Help needed with 555 Horn circuit Please

[Scruffneck]

Hi, I found a video on Youtube that shows the schematic and demo of a police horn (not siren). I'm a noob but I thought I could crack it with a little research and good enough solder skills. I'm not smart enough to verify the circuit however. Well, I tried once to make it really small on a project board, then again on a veroboard, then a less cramped attempt on same veroboard. Then I bought a breadboard and I Still can't get it to work.
Here's a link to the video which I uploaded to my channel:

and here's the same schematic I found after a search,

, and here's an idea of me working on it:

. Suffice to say I haven't cracked it. If anyone can help, I don't know how, but I need some... Oh, maybe a breadboard diagram and verifying it should work, that would help!

 

[jcurrie]

far from a expert on this but the 27k ohm resistor on pin two of first IC to pin 6 of second IC is bypassed on the schm. you posted don't know if it makes a diff.
jc

 

[Scruffneck]

far from a expert on this but the 27k ohm resistor on pin two of first IC to pin 6 of second IC is bypassed on the schm. you posted don't know if it makes a diff.
jc

Thanks, yeah I know, I thought that was odd so when building it I left the bypass until it didn't work then added the bypass after. When I did the breadboard I bought a switch aswell to test for a difference (you might see the switch on the breadboard pic, haha). Anyway, it didn't make a difference but thanks for pointing it out.

I'm really so clueless myself, I made further purchases for a higher voltage 1mF capacitor (63v after 50v), ceramic disc 10nF after trying polyester film, and tantalum bead 100nF after trying 100nF polyester film capacitor. No, I didn't think it would make a difference as I'd already done my preliminary research once it occured to me, but I had to try.

 

[jcurrie]

also noticed that the schm. is running B+ into the reset pin 4 on the 555, try looking up rob paisley's web site he has a circut for a sweeping siren that works you would have to play with the oss circuit to get a horn sound.
jc

 

[Scruffneck]

Ok, got something working. It's not the horn sound yet but it IS sound. The first video clip is my breadboard. The second one below that is the sound I'm after

 

[jpanhalt]

The original circuit you show is bizarre. Can you post the circuit diagram (i.e., schematic) of what you are currently using?

John

 

[Scruffneck]

Hi John, thanks for replying. Let me get back to you with a farad video. That diagram was what I had to work with but I see I only put the medium size copy from imageshack. So I'll put the larger version below here now. One thing I've missed is the diode, it's meant to be a 1N4001 and I only have 3mm led's until tomorrow. I'm just looking up the forward voltage drop now for the farad.com/circuit simulator at 1 amp (e.g. default in simulator is "805.904783m")

 

[Scruffneck]

Just to say, the bypass around the 2.7k R is weird and makes no sense so I think we're basically ignoring it.

 

[jpanhalt]

Pin 2 is trigger, pin 6 is threshold, both are inputs to comparators. Pin 5 in 555#2 is also a comparator input. It is the control voltage for threshold.

If one assumes the bypassed resistor is a silly mistake, which version is correct? The comparators draw almost no current. What is the purpose of the 555 on the left? The one on the right is set up as a simple oscillator (astable), which is why you get some sound.

You seem to want some sort of siren, and I suggest going to a more reliable source like Paisley for a circuit.

John

 

[Scruffneck]

Thanks, I'll have a closer read in a minute what you've said. It's not however a siren I'm trying to make, it's more a DAT VOICE sound, like crows. I think I understand one thing you're saying, as I noticed with the farad sim I could get the same effect by mirroring the resistor setup on 555-2 onto 555-1. Here's the farad sim vid I just made. As you know, I don't have the 1n4001 with a forward voltage of 930mV until tomorrow...

I don't know what difference it will make though yet.