Another pest device needed

[MrDEB]

I added the inverter transistor.
You have several different resistor values.
Going to assemble the BAT REpeller using an LM386 BUT will try out your new values.
I like the performance of your circuit but the heating problem has me concerned. Will try out this circuit w/ new resistor values BUT might still go with the MOSFETS for my CRITTER RIDDER automotive design.
The birds really hate this device. Finally got to try out on a groupe of 6 deer. Pulled within 20 feet, they just looked at me.
TURNED ON the CRITTER RIDDER = they couldn't run fast enough. Ran about 40-50 feet then just kept walking away looking back at me.
Seems horses are slightly annoyed as are cattle.
Still waiting to see if this thing is legal on the highway.

 

[audioguru]

I calculated the new resistor values so that little BC337 and BC327 transistors (or 2N4401 and 2N4403) can drive a piezo load with 100mA peak when the supply is 9.0V.
The output will be about 17.8V peak-to-peak as shown on an oscilloscope. Nothing gets warm.

If you use an LM386 amplifier with a 9V supply the output will be only 7V peak-to-peak. The difference is 6.5 times less power.

 

[MrDEB]

For this BAT APP I really don't need alot of volume as the space is indoors in an attic.
Thanks for recalculating resistors. Sounds like you actually built the amp?
Have Boncuks design. but will rewire as per your new schematic as I am going with the LM386 for the BAT APP. (I like the sound of BAT APP.-lol)and its compact size and ease of assembly and cost as this BAT APP is a free gratis
Will let you know results on the new amp design but I take your advice as bible.
If it works as hoped maybe I will not bother with the MOSFET design?

 

[MrDEB]

Well the LM386 with 200 gain (cap across pins 1 and 8 works rather well.
Now seeing how a bunch of old bats like me hang out here (lol) was thinking of having this BAT APP output sound either randomly or every 10 minutes or ??
This would "confuse" the bats maybe plus allow the unit to last longer instead of running 24/7
Using the CRITTER RIDDER code for a 18F1320 (programed to randomly output desired frequencies, in this case 18-26khz) so adding a timer would be a simple matter of a few lines of code.
Looking at other repellent circuits that use a 555, 4017, 4013 etc, using a pic saves lots of silicone chips.
any suggestions on time on/time off?

 

[Boncuk]

Hi MrDEB,

just for your info: Bats can produce frequencies between 9 and 200KHz.

Since 9KHz is within the audible range of humans I recommend to start at 16KHz and extend the sweep up to 200KHz.

Be aware that dogs can hear 16KHz pretty well. 16 to 20KHz are used for dog whistles by hunters in Germany.

Boncuk

 

[MrDEB]

Have been there done that on my CRITTER RIDDER version 2. Version 1 is only audiable. Version 2 has ultrasonic 15-20khz. Deer seem to have a quicker response.
As I mentioned several posts back, the "bat box" as some of the parishioners call it, seemed to affect small children. Very uneasy "misbahaving at mass.
The bat box was located in an occupied area. This "BAT APP" as I call it will be placed in the belfry attic space away from the occupied area adjecient to the choir loft.
My big decission now is run it 24/7 or maybe 10 miniutes on, 20 miniutes off or ??
Thanks for your input.
What do you know about Swordfish basic and DS18B20 temperature sensors? Trying to get some code to see my sensor.

 

[audioguru]

Well the LM386 with 200 gain (cap across pins 1 and 8 works rather well.

Why is the gain so high at 200? Then is its input only 0.01V peak from a microphone?

Its max allowed input voltage is only 0.4V peak. If you are feeding it 3.85V peak from a 555 or 2.5V peak from a micro-controller then the input voltage is way too high and will probably destroy its input transistors.

You need two resistors to attenuate the input to a little less than 0.4V peak and use a gain of 20.

Why use an LM386 power amplifier? A piezo tweeter or a few in parallel can be driven directly from a 555 that has a little more output level than an LM386.

