Check this circuit Please

[Juan]

Hi I am new to electronics and trying to make a circuit that will drive away bats from bush close to my house.
I downloaded the circuit  shown but  had to change IC 1 to a recognizable Astable 555 because the original design was not covered in any 555 frequency calculator . The values in red are what I have calculated using Electronics assistant version 4.31 to get 30 khz . Can someone far more experienced than me check over this circuit and determine if it can work with the design and  values stated . The exact frequency is irrelevant as long as it's reasonably  close to 30 khz so no person  can hear it except the bats . Would really appreciate some help .

[DrGeoff]

How far from the horn tweeter to the bats?
92dB SPL @ 1m will fall away to about 68dB SPL 16m away.

[Juan]

They are in several tees about 8  meters from my bedroom and driving me nuts .
People say to burn drums of oily rags under the trees but I don't want to harm them just move them away and its so  close to my house for all that toxic smoke .

[DrGeoff]

They are in several tees about 8  meters from my bedroom and driving me nuts .
People say to burn drums of oily rags under the trees but I don't want to harm them just move them away and its so  close to my house for all that toxic smoke .

You'd probably need to put the speaker in the trees then.
However, out in Australia the wildlife people used LF pulses to move bats on from the botanic gardens and hyde park areas in the CBD. Sonic LF booms apparently work better to disperse them.
Have you done any experimentation to see if the 30kHz works?

Edit:
Here's an interesting paper using sound to deter bats that might be helpful. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7018087/

[Juan]

OK thanks ,  I can extend the speaker to the trees as its on my land thats not  hard .
No have not had any circuit working yet to try . This one was supposed to have a bit of power like 4 amp output .
The driver transistors will be on heat sinks ,  I have them already . I think its against the law where I live to use low frequency stuff as  it could make people sick . If I can get the circuit checked by someone I could then build it . I don't want to waste any components making mistakes as they are hard to come by .  Thought I would start at 30 khz well above human hearing. I just need to know if the circuit design is correct . If not please correct it .
That paper is too technical for me .

[DrGeoff]

What's driving the transistors on the right (TR2/TR4)?
You have the trigger pin connected to the bases, which is an input to a comparator in the 555.

[Juan]

You are asking me questions I can't answer . I am new to electronics and struggling with it.
This is the original circuit as downloaded from the net .  If you think anything is not correct please draw me a new circuit . I changed IC 1 set up because the original design was not catered for in any frequency calculator that I could find  .

[floobydust]

That schematic is wrong, you can see the outputs pin 3 of two 555 timers is connected together- so they will arm-wrestle and get hot.
Swap pin 2, 3 on IC2 I think is the correction.

[DrGeoff]

At first glance I'd say the trig and op pins of IC2 are reversed.
What is the idea of the circuit, it looks like it gives a 16us burst of 30kHz triggered by the 30kHz waveform.
What are you hoping for?

[Juan]

Thanks for the replies . This is all the info I have
Ultrasonic Transmitter
The ultrasonic transmitter  uses a standard 555 timer IC1 set up as an oscillator using a single RC network to give a 40 kHz square wave with equal mark/space ratio.

This frequency is above the hearing threshold for humans .  Since the maximum current that a 555 timer can supply is 200mA an amplifier stage was required so a high-power H-bridge network was devised, formed by 4 transistors TR1 to TR4. A second timer IC2 forms a buffer amplifier that feeds one input of the H-bridge driver, with an inverted waveform to that of IC1 output being fed to the opposite input of the H-bridge.

Circuit diagram:

This means that conduction occurs through the complementary pairs of TR1/TR4 and TR2/TR3 on alternate marks and spaces, effectively doubling the voltage across the ultrasonic transducer, LS1. This is optimised to generate a high output at ultrasonic frequencies. This configuration was tested by decreasing the frequency of the oscillator to an audible level and replacing the ultrasonic transducer with a loudspeaker; the results were astounding. If the bat repellent circuit was fed by a bench power supply rather than a battery that restrict the available current, the output reached 110dB with 4A running through the speaker which is plenty loud enough!

The circuit is  activated using a normal open switch S1 to control the current consumption, but many forms of automatic switching could be used such as pressure sensitive mats, light beams or PIR sensors. Consider also using a lead-acid battery if desired, and a single chip version could be built using the 556 dual timer IC to save space and improve battery life.

[floobydust]

Some bat species echolocate below 35kHz, others are above. It would be good if your circuit frequency was adjustable.
On the question of the duty cycle (for the second 555), I found this:
"Anti-bat ultrasound production in moths is globally and phylogenetically widespread"
tldr: "We found that animals that produce ultrasound to playback of bat attack {e.g. moths} emit frequencies centered around ~65 kHz
[± ~40 to 110 kHz at 15-dB range; matching the frequency of best hearing in most bat species (39, 40)] and a substantial range of duty cycles..."
"...duty cycles of at least 18% (this parameter is sensitive to analysis approaches) seem to be necessary to interfere with the processing of returning echoes from echolocating bats"

I think the original circuit was trying to conserve some power with the second 555 keeping the duty cycle slim. So it should be supporting that (at least 18%)? But this is for the moth's to elude detection? Not sure.

