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Audio Interface for Morse Code

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djnik1362

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hi
I am designing a Morse Code demonstration system
and need to produce an audio signal for it.

I don't know how design this audio interface.

My logic output is Morse Code at TTL voltage level .
(Dot : 100 ms High 100 ms Low--- Dash : 350 ms High 100 ms Low)

Should i produce pulse or sine wave on this levels for producing audio ?
Should i use speakers or buzzers or anything else ?

Please give me a hardware solution.

Thanks for your support.
 

betwixt

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Unless you are really worried about the quality of tone, you can use almost any waveform to drive the loudspeaker, it wont make alot of difference if you use sine or pulses.

Your options are:
1. use the logic output as an on/off signal to an external oscillator and feed it to a loudspeaker
2. create the tone by rapidly pulsing the logic output, in which case you can feed the loudspeaker directly
3. use the logic output to turn a tone generating buzzer on and off. By this I mean a buzzer that produces its own tone when power is applied to it.

If you use a loudspeaker it might be necessary to use an amplifier, it depends on how loud it has to be.

Brian.
 

BradtheRad

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The signal you produce is not in the audio range.

You cannot use a loudspeaker directly. You might get clicks. But that's all.

You want beeps.

The easiest way to make beeps is to attach a piezo buzzer. It needs to be the kind that creates tones internally. (The reply above said the same thing in point #3.) You cannot use a plain 2-wire piezo unit.

Since your supply is 5 V, a piezo buzzer will be loud enough for everyone in the room to hear.
 

djnik1362

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The signal you produce is not in the audio range.

You cannot use a loudspeaker directly. You might get clicks. But that's all.

You want beeps.

The easiest way to make beeps is to attach a piezo buzzer. It needs to be the kind that creates tones internally. (The reply above said the same thing in point #3.) You cannot use a plain 2-wire piezo unit.

Since your supply is 5 V, a piezo buzzer will be loud enough for everyone in the room to hear.
So i should send my TTL level to piezo directly ?
When the Level is High the piezo is on and in Low level the piezo is off ? am i right ?
 

BradtheRad

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So i should send my TTL level to piezo directly ?
When the Level is High the piezo is on and in Low level the piezo is off ? am i right ?
Correct.

I may have misspoke. There are 2-wire and 3-wire piezo buzzers/beepers. You must make sure to get a unit that generates beeps by itself.

Because there are also 2-wire and 3-wire piezo transducers. You should not get a simple transducer. This type must be driven by pulses at an audio frequency. You would have to construct an oscillating circuit to do this. The oscillator would be turned on and off by TTL levels.
 

Syncopator

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A buzzer, of any type, is very irritating to listen to, especially a piezo one, the frequency of which is far too high. Don't use either of them - PLEASE! Your audience will thank you.

Use the TTL to switch a decent audio (sine wave) oscillator on and off, or gate its output. Most people seem to use something around 1kHz, but that's too high for long listening. A comfortable frequency is around 500 to 700Hz.

I'm an ex-professional operator. Believe me.
 

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