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| [SOLVED] NE555 as a tone generator for Morse code practice |
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| Zero999:
--- Quote from: MarkF on September 16, 2019, 03:56:48 pm --- --- Quote from: soldar on September 15, 2019, 09:06:31 pm ---By switching the power supply the first few cycles are unstable until the frequency stabilizes so I generally do not switch the power supply but leave it running continually and switch the speaker on/off. That way the problem is avoided. --- End quote --- Switching the RESET pin would probably be a better option than switching either the power pin or the speaker. --- End quote --- The downside to switching the speaker or the reset pin is, the quiescent current of the 555 will drain the battery fairly quickly. I wouldn't bother with a 555 circuit for this. I'd just use a piezo buzzer. Granted, it's not so educational, as using the 555, but much easier and will get the job done. If you want to learn, use a three wire piezo transducer and drive it with a single transistor oscillator circuit. The next step is to use a two wire transducer and the classic two transistor astable, which is louder. D1 & D2 aren't needed for supply voltages under 6V. |
| soldar:
I have made many alarms with this basic circuit and it works well. Water tank overflow, open gate alarm, etc. Plenty uses. I should add that I was using the older bipolar version because it may be the CMOS has higher output impedance. Also, I was using a wall wart to power the thing. I avoid using batteries if I can but if it is for Morse code practice you can just provide a power switch. Does anybody really use Morse code any more? I had to pass the test to get my ham radio license decades ago but I don't think I could do much today. |
| bd139:
Yes we do use morse code. I don't use any other mode on amateur radio. It goes a very long way with crappy propagation, low power and very simple radios and is fun. There are literally thousands of people using it on the average weekend all over the world. As for the morse code practice oscillators, the 555 I don't recommend. One of the things you will find is it's a square wave and this is fatiguing rather quickly. There are a lot better designs out there that use phase shift or twin-t oscillators to produce a sine instead. You can listen to that for hours without ending up with a brain ache. Good design here: http://k4icy.com/weekend_radio_3tr-audio-amp.html |
| Zero999:
--- Quote from: bd139 on September 17, 2019, 09:47:18 am ---Yes we do use morse code. I don't use any other mode on amateur radio. It goes a very long way with crappy propagation, low power and very simple radios and is fun. There are literally thousands of people using it on the average weekend all over the world. As for the morse code practice oscillators, the 555 I don't recommend. One of the things you will find is it's a square wave and this is fatiguing rather quickly. There are a lot better designs out there that use phase shift or twin-t oscillators to produce a sine instead. You can listen to that for hours without ending up with a brain ache. Good design here: http://k4icy.com/weekend_radio_3tr-audio-amp.html --- End quote --- I agree about using a sine, rather than square, wave but that design is more complex than necessary. The LM386 itself can double as the oscillator, as well as power amplifier. There's a Wien bridge oscillator design on the LM386 data sheet: refer to figure 16, page 12. http://www.ti.com/lit/ds/symlink/lm386.pdf |
| bd139:
That's not a bad idea with the LM386 actually. I might use that for something else :) However the complexity is probably necessary here. There's a keying envelope that needs to be used for best copy. Turning an oscillator on and off tends to lead to overshoot, thumping and warbling while it stabilises, especially lamp feedback wein oscillators. If you just gate the signal then you end up with fast rise time edges which results in clicking at the start and the end of the tone. Both of these lead to interpretation problems. Thus you usually have an oscillator, a gate with an RC curve on the leading and trailing edges, then a power amplifier. This generates a nice envelope like this: This is one of those problem domains that is a lot more complicated than it looks. It's like a mono-note analogue synthesizer really! Edit: incidentally a lot of the proper CW transmitters do exactly the same thing to the power output envelope on transmit. |
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