BAT DETECTORS

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    31-Oct-2014

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<p>Detector de lilieci</p> <p>Lilieci, in oras, mai rar. In schimb, motoare cu combustie, gandaci, tantari, soareci, caini, pisici, pesti, arcuri electrice, frecari si deformari mecanice, scurgeri de gaze, ... - toate generatoare de ultrasunete de 25 pana la 60KHz sau mai mult. Circuitul include un amplificator de semnale ultraacustice (T1,2), ce utilizeaza ca microfon ultrasonor un tweeter piezo, apoi un oscilator sinusoidal(T3,4) cu frecventa(30-60KHz) reglabila(SR), un mixer(T5) ce translateaza, prin heterodinare (schimbare de frecventa), semnalul util ultrasonor in banda audio, lasand sa treaca inspre amplificatorul audio clasa B(T6, 7,8,9,10) numai semnalul diferenta a celor ce intra in mixer.</p> <p>R1,3 - 220K; R2,4,13,15 - 2K2; R5,14 - K27; R6 - 1K; R7,8 - 82K;R9,11 - 10K;R10 - 3K9;R12 - 100K;R16 - 4R7; R17 - 4K7; R18 - 15K; R19 - 56K; R20 - K68; R21 - 1K8; R22,23 - 10R; R24 - K39; SR - 47K; Vol - 10Klog C1,12,14 - 220m; C2,3,6 - 22n; C4,5 - 1n; C7,8 - 100n; C9,13 - 10m; C10 - 47n; C11 - 680n. T1,2,3,4,6,7,8,9 - BC171; T5 - BF245C(A,B), MPF102</p> <p>Build a Simple Bat Detector . The basic circuit of the Simple Bat Detector is shown in the schematic diagram to the right. It is essentially composed of 3 integrated circuits, or ICs. The signal from an ultrasonic transducer is fed to IC-1, an LM386 audio amplifier, which is configured to provide a signal gain of 200. The signal is coupled to IC-2, a second LM386, by a .05 uf capacitor. IC-2 is configured to provide an additional gain of 20, for a total system gain of 4,000. The output of IC-2 is direct coupled to the input of IC-3, a 7 stage CMOS digital divider circuit. The input stage of the divider acts as a zero crossing detector, triggering on the negative transition of the signal from IC-2. The divide by 16 output is connected to a potentiometer, which serves as an audio level control. A high impedance ceramic earphone is connected to the output of the level control. The 10K level control is a small printed circuit pot that is set and forgotten. The detector circuit is powered by a nine volt battery. ( The numbers next to the IC nodes refer to the pin numbers of the IC's. Note the additional pins listed at the bottom of the schematic that need to be tied to ground. )</p> <p>Build an Enhanced Simple Bat Detector ...</p> <p>The circuit is basically the same as the original, with the following additions:</p> <p>Component positions are available to set gains of both LM386 amplifiers ( C2, C3, R1, R2 ) Capacitive input coupling is provided for ( C6 ) Capacitive output coupling is provided for ( C9 ) Power supply isolation components are added for the first amplifier stage ( C7, R4 ) Standard LM386 stability components are provided for ( C5, C8, R3, R5 ) Component Value Varies with transducer used N/A 220 ohms 10K ohms .047 uf 10 uf 470 uf N/A .022 uf 220 uf .022 uf Purpose of Component Sets gains of amplifier stages Amplifier stability components ( not used at this time ) Power supply isolation for first amplifier stage Volume setting potentiometer Signal coupling between amplifier stages Amplifier gain control components Main power supply filter Amplifier stability components ( not used at this time ) Couples transducer signal to input of first amplifier stage First amplifier power supply filter Couples detector output to earphone</p> <p>Circuit Designator R1, R2 R3, R5 R4 RV1 C1 C2, C3 C4 C5, C8 C6 C7 C9</p> <p>The transducer listed above will require a R2 gain resistor that may vary in the range of 470 ohms to 2.2K ohms. I usually suggest 1.5K as a good starting point. If the detector is too noisy, or oscillates, then stepping up to a 2.2K resistor will usually settle it down. If the detector seems to be insensitive to bats that are nearby, a 470 ohm resistor might solve the problem by pushing the gain of the second stage amplifier closer to the limit. One method for setting the gain resistance is to use a 5K ohm potentiometer for R2 to determine the optimum resistor value to use to provide the best gain achievable with your specific bat detector. I have even built detectors with a 5K pot for R2 as a permanent feature sp that the gain could be adjusted in the field. The Mouser Transducer listed in the parts list should have a 6.8 mH coil wired in parrallel across the back of the transducer for the best possible frequency response for the Simple Bat Detector. Wired in this way, the typical frequency response of the detector will cover 30-50 kHz with an added response node at 20 kHz. Generally, the R1 value for this transducer is 150 ohms. The R2 value will vary from 220 ohms to 2.2K ohms depending on your specific transducer and wiring layout. R4 is at the top left. Below R4 is R1, and to the right is R2. All component positions are silkscreened on the circuit board. BAT DETECTOR 1. Ultrasonic signals are collected by the transducer and amplified by the two LM386 audio amplifier chips. The