VHF Field Strength Meter

Above Circuit Show wide band VHF field strength meter. The field strength is measured by converting the radio signal to DC and measuring it. The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This circuit is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations).

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Filed Under: Detector

Wireless Electrocardiogram

Description:

The purpose of this project is to create a portable Electrocardiogram (ECG) to monitor patients who are in their houses or employees with risk of heart attack.The context for this project is the integration of wireless communication in medical applications for home healthcare.This means that, patients are no longer bound to a specific healthcare location where they are monitored by medical instruments.Wireless communication will not only provide them with safe and accurate monitoring, but also the freedom of movement.

This portable ECG will monitor the patients with 3 electrodes that will measure the body information.

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Filed Under: Detector, hobby project

Bomb Disposal Robot

Wireless Bomb Disposal Robot uses a control application, at the user end to control the robot remotely using Wireless technology. The bomb technician controls the robot using this application. Input from the user is transmitted serially over an RF link to the Robot, where it is received, identified and relayed to the appropriate module.

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Filed Under: Detector

Gas Leakage Alarm

LPG gas is supplied in pressurised steel cylinders. As this gas is heavier than air, when it leaks from a cylinder it flows along floor and tends to settle in low spots such as a basement. This can cause fire or suffocation if not dealt with it.Here is a circuit that detects the leakage of LPG gas and alerts the user through audio-visual indications.Above Fig shows the circuit of the gas leakage alarm. The circuit operates off a 9V PP3 battery.Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module.

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Filed Under: Detector

12V Lead-Acid Battery Monitor

This circuit makes it posible to monitor the charging process to a higher level. If you need more information then check out the LM3914 Datasheet.
Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy.
Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up.Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts.

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Filed Under: Detector

Ultrasonic Movement Detector

This ultrasonic movement detector circuit uses a crystal locked circuit to get maximum performance from the ultrasonic transmitter. However, the detection circuit is different. think it is more sensitive.
ASSEMBLY INSTRUCTIONS:
Check all the components against the parts list. It is generally easier to solder in the lowest height components first - the resistors and diodes. Make sure to get the diodes in the correct way. The black circle or band on the diodes must match the bar of the diode symbol on the overlay.There are a lot of resistors. Use the resistor color code printed on the back of the header card to work out each value.
The 40 kHz crystal can be inserted either way. Holes have been provided to secure its case to the PCB. Use one of the leads cut from the resistors. You can also quickly solder the wire to the case of the crystal.

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Filed Under: Detector

Parking Detector

This schemetic can be used as an aid for sensing the distance between the rear bumper of the car and any obstacle behind the car. The distance can be understood from the combination of the LEDs (D5 to D7) glowing. At 25cm D7 will glow, at 20 cm D7&D6 will glow and at 5cm D7, D6 and D5 will glow. When the obstacle is beyond 25 cm none of the above LEDs will glow.
Two ICs are used in the circuit. The IC1 (NE555) is wired as an astable multivibrator for driving the IR Diode D1 to emit IR pulses. The operating frequency of the transmitter is set to be 120Hz.The IR pulses transmitted by D1 will be reflected by the obstacle and received by the D2 (IR photo diode).The received signal will be amplified by IC2a.

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Filed Under: Detector

Phone Line Detector

This kind of circuit speaks for itself. While the phone line is okay, Q1 works as a short that has a extremely high resistance/ohms value via R1, R2, and R3 for a total close to 66 MegaOhm, so it is very high. When the phone line is cut (open), it triggers the MosFet (Q3) via transistor Q2 to drive the load. Replacements are acceptable, not one of the parts are crucial.
The ‘LOAD’ can be anything you like. A lamp, relay, motor, tape-recorder, stereo, security system, or anything else.

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Filed Under: Detector

Electromagnetic Field Sensor

This circuit that can be used to sense electromagnetic radiations. The circuit can even detect hidden wrings. A 1mH inductor is used for sensing the electric field. The electric field will induce a small voltage in the sensor inductor and this induced voltage is amplified by the opamp.The headphone connect at the output of the opamp will give an audio indication of the electric field. For example, the electric field around a mains transformer can be heard as a 50 Hz hum. The POT R4 can be used to adjust the gain of the amplifier. By keeping the sensor inductor near to a telephone line, you can even hear the telephone conversations.

