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Simple frequency generator

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Chazz

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I'm trying to build a cuircuit that is to generator a certain frequency for half a second, then move to the next for half a second and so on. Basicly this would be trigged by a button.

I mabey be needing to design several hundred of theses circuit so I'm trying to look into a cost efficient way of building them.

My idea was to use a microcontroller, which from my understand would need a crystal to regulate and 2 diodes. Then I would need a battery to power everything and some sort of speaker for the frequency.

Is there a better cost/efficient way to design. I'm I thinking about the right materiels or I'm I missing something important for the curcuit to work?

To be more exact, my dad used to work on telephone line (had hi sown compagny) and told me if you use a device that would produce the dial tone frequencies up to the phone speaker, you could dial the number. I'm trying to make a device that can reproduce those frequency simply loud enough for the phone microphone to pick them up.
 
Depending on the frequencies you need here is what I'd do. Well actually excluding RF this is what I'd do period.

But assuming they're fairly low, then it can be done for under like 5 dollars, with a bit of knowledge.

I'd get an 8051 Intel Microprocessor (very cheap), and an D/A and simply write the code to generate the frequencies. Now I'm assuming that you need sinusoids, but if you need square waves there are other ways.

If this will work for you let me know and I'll explain further.
 
I did some research and there called DTMF Signals. Basicly the tone are 100ms with 40ms break time. The frequency are a mix if I understand well off
(1209, 1336, 1477, 1633)
and
(697, 770, 852, 941)
In Hz I beleive.
There is suposed to be a IC that hoock up to a keypad but I need them to be pre programmed "Speeddialed" from a single button and output through the air to be inputed into the telephone microphone so the IC would probably just complicate my circuit I beleive.
 
Chazz said:
I'm trying to build a cuircuit that is to generator a certain frequency for half a second, then move to the next for half a second and so on. Basicly this would be trigged by a button.

I mabey be needing to design several hundred of theses circuit so I'm trying to look into a cost efficient way of building them.

My idea was to use a microcontroller, which from my understand would need a crystal to regulate and 2 diodes. Then I would need a battery to power everything and some sort of speaker for the frequency.

Is there a better cost/efficient way to design. I'm I thinking about the right materiels or I'm I missing something important for the curcuit to work?

To be more exact, my dad used to work on telephone line (had hi sown compagny) and told me if you use a device that would produce the dial tone frequencies up to the phone speaker, you could dial the number. I'm trying to make a device that can reproduce those frequency simply loud enough for the phone microphone to pick them up.

Get yourself a decade counter (a 4017 should work), make yourself an astable multivibrator with 2 NPN transistors (see play-hookey.com's electronics for the multivibrator), and then instead of connecting the resistor to +ve, in the multivibrator, connect it to an output of the counter. now add another resistor to the transistor base (now you are making a bush of resistors).

When the circuit is done properly, each clock pulse applied to the counter will change the frequency. The frequency is dependent on the resistors and capacitors.

A microcontroller doesn't necessarily need a crystal. All it needs is a simple clock (external pulse), and crystals are commonly used in clocks.
 
Chazz said:
I did some research and there called DTMF Signals. Basicly the tone are 100ms with 40ms break time. The frequency are a mix if I understand well off
(1209, 1336, 1477, 1633)
and
(697, 770, 852, 941)
In Hz I beleive.
There is suposed to be a IC that hoock up to a keypad but I need them to be pre programmed "Speeddialed" from a single button and output through the air to be inputed into the telephone microphone so the IC would probably just complicate my circuit I beleive.

Well those are pretty specific timings. And I'm going to be honest, I am just a fan of software more so than hardware which is why I'd use one. And if I had to design what you're proposing I would do it with a microprocessor or a dsp processor, which ever would work better for you. You can also interface an LCD and keypad if you need them.

It really wouldn't be that bad of a design (assuming you can do all the interfacing correctly) and it would be cheap. You could probably do a hardware design cheaper, but it wouldn't come with all kinds bells and whistles a software design would :)

If you want to help you out with the methodology of the design I'd be willing to give you a hand, just let me know.
 
Chazz said:
I did some research and there called DTMF Signals. Basicly the tone are 100ms with 40ms break time. The frequency are a mix if I understand well off
(1209, 1336, 1477, 1633)
and
(697, 770, 852, 941)
In Hz I beleive.
There is suposed to be a IC that hoock up to a keypad but I need them to be pre programmed "Speeddialed" from a single button and output through the air to be inputed into the telephone microphone so the IC would probably just complicate my circuit I beleive.

If you search for PIC and DTMF, you will probably find exactly what you need! - I've seen PIC designs for generating DTMF tones in PIC software.

You need to be aware that it uses two tones at once, and the values are specifically calculated to not be harmonically related.

At one time such devives were freely available in the shops at very low cost (apparently even crap places like RadioShack sold them!).

However, they are probably pretty rare these days, as there doesn't seem to be much use for them? - why are you wanting to build them?.

Quick thought! - probably the last place I saw one was with an answerphone, used for remote listening to your messages!.
 
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