Check this circuit Please  - Page 1
Forum section: electronics / beginners

author: Juan
author_rank: Contributor
timestamp: April 08, 2023, 11:53:06 pm
content: 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 .

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 09, 2023, 12:02:10 am
content: How far from the horn tweeter to the bats?92dB SPL @ 1m will fall away to about 68dB SPL 16m away.

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 12:04:53 am
content: 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 .

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 09, 2023, 12:13:57 am
content: Quote from: Juan on April 09, 2023, 12:04:53 amYou'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/

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 12:33:57 am
content: 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 .

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 09, 2023, 01:05:22 am
content: 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.

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 01:38:02 am
content: 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 .

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2023, 01:41:40 am
content: 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.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 09, 2023, 01:43:41 am
content: 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?

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 01:58:36 am
content: Thanks for the replies . This is all the info I haveUltrasonic TransmitterThe 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.

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2023, 02:08:15 am
content: 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.

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 02:13:35 am
content: 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 .

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 02:20:23 am
content: Quote from: floobydust on April 09, 2023, 02:08:15 amIf 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 .

author: themadhippy
author_rank: Super Contributor
timestamp: April 09, 2023, 03:10:22 am
content: why not try simulating it ,https://www.falstad.com/circuit/circuitjs.htmlis simple to use and will give an idea of whats going on

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2023, 03:54:05 am
content: 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.

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 04:41:52 am
content: 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 .

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 04:45:52 am
content: Quote from: floobydust on April 09, 2023, 03:54:05 amOK 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 .

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2023, 04:59:50 am
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: April 09, 2023, 05:25:17 am
content: Given that description (Juan'sreply #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 versionIt 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.LTspicesimulations attached.* Add a diode across the discharge resistor, cathode to the timing capacitor, so the charging time can be shorter than the discharge time.

author: Ian.M
author_rank: Super Contributor
timestamp: April 09, 2023, 05:49:16 am
content: 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!

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 07:12:13 am
content: Quote from: floobydust on April 09, 2023, 04:59:50 amThanks so much this gives me more options . I will order another breadboard and try again but it will take some weeks to arrive .

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 07:13:32 am
content: Quote from: Ian.M on April 09, 2023, 05:25:17 amThanks so much this gives me another option to try . Ordering a new breadboard .

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 09, 2023, 07:24:11 am
content: 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).

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 07:47:40 am
content: Quote from: Ian.M on April 09, 2023, 05:49:16 amOK thanks for the tip , It's not against the law to drive bats away where I live .

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 07:52:57 am
content: The speak will be a compression horn tweeter rated to above 30khz .

author: Juan
author_rank: Contributor
timestamp: April 09, 2023, 08:06:26 am
content: This is a lot to process and my head is spinning a bit . I am not that smart anyway .This is the best forum on the net because I have tried most of them and got almost no usable help from the others . Thanks to everyone and I will get back to you on any results when I can .Feel free to keep posting if any new ideas come up and I will check in when I can .Obrigado .

author: Juan
author_rank: Contributor
timestamp: April 11, 2023, 11:51:13 am
content: I have redrawn the circuit with reference to the advice as best I can and changed the power transistors to higher current devices which I can buy . I could not find BD131 or BD132 Transistors .Does this look a better circuit ? Hope I have it right now . I will try this one first before making any radical changes.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: April 11, 2023, 12:23:46 pm
content: Do you really want to drive those transistors without anything to limit the base current? Poor 555's might cook a bit.

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2023, 12:41:09 pm
content: Yes, BD131 and BD132 are no longer in production by NXP (Philips), and although there is still limited production from lesser known 3rd party manufacturers, there's certainly no point in paying the premium for Philips N.O.S. for a new build. The only issue is the lower current gain (BD175: hFEmin. 15 @1A vs BD131 hFEmin. 20 @2A) but odds are you'll get away with it for a one-off as that's a limiting value and the typical hFEis usually a bit higher - the graph in the datasheet says hFEmin|30 @2A, and worst case it would simply have a bit less output power.Have you got an oscilloscope or at least some means of measuring frequency up to say 100Khz? (e.g. a decent DMM with a frequency range) If not you are going to have a hard time verifying the circuit is operating correctly. The easiest option if you don't is temporarily replace C1 and C4 with 100nF parts which will bring the frequency down by two orders of magnitude to where you can certainly hear it. 10nF for a one order of magnitude reduction would *probably* be enough, unless you have high frequency hearing loss.@DrGeoff: they are emitter followers, so the base current is limited to Iload/hFE- simply don't overload the output!

author: Juan
author_rank: Contributor
timestamp: April 11, 2023, 01:08:31 pm
content: Sorry no oscilloscope . The data sheet for the BD 175 /176 says it can handle 3 amps collector current and they will be on large heat sinks . As I said before the exact frequency is irrelevant as long as it's reasonably close .Thanks for the heads up on the 555 not overheating in the circuit that had me worried again .If I place a candle in front of the tweeter horn it should tell me if it's working or I can detune it as you mention .What load could I put on the output ? One 8 ohm tweeter or two ?

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2023, 02:21:54 pm
content: If they are moving coil tweeters, try 2x 8 ohm in series initially (for nom. 16 ohms) , and check how much current it draws from the battery. If its under about 1.2A, you could remove one of them. I don't think it could ever drive two in parallel.

author: Juan
author_rank: Contributor
timestamp: April 11, 2023, 11:10:13 pm
content: Quote from: Ian.M on April 11, 2023, 02:21:54 pmOK that a really important tip . I would have made a bad mistake there , thanks . I am not sure about the moving coil part . I was going to use a compression horn tweeter that shows a good response at 30khz something like a Motorola KSN1025A or B , a Piezo device , if available or a replacement , other than that I don't know much about speakers in general .What other tweeters do you think would be suitable ? I thought a horn type device would project the sound better than a dome tweeter . I could be wrong . I am sure you will steer me straight . I checked my Digitech multi meter and it does indeed have a frequency test . 5 khz to 10 mhz 1.2% accuracy at 50khz . How I use that properly I don't have a clue . The instructions are very poor. I guess I put the negative probe on the negative side of the circuit and the positive probe on the output pin of the 555 . Does that sound right ?

author: Ian.M
author_rank: Super Contributor
timestamp: April 12, 2023, 12:01:43 am
content: For a Piezo horn, I'd just connect one. N.B. a Piezo element that isn't tuned to resonance is typically a very capacitive load - so it is likely to pull large current spikes from the supply every time the H-bridge switches, and may overheat the transistors.Check the supply current - it nearly all ends up going through the transistors, with one digonal pair on at a time, so if that's under 1A and the transistors aren't heating up (especially the upper ones) you are probably OK.

author: Juan
author_rank: Contributor
timestamp: April 12, 2023, 12:56:02 am
content: Ok , so if a speaker is moving coil type I can use two 8 ohm in series connection for approx 16 ohm total .If speaker is a Piezo type device then only connect one speaker .Monitor transistors for overheating , check the supply current . They will all be on large isolated heat sinks anyway with conducting paste applied . I learnt that from a previous project .In your esteemed opinion what type of speaker should I use as too many choices tend to confuse me .However I feel I am getting somewhere now , thanks ever so much .