I build this one shot circuit. But? it dose not work every time i
push the SW.

Can somebody tell me what's wrong.

Also! I would like two use an npn transistor to replace the switch.What parts will i need to include to trigger with the transistor.Once i get the switch to work every time i press it.


Thanks

 

What are the RC values you are using?

For a circuit that works, see post number 4 in this thread. http://forum.allaboutcircuits.com/showthread.php?t=69965

ETA: My mistake. That's an astable. Here's the thread with a one-shot in post 13. http://forum.allaboutcircuits.com/showthread.php?t=69944&page=2

 

I build this one shot circuit. But? it dose not work every time i push the SW.

Does that mean it works some of the time you push the switch? See the circuit I posted for a signal conditioner on the trigger circuit.

What is your power source and what is the voltage?

 

Or you could refer to the reference material in the AAC book.

Chapter 8: 555 TIMER CIRCUITS

555 MONOSTABLE MULTIVIBRATOR

Read the theory of operation. You are missing a input conditioner, among other things.

 

Does that mean it works some of the time you push the switch? See the circuit I posted for a signal conditioner on the trigger circuit.

What is your power source and what is the voltage?

Power source is a 3.6 1cell 2400MAh. I stated the voltage.

It works but? not every time i press the SW. I already mention this.

thanks

 

Or you could refer to the reference material in the AAC book.

Chapter 8: 555 TIMER CIRCUITS

555 MONOSTABLE MULTIVIBRATOR

Read the theory of operation. You are missing a input conditioner, among other things.

Can you kindly, tell me what ami missing. Is an input conditioner another
resistor plus capacitor. If it is where do i connect it.

The only thing i see on most of these circuits is an cap on pin 2 an a added resistor tied high.

I stated it dose work. but? Not every time i press the Switch. Please clarify.

thanks

 

Does that mean it works some of the time you push the switch? See the circuit I posted for a signal conditioner on the trigger circuit.

What is your power source and what is the voltage?

Ok i got it. The only thing i need is the conditioner. As you can see in my circuit the pull up resistor it 20k can i use another 20k an a 1uf or 0.1uf for the conditioner.
Will this solve the problem of not turning on every time i press the SW.

Thanks

 

Just curious, did you even try to read the 555 MONOSTABLE MULTIVIBRATOR article?

It is pretty well spelled out in there, schematic and all. If there is a part that wasn't clear, please refer to it.

It is an illegal condition for the input to stay low for this design past timeout. For this reason R3 and C1 were added to create a signal conditioner, which will allow edge only triggering and prevent the illegal input. You can prove this by connecting the red wire between ground and point A. The timer will start when the wire is inserted into the protoboard between these two points, and ignore further contacts. If you force the timer input to stay low past timeout the output will stay high, even though the timer has finished. As soon as this ground is removed the timer will go low.

Reading is your friend, always.

 

Just curious, did you even try to read the 555 MONOSTABLE MULTIVIBRATOR article?

It is pretty well spelled out in there, schematic and all. If there is a part that wasn't clear, please refer to it.



Reading is your friend, always.

Yes i know. But thanks anyways for linking that part.The input needs a shorter lower pulse rate.''conditioner'' This is way it wasn't working every time i press the SW. I will try it with the added parts.

Thanks Bill

 

I found the article at the link below to be very helpful to learn about the 555 timer. It has examples with equations.
Hope this helps.
see
http://www.kpsec.freeuk.com/555timer.htm

 

Hi, de-bounce the switch.

 

You do realize a monostable is a time honored way to debounce a switch?

 

Hi, de-bounce the switch.

I did that, with the conditioner.Same thing. Buy adding a cap and resistor to one side of the SW. As tracecom and Bill marsden suggested.


Thanks for your input. And to everyone who posted in the thread.

 

The circiut is working. everytime i press the switch the LED comes on for the duration
time i set it for.

Next! I need to replace the SW with a npn transistor to trigger the 555 as the SW done. Any suggustions on how to get the transistor to trigger the circuit so the led comes on,Then shuts off for the time i have it set at.

 

Not sure what you mean. You want the LED to be on while timing?

If so take another look at 555 MONOSTABLE MULTIVIBRATOR , as it does just that, no transistor needed. The chip is rated for 200ma, so it can handle 100ma easily. If you need more power than that I can show you how.

 

you can try this circuit with built in debounce so its triggered every time.....

 

Not sure what you mean. You want the LED to be on while timing?

If so take another look at 555 MONOSTABLE MULTIVIBRATOR , as it does just that, no transistor needed. The chip is rated for 200ma, so it can handle 100ma easily. If you need more power than that I can show you how.

Bill

I don't want to change the circuit.I want the circuit to function as i have it.But? Have a transistor to trigger pin (2) instead of the SW.

 

Bill

I don't want to change the circuit.I want the circuit to function as i have it.But? Have a transistor to trigger pin (2) instead of the SW.

Just trying to make this clear. You want to remove the switch and put in a transistor of some kind to trigger the 555 circuit. Is that correct?

What do you plan on using to trigger the transistor?

 

Just trying to make this clear. You want to remove the switch and put in a transistor of some kind to trigger the 555 circuit. Is that correct?

What do you plan on using to trigger the transistor?

BSomer


That's correct?

I plan on using positive 1.3Volts to bias the npn transistor.
how much current will i need to trigger the monostables
negative pulse so it will start the time duration of the 555.
the collector connects to pin 2 emitter to ground and positive
voltage to base. Will this work. Using 2n4401 or a 2n3904

 

Can some one tell in my post #19 will work.