hi Everyone,

I am just trying to make the led blink.

Please check the image below:



The led is continuously glowing. Is it due to frequency of timer 555 or because I am using 12v for both n-channel mosfet and timer 555?

thanks

 

Is it due to frequency of timer 555 or because I am using 12v for both n-channel mosfet and timer 555?

Can't be the latter, so it must be because the frequency is too high. Do you have an oscilloscope or a high end logic probe (e.g. HP545A)?

BTW, that's a mighty ugly schematic.

 

Remove D1 and try again.

 

Remo

I already removed it.

 

Ok then can you post pictures of the circuit board that you're working on.

The frequency is approximately 3Hz

 

Ok then can you post pictures of the circuit board that you're working on.

The frequency is approximately 3Hz

it is on breadboard. 3hz I assume led should twinkle

 

Post pictures of the works, you may have a wiring mistake. Have you got a DVM ?

 

it is on breadboard. 3hz I assume led should twinkle

It depends on the pot setting. With the pot set to 0 ohms, frequency would be over 100Hz.

 

hi rahub,
The frequency is 6Hz and the LED is On for only approx 7 millisec.
The R1 and R5 values are much too low.
E

Update:
For a quick test change R1 the 1k to say 100k

Added image.
Both R1 and R5 are 100k.

 

Post pictures of the works, you may have a wiring mistake. Have you got a DVM ?

no, sorry, i don't have

 

no, sorry, i don't have

What made you think you could build circuits without a DVM?

 

What made you think you could build circuits without a DVM?

I have dvm but not oscilloscope I mean

 

I have dvm but not oscilloscope I mean

What is the approximate pot setting?

 

What is the approximate pot setting?

I used 50k pot also for testing. moved it to from 0 to full. led still on. do I need to reduce voltage of the logic?

 

I used 50k pot also for testing. moved it to from 0 to full. led still on.

How are we supposed to help you if you don't give us the required information? We were all making assumptions about the setting on the "22k" pot, but you were using 50k.

do I need to reduce voltage of the logic?

Frequency is independent of supply voltage.

 

How are we supposed to help you if you don't give us the required information? We were all making assumptions about the setting on the "22k" pot, but you were using 50k.

no, sorry. I mean, I used 22k first, result was the same. then I used 50k pot for testing but the result turn out to be same.

Ok. I think it is related to frequency only because when I removed connection from pin 3 of timer 555, the led turned off

 

If you can put pictures of the breadboard then we can see your work, you may have the Fet the wrong way round.

 

I think it is related to frequency only because when I removed connection from pin 3 of timer 555, the led turned off

It should be pretty obvious why essentially removing the timer from the circuit would turn the LED off.

Incidentally, why are you using a MOSFET? You could drive the LED high side from the timer.

 

Hello,

As @dl324 said, you can drive a led directly from the 555.
The cmos version can deliver 100 mA at its output.
The bipolair version can even deliver 200 mA at its output.

Bertus

 

Circuit schematic redrawn, driving LED direct.