Back to repelling bats

[MrDEB]

Have a request for a bat repellent device. Back to this circuit using a 9v 200 ma wall wart and Audios suggested circuit for the LM386
outputting to a piezo tweeter.
any other suggestions before I etch a circuit board?
want to add an LED to indicate when the unit is outputting ultrasonic sound every 5 minutes for 1 minute.

 

[audioguru]

The output of the LM386 amp is only 6V to 7V p-p with a 9V supply. If you use a TDA7822M bridged dual amp instead then the output will be 14V p-p with a 9V supply.

 

[ronv]

I don't know what the output level is from IC1, but I bet you want the 1.8K on the other side of the 10K so it will attenuate the signal before the 386 amplifies it. Even using 12 volts for the 386 would help chase away the big bats.

 

[MrDEB]

Having to use what I have on hand.
Was looking at using the circuit w/ 2-NPN and 2-PNP transistors but would need to purchase more parts.

 

[ronv]

I bet you want the 1.8K on the other side of the 10K so it will attenuate the signal before the 386 amplifies it.

 

[MrDEB]

the circuit I posted was suggested by Audio Guru (the one on the right w/ white background.
I wondered why the 10k is on top?
Perhaps Audio Guru could shed light on why?

 

[ronv]

I don't know what the output level is from IC1,

If the output is 5 volts and the 386 has a gain of 20 it will try to make its output 100 volts, but since you only have 9 volts it can't do it so it will just go bang bang.

 

[MrDEB]

see post #2

"The output of the LM386 amp is only 6V to 7V p-p with a 9V supply. If you use a TDA7822M bridged dual amp instead then the output will be 14V p-p with a 9V supply. "

 

[audioguru]

The coriginal circuit with a black background has the 10k resistor is the wrong location.

The 10k to 1.5k (1.8k in parallel with the 50k input resistance of the LM386) attenuates the 5V p-p output of the microcontroller to 652mV p-p. The LM386 has a voltage gain of 20 so its output will try to be 13V p-p but will clip at 6V to 7V p-p with a 9V supply.

 

[Mr RB]

Just a thought, you could put a LDR light sensor on it so it turns itself on at night.

You can get low quescent current 5v regulators that only waste some microamps, and leave the PIC in sleep during the day. The power the LM386 via a transistor from the battery so the LM386 is turned off during the day too.

For that matter, you could turn power to the LM386 off too between output sounds for max battery life.

 

[ronv]

Have a request for a bat repellent device. Back to this circuit using a 9v 200 ma wall wart and Audios suggested circuit for the LM386

He has a power supply, but the dogs might appreciate it.

 

[MrDEB]

I see where I made the mis connection on the 10K
Need to correct.
Presently having issues w/ the board. The toner transfer didn't want to stay put.
I guess a first time for everything.
Having to do lots of trace repair.

 

[Boncuk]

Hi MrDEB,

I'm unable to understand why you want to repel bats.

Bats are useful animals and eat thousands of bugs within one night, bugging you probably at night.

Moreover they are cute to look at if they have settled at the ceiling of a room finding no echo to navigate with.

Opening all windows and doors they will eventually find out their way to freedom.

Furthermore a bat repeller must be able to cover a frequency band of 35 to 120KHz to work properly and have those tiny creatures crash into a wall because of loss of orientation - falling onto the ground and be killed!

My suggestion: Leave the bats alone and take care of more important things. Bats are not harmful to humans!

Just give it a thought.

Boncuk

 

[Mr RB]

The bats I get in my fig tree are as big as cats... They are very noisy and their poops make a splat on the ground as big as your hand. When they fly over your head they make a slow low-freq "shoof shoof shoof" sound from their big wings. If there were "cute little bats" the big bats would just eat them.

 

[audioguru]

I think your big bats are actually prehistoric flying reptiles. They were huge.

 

[Sceadwian]

Has to be a larger species of fruitbat, only they get that large. Net the trees, keeps them from roosting, if they're not persistent enough to rip through the netting they'll be gone in a few weeks.

 

[ronv]

It's not a pretty picture.

Funny, but not pretty.

 

[Mr RB]

Yeah they are fruitbats or "flying foxes" is more technically correct. There are swarms in the tens of thousands that roost about 15 miles from me. The farmers hate them but I don't mind really as the fig tree is 50 yards from the house so they can eat figs as much as they want. People that have date palms next to the house get droppings on their walls and windows etc, that's nasty...

 

[Sceadwian]

As I said, the best way to combat the problem is to net the trees. You'd have to put a transducer in a tree of a few thousand true watts of output to deter. You're basically beating on their ears instead of throwing a net around the tree for roosting protection. Pulses of a few thousand watts or higher on a very short interval may work.

 

[Mr RB]

Well it wasn't me but MrDeb that wanted the repeller device.

Do you really think it would require thousands of watts of ultrasonics to repel bats?

If their ears are sensitive enough to hear the echo of their own voice bounced off a tiny insect, surely even a watt of ultrasonic sound would be incredibly loud and irritating to them? A good HiFi amp at one speaker watt is quite loud, and if that 1 watt was all HF content it would be extremely irritating to humans I guarantee.