Download doc - BAT DETECTORS

Transcript
Page 1: BAT DETECTORS

Detector de lilieci 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

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 bandaaudio, lasand sa treaca inspre amplificatorul audio clasa B(T6,7,8,9,10) numai semnalul diferenta a celor ce intra in mixer.

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. )

Page 2: BAT DETECTORS

Build an Enhanced Simple Bat Detector...

The circuit is basically the same as the original, with the following additions:

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 )

Circuit Designator Component Value Purpose of Component

R1, R2 Varies with transducer used Sets gains of amplifier stages

R3, R5 N/A Amplifier stability components ( not used at this time )

R4 220 ohms Power supply isolation for first amplifier stage

RV1 10K ohms Volume setting potentiometer

C1 .047 uf Signal coupling between amplifier stages

C2, C3 10 uf Amplifier gain control components

C4 470 uf Main power supply filter

C5, C8 N/A Amplifier stability components ( not used at this time )

C6 .022 uf Couples transducer signal to input of first amplifier stage

C7 220 uf First amplifier power supply filter

C9 .022 uf Couples detector output to earphone

Page 3: BAT DETECTORS

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 DETECTOR1. 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; it’s 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 I’m using). I also omitted the stability components (the 10 ohm resistor and 50nF capacitor) from the amplifier IC’s 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 didn’t bother. The missing components are shown greyed-out in the circuit diagram above).

2. Steven has been experimenting with the circuit and reports to have increased sensitivity by adding a 0.1uF capacitor from the amplifier stage (Steven has connected to pin 1 on the binary counter) to the potentiometer.

Page 4: BAT DETECTORS

eva

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.

Page 5: BAT DETECTORS

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 !).

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

Page 6: BAT DETECTORS

Bat Detectors

      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.

 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

Page 7: BAT DETECTORS

Frequency division detector parts

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.

Across the supply I connected a 100uF capacitor for noise reduction and power stabilisation (not shown on the picture).Future enhancements

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.

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-amplifier. The current consumption is about 1 mA at 6V supply.

The pre-amplifier consists of three essentially identical transistor stages. They are biased for a current of about 0.2 mA and an output collector voltage of 3V, giving a gain of 70 each. Biasing in this circuit relies on the value of hfe to be about 250, which means that the choice of transistor is important. On the other hand, this biasing scheme requires only a relatively small number of components.

Page 8: BAT DETECTORS

The capacitors between the transistor stages give the pre-amplifier a high-pass characteristic to reduce the influence of audible sounds, although this is not a great problem with piezo transducers. The 100pF capacitor at the last stage limits the bandwidth to about 100 kHz to reduce noise. It is perhaps better to place this capacitor across the collector of the middle transistor, where the signal is more linear.The signal coming out of the pre-amplifier is biased at exactly half the supply voltage by the two 150k resistors and then fed into the schmitt-trigger input of the 4024 CMOS IC. From pin 6, the divide-by-16 output is taken to a crystal earpiece.The crystal earpiece can be driven without any additional end-amplifier, saving in current consumption (a single LM386 already consumes about 4 mA when idling!).Some improvements to this idea are:

Adjustable detection treshold by replacing the 15k resistor connected to the middle transistor by a potentiometer.A 10k pot will work.

More effective low-pass filtering by adding capacitors across the collectors of the other two transistors.

A low-pass filter at the output to reduce the high order harmonics of the output square wave. Also a combination of an output coupling capacitor to the crystal earpiece and a high-value resistor across the earpiece would reduce the earpiece DC voltage.

A volume control for the output to the earpiece.This can be easily done by connecting a 100k pot to the output and connecting the earpiece to the wiper of the potmeter.

A clever wiring scheme that energises the circuit when the earpiece is plugged in, obviating the need for a power switch, as shown on the pages of Tony Messina.

A means of keeping the supply voltage constant. Because the total gain depends strongly on the supply voltage, a variation in the supply voltage would a strong variation in gain.

Continuing on that last point, constant supply voltage, I found a simple circuit to regulate the supply voltage. It is shown on the right.The lower transistor senses the output voltage and drives the upper transistor to keep the voltage at the lower transistor's base equal to about 0.55V. In this case, it will result in an output voltage of about 6V, relatively independent of the input voltage.I have also considered a 7806 regulator, but these regulators consume more current than the circuit itself does.Another solution is to use a battery that keeps a constant voltage, like a rechargeable '9V battery' (actually 7.2V). Using this simple regulator, the circuit seems to work pretty well. I have some problems with oscillations when the detector is in its most sensitive setting, but I expect that is partly because of stray capacitance on my breadboard.

Yet another simple circuit

I found out that the hfe of the BC550B transistors actually turns out to be closer to 300 than tp 250, so I increased the base resistor to 3.9 mega-ohm. The 4024 CMOS IC is fed directly from the collector of the rightmost transistor, instead of being fed from a separate voltage divider. I added a red led in the power supply line to indicate whether the detector is on. I also added a 100k pot for volume control.The current consumption for this circuit is very low at about 2 mA, 1 mA for the pre-amp and another 1 mA for the CMOS IC. Inserting the crystal earphone plug into the detector switches the detector on. It should be wired such that the actual earphone is connected between points A and B. Points B and C should be connected when the plug is inserted. This method is given in more detail here.

Page 9: BAT DETECTORS

The BatLogger II

The circuit for the Simple Bat Detector is modified only a little for use with the PIC data conversion circuit. The DIV-16 output from the CD4024 divider is attenuated to provide a monitor output signal to set up the logger. The DIV-32 output from the CD4024 is brought out to feed the sampling input of the PIC.