Here is the remote control tester circuit. This circuit is really a simple and easy tester for verifying the basic operations of an infrared remote control unit. It is low-cost and very easy to construct.

The tester is designed around infrared receiver module TSOP1738. Operation of the remote control is identified by a tone from the buzzer. The circuit is sensitive and has a range of about 5 metres. The integrated IR receiver detects, amplifies and demodulates IR signals from the remote control unit. The piezobuzzer connected at its output sounds to tell us the existence of transmission from the remote control unit.

As displayed in above circuit diagram, output pin 3 of IR receiver module TSOP1738 (IRX1) normally stays high and the piezobuzzer is in silent mode. When the IR module IRX1 receives an infrared signal, its output is going low and, because of this, the piezobuzzer sounds to signify the reception of transmission from the remote (for example television remote control unit).

Power supply for the circuit is taken from the mains making use of a capacitive potential dropper, a half-wave rectifier, a shunt regulator and related parts. Ensure that capacitor C1 is of X2 type. Work with a appropriately small enclosure for making the unit handy.

Assemble the circuit on a general purpose PCB and enclose inside a box. Ensure that the IR receiver module is positioned around the front panel of the box/cabinet so that it can get the IR signals easily. Well, before soldering/connecting the shunt regulator and IR module, please check up the following TL431 and TSOP1738 pin configuration.

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Component Part List:

• C1 = 1uF 25V
• C2 = 220uF 25V
• R1 = 2.2K Ohm
• Q1 = 2N3904 / 2N2222
• D1 = 1N4148 / 1N4001-1N4007
• K1 = 12V SPDT Relay / Any appropriate relay with 12V coil
• U1 = LS7220 Digital Lock IC
• S1-S12 = SPST Momentary Pushbutton? Keypad (see notes)
• HD1 = 12 Position Header

Circuit Notes:

This could be the circuit diagram of a easy electronic combination lock by using IC LS 7220.This circuit may be applied to activate a relay for controlling (on & off) any device each time a preset combination of 4 digits are pressed.The circuit may be operated from 5V to 12V.

To set the mixture connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination is going to be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.

When the correct key combination is pressed, then the output ( relay) will be activated for a preset time driven by the capacitor C1.Here, it is set to be 6S.Increase the value of C1 to increase the preset time.

For the keypad, arrange the switches in a 3X4 matrix on a PCB (Printed Circuit Board).Write the digits on the keys by using a marker.Instead of applying numbers I wrote some symbols!.The bad guys is going to be more confused with this.

Download LS7220 datasheet from the following link:

LS7220 Datasheet - MOS digital lock circuit

1 file(s) 63.51 KB

Download Datasheet

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Tone Detector diagram 1

Tone Detector diagram 2

Tone Detector diagram 3

Tone Detector diagram 4

Tone Detector diagram 5

Circuit source: Sound activated switch for robot

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The circuit uses IC LM101A, a general purpose operational amplifier (op-amp) and IC LM111, a high-speed voltage comparator device.

This circuit provides sine and square wave at frequency of below 20Hz up to above 20KHz. The benefit of this circuit diagram is that you can adjust the output frequency by varry the variable resistor of R3. You can also adjust the amplitude of output sine/square wave by adjust the potensiometer R6.

How to define the frequency value at output line, provided on above scheme diagram image.

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Resistor R1 biases the potentiometer to match the input range of U1. Full counter-clockwise rotation of the pot corresponds to maximum-speed reverse rotation of the motor. Mid-scale on the pot corresponds to motor off, and full clockwise rotation of the pot produces maximum-speed forward rotation in the motor.

The characteristics of a given motor may allow you to eliminate the amplifier’s output filter (L1, L2, C1, and C2). But, unless the control circuitry shown is located near the motor, you should include the filter to reduce EMI.