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Filed Under: Detector

Water Level Detector With Alarm

This is a simple alarm circuit which produces a musical tone when water or some conducting liquid comes in contact with the two sensor wires provided. The circuit is based on four transistors and one melody generator IC (M 3482). When water comes in contact with the sensors wires A & B, the base of Q1 gets connected with the negative and it conducts.This makes Q2 and Q3 ON. When Q3 is ON the power is available for the music generator circuit and it starts producing 12 different melodies one after another. The music continues as long as there is water between the sensor wires. The POT R12 can be used as a volume controller.

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Filed Under: Detector, Water level

Liquid Level Indicator Using LM1830

LM1830 is a monolithic integrated circuit that can be used in liquid level indicator / control systems. Manufactured by National Semiconductors, the LM1830 can detect the presence or absence of polar fluids . Circuits based on this IC requires minimum number of external components and AC signal is passed through the sensing probe immersed in the fluid. Usage of AC signal for detection prevents electrolysis and this makes the probes long lasting. The IC is capable of driving a LED, high impedance tweeter or a low power relay at its output.

Low liquid level indicator (LED)
The circuit of a low liquid level indicator with LED is shown above. Capacitor Ct sets the frequency of the internal oscillator. With the give value of C1 the frequency will be around 6KHz. Capacitor Cb couples the oscillator output to the probe and it ensures that no DC signal is applied to the probe. The circuit detects the fluid level by comparing the probe to ground resistance with the internal reference resistor Rref.
When the probe to ground resistance goes above the Rref the oscillator output is coupled to the base of the internal output transistor making it conducting. The LED connected to the collector (between pin 12 and Vcc) is driven. Since the base of the transistor is driven using the oscillator, actually the transistor is being switched at the oscillator’s output frequency @50% duty cycle. There is no problem in driving the LED using AC signal and this method is very useful when it comes to use a loud speaker as the indicator. Loud speakers can be driven only by using AC signals and a DC signal will not produce any sound out of the speaker. The circuit diagram of a liquid level indicator using loud speaker at its output is shown below. The circuit is similar to the first circuit except that the LED is replaced by a loud speaker and the load current limiting resistor is changed from 1.2K to 1.5K.
Low liquid level warning (audio)
Low liquid level indicator with external reference resistor
Some time there may be situations when the fluid resistance (probe to ground) do not match with the 13K internal reference resistor. In such cases there is option to avoid the internal reference resistor and an external reference resistor of your choice (Rx in the circuit) can be employed. The oscillators output is directly available at pin 5 and the Rx connects the oscillator output to the probe through the blocking capacitor. The circuit diagram for the above said scheme is shown below.
Level indicator using external reference resistor
High liquid level activated switchHigh liquid level activated switch
A method for activating a relay when the liquid level exceeds a predetermined level is shown here. DC voltage is required for driving the relay and AC voltage cannot be used here just like what we did in the case of LED and speaker. Pin 9 of the IC can be used to solve this problem. A capacitor connected from this pin to ground will keep the internal output transistor steadily ON whenever the probe resistance goes higher than the reference resistor. External transistor Q1 is connected to the collector of the internal transistor. The load that is the relay is connected at the collector of Q1. When the probe is not touching the water it equal to an open circuit situation and surely the probe resistance will be many M ohms and it is greater than the Rref(13K). The internal transistor will be switched ON and Q1 whose base is connected to the collector of the internal transistor will be in OFF condition keeping the relay inactive. When the reverse scenario occurs (fluid level touches the probe) the internal transistor is switched OFF and this in turn makes the transistor Q1 ON resulting in the activation. The load connected through the relay whether pump, lamp, alarm, solenoid valve or anything is driven. Resistor R3 limits the collector current of the internal transistor while resistor R4 provides protection to the IC from transients.
High liquid level activated switch
Probe: The probe used here can be any metal rod with size and shape of your choice. The tank must be made of metal and it should be properly grounded. For non metal tanks fix a small metal contactor at its bottom level and ground it. The probe must be placed at the level you want to monitor.
Notes.
> The circuit can be assembled on a Perf board.
> I used 12V DC for powering the circuit.
> Maximum supply voltage LM1830 can handle is 28V.
> The tweeter I used was of a 16 ohm type.
> The relay I used is a 200 ohm/12V type.
> Maximum load current Q1 (2N2222) can handle is 800mA.
> The switching current/voltage ratings of the relay must be according to the load you want to drive using it.
> It is recommended to mount the IC on a holder.

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Filed Under: Detector, Water level