NE555 & BD139 Siren

SamR

Joined Mar 19, 2019
2,247
According to one cross reference guide, there are 4 transistors in the same "replacement group"
BD437 BD439 MJE800 2N6039

Doing a google search may turn up available devices.

However, using a replacement may require re-biasing the circuit to support the replacement xstr.
http://matthieu.benoit.free.fr/cross/b.htm
 

SamR

Joined Mar 19, 2019
2,247
Try Googling siren circuit. That particular dual 555 timer siren circuit is pretty common. And Welcome to AAC!
 

AlbertHall

Joined Jun 4, 2014
10,015
I don't think this circuit will work for a number of reasons.
e.g.
The left hand '555 has a 20K charging resistor (2 x 10k) and a 1K to the base emitter of the BD139. The cpacitor will never to the threshold voltage.
The 100uF at the top of the diagram has no discharge path. Is one of the diodes supposed to be the other way round?
 

Audioguru again

Joined Oct 21, 2019
1,576
I agree that the circuit probably will not work.
I think the power transistor will load down the capacitor so much that the 555 will not oscillate. The power transistor should be an emitter follower to reduce the load in the capacitor.

I tried to see an Instructable that might describe this circuit but it needs me to log in! Is this circuit the instructable?
 
The schematic is wrong, the left 555 timer's output pin 3 should be going to the BD139, not pin 2+6.
2SD882 is fine for a substitute, this is only a 5V siren. Best to have a diode or snubber across the speaker if you want more power like at 12V operation.
 
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Thread Starter

dadadiouffy

Joined May 4, 2020
66
The schematic is wrong, the left 555 timer's output pin 3 should be going to the BD139, not pin 2+6.
2SD882 is fine for a substitute, this is only a 5V siren. Best to have a diode or snubber across the speaker if you want more power like at 12V operation.
There its wrong as you said but check how it is working in this video. you can witness how its soldered at YouTube >
 

Dodgydave

Joined Jun 22, 2012
9,201
The 1N4001 diodes are back to back,,. The transistor is across the capacitor on pins 2,6 , picking up the Sawtooth wave signal, making a sweeping sound.
 

Audioguru again

Joined Oct 21, 2019
1,576
Why are most electronics videos on You Tube from India now? I could not understand what he was saying. The tiny speaker has a very high pitch (a squeaker).

The schematic is wrong, the output is a squarewave from pin 3 of the 555, not a triangle wave from pin 2 which would prevent oscillation. The frequency sweep is caused my modulating the DC voltage on pin 5 as shown in the datasheet.
 

Attachments

SamR

Joined Mar 19, 2019
2,247
There are modern versions of the typical dual 555s siren circuit available that are much simpler. For Example:
1589474330842.png
Instead of the R1/R2 and R4/R5 voltage dividers, use potentiometers to play with the sound until you have achieved it's most dastardly evil noise level.
 

Audioguru again

Joined Oct 21, 2019
1,576
The simple circuit simply "switches" the frequency like in Europe. Bee, boo, bee, boo etc.
The circuit in this thread "sweeps" the frequency up and down like in North America.
If the speaker is 8 ohms then its high current might zap the 555 but the weak little 9V battery will not allow it.
With a new 9V alkaline battery then the voltage, current and power in the speaker will be about 6Vp-p, 375mA peak and 1.1W including all the squarewave harmonics, not loud unless you hold the speaker to your ear.
 

SamR

Joined Mar 19, 2019
2,247
Indeed, that is what the LM386 is for... A simple addition.
An "Americanized" version... Plenty to choose from on Google...
1589481114356.png
I would also note the there are several "siren" IC dip chips manufactured. One in particular has the US used 4 tones (police/ambulance/fire) plus a flipflop for the flasing lights bar all on one chip.
 
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There its wrong as you said but check how it is working in this video. you can witness how its soldered at YouTube >
Take a look where the 1k resistor goes, in the built circuit. It's to pin 3. The two control voltage diodes are also opposing.
The schematic is full of mistakes. So much for Kiyani Tech.
 

Dodgydave

Joined Jun 22, 2012
9,201
Indeed, that is what the LM386 is for... A simple addition.
An "Americanized" version... Plenty to choose from on Google...
View attachment 207185
I would also note the there are several "siren" IC dip chips manufactured. One in particular has the US used 4 tones (police/ambulance/fire) plus a flipflop for the flasing lights bar all on one chip.
I made this back in 1978 when it was all the rage to have a "Kojak" siren in your car, i used a push pull output ..
 

Thread Starter

dadadiouffy

Joined May 4, 2020
66
Why are most electronics videos on You Tube from India now? I could not understand what he was saying. The tiny speaker has a very high pitch (a squeaker).

The schematic is wrong, the output is a squarewave from pin 3 of the 555, not a triangle wave from pin 2 which would prevent oscillation. The frequency sweep is caused my modulating the DC voltage on pin 5 as shown in the datasheet.
Thanks very big brother! the 1N4007 WITH 1K Resistor was upside down in the circuit as well..
 

Audioguru again

Joined Oct 21, 2019
1,576
Does a police siren in India have its frequency slowly rise then stop for a while at its highest frequency then quickly reduce its frequency? This circuit does that because its slow oscillator uses two resistors to slowly rise its output then uses only one of those resistors to quickly drop its output. I do not know which directions the diodes are connected, they might make it worse or might over-do trying to make the up frequencies the same length of time as the down frequencies.
 
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