Download more explanation about the circuit diagram of motor speed control with MAX4295 in PDF version:
[wpdm_file id=47]

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A 32 ohms earphone is used in the output unit of this project as recommended by the manufacturers of the TDA2822M IC. According to the IC’s datasheet, this 32 ohms earphone will produce an output of about 1.3 watts. In the circuit above, capacitors C11 and C12 are called coupling capacitors. Their functions are to block any DC components in the input and outputs of the pre-amplifier. The pre-amplifier comprises of R5 and capacitor c13 which decouples the power supply of the preamplifier stage, while capacitor C12 and resistors, R2, R3 and R4 with transistor T1 forms a negative feedback amplifier which stabilizes the overall gain (A). Resistor, R4 is known as an emitter swamping resistor which also adds stability to the amplifier. The medium power amplifier amplifies the output of the pre-amplifier to an audible level. It comprises of the TDA2822M IC and those external components needed to make the IC function properly. This other external components are capacitors C14, C15, C16, C17, C18 and resistors R6 and R7. Resistor, R5 and capacitor, C13 form an RC decoupling circuit which are connected across the power supply to smooth out noise. Finally a 32 ohms earphone is used in the output unit.

Sound Amplifier for Ears : The Part List

The components used are: condensed mic, 1=2.2kΩ, 2=330kΩ, 3 = 680kΩ,12 = 33Ω,
5=10kΩ, 6 =220Ω, 7=4.7Ω, 8 =4.7Ω, , 1 =BC547A , 1 =0.01,4=100, 3 = 47, 4 = 10, 5 = 0.01 , 6 = 100, 7 = 0.1, 8 = 0.1, V1=10kΩ, LED- Red, TDA 2822M, switch and battery (3V) and earphone.
The components for the sound amplifier for ears circuit were first assembled on a bread board and tested. After it was found to work as anticipated the components were transferred to a Vero board for the final construction.

Abstract: Hearing aid device is a small electronic gadget that is fit in or behind the ear to improve one’s hearing and consequently communication ability. This research work involves the design and development of a hearing aid device with pre-amplifier; an acoustic signal picked-up using a condenser microphone. TDA 2822M IC is configured to produce an audio amplification which is converted to audio signal through a headphone. Design equations were employed to calculate the physical parameters of the circuit. After the design, the circuit was constructed and tested on 5 people with partial hearing problem. The result showed that there was a significant improvement in the hearing ability of all the patients tested. Recommendations were proposed for further improvement.

Download: Small Hearing Aid Project Document | TDA2822M Datasheet

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Here is the simple and low cost mosquito repellent circuit design. The circuit serves to keep the mosquitoes out of the room or the location where the device is installed. According to certain publications, the frequency emitted by the male mosquitoes is said to be around 20??”25 kHz, and so within the realm of ultrasound. But according to others, it is in the region of 5??”7 kHz instead; frequencies that a human ear, even an elderly one, can still hear very well. Rather than spending lots of money buying such a device, which moreover generally have a fixed frequency, we’re suggesting building one yourself , especially since the circuit proposed is very simple and cheap to build.

Mosquito Repellent Works

The low cost mosquito repellent circuit uses just a single IC, a CMOS type 4047. This very multi-purpose IC can be wired in very many operating modes, including that of the multivibrator or astable used here. The operating frequency is set by the external components C1, R1, and P1. The latter makes it possible to slightly adjust the frequency, given the uncertainty that exists over the most efective value. To best reproduce the high frequencies produced by the generator, the output transducer used is a simple tweeter, but it must be a piezo one. Such a tweeter behaves in fact much like a capacitor, and so doesn’t overload the CMOS IC outputs that are incapable of supplying a substantial current.

To obtain an output signal of sufficient amplitude while being powered from a single 9 V battery. The tweeter is connected between the 4047’s Q and Q outputs. With this condition, it possible to apply complementary (antiphase) signals to the tweeter so it ‘sees’ an alternating voltage of double the supply voltage. In purely theoretical terms, this quadruples the output power available. In practice, it’s better to regard it as tripling it, but the beneft achieved by doing it this way is nonetheless very real. All that remains is for you to place the project in the middle of the patio table or beside your lounger in order to get a taste of the calm of a summer’s evening without mosquitoes bothering you acoustically or worse, biting. At any rate, that’s what we wish for you.

Source: eeweb

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This is the circuit design of the protector for electronic appliance with three-phase power supply. Many of electronic appliances need three-phase AC supply to work. If there is any failure of any of the phases, then it will make the appliance prone to erratic functioning and may even lead to failure. Hence it is of paramount importance to monitor the availability of the three-phase supply and switch off the electronic appliance if found any failure on one or two phases. The power to the appliance should resume with the availability of all phases of the supply with certain time delay in order to avoid surges and momentary fluctuations.

