Event Contest Timer. Build and Questions for Improvement

Thread Starter


Joined Apr 18, 2017
I am currently building a contest timer, one that will be used for events.
This is how it will work:
1. The Contestant will "press the button" to start the timer.
2. They will complete the required task to win a prize.
3. Once the Task is complete they will "press the button" to Stop the timer.
4. The person with the best time wins the PRIZE!!!

So far I was able to modify a basic StopWatch (Ultrak 410) and connect it to a button. Please refer to pictures attached.

Need some help for the rest!
My plan is to hook up a horn(a car horn). When the contestant/user "press the button" the horn goes off and the stopwatch starts or stops.

I have attached a diagram of my circuits and voltages. (I do not have much experience in this so it may no be 100% accurate)

My question is:
How can I hook up my horn and stopwatch to the same button. With-ought feeding to much power to the stopwatch?


-The Horn Is Connected to a 12v Battery
-The Stopwatch can only take 2.62v. Anymore power through this and it will no longer work.

I have attached a poorly drawing schematic of the general idea. However this option will not work. There must be correct solution.
Thanks you.

stopwatch.jpg watch1.jpg