[Juan]

From what I understand and that is not much IC 2 acts as a 1 shot that delivers a pulse when IC1 waveform is negative or something like that . The idea I think is that the push pull waveform goes above and below the 0 volts line and doubles the output on the speaker.
All I want is a loud high frequency noise that humans can't hear . I don't have any pets anymore and my neighbors area good distance away so it's practical if I can just get a good circuit  . 

[Juan]

Some bat species echolocate below 35kHz, others are above. It would be good if your circuit frequency was adjustable.
On the question of the duty cycle (for the second 555), I found this:
"Anti-bat ultrasound production in moths is globally and phylogenetically widespread"
tldr: "We found that animals that produce ultrasound to playback of bat attack {e.g. moths} emit frequencies centered around ~65 kHz
[± ~40 to 110 kHz at 15-dB range; matching the frequency of best hearing in most bat species (39, 40)] and a substantial range of duty cycles..."
"...duty cycles of at least 18% (this parameter is sensitive to analysis approaches) seem to be necessary to interfere with the processing of returning echoes from echolocating bats"

I think the original circuit was trying to conserve some power with the second 555 keeping the duty cycle slim. So it should be supporting that (at least 18%)? But this is for the moth's to elude detection? Not sure.

If I can get it working I can adjust the components to higher or lower frequencies .
Can we please just forget about the bats for now there is over 100 species here . I just need to get the circuit fault checked . So I have a chance of getting it to do something . 

[themadhippy]

why not try simulating it ,  https://www.falstad.com/circuit/circuitjs.html is simple to use and will give an idea of whats going on

[floobydust]

I think the original circuit sucks, seems to be another fake Interweeb circuit that is a hack, full of mistakes. I can see original Elektor graphics but could not track it down, typo's included- it must be from a summer circuits special with Photoshop as well.
To fix:
C2 goes from pin2+6 to GND, 10nF and that (first) R2=2k2 for bipolar 555 to give ~32kHz around 50% duty-cycle from IC1.
IC2 trigger to IC1 O/P, IC2 pin 3 to TR2/TR4. Original 1k/10nF work OK. IC2 is just acting as an inverter.

Note this is a lot of ultrasonic power! I would add a warble-tone and use much less speaker drive, as an experiment.

[Juan]

Thanks but you have to know a lot to use it , way too difficult to work out and I could not see any 555 circuit that matched .

[Juan]

I think the original circuit sucks, seems to be another fake Interweeb circuit that is a hack, full of mistakes. I can see original Elektor graphics but could not track it down, typo's included- it must be from a summer circuits special with Photoshop as well.
To fix:
C2 goes from pin2+6 to GND, 10nF and that (first) R2=2k2 for bipolar 555 to give ~32kHz around 50% duty-cycle from IC1.
IC2 trigger to IC1 O/P, IC2 pin 3 to TR2/TR4. Original 1k/10nF work OK. IC2 is just acting as an inverter.

Note this is a lot of ultrasonic power! I would add a warble-tone and use much less speaker drive, as an experiment.

OK I will try those changes but I want power to throw as far as possible.
Is their anyone who could bread board the circuit for me and get it going at a lower audible frequency to prove it . I have never had any luck with bread boarding I think mine is faulty .

[floobydust]

I added a schematic with the corrections to the original one. You can simply make C3 2-10x larger say 100nF to make this audible.
If your breadboard dows not work, post some pictures we can figure it out.

[Ian.M]

Given that description (Juan's reply #9), the original circuit seems rather bogus. 

Apart from the swapped Trig and Out pins DrGeoff noted above, there are duplicated component designators 'C1' and 'R2', indicating little care was taken drawing the schematic.

That timing circuit configuration with a single timing resistor connected to Output will only give a 50% duty cycle if you use a CMOS '555'.  If you use a bipolar NE555, its output can never get higher than 2 Vbe drops from the Vcc rail, and droops considerably more under load, as its high side output transistor is a NPN Darlington pair.   This has the effect of increasing the time it takes to charge the timing capacitor  to 2/3 Vcc (with respect to the time to discharge from 2/3 Vcc to 1/3 Vcc), so making the output high period longer and decreasing the frequency.   

Edit: You don't *want* to use a CMOS '555' as although they'll drive rail-to-rail unloaded, they typically have much lower output current capability than a bipolar NE555 or direct equivalent, so will be incapable of providing sufficient base drive to the simple transistor H-bridge if  it is heavily loaded.