The electronic appliance protector needs three-phase AC power, three 12V relays and a timer IC NE555 along with 230V coil contactor having four poles to switch on and switch off the appliance.

How the protector circuit works

Relays RL1 and RL2 act as a sensing devices for phases Y (Yellow) and B (Blue), respectively. These relays are connected such that each acts as an enabling device for the subsequent relay. Therefore the combination of the relays forms a logical AND gate connected serially.

The availability of phase R (Red) energises relay RL1 and its normally opened (N/O) contacts close to connect phase Y to the input of transformer X2. The availability of phase Y energises relay RL2 and its N/O contacts close to connect phase B to the input of transformer X3, thus applying a triggering input to timer IC NE555 (IC1).

Therefore the delay timer built around NE555 triggers only when all the phases (R, Y and B) are available. It provides a delay of approximately four seconds, which energises relay RL3 and its N/O contact closes to connect the line to the energising coil of four-pole contactor relay RL4. Contactor RL4 closes to ensure the availability of the three-phase power supply to the appliance.

The rating of contactor RL4 can be selected according to the full-load current rating of the appliances. Here the contact current rating of the four-pole contactor is up to 32A. The availability of phases R, Y and B is monitored by appropriate LEDs connected across the secondary windings of transformers X1, X2 and X3, respectively. Hence this circuit does not require a separate indicator lamp for monitoring the availability of the three phases. When phase R is available, LED1 glows. When phase Y is available, LED2 glows. When phase B is available, LED3 glows.

The main advantage of this protector circuit is that it protects three-phase appliances from failure of any of the mounted on the backside of cabinet. Connect the appliance through external wires.

WARNING: The circuit contains mains high voltage. Make sure the AC mains is disconnected during assembly of the circuit and double check everything before connecting your circuit to the AC mains.

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Initially, when the water level is below the L1 strip, supplying electrical oscillation frequency is not transferred to the diode D1. Thus the low output and LED1 does not light. Also, because the base voltage of the transistor T1 is low, it is in a state of cut-off and the collector voltage is high, which enables to produce melody IC1 (UM66) and the alarm is sounded.

When the water is just touching the L1 level detector strip, the oscillation frequency of the supply transferred to the diode D1. This straightening supply voltage and positive DC voltage developing capacitor C1, which is lit LED1. At the same time the base voltage of the transistor T1 becomes high, which makes forward bias and collector voltage falls to near ground potential. Disabling IC1 (UM66) and the alarm is inhibited.

Depending on the quantity of water present in the tank, which shows the level of the corresponding LED lights up. It thus showing medium level of water in the tank with a bar-chart style.

When the water in the tank just touching the highest level detector lines L12, DC voltage developed in capacitor C2. This makes it possible to produce a melody IC1 (UM66) and the alarm sounds again.

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This is indicator circuit to indicate that there is blown fuse, it will show the condition of fuse through LEDs. This circuit works for fuse 220V mains. This compact circuit is very useful and reliable. It is a low cost circuit which use very few components. Generally, when an electronic device indicates no power, the potential cause may be just a blown fuse.

Under normal conditions (when fuse is alright), voltage drop in first arm is 2V + (2 x 0.7V) = 3.4V, whereas in second arm it is only 2V. So current flows through the second arm, i.e. through the green LED, causing it to glow; whereas the red LED remains off.

When the fuse blows off, the supply to green LED gets blocked, and because only one LED is in the circuit, the red LED glows. In case of power failure, both LEDs remain “off”.

LED Indicators:

• RED LED : the fuse blows
• GREEN LED : normal condition, the fuse is OK
• Both LED Off : power failure, the mains is off or the circuit is broken.

This circuit can be easily modified by adding alarm/buzzer circuit to produce a siren in fuse-blown condition (see Fig. 2). An optocoupler is used to trigger the siren. When the fuse blows, red LED glows. Simultaneously it switches “on” the siren.

In place of a bicolour LED, two LEDs of red and green colour can be used. Similarly, only one diode in place of D1 and D2 may be used. Two diodes are used to increase the voltage drop, since the two LEDs may produce different voltage drops.

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