Disconnect the mains lamp.

Connect the speaker between pin 12 and ground.
Do you hear a faint buzz ?

Then connect the speaker between pin 39 and +5volts.
You should get a similar buzz, but the volume should vary
as you change the speed.

Mon Jun 25 2018, 10:19 AM
hi sir
as per circuit diagram i have checked the frequency it was about 100hz at pin no 12 and the fan was rotating only at level 8 and otherwise it remains ideal

but sir i have manually changed the frequency at 25 hz on pin no 12 its working fine

link below

sir can u let me know how can i change frequency at pin no 12 by changing program or hardware if yes then how???
Tue Jun 26 2018, 02:03 AM
This kind of circuit will never be able to properly
control the speed of the motor/fan you have.
Use a light bulb for now.
Please repeat your test with the original connections to pin 12.
Monitor pin 12 and pin 39 on your oscilloscope to compare input and output.
I would set both channels to DC.
I look forward to seeing the video.

Wed Jun 27 2018, 01:23 AM
hi sir
i have connected circuit originally as mentioned and sir i get frequency about 136-148 hz on pin no 12

yellow line is for pin 12 and blue is for pin 39 on osilloscope
link below
Wed Jun 27 2018, 06:10 PM
Interesting video.
>i get frequency about 136-148 hz on pin no 12

That is very odd it should be 100Hz (or 120 HZ if your local supply is 60Hz)
Can you check that again.
What power supply are you using ?

Are you sure the signal is actually reaching pin 12, is there any chance of a dry joint
on the socket ?
From the video it seems you only get a pulsed output on the top two settings
is that correct ?

There seems to be a lot of noise on the scope display.
This circuit has poor smoothing, which could cause the misfiring.
Add a 0.1uF ceramic and a 100uF (or bigger) electrolytic capacitor to the output of the
5 volt regulator.

Attached is some very simple test code.
It just copies the input on 12 to the outputs on pin 39 and 17
so all three should be the same.

[ Edited Wed Jun 27 2018, 06:16 PM ]
Fri Jun 29 2018, 05:15 AM
hi sir
i have changed the input supply finally its giving me an 100-103 hz on pin no 12
but sir waves on oscilloscope of pin 39 comes only on 7 and 8 level of bar graph led
yellow line is for pin 12 and blue is for pin 39
link below
Fri Jun 29 2018, 03:49 PM
>i have changed the input supply
Do you mean you have added the capacitors I asked you to ?

Try the program I posted last time.
Sat Jun 30 2018, 10:58 AM
hi sir
no sir i haven't connected any kind of capacitors instead of that i have changed the input power supply its giving me perfect 100hz on pin no 12
now do u want me to added capacitor ????? yes or no??

and sir i haven't tried the program yet now
Sat Jun 30 2018, 05:00 PM
Yes, add a 0.1uF ceramic and a 100uF (or bigger) electrolytic capacitor to the output of the
5 volt regulator.

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Tue May 19 2020, 06:29 PM
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