signal is then fed to the CD4024 binary counter which divides the frequency by 16. Output from the frequency divider is passed through a variable resistor (for volume control) and on to a high impedance ceramic earphone. This circuit treats the ultrasonic waves as a series of binary pulses; its basically a 2 bit analogue to digital convertor, the wave is either on or off. The CD4024 counts (in binary) 16 pulses and then outputs a single pulse. The resulting sound is kind of like a Geiger counter, i.e. a series of clicks. This ultrasonic transducer can operate as both a transmitter and a receiver; Tony suggests de-tuning the transducer with a 6.8mH RF choke. When wired in parallel across the transducer the choke flattens the transducers frequency response. The transducer will be less sensitive at 40kHz but will have a larger frequency range (possibly as great as 20 to 50kHz) Unfortunately introducing an RF choke caused my circuit to oscillate so I left it off (it may be a problem with the type of transducer Im using). I also omitted the stability components (the 10 ohm resistor and 50nF capacitor) from the amplifier ICs because of problems with oscillation; and I removed the 220uF power capacitor because I ran out of space inside the lighter (With the 220uF cap. removed you could also omit the 220 ohm resistor, mine was already soldered in so I didnt bother. The missing components are shown greyed-out in the circuit diagram above).</p> <p>2. Steven has been experimenting with the circuit and reports to have increased sensitivity by adding a 0.1uF capacitor from the amplifierstage (Steven has connected to pin 1 on the binary counter) to the potentiometer.</p> <p>eva</p> <p>Going from the left to the right, we first see an amplifying and buffering opamp stage. This opamp is biased to half the supply voltage by means of the two 1 megaohm resistors. It has a gain of about 10 times. The next part of the circuit is the switching mixer. The opamp in this mixer inverts the bat signal (i.e. gain of -1). The transistors do the actual multiplication of the bat signal with the oscillator signal, by alternatively conducting the inverted or non-inverted bat signal. The oscillator signal is a square wave, generated by the 555 in its familiar astable configuration. The multiplied signal now contains the desired difference frequency and the undesired sum frequency component. The latter is removed by means of the second order low-pass filter. This circuit may look simple, but that's because I made considerable effort to simplify the circuit. It requires only a small amount of components and it has low current consumption (15 mA). Enhanced TCA440 bat detector From the left to the right, this circuit consists of a tranducer, a simple transistor pre-amp, a TCA440 IC that contains an oscillator and mixer, a second-order low-pass filter and a audio-amp consisting of a LM386 IC. You can download a few bat sounds recorded with this detector through my bedroom window. The transducer that is used is a piezo-electric transducer, which is quite sensitive but unfortunately has a relatively limited frequency range. By connecting a coil parallel to the transducer, the response can be broadened somewhat, at the expense of decreasing overall sensitivity. The signal from the transducer is first amplified by a simple transistor stage, consisting of a single BC550C transistor. It is biased for a current of approximately 0.7 mA. The capacitor from the emitter to ground causes a +6 dB/oct gain slope for frequencies higher than 16 kHz. After this it enters the TCA440 at pin 1. In the TCA440 this signal is multiplied with the signal of a built-in tuneable oscillator. The oscillator can be tuned with the use of the potmeter connected to pin 6, from about 18 kHz to 100 kHz. The potmeter must be connected such that it has the lowest resistance when the wiper is turned counterclockwise. This gives a reasonable linear relation between wiper position and tuning frequency, but means that CCW is highest frequency and CW is lowest. The oscillation frequency is determined by the product of the capacitor between pins 5 and 6 and the resistor going from pin 6 to the positive supply connection. The highest frequency is therefore set by the 1n8 capacitor and the 2k resistor, while the lowest oscillator frequency occurs when the circuit sees a 2k+10k=12k resistor going from pin 6 to the positive supply connection. This means that the ratio between the highest and lowest frequency is equal to 12k/2k=6. From pin 16 the signal reappears and enters a low-pass filter. This is a second-order filter with a cut-off frequency of 3.4 kHz, giving a range of about 7 kHz around the oscillator center frequency. Finally the down-converted and low-pass filtered signal is fed into a LM386 audio amplifier which can drive a set of normal low-impedance headphones. I used a stereo 3.5mm jack chassis with the left and right leads connected together to give mono output. Components values aren't very critical, however I used metal film 1% resistors for the input stage. Also for the capacitor connecting pins 5 and 6 of the TCA440, you should use one with reasonable tolerance. For the 100uF and 47uF capacitors, I used electrolytics (watch the polarity !).