On my previous car I installed a set of Hella Supertones but the were ridiculously loud and I feel even when I just chirped the horn people freaked out. However, I cant argue with how well they worked they saved me a couple times from soccer moms not paying attention. Their earsplitting sound always scares cause people the immediate reaction to stop.

So now I came up with the idea to keep the supertones and the oem horns... rather than having a separate switch for the supertones, I wired up a time delay circuit for .75 seconds. so when I honk first the regular horn honks for .75 seconds before the Supertones are engaged. The best part is it was a simple and cheap to do. I'll post the install once it gets warm enough to put them on the car.

Below is the wiring I had to do, using a 555 IC chip in MonoStable mode.

R2 is a 10 K-ohm resistor and C2 is a .1 uf capacitor
C1 and R1 is what result in the time delay and can be found using the equation T= 1.1*R1*C1
I used a 4.7 uf capacitor and a 147 k-ohm resistor netting me .7599 seconds delay.
I am also considering an alternate setup where after the allotted time the oem horn disengages and the Hella's engage its not that much more complicated just another relay and 2 more diodes.

 

here is the setup for switching from oem to hella's I'm still debating which I am going to do... I think the first way just as a fail safe incase something goes wrong I still have a horn

 

Sound clip?