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555 1 Hz pulse generator? Answered

Hi,I have a simple buzzer which I want to convert to an oscillating buzzer so as to obtain the sound similar to that of an automobile's reverse indicator.I've posted a schematic(borrowed from electroschematics.com) below.I intent to replace the LED with my buzzer and omit the resistor.I hope by building this circuit,to make my buzzer 'buzz'(or make noise) at an interval of 1 second(since its a 1 Hz pulse generator).Would the results be similar to my needs?


Yes, it will work, the only thing I'd check is the current requirement for the buzzer

Thank you Steve.I had checked for its current requirements but the device came in a black plastic containment with nothing marked on it.I am not sure of its current requirements and hence decided to omit the resistor to prevent any shortage.Since its a buzzer that runs on a wide range of voltage input(3 volts-12 volts),I figured a bit too much current wouldn't be a problem either.

It will be a problem for the 555 !! It can't supply an infinite amount of power. You MIGHT get away with just the chip. Measure the current of the buzzer on your bench.

Special thanks to steveastrouk and framistan for your help.Things I'm gonna do considering your suggestions-
*Check the current requirements of the buzzer
*Get a pot to replace R1 to acquire the desired duty cycle
*Use a transistor to power the buzzer acquiring indirect current from the timer.

There are EQUATONS to calculate the resistors for desired output, but I bypassed those many years ago and just did experiments to determine aproximate value for the charging capacitor to get desired output. Here are my results:

for charging capacitor C1:

C1=39pF.................... 180kHz Max
C1=114pF.................. 42 to 80 kHz
C1=264pF.................. 28 to 53 kHz
C1=500pF................. 20kHz max
C1= 1000pF.............. 10 kHz max
C1= .047 uF............ 1000 Hz max
C1= 0.1 uF.............. aprox 100 Hz

That's as far as I went... so your value of 10 uF sounds about right for 1 Hz.

Also, for the values of resistors R1 and VR can effect the DUTY-CYCLE. That is the ratio of ON-TIME to the OFF-TIME of the waveform. If the thing you build seems to pulse at ONE second, but it is only a quick "ON-PULSE" then the OFF PULSE seems to last a lot longer... you need to place a variable resistor in place of the R1 resistor and adjust the two variable resistors untill you get the desired DUTY-CYCLE.

The 555 circuit you are building will put out a one second pulse, but will not make the TONE you want to hear. But you say you are using a BUZZER for that or just lighting an LED. Be sure the current drain of the buzzer is not more than the amperes available from the 555 timer (which isn't much). You may have to make the 555 output drive a small general transistor like a 2n3904 which will power the buzzer.

And hey,If I had to add an additional amplifier for the buzzer,should it go before the 555 timer or after.I think it should be before the timer but correct me if I'm wrong

You're adding a transistor as a switch, its driven by pin 3 of the 555.