</p> <p>Update! The value of the capacitor between pins 5 and 6 has turned out to be too low. A value of 2.7 nF (instead of 1.8 nF) is recommended. This improves the frequency range. In a future detector, I would exchange all 10 nF capacitors with 100 nF capacitors, to be sure that no signal is lost due to insufficient coupling The value of the coil parallel to the transducer is not optimal. A value of 8.2 mH or 5.6 mH is probably better suited to broaden the frequency range of the transducer. See also the page about detuning</p> <p>Bat Detectors</p> <p>Here is my latest experiment in building a bat detector. This one displays a visual of the bat chirps with LEDs as well as providing the sound. The video section is built around a CD4017BE decade counter. At the front end a high gain amplifier is built through three of the op amps in a TL074CN quad op amp IC. The fourth op amp is wired as a oscillator to drive the decade counter. The decade counter drives the LEDs sequencing about one for every 10KHz. With a 40KHz transducer the frequency is limited, so the effective range of the LED sequence is from about 20 to 50 KHz. The audio section of the "A/V Detector" is a standard frequency division detector using LM386N audio amplifiers and a CD4024BE as a binary divider. There is an internal speaker, a headphone jack, and switches for power and to select audio, visual or both at the same time. The enclosure I used for this detector is an old dial-up modem case that I once used with a one-time Mac Plus computer.</p> <p>This Heterodyne Bat Detector was built with a circuit similar to the one above except, I experimented using ICs for the first amplifier stages instead of transistors. The first stage is a LM358 op-amp with an adjustable gain trimmer and the second stage is a LM386 set up for 20 gain. Also, the output stage is a LM386 set up for adjustable gain of up to 200 with a 10uf capacitor and a 10k trimmer pot. Included are a speaker and a headphone jack. The eyes of the bat flash when a bat sound is detected</p> <p>Frequency division detector parts</p> <p>Two identical transistor stages for amplification. The transistors are BC550, which are low noise versions of the standard BC547 NPN transistors. This is a standard transistor amplification stage: resistors 27k and 150k set the DC bias, the 1k resistor then sets the current and the 10k resistor sets the gain. The emitter is decoupled by a 100nF capacitor The transistor stages have a power supply decoupling consisting of a 100 Ohm resistor and a 100nF capacitor. The gain should be about 120x for each stage. A LM386 (pdf) opamp. This opamp needs very little external components and gives a output DC bias nicely centered around half the power supply voltage. If you need more gain, you can boost it by adding a series connection of a capacitor and a resistor across pins 1 and 8 (the pins on the left). Look into the datasheet of the LM386 for more details on this. The opamp has a power supply decoupling consisting of a 100 Ohm resistor and a 10uF capacitor. A 4024 (pdf) CMOS IC which performs the actual frequency division. It is set to 16 times division. A potentiometer to set the volume to the earphones. Instead of a 2k2 potmeter parallelled by a 1k resistor I think it's better to use a 1k potmeter without a parallel 1k resistor. Make sure that you use a logarithmic potmeter and wire it the correct way ! Another LM386 opamp to give enough power to drive headphones or a speaker. The output is connected to a 3.5 mm stereo jack. The connections for left and right on the jack bus have been connected, so the speakers are in parallel.</p> <p>Across the supply I connected a 100uF capacitor for noise reduction and power stabilisation (not shown on the picture). Future enhancements</p> <p>The input stage is quite complicated, requiring a lot of components. Perhaps a simple opamp pre-amplifier works better. Although I haven't had any problems, an opamp pre-amplifier should also be more stable with respect to supply voltage and temperature. In a future version, I would use a 1k pot for the volume control. The LM386 just before the 4024 is perhaps better replaced with a real comparator, with faster response time. The coupling cap between the final LM386 stage and the speaker should probably be chosen bigger, something like 100 uF instead of 10 uF. Perhaps the use of the LM386 as an output amplifier is overkill, because the output of the circuit is a simple square wave that can be amplified with a low quality amplifier, like a single transistor.</p> <p>Simple frequency division detectors Ultra-simple division bat detector [unfinished!] I have been thinking about an even simpler frequency division bat detector with super-low power consumption, consisting of a few transistors that perform pre-amplification, a 4024 CMOS for frequency division and no end-...</p>