Introduction: Honk Harder - Time Delayed Second Horn
Have you ever wanted to really blast someone to get their attention on the road, but don't want to blast yourself when you lock your car or just need to beep real quick? If so, this is for you!
Is this legal? I'm not an expert, so the burden is on you if you choose to do this project. I would guess that adding a second horn to a vehicle (as long as it's a reasonable one) is allowable in many places, but I'm sure there are others where making a modification like this wouldn't pass inspection if your state/country has one. Be cool!
A good practice when adding something electrically demanding to a vehicle is to use a relay to switch the load. This is a good idea for a couple of reasons: it doesn't put extra load on the existing wiring (which wasn't designed for it, and could blow a fuse or start a fire), it lets you use a small switch for control (instead of switching the entire load), and it can minimize the amount of heavy gauge wire needed by making a shorter run between the battery and the load.
- R1 - 2.2k resistor
- R2 - 0-10k potentiometer
- R3 - 10 k再保险sistor
- C1 - 100uf electrolytic capacitor
- D1 - 10v zener diode
- U1 - IRFZ44 N-Channel Mosfet
These may not be the optimal components to use, but they are what I have on hand. This circuit is almost certainly not the best design for the purpose, but I'm an amateur and like to keep expectations low!
The purpose of the potentiometer is to give some adjustability of the time between powering the circuit and the relay switching on.
上述第一图像演示了施加12V之间的时间延迟和继电器开关。蓝线是电路的“新号角”的一面，而黄色的痕迹是从汽车的现有喇叭的“信号”的一面。有关于信号和继电器开关之间的第二半 - 正是我们希望的。
Second image: Idle
This should show that while 12 volts is always present on the wire from the battery, it is not flowing through the relay
At this point the existing horn has been switched on, supplying 12 volts though the wire at the upper left.
- Voltage is also present and rising at the zener diode. The voltage here rises slowly, the rate is determined by the resistance of the potentiometer and the capacity of the capacitor.
- Current does not flow through the zener diode because the voltage is below it's threshold of 10 volts. Because no current is flowing into the gate of the Mosfet the relay remains open
- At this point the voltage at the zener diode has reached the threshold and it immediately begins conducting
- Now the mosfet completes the circuit allowing current to flow through the coil of the relay
- When the relay closes it switches power to the load (second horn)
No Image: Done
- When the horn is released no more current can flow through the gate of the mosfet, this causes the relay to open and all the action is stopped
Step 3: Putting It All Together
I'm not going to explain exactly how I blobbed this together in too much detail, if you are reproducing this I recommend using the circuit diagram and doing it however suits you. I used a small plastic container to make this somewhat waterproof.
Use a good length of heavier gauge wire (depending on the load) for the battery, ground and load, and you can use a smaller gauge wire for the "signal" as it will carry very little current (probably 50-150 mA depending on your relay).
获取功率从电池：absolutely use a fuse, and
connect directly to the battery. The fuse tap pictured above is not for powering the second horn, it was to pick up the "signal" voltage from the existing horn and would carry a very small current.
Getting the horn "signal":the easy way to do this is to splice into your car's wiring. I didn't want to do that, so I chose to get it out of the fuse box. If car's horn fuse is normally hot you may need to figure out a way to get power from the existing relay instead. This was what happened in my case (the fuse tap was a good idea, but ended up not working out).
This part is easy. Quick beeps of the horn are just like normal, but if you hold it down for more than a half-second or so the second one starts up and makes more noise. Now I've got more options to express myself while I'm driving!
Participated in the
Motor Vehicle Contest