Ultrasonic pest repellent circuit

There are many ultrasonic pest repellent devices available on the market but a major drawback is that their power output is low and their effectiveness suffers. This electronic pest repellent generates powerful ultrasonic signals to repel pests.

In addition to the ultrasonic frequency oscillator built with CD4047, separate push-pull power amplifier (with 2N3055 or TIP31C) and transformer are used to boost ultrasonic signals. The output of the power amplifier is coupled to a tweeter through output transformer X1, which is wound over ferrite core (UU or CC core).

Primary winding consists of 150 turns of 20 SWG while the secondary winding is 40 turns of 24 SWG wire. Adjust potentiometer VR1 for maximum effectiveness.
This circuit has not been tested.

Caution!This is a powerful sonic pest repellent circuit so use it only in outdoor places. Do not use this ultrasonic pest repeller near babies or animal pets.

Pest repellent circuit diagram

Audio Wattmeter circuit with LM3915

You need one LM3915 IC and add a few passive components and you got a simple but effective audio wattmeter.
This sound wattmeter uses a row of colored LEDs as a scale to show the relative power output of your amplifier in watts. It is easy to be inserted into the speaker box. All you need is to hook a supply voltage to it. The value of R1 depends upon the impedance of the speaker being used. The table near the sound wattmeter diagram shows the necessary values of R1.

LM3915 audio wattmeter circuit diagram

If you want to apply the circuit to stereo systems you must build two identical circuits.

The supply voltage of the circuit is 12…20 volts/50 mA DC adapter. Take note that the LM3915 indicates only the positive swing of the signal. Anyway, by testing amplifiers it does not matter anyhow since a sine wave is normally used as a test signal. To test the circuit without using an actual speaker, you can connect a dummy resistor with a value of either 8 or 4 ohms.

PCB layout and parts for the audio wattmeter

Source:http://www.hqew.net/circuit-diagram/Audio-Wattmeter-circuit-with-LM3915_8503.html

LED dimmer circuit

This simple LED dimmer circuit has 2 transistors, 1 resistor and 2 potentiometers.
Typical segment displays LEDs consume around 25 mA for each segment and should be limited to it with resistors. If a six digit display is to be current limited, at least 42 series resistors are needed.
To counter the above described problems, the led dimmer circuit it allows for eventual adjustments of the display’s brightness.

The series resistors are not needed anymore for the segment display which simplifies the pcb design and contruction.
The circuit is simply a voltage regulator with variable voltage output.

The brightness of the LEDs are dependent on the output voltage. Since the voltage regulator is variable, the brightness of the LEDs is also variable. Potentiometer P1 is used for rough adjustment while P2 is used to trim the brightness in finer resolution. The output of the regulator circuit can be varied from 0 to 4.3 volts.

Before tuning the circuit, set the pot to zero point, then slowly adjust the pots until the desired brightness is achieved. In a typical six segment disply, the maximum current must not exceed 1 ampere. For example: if one segment consumes 25 mA each, then 7 segments of a six digit display will consume around 1050 mA. That is a bit more than 1 ampere! The transistor T1 must be heatsinked because high current consumption will produce a lot of dissipated heat.

LED display dimmer circuit diagram

Printed circuit layout for the LED segment dimmer

Parts placement layout for the LED dimmer

Chug-chug

A CA3240 dual MOSFET-input device is used as a white-noise source. Op amp IC2 is used as a driver stage for the push-pull output stage formed by Q5 and Q6. Transistors Q2, Q3, and Q4 form a variablefrequency multivibrator. Rll, the speed control, is used to control the multivibrator`s frequency. The output is differentiated by C8 and applied to modulator transistor Ql, through Dl and R7. Transistor Ql modulates the gain of the output amplifier stage by changing the impedance to ground, through R6 and C4. When the multivibrator`s frequency is reduced using Rll, C8 discharges slowly, creating a sound similar to escaping steam from a stopped locomotive.
To find the proper value for R3, short Ql `s collector to ground. Then, increase the value of R3 until the current drain from the power supply is less than 60 mA. Then remove the short from Ql. To see if the device is operating properly, close switch Sl and reduce the resistance of Rll. Wait 10 seconds, then rotate Rll slowly. You should hear a sound similar to a steam locomotive picking up speed.
Source: http://www.hqew.net/circuit-diagram/Chug$2dchug_14851.html

Microphone preamplifier with TLC251

A microphone preamplifier using: om CMOS op amp with its own battery, is small enough to be placed in a case of small microphone. The amplifier operates from a 1.5V battery cathode mercury low supply currents. This preamp will operate at very low power and maintain a reasonable frequency response as well. The TLC251 is operating in low bias (operating at 1.5 V) draws a supply current of only 10 and has a year - frequency response of 3 dB 27 Hz to 4.8 kHz. With 8-pin grounded, which is designated as the polarization state high limit increases above 25 kHz.
Supply current is only - 30 pA under these conditions.

Sound-effects-generator

A variable dock-pulse generator is made up of two sections of IC1 (a 4069 CMOS hex inverter). Rl, Sl, and capacitors Cl through C6. By adjusting Rl and switching one of the capacitors into the circuit, the clock`s pulse rate can be varied over a wide range. The TL507C converts analog signals-in this case the output of IC3, an LM386 audio amplifier -into digital signals.
The conversion is accomplished using the single-slope method; it involves comparing an internally generated ramp signal to the analog input signal and a 200-mV reference voltage. The square-wave output from the aid converter is fed to IC3 through a network consisting of R2, R3, and C7. Resistor R2 controls the amplitude of the pulses. Resistor R3 and capacitor C7 form a variable tone-control filter and a differentiator circuit that converts a square wave into a spiked waveform. That waveform is amplified by IC3, and the resulting output is fed back into the analog input of IC2, as well as to an 8-0 speaker. By adjusting Rl and selecting one of the six capacitors with Sl-thus varying the clock frequency-and by varying R2 and R3, you can produce many sounds.

Waa-waa circuit

The waa-waa effect is achieved as certain frequencies are amplified more than others. A phase shift RC oscillator makes up the basic circuit. Negative feedback is obtained by feeding part of the signal back to the base. When adjusting initially, RV1 is turned to minimum. RV2 is adjusted to a point at which an audible whistle appears indicating oscillation. RV1 is then adjusted till the oscillation just disappears.