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Another pest device needed

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MrDEB

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Well so far my critter ridder deer repellant seems to work Need to get the Mosfets instead of using transistors. The base resistors get hot quick.
Now another pest (BATS) in church steeple.
Planning on using a pic that outputs varying frequencies but driving the tweeter.
Don't need much of an amp and beside this unit will be running 24/7 so the push pull amp will surly get warm?
how to safely power a tweeter using the pic output.
Thought about using just a 555 but want the variying frequiencies.
maybe just a 2n2222 on output?
The schematic with two transistors, I will only be using one
The mosfet amp I think is before reversing the mosfet input from Vdd.
Hopefully the one 2n2222 will work. Inserting a resistor to limit current as the piezo tweeter has no resistance?
any suggestions
 

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Your transistors will do nothing because they do not have a DC load.

A single NPN transistor needs to have a collector resistor from the collector to the positive supply voltage. The resistor will waste a lot of power making lots of heat. The transistor will not have enough base current from the PIC to drive an 8 ohm tweeter because the collector resistor will be about 8 ohms for half the power to go to the tweeter then the peak collector current is about 3A and the base current must be 300mA.
The max allowed output current from a PIC is only 25mA.
 
Going to use a piezo tweeter
Then why does your first schematic show an 8 ohm tweeter and a piezo tweeter??

The transistor needs a collector resistor to the positive supply because the piezo tweeter does not conduct DC current.
 
revised schematic

Here is revised schematic.
Power supply is a LDO 5v for the PIC Using a 9v dc wal wart
this is going into an attic space so the area is not very big so amplification is minimal.
 

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Connected the piezo tweeter to output of 555 astable pin 3. DMM says .200ma current draw.
I tried using a 2n2222 as in schematic but nothing, no sound.
Running on a 9v battery.
Maybe try the push pull amp with 2n2222 and 2n2904PNP? for more output.
Woried about heat again??
 
Hello Mr DEB, didn't you hear me?
A transistor does nothing without a collector load resistor. A piezo is not a load resistor, it is a capacitor that does not conduct DC current.

A DMM can measure 50Hz or 60Hz accurately. But it cannot measure 10kHz to 20kHz voltage or current without a huge error. It will show a reading that is much too low.
Or maybe you measured the DC current drain of a Cmos 555.

I can't remember if you ever made a push-pull amp that works.

EDIT:
RadioShack knows nothing about electronics or electronic parts. Usually they spec the weight of an electronic part instead of its technical details. Half of their parts don't work properly anyway.
 
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The push pull amp you posted WORKS great

but the base resistors get HOT!
You then suggested using mosfets. Great but not readly available . Would have to order from Mouser.
Contemplating this amp
https://www.electronic-circuits-diagrams.com/homegardenimages/1.gif
here is the mosfet circuit you suggested. Not sure if this has correct source connections. Need to check. I recall you mentioned I had them backwards but not sure the posted schematic here is correct?
 

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but the base resistors get HOT!
Which resistors get hot? Every transistor has a base resistor.

The 33 ohm resistors pass 348mA for half the time so they dissipate 2.0W. Their value is low because the H-bridge circuit had its part values caluculated to drive a 3A motor, not a low current piezo speaker.

here is the mosfet circuit you suggested. Not sure if this has correct source connections. Need to check. I recall you mentioned I had them backwards but not sure the posted schematic here is correct?
All the Mosfets are backwards.
 
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Hi MrDEB,

may be that circuit (with minor changes in frequency) will do the job.

I made it about two years ago for a friend of mine whose car cables were regularly eaten by a marten.

Timer 1 switches the outputs of a decimal counter with different resistors connected to sweep through four frequencies from 60 to 80KHz generated by the second timer. The 4013 divides the frequency by 2 to result in 30 to 40 KHz.

You should use a strong tweeter at the output - otherwise --> poof.

The board is purlely single sided and measures 65X61mm (2.575X2.4inches).

Boncuk
 

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Boncuk's circuit uses a Cmos logic IC to drive the bridge transistors with 13V pulses that are not available from a PIC.

My h-bridge circuit uses 33 ohm resistors and yours uses 50 ohm resistors. Of course they get hot, their value is low enough to drive a 3A motor.
I can't remember the spec's for your piezo tweeters (no-name-brand, no spec's?) but their high frequency current will be much less than 3A so the 33 ohm or 50 ohm resistor values can be increased maybe to 1k ohm and then they will dissipate only 0.07W each.
 
I have some more PNP / NPN transistors from RS

Tip31 and TIP42
I know they are not the greatest but maybe get an idea on performance.
Looking at Boncucks circuit compared to one Audioguru posted.
Basically the same?
 

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Mr DEB,
Frequently, I wonder if you know anything about electronics.
 

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Hi MrDEB,

here is audioguru's H-bridge again, this time including a PCB layout - single sided, as usual. :)

Board dimensions are: 54X32mm (2.1X1.3inches)

I guess a 3A H-Bridge is 100 times overkill for a pest repeller. :D

Boncuk
 

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radio shack only carries one type of mosfet. not even sure if P or N channel.

Radio Shacks only MOSFET is an IRF510 N channel I think (I have some trouble memorising P and N types)

It's a power MOSFET and I'm not sure weather you want to use this in your circuit or not.
 
PLAN is to buy from Mouser. The bat repellent is needed ASAP (I informed my pastor that I could assemble one by weekend.
I have a 555 astable running on 5 volts. Using the amp that Boncuck posted and connecting to 9v to power the amp it amplifies the signal. Need to measure output voltage but my estimate it is 3x louder that just the 555 output.
The H bridge that Audioguru posted works GREAT but need to go with Mosfets as the base resistors R5 & 6 get very hot (2-100ohm 2watt resistors in parallel.
Will try subbing with 1K resistors. Hopefully they won't get hot.Not needed using Mosfets.
But for now going with Boncucks amp as the space I am putting in is relative small.
NOTE one of the mothers in the discussion of the "BAT BOX" stated that when it was running, her two kids were hard to manage ("BAT BOX" device was next to bacloony upstairs adjecent to choir loft. Unit was less than 10 feet from humans on same level. The unit I am building will be placed in the belfry attic space, away from humans. Might still affect?
 
Not the results I was looking for?
4.5v on the 555 and 9v on the amp
A volt meter across the piezo tweeter = .7v
tweeter to ground = 1.7v
I wonder if an LM386 would be easier? Its not like it needs to be loud?
Going to run 15-26KHZ with a 9v wal wart
 
A volt meter across the piezo tweeter = .7v
tweeter to ground = 1.7v
A voltmeter set to AC can accurately measure the sine-wave at 50Hz or 60Hz of the electricity mains.
Measuring the square-wave from this circuit at 10kHz to 20kHz a voltmeter is plain wrong.

Maybe you forgot to add the transistor inverter that drives one side of the H-bridge like this:
 

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