When you're cycling, it's important to have some kind of sounding device. A bell can be heard by pedestrians and cyclists but to be heard by drivers, you need something louder such as a horn. Car horns can be heard by drivers when their windows are rolled up. In this setup, the horns were attached underneath a bike basket and the battery and relay were stored in the basket.


  • 112 dB @ 1 metre
  • Combined high and low note horns for better perception
  • Handlebar mounted horn button
  • On/off switch to prevent accidental horn trigger when stored in public places such as public transit

Step 1: Materials

The parts can be found at hardware stores, electronic component stores, and battery stores. Canadian Tire and Lee's Electronics carry the materials.

  • Bicycle with a fixed front basket (The basket should be made of thick metal wires.)
  • 6 - position terminal block
  • Horn button
  • Twin car horns (The FIAMM El Grande horns were used. Select a high and a low note horns. Horns with grill covers are easier to install as they have more areas to tie to.)
  • 12V sealed lead acid battery (The battery should be at least 1.2Ah. I used a 4Ah battery and it worked well. If you're not sure that the battery can be used, read the data sheet or test it by connecting it with the two horns. It has to be able to supply at least 12A to the horns.)
  • Pair of two-wire connectors
  • FIAMM 12V 30A relay
  • 20A fuse
  • In-line fuse holder
  • 18 AWG wires
  • 22 AWG wires
  • On/off switch
  • Crimp connectors
  • Screws
  • Nut
  • Washers
  • Box
  • SLA battery charger (The 12BC0500D charger was used. A smart charger is recommended for battery longevity because it stops charging when fully charged.)
  • Cable ties
  • Tape
  • Plastic film
<p>Your parts list is excellent.</p><p>I upgraded the weak little horn <br>in my Toyota, and plan on using the original beeper on a city bike one <br>of these days. I think this is a good approach (if you own a car). That <br>way you get a LOUD horn in the car and a much smaller lighter one on the<br> bicycle, that's still loud enough for a bicycle. I will dig around and <br>find the horn later today and add a picture for you. </p><p>The problem with super loud horns on a bike are (1) they are bulky and heavy (2) they are SO loud you will refrain from using them after watching the hair stand on end of the car driver in front of you a few times -- this can be satisfying sometimes but most of the time you want something loud but not painfully loud else it becomes a weapon instead of a signalling device. </p><p>If you <br>integrate a 12v lighting system then you can more easily justify <br>carrying a 12v battery around for the horn. I am especially fond of the <br>many options for 12v LED running lights available now. I have had good <br>luck finding them at Superbrightleds.com. Look for &quot;rectangular truck running lights&quot;. Use RED on the back and AMBER on the sides and possibly front. White belongs ONLY on the front. Blue is for emergency vehicles ONLY.</p><p>I4AH <br>or 5AH battery is plenty big enough for both lights and horns. In fact, you can <br>add a 12V-USB adapter and power up a smartphone too. I wish I could go with lithium batteries. There are really nice 12v lithium iron phosphate batteries out now too. Lightweight but too expensive for me (did I mention I have a Toyota not a Tesla? :-)</p><p>My favorite <br>battery charger for this kind of set up is the Battery Tender Junior. The one you choose it probably the same for all practical purposes. Just another option.</p><p>My<br> favorite connectors are Anderson Powerpoles. If you use powerpoles you can completely eliminate the terminal strip from your set up. Your approach is a little more flexible but harder to mount and possibly more prone to short circuits. You can eliminate the separate charging connector, the terminal strip, and the metal box. To charge you just unplug the battery and plug in the charger. Been doing this with ham radio set ups for years now. Works great.</p><p>You said &quot;put the fuse close to the battery&quot;. Great advice! I put ATC fuseholders ON the battery, I tape them down permanently to the top of the battery so they are always in the circuit. (I don't PLAN on blowing fuses so having them taped down is okay.) Then the output from the fuse goes to a powerpole connector, this makes swapping out or disconnecting the battery really easy. I usually buy powerpoles from West Mountain Radio.</p><p>Fuse holder suggestion: </p><p><a href="http://www.allelectronics.com/make-a-store/item/fh..." rel="nofollow">http://www.allelectronics.com/make-a-store/item/fh...</a></p><p>All Electronics has a good price on the relay too: </p><p><a href="http://www.allelectronics.com/make-a-store/item/rly-718/12-vdc-30a-spst-n.o.-relay/1.html" rel="nofollow">http://www.allelectronics.com/make-a-store/item/rl...</a></p><p>Using foam to pad the battery is a good idea. </p><p>Solid state relays are more finicky generally. Building your own (say using a MOSFET transistor) is not worth it. Mechanical relays are very, very reliable and cheap as long as you don't let them fill up with rain water. (Yep. Happened under the dash in my '71 VW bus! Leaky windshield seal. And they will even work when filled with water for about a month... that's how reliable they are.)</p><p>Cheers and keep riding!</p>
<p>I might use the battery for spare lights. If you're running bike lights with SLA, you would have to top it up every ride to prevent sulfation. Deep cycle batteries would be better. Battery backups always float charge their lead acid batteries. Solar charging might be more convenient because it charges while your bike is parked.</p>
<p>I use a bell when passing cyclists and pedestrians. An effective horn should cause a driver to brake. I find that I tend to pulse it because they are close to my ears and unmuffled. When the windows are up or the stereo is on, the horn needs to be loud. To test it, you can have someone blow the horn while you're in a car. The times that I use it include a car about to turn right in front of me and pull outs without slowing down. Usually they stop. When I'm near conflict zones, I slow down so that I can see if the cars have stopped or there's a safe gap. Ride safely.</p>
<p>Thanks for the ideas!</p>
Great idea for Vancouver, BC. In my experience they are the worse drivers I have ever seen. I am curious as to the weight of the lead acid battery. As well as my bike I would be very interested in putting this on my Motorino scooter. Motorino makes good scooters with crappy lights and an even worse horn. Thanks
Here are the details for a 12v 4ah SLA BATTERY.<br>http://leeselectronic.com/product/81045.html?search_query=Sla&amp;results=27
<p>wonderful day!</p>
<p>Whats all the junk and scraps of paper? Camouflage?</p>
<p>Camouflage and insulation.</p>
<p>Hey, camo is an important component of any city bike to reduce the risk of theft. Also parking next to fancy bikes when possible helps. Hmmm. horn could be part of antitheft system... hmmm.... </p>
<p>This will defineteilly draw everyone's attention ;-) </p>
<p>This seems like a really great idea. Definitely will make the roads safer for the cyclists!</p>
great idea; you should patent it and sell it

About This Instructable




Bio: Autistic person who's interests include in utility cycling, recreational cycling, cycling safety, electronics, gardening, Arduino, and LEDs.
More by hanlin_y:78.125 KHz ATtiny85 Based Boost LED Driver Sunrise Simulator with Adjustable Lamp Colour and Intensity Wiring a Tactical LED for an External Power Source 
Add instructable to: