How to use the SparkFun Car Horn

Other Hardware General Electronics
1

Hi there!

I'm trying to figure out how to program the SparkFun Car Horns to work: https://www.sparkfun.com/products/10966. They are 12V 8A horns. I guess that means I would need 12V to run them, yes? I'm going to be using anything from a 9.4V to an 11.1V battery to power my Arduino Mega.

I could really use some help in this department. This needs to be light and easy to carry (no car batteries). I tried to find some projects online, but nothing that didn't use a car battery. I know SparkFun used one of their 11.1V Li-Po batteries, but they never released the specs or schematics for it (the Oh Fudge! box).

Any tips?

2

If you look at the spec on the page you linked to it reads...

Rated Voltage: 12V
Rated Current: 8A
Sound Level: 95 - 110db

This means that each horn needs 8A , so 2 horns would need 16 Amps.

You won't need a car battery to deliver this much current, but you do need something quite substantial, depending on how long you want to run the horns for.

I suggest that you look at model aircraft batteries, you can't get 12V, but you can get 11.1V which may be enough.

Lipo batteries can deliver high currents.

I'm not sure if this battery would have enough capacity, it depends on how long you want to run the horns for

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8932

If you are only running the horns for short infrequent bursts, you can probably use a smaller battery.

But. I'd also post a question to the Sparkfun product page to find out if the horns would work on 11.1V

3

Thanks for the reply!

Do you think this will work? http://www.ebay.com/itm/330990442426

I'm planning to use them at short, 1-1.5sec intervals (ON for 1 sec, OFF for 1 sec, repeat).

4

Also, how do I get that 11.1V to the speaker? The Arduino only outputs 5V, yes? Do I just route the power directly to the Arduino AND the horns? So, the positive of the battery would go direct to the speaker's positive AND the Arduino's input power?

I'm going to need a relay in the middle to control the horns as well, yes? Do I need to use the Beefcake relay? Or can I get by with something cheaper?

Thanks for all of the help!

5

$34.95 over $8.50 and you're worried about a $5.00 relay?

6

steinie44:
$34.95 over $8.50 and you're worried about a $5.00 relay?

Haha! I guess you're right :stuck_out_tongue: Forget the "cheaper" part. Do I need the beefcake relay to control these horns? :slight_smile:

7

Use 2 relays e.g.

One for each horn. Each relay is rated at 10A.

Theses relay modules have normally have onto isolated inputs, and don't take much current, so you should only need to use one output pin on the Arduino can connect it to both inputs at the same time.

Btw you need to wire this up with thicker than normal wires. Go to a car shop and buy some wire suitable for car horns.

8

rogerClark:
Use 2 relays e.g.

5V Two 2 Channel Relay Module With optocoupler For PIC AVR DSP ARM Arduino | eBay

One for each horn. Each relay is rated at 10A.

Theses relay modules have normally have onto isolated inputs, and don't take much current, so you should only need to use one output pin on the Arduino can connect it to both inputs at the same time.

Btw you need to wire this up with thicker than normal wires. Go to a car shop and buy some wire suitable for car horns.

Awesome! Thanks! So, it sounds like you're saying I can power one of these "double relays" with the regular 5V from the Arduino? I can get my hands on 12AWG wire. Is that thick enough?

Thanks for being so much help! I'm still learning the electrical side of things :slight_smile:

9

Some of those relay modules run from some use 12V, but they do accept the 5V ON/OFF signal from the Arduino

I just found a 2 relay unit on eBay as an example (I find that no 2 identical things I order from eBay are every quite the same unless I order several of the same item at the same time. It seems to be that these eBay sellers, in China, get the modules from wholesale markets, i.e they buy 50 of them etc and then sell them singly on eBay and make a small profit)

However, I have used these sorts of relay modules and they worked fine, but I can't recall whether they need the 12V as their main supply (i.e the 11.1V for the horns would be OK for this)

Either way, it should work :wink:

10

rogerClark:
However, I have used these sorts of relay modules and they worked fine, but I can't recall whether they need the 12V as their main supply (i.e the 11.1V for the horns would be OK for this)

Either way, it should work :wink:

So, I need to POWER them from the battery DIRECTLY and NOT through the Arduino (since it can only output 5V), correct? I can only CONTROL them with the 5V from the Arduino.

11

The relays I got from eBay are V5 ones, so from what I recall I connected the VCC pin on the relay module to 5V and the input to a pin on the Arduino (and GND to GND) and it worked OK.

The link I sent looks like they are 5V relays (the model number seems to have 05 in it. (actually the description is 5V ....) So you should be able to connect 5V from the Arduino to VCC on the relay.

Either way, you can connect always GND on the LIPO battery to GND of the Arduino and use VCC of 11.1V from the LIPO to the relay modules if 5V Vcc isnt enough.

12

rogerClark:
The relays I got from eBay are V5 ones, so from what I recall I connected the VCC pin on the relay module to 5V and the input to a pin on the Arduino (and GND to GND) and it worked OK.

The link I sent looks like they are 5V relays (the model number seems to have 05 in it. (actually the description is 5V ....) So you should be able to connect 5V from the Arduino to VCC on the relay.

Either way, you can connect always GND on the LIPO battery to GND of the Arduino and use VCC of 11.1V from the LIPO to the relay modules if 5V Vcc isnt enough.

OK, I think I got it. Try powering the relays (I just bought the ones you linked to just now) with the 5V from the Arduino. If that isn't enough power, go with all 11.1V from the Li-Po battery?

Thanks!