555 Timers & creating different frequencies


Old 05-11-04, 02:24 AM
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Exclamation 555 Timers & creating different frequencies

I have a high school assignment to design and build a circuit that will produce two different frequencies of sound for different lengths of time.

Components to be used:
Resistors, Capacitors, Diodes, Transistors, 555 Timers.

Unfortunately i have limited knowledge of electronics =(

Any form of help/information will be great.
Thanks in advance.
Old 05-11-04, 05:01 AM
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Go to Yahoo or Google and search for
"555 timer" project
and you will find lots of good examples and tutorials for this little magic chip.
Old 05-11-04, 06:58 AM
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thanks. i still find this confusing haha.
ive experimented with a simulation program and i can make 2 led's flash for different periods using a 555. But no use with sounds.
Old 05-11-04, 10:19 AM
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Radio Shack used to have a pamphlet full of 555 timer circuits. I don't know if it is still available, but it is worth a look. It sounds like you can use the transistors to selectivly power a 555 to determine your tone length. The output of this timer can be used as a gating input into a second timer which controlls the tone. A transistor could be used to determine which timing circuits are enabled at any point in time.
Old 05-11-04, 10:31 AM
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To make sound you need make a 555 oscillate at an audible frequency. I would pick somehitng in the 5kHz-8khz range. Then you need to amplfy it so that you can hear it.
Old 05-11-04, 08:06 PM
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I think that you will be able to directly drive a speaker with the output of a 555 timer. You won't need amplification to hear it on a speaker especially if you have a speaker output transformer to work with. Radio Shack should have everything you need to get something that will work. A 555 timer is a nice chip. Building a timer or oscillator is an easy & staightforward job. I would suspect that the reason you have the HS assignment is to learn a little something about electronics. Don't try to get the whole assignment designed by someone else, try to do as much of the work yourself as possible and you will be rewarded in the long run.
Old 05-12-04, 01:19 AM
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Thanks to all replys.

It is a senior Physics assignment, we have just started electronics and we need to investigate all this ourselves.

Also the sounds i must generate includes the note "D" and another of my choice, both for the same amount of time.

I have a rough idea of what the circuit should look like, yet i am unsure as how the different resistors affect the sounds frequency and time intervals.
Old 05-12-04, 01:43 AM
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I did a quick search and came up with all kinds of info on the 555 timer. Today there's more & better info out there on the internet than there ever was when I was messing with that kind of stuff years ago. There's a formula for the 555 that I found right away. It was:

freq = 1/(0.693 * C * ( R1 + 2 * R2)) where:
f= cycles per second
C = farads
R= ohms

You can make a circuit to do just what you want and can even directly drive a speaker with just a 10mfd capacitor in series with the speaker. The 555 has lots of drive on it's output and is hard to destroy unless you hook it up backwards. I used to build stuff with that chip years ago and it's easy to get things to work using it. My public library has many books available with various circuits for the 555 and on my first internet search I came across about a dozen sample circuits and the complete theory of operation of the chip. You will have to spend a little time reading up on the theory of RC timers, but all the information is real easy to find.

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