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Homemade Ecaller Advice

Ricco

Jan 7, 2015
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Hello All, My first post in here. I'm by no means an Electrician, but I've always had a knack for electrical residential work. Bu this project I could use some help on.

I'm building a homemade Ecaller, its a sound producing device used to call in Predators such as Coyotes.

Here is a link to one of the top of the line Ecallers. http://www.gofoxpro.com/site/products/digital-calls/fusion

As you can see they are pretty pricy.

So here is my plan.

50 Watt Horn here, or a 100 watt horn here.
Battery Powered Amplifier Here

Then an mp3 player with a 1/8 inch stereo jack.

Plug the MP3 player into the amplifier, and the amplifier into the horn. From that point I should be able to take all the contents, put them in a bag and go set them out in the middle of the field and hit play.

Can anyone comment on whether this will work or not?

And my other question is, how do i find out what the output of the amplifier is, do I get the 50 watt horn or 100 watt horn?

Lastly, if I want to control the unit from a long distance, say 100 yards, can I run a signal that far through 100 yards of speaker cable to the horn, or will it degrade across that distance? How can I control the sounds playing and the volume from 100 yards away? Whether wired or wireless.

Any help is appreciated.
 

Gryd3

Jun 25, 2014
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The amplifier you posted in junk ;)
The output is going to be far too low.

As an alternative google around and buy a class-d amplifier board. http://www.ebay.com/bhp/class-d-amplifier-board
They will be able to provide the power you want for the 100W or 50W horn.
You need to supply your own battery, and need to calculate how long you want it to play for.. bigger battery = longer play-time.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Hi there and welcome to Electronics Point :)

Thanks for giving us the background to your project. This makes it a lot easier to give you useful answers right from the start.

Starting from the basics...

As Gryd3 says, that amplifier is totally unsuitable. Its output power will be around 1~2 watts maximum.

The 100W horn speaker you found at Radio Shack has the following specifications, according to the User's Guide that you can download from the product page:

Nominal impedance: 8Ω - this is significant; see below
Frequency response: 350~9000 Hz - is this wide enough for your application?
Power Handling: 50 watts (the 100W rating is the "maximum power handling" specification).

Your battery is going to need to be able to deliver a fairly large amount of power for short periods. Probably a battery of lithium ion or lithium polymer cells would be a good choice. VRLA (valve-regulated lead-acid) (sometimes called SLA) batteries would also be suitable and are fairly cheap, but they are a lot heavier than lithium cells. For example, an array of four 12V 2.4Ah VRLA batteries would occupy about 18 x 14 x 6 cm and weigh about 3.2 kg. That would be the smallest VRLA battery option I would recommend.

Battery voltage is important because in conjunction with the speaker's impedance and the type of amplifier, it determines the maximum power that can be delivered into the speaker.

The best type of amplifier is a class D bridge-tied load ("BTL") amplifier, which actually has two output stages, with the speaker connected between them. This arrangement allows the amplifier to deliver nearly twice as much voltage, and nearly four times as much power, to a given speaker, for a given supply voltage, compared to a single-ended amplifier, and class D amplifiers are a lot more efficient than other types.

If you want to be able to deliver 100W into an 8Ω speaker using a BTL class D amplifier, the amplifier's supply voltage needs to be at least 45V. That's at least thirteen Li-ion cells, or at four 12V VRLA batteries, and they will need to be able to provide about 4A during the loud sounds. The capacity (amp-hours) is not a big factor since the amplifier will only be used periodically, I assume.

Moving on to the amplifier. I found this one on eBay: http://www.ebay.com/itm/TDA8920-CLA...t=US_Pro_Audio_Amplifiers&hash=item3a60929b23

I've downloaded the data sheet for the TDA8920 IC that it uses, and it looks very well suited for your application. It will deliver over 100W into a single 8Ω speaker with a supply voltage of 45~50V. Assuming that board is properly designed and constructed, I would definitely recommend it.

Finally, the question of how to control it remotely. You're right that you would have too much loss if you ran the speaker cable 100 metres. It makes sense to have the battery, the amplifier, and the speaker all together. Running the audio signal 100 metres is also not a good idea.

I would try to find some kind of radio system to send audio from your hiding place to the unit. 100 metres is too far for Bluetooth or Wi-Fi but there will be alternatives. A baby monitor probably wouldn't have that range, and would likely have poor audio quality. A digital system would be best, and it could include circuitry to power the amplifier up and down, to save battery power. Digital walkie talkies might be an answer. We could help you modify them to get a clean signal out of the receiver and feed your MP3 player audio into the transmitter. This one definitely needs more thought.
 

chopnhack

Apr 28, 2014
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Instead of trying to send audio remotely, why not just use some sort of remote control to turn the system on and off? Many 27 and 49MHz are very common and cheaply had. Chances are you could find the remote control from a damaged RC car for fairly cheap or free and scavenge the remote and receiver and use that as your switch. I am not sure of the maximum range and the cheaper toys may be more limited, but from what I understand 27MHz's wavelength is a bit over 35' so it should function out to at least 10 wavelengths, no?
 

KrisBlueNZ

Sadly passed away in 2015
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The reason I suggested sending the audio remotely is that I assumed the OP would prefer to be able to choose the audio depending on the behaviour of the animal(s) he is trying to attract. If he simply wants to play a predetermined sequence of sounds, then an on/off control would be fine.

Edit: Obviously, another option would be to send numbered commands to select from a menu of predefined sounds that are generated at the remote end.
 

chopnhack

Apr 28, 2014
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Very good point Kris. I was going by his press play statement. I agree with your edit and was thinking if the commands from a rc car remote would be adequate: forward, reverse, left and right - 4 distinct "button presses" if you will.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Yeah. I guess all we can do is present some suggestions and let him have a think about it.
 
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