 

[MrDEB]

powering the 555 off of 5v and the PIC off of 5volts. Using the 555 as a test signal but going to use a 18F1320 for final unit.
The LM386 off of 9v
can remove the cap between pins 1 and 8 to reduce gain to 20. Not much difference in volume. A little louder but not much.
Reason for the LM386 - very few parts needed, had one on hand and project is free gratis.
You suggest adding resistors to input?
I have a coupling cap between the 555 output and LM386 input. NO volume control resistor and no cap on output. Do have a 10ohm,cap in series to ground on the output of LM386 as per data sheet.
Probally should conjure up a schematic?

 

[audioguru]

The output voltage of a 555 and of a PIC are much more than the 0.4V peak max allowed input for an LM386 power amplifier. The over-voltage will probably destroy the input transistors of the LM386. So of course you must make an attenuator with two resistors.

The PIC will have an output of 2.5V peak if it feeds its signal to the LM386 through a coupling capacitor. Then the two attenuator resistors at the input of the LM386 are 10k in series with 1.8k to ground. The PIC feeds the 10k resistor and the input of the LM386 across the 1.8k resistor will be 0.38V peak.

 

[MrDEB]

something like this?

quick schematic for changes
This is all new to me.

 

[audioguru]

Nope.
Do it like this:

 

[MrDEB]

Revision to amp circuit posted

Looking at the revised amp circuit you posted, I noticed that you had to-92 cs transistors for all.
My worry is overheating as presently all the transistors are getting hot as well as the resistors.
I revised the power transistors to TIP31 and TIP42 (to-220 cs) and used 2n4401's for others.
This is ment for an automotive app thus 12-14 volts BUT think the output is really high so inserting a 9v reg thus the amp to run on 9v.
Let me know if any other suggestions
THANKS

 

[audioguru]

Your cheap no-name-brand piezo tweeters have no important spec's.
I have the sales sheet for a name-brand piezo tweeter that lists the capacitance at 0.13uf. Then at 20kHz it is a load of 62 ohms. With a 12V supply, the peak current is only 190mA and the little transistors I selected have a max current rating of 500mA to 800mA.
How many piezo tweeters will one amplifier be driving?

The TIP31 and TIP42 transistors switch 100 times slower than little transistors so when driving the easy load of a piezo tweeter they are ramping (instead of quickly switching) which makes them get hot. Also, the slowly switching transistors short circuit the supply for a certain amount of time when one side is turning on and the other side is still turning off, which also heats them.

 

[MrDEB]

That makes sense.
What brand, source of tweeter dids you buy and aprox cost.
The cheapy tweeters I bought are basically for building a proto-type.
IF I can get a good price on some better tweeters then great but they have to be low cost and weather proof (plastic)
Have a little extra money so I can purchase some better parts. I had a hunch the switching aspect might be causing the heating as you suggested in an eairler post.
Thinking that if I go with 14 volt for the amp instead of 9v, how much louder?(trying to keep costs down by not using another regulartor

 

[MrDEB]

Forgot - am driving two tweeters in parallel.

 

[MrDEB]

I forgot to mention that this amp has a PIC as its input so input = 4.5v not 7.4.
You or I got confused as working on two separate aps.
am going to hopefully recalculate to achieve same current draw on all using 4.5v input voltage and 14v power

 

[MrDEB]

revised for 14volts

hope this is right?
Need to order parts.
Thinking of using 1/2 watt resistors but not really needed.

 

[MrDEB]

I THINK I caculated R5 and R2 wrong.
When Q7 is ON then 14v to ground = 2680 ohms (disregard transistor loss) then at 9v =R5 has 13ma
with 14v R5 has 20ma
recalculating at 14v so I have 1.3ma R5 and R2 should be = 2168 each
RIGHT or WRONG AGAIN?

 

[EDSONCAN]

Hi
I use a KA2148, look in my site **broken link removed**
Edson

 

[MrDEB]

Those are not piezo elements
wouldn't be loud enough for app.