Maker Pro
Maker Pro

Help with siren circuit

dislocations

Feb 21, 2012
25
Joined
Feb 21, 2012
Messages
25
Hi,
Hope u are all well since my last visit here (2 years ago?).
I'm looking for a bit of help with a circuit I'm building. It's a siren based on a 555 which is familiar to many of you. I'd like to make the rise and fall quite long, around 10 seconds from low to high and back to low. I would like to make this a sine wave.
I also thought of using a 40106 instead of a 555 as I prefer the ease of use. If I did it that way I would use 2 40106's......one modulating the second.
In the past I've sort of acheived this kind of thing by putting a large cap from the output of the first to ground. I realise this is not the best way? I'd also like to be able to alter the frequency of the first.
Thats probably as clear as mud? Sorry!!! :eek:
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
You could start by posting a schematic of your ideas so far.

You would like to make "this" a sinewave? The audio signal, or the modulation signal?

You can use a 40106 as a modulated oscillator, but the thresholds are not well-controlled, compared to a 555 where the thresholds are pretty close to 1/3 VCC and 2/3 VCC.

If you want a slow sinewave for your modulation frequency, you might be best to use a two-op-amp triangle/squarewave oscillator followed by a sine shaper. Alternatively you could use direct digital synthesis, but if you go digital it would be simpler to do the modulation inside a microcontroller, using a sinewave lookup table.
 

duke37

Jan 9, 2011
5,364
Joined
Jan 9, 2011
Messages
5,364
Old electronic organs used a phase shift oscillator to generate low frequencies for vibrato. These ran at about 1Hz. Larger capacitors would give lower frequencies I could look up the circuit if you wish.
 
Top