The 1nF value of IC1's timing capacitor 'C1' is suspect - as-is I believe it will oscillate at hundreds of KHz, highly dependent on propagation delays in IC1.   The mismatch with the time constant of IC2's timing network results in a very odd highly asymmetric waveform across the speaker.  Changing it to 10nF, same as C4, gives simulation results of 60KHz and a much better waveform but the LTspice NE555 is ideal so, even though I added two diode drops to the output to simulate droop, with the propagation delays of a real NE555, wide tolerance resistors and capacitors at the upper end of their tolerance range, and a heavy load on the output causing excessive droop, its conceivable that it could have operated at 40KHz.

However a 555 can be used as an inverter without *any* timing network so I propose a simplified version

It will give a better squarewave, and has a lower component count. If you cant get it up to the desired frequency, decrease R1. 

I think that chirping it is a good idea, both to be more effective at annoying the bats, and to reduce power consumption and heating of the tweeter voice coil.  A third 555, setup for about a 10% duty cycle in the traditional 555 astable circuit^* at a few tens of Hz, with its output connected to the Reset pins of both 555s driving the bridge could do that.

LTspice simulations attached.

* Add a diode across the discharge resistor, cathode to the timing capacitor, so the charging time can be shorter than the discharge time.

[Ian.M]

N.B. Bats are protected in many developed countries (e.g. All native bat species in Europe are protected), and disturbing them in their roost may be a criminal offense, so anyone wishing to experiment with circuits of this type in countries with bat protection laws prohibiting disturbing bats, should keep the output power down (e.g. reduce the supply voltage) and not use them near any known bat roosts, or near groups of feeding bats. 

Also, high intensity ultrasound may cause temporary or permanent hearing loss, so be careful, partially mute the transducer with several layers of towelling over it while bench testing, and use earplugs!

[Juan]

I added a schematic with the corrections to the original one. You can simply make C3 2-10x larger say 100nF to make this audible.
If your breadboard dows not work, post some pictures we can figure it out.

Thanks so much this gives me more options . I will order another breadboard and try again but it will take  some  weeks to arrive .

[Juan]

Given that description (Juan's reply #9), the original circuit seems rather bogus. 

Apart from the swapped Trig and Out pins DrGeoff noted above, there are duplicated component designators 'C1' and 'R2', indicating little care was taken drawing the schematic.

That timing circuit configuration with a single timing resistor connected to Output will only give a 50% duty cycle if you use a CMOS '555'.  If you use a bipolar NE555, its output can never get higher than 2 Vbe drops from the Vcc rail, and droops considerably more under load, as its high side output transistor is a NPN Darlington pair.   This has the effect of increasing the time it takes to charge the timing capacitor  to 2/3 Vcc (with respect to the time to discharge from 2/3 Vcc to 1/3 Vcc), so making the output high period longer and decreasing the frequency.   

The 1nF value of IC1's timing capacitor 'C1' is suspect - as-is I believe it will oscillate at hundreds of KHz, highly dependent of propagation delays in IC1.   The mismatch with the time constant of IC2's timing network results in a very odd highly asymmetric waveform across the speaker.  Changing it to 10nF, same as C4, gives simulation results of 60KHz and a much better waveform but the LTspice NE555 is ideal so, even though I added two diode drops to the output to simulate droop, with the propagation delays of a real NE555, wide tolerance resistors and capacitors at the upper end of their tolerance range, and a heavy load on the output causing excessive droop, its conceivable that it could have operated at 40KHz.

However a 555 can be used as an inverter without *any* timing network so I propose a simplified version

It will give a better squarewave, and has a lower component count. If you cant get it up to the desired frequency, decrease R1. 

I think that chirping it is a good idea, both to be more effective at annoying the bats, and to reduce power consumption and heating of the tweeter voice coil.  A third 555, setup for about a 10% duty cycle in the traditional 555 astable circuit^* at a few tens of Hz, with its output connected to the Reset pins of both 555s driving the bridge could do that.

LTspice simulations attached.

* Add a diode across the discharge resistor, cathode to the timing capacitor, so the charging time can be shorter than the discharge time.

Thanks so much this gives me another option to try . Ordering a new breadboard .

[DrGeoff]

An 8 ohm moving coil speaker? Pretty inefficient at 30kHz. You might be better off with a piezo horn device which can be more efficient at 30kHz. And they are usually quite cheap and almost indestructible (at least at this power level).

[Juan]

N.B. Bats are protected in many developed countries (e.g. All native bat species in Europe are protected), and disturbing them in their roost may be a criminal offense, so anyone wishing to experiment with circuits of this type in countries with bat protection laws prohibiting disturbing bats, should keep the output power down (e.g. reduce the supply voltage) and not use them near any known bat roosts, or near groups of feeding bats. 

Also, high intensity ultrasound may cause temporary or permanent hearing loss, so be careful, partially mute the transducer with several layers of towelling over it while bench testing, and use earplugs!

OK thanks for the tip , It's not against the law to drive bats away where I live .

[Juan]

The speak will be a compression horn tweeter rated to above 30khz .