Use a schmitt trigger for turn on / off slowly LEDs with an automatic duty cycle

[xAmaranx]

This its my ckt I have already achieved the LEDs on and off slowly, but I do not get is that the work cycle is automatic please give me a help

 

[Harald Kapp]

Welcome to EP.

What's the value of the potentiometer VR1? Here's some info how to select component values for a given frequency.

 

[xAmaranx]

Im using 100kΩ

 

[Harald Kapp]

That should give a frequency of ~0.18Hz.
Check the inputs to the other (unused) gates of the 40106. They should be tied to ground or Vcc, never left unconnected.
Check the output of the 40106 before the RC filter (R1, C3).

 

[xAmaranx]

hi mister, this it's the signal between R1 and C3

 

[(*steve*)]

I would consider using a mosfet in this circuit. It would allow the turn on and turn off to be relatively symmetrical.

as it is now, the LEDs are likely to turn off faster than they turn on.

 

[xAmaranx]

This its a designar that i'll make i have no traying to use a MOSFET; someobe told me that MOSFET will make more stable the current on all leds xD, but i need that all led turn on abd off slowly and change the automatly duty cycle

 

[Harald Kapp]

hi mister, this it's the signal between R1 and C3

This looks o.k. What then is your issue with 'I do not get is that the work cycle is automatic'?

 

[(*steve*)]

i need [to]... change the automatly duty cycle

Check out the circuit near the bottom of this page

 

[xAmaranx]

My problem it's the automáticamente duty cycle, i was think using a counter or FF jk in the signal out of the trigeer.

 

[(*steve*)]

I don't understand. What is your problem?

 

[xAmaranx]

I need to do an automatic duty cycle on this ckt

 

[Harald Kapp]

I need to do an automatic duty cycle on this ckt

Please explain: What is an 'automatic duty cycle' to you? We are not familiar with this term, so what is the circuit expected to do?

 

[xAmaranx]

Ok the ckt most be
"Use a schmitt trigger for turn on / off slowly LEDs with an automatic duty cycle"

I need to change the duty cycle on the exit for turn on/off led in different moment's
Unwatch Thread

 

[Harald Kapp]

What I can imagine is that the task description calls for a completely different solution: An LED where the intensity is controlled by a PWM signal. To turn the LED slowly on or off, the duty cycle of the PWM needs to be controlled automatically (e.g. by a ramp). Is this what you are looking for?
The principle is shown here:

The blue line is the ramp signal: slow turn-on, stay on for some time, slow turn-off.
The triangular signal (not shwon in the diagram) would be a fast triangle wave with a frequency e.g. >100Hz to make the resulting flicker of the LEDs invisible to the human eye.
The comparator creates the PWM with 'automatically changing duty cycle' to turn the output power slowly on or off.

I suspect this is homework or an assignement (given the task description in your last post). I will therefore:

• Move the thread to the homework section
• Not diclose the complete circuit. From the above principle, design your own circuit. Show us your effort and we'll gladly help you fill in the gaps.