Square Wave to 555

Thread Starter

Smijo

Joined Nov 15, 2012
26
I have a project where I'm taking a square wave output from an IR detector and I need some way to use that signal to trigger a 555 timer in astable mode. I think I need to connect the output of the detector to Vcc of the 555 (5V), but I'm not sure how or if that is right. I have the 555 circuits figured out and they simulated correctly. Does anyone have any ideas?
 

tracecom

Joined Apr 16, 2010
3,944
There are dozens (maybe hundreds) of ways to use a 555. What do you want it to do?

What is the voltage and frequency of the square wave?
 

Thread Starter

Smijo

Joined Nov 15, 2012
26
I want it to blink an LED, and another two wired to create a siren from a piezo transducer. I believe the frequency of the square wave is 1250Hz, and it should be 5V.
 

Audioguru

Joined Dec 20, 2007
11,248
"....trigger a 555 timer in astable mode".????
It does not make sense. A monostable 555 is triggered. An astable oscillator is not triggered, instead it is turned on and turned off.
 

Thread Starter

Smijo

Joined Nov 15, 2012
26
That's what I meant. I just need to have the timers turn on when the IR detector senses IR light. i.e. blink the LED and sound the siren.
 

Ron H

Joined Apr 14, 2005
7,063
You can turn an astable 555 on and off by controlling the reset pin.
Vreset=0: Oscillator off
Vreset=vcc: oscillator on
 

THE_RB

Joined Feb 11, 2008
5,438
You can also hold the 555 cap either high or low to stop the astable, a diode is enough (between the square wave signal and the cap).

That does require that the square wave is able to drive the cap, so it needs to "overcome" the 555 driving the cap, which is normally fine as the 555 would have fairly high value resistors driving the cap and the square wave is usually a logic output pin (with low resistance).
 

MrChips

Joined Oct 2, 2009
30,708
One of the most difficult things to do is to be able to explain completely what you have in mind to someone who cannot read your mind. This requires a certain degree of communications skills.

Forget about the 555.

Tell us what you want to do with the IR detector with no reference to hardware or chips.

Draw a block diagram.

Otherwise I have no idea what you are trying to say.
 
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