There is no mention of output compensation in the text of the data sheet, although I can see a series 50nF/10R on the output in some diagrams which may be intended for stability. I've no idea how to calculate it, but just comparing the values with the ones in my low-pass filter, I think it would lose the upper frequencies that I want.Take a look at the data sheet for some values for the output compensation.
I've tried this - see first message.Also concider the bypass cap shown there.
They are - see first message.If it is powered from a 9 volt battery the filter caps on the supply pin should be large.
I've done so.Keep wires from the output away from the input.
I'm not sure I understand this...When the circuit is working properly no filter should be needed.
Sorry - it would have been more helpful to have attached this in my first message.Maybe you could post your component values.
Haha - I thought it was just me who suspected that!attempting to use LM386's in place of op-amps.....obviously from people who don't know anything about electronics
Surely a 741 would have enough gain to achieve the 20x20 which this circuit does.I'm not sure why it uses LM386s rather than op-amps.
I'm no expert but as I wrote in my first message Surely a 741 would have enough gain to achieve the 20x20 which this circuit does. I think a circuit with a 741 with a low-pass filter, negative feedback, two zener diodes to clamp the output to 0-5 volts, then the 4024 binary counter IC then a 386 for output might work.
so quite appropriate for a low spec antique like me.....I haven't made any circuits for years, so it's just a name I remember!they are low spec antiques
I am a bit puzzled why the designer of the original circuit used 386s, but that might have been why - it saved him having to work out biasing and feedback, which is understandable if he was more interested in wildlife than electronics.LM386 power amplifier already has negative feedback built-in and inputs that are biased.....
I'm not sure about biasing the op-amp though, is it necessary if it's just a switched DC output that I want for the 4024 logic chip?its (+) input must be biased.....
I have built this bat detector circuit, the ultrasonic detector and earphone are not shown in the diagram. I hope to pick up bat sounds between about 12KHz-200KHz with it.
Its an HY12. I'll be happy if I can just pick up the ones in the lower range to start with, I could always build a more advanced one later. I think the one in my garden is possibly a Common Pipistrelle, from the sound, size and activity and that would be around 40-50KHz. As you say, a few British species are over 100KHz, but most are below 80. I'm told there are a load of bats in one of my local parks, but I don't know which species although I am aware that there is one that hunts over water and there is a very large pond there.What transducer are you using?
Tha's no surprise! Thanks for your constructive criticism, I'll add a ground rail between + and -.Your opamp circuit had a few mistakes that causes it not to work.
That's great! Very useful, just the sort of help I wanted. If I was starting from scratch I'd use that as it stands. Since I have a completed circuit I'll pick out the most useful bits and apply them to my circuit, probably a bit at a time. The first two opamps are doing exactly what I was trying to do in my circuit, so I will start by copying them and leaving out the next two because there is no room on the current board. I misunderstood the diagrams I had seen about earthing the +input, I had forgotten that it is assumed that you use a balanced power supply, so I will add the two 100K resistors to create the ground rail. I will increase the value of the input resistor (and feedback resistors) to increase the input resistance.I've attached a sketch of a version I built about 20 years ago. Might give you a useful suggestion or two?
Simple is good and batteries always run out when it's most important that they don't!Very simple - and low current! (useful for battery life!)
I think I've got a TL074 in my bits box.You might like to use a better quad op amp - but the TLO64 was the only suitable low current device at that time.
I am using an earpiece and a voice recorder, but the earpiece is annoying so I may add the sounder later.To save power, the output from the 4017 counter drove an AC piezo directly. No audio amp..
As you can't tune a freq div type, and the transducer is only detecting the 40 KHz part of the bat ultrasound, it doesn't really matter what the output actually sounds like!
Hand drawing is so much quicker I'd use it if I had a scanner.Sorry about the sketch. I did try and do one of these 'proper' schematics for another post, but it took ages, and only one or two bothered to look at it anyway.
So I dropped the time consuming 'pretty' drawing idea, and hope you can read what I've posted.
If it's of any use, and you can't read something, I can post further details?....
I may build one of these later if I get really enthusiastic about bats, Nigel has posted a circuit for one.You really need to do a heterodyne, to be able to distinguish between the species, but you will hear the pipestrelles OK. And the Daubentons. (which are the one that hunt over water). They're much quieter though. They sound like a fire 'crackling' on a freq div detector!
For a heterodyne, you will need a quieter preamp!
Something I had been consideringBTW, the gain control on the circuit is to allow you to set the gain to avoid opamp 'noise' from setting the device off at high gain. You might get better signal to noise with a more modern lower noise opamp.
This is an extremely useful tip. As you say, the keys only check whether it works and a hint I saw somewhere else, of using a couple of 2p pieces, is somewhat more sensitive but only in the same sort of order of magnitude I think. I have been very limited in testing the circuit because the bat seems to have been on its holidays for a few days. I tried the digital(!) test on the current (386) circuit and the circuit is not sensitive enough, so my filter has been successful in stabilising the circuit but has reduced the sensitivity too much. It might be for what I want though because I'm mostly interested in short range. I can calibrate the digital test next time the bat appears and I know if the current circuit picks him up.Edit: one further suggestion for testing. To be of any real use, your detector will need to work to detect bats over 20 or 30 metres away. To get a simple idea of whether you are in the 'ball park', sensitivity wise, you can gently rub your thumb and forefinger together, directly in front of the transducer. Even though you won't hear any significant audible sound, that action should generate enough ultrasound to activate the detector.
The 'old chestnut' of detecting ultrasound from shaking a bunch of keys will confirm your detector is working, but if it can't 'hear' your fingers rubbing together, you'll probably be disappointed in the range of the device.
Maybe they have individual accents...And these little critters can move fast, in all directions, as you know.
How they ignore the ultrasound generated from other nearby bats, and just isolate their own 'echoes' amazes me. Incredible creatures......
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