0 Room Noise Detector Schematic Circuit

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively. Current drawing is 1mA with LED off and 12-15mA when the LED is steady on.

Circuit diagram :

Room Noise Detector Circuit diagram

Parts List :

R1____________10K 1/4W Resistor
R2,R3_________22K 1/4W Resistors
R4___________100K 1/4W Resistor
R5,R9,R10_____56K 1/4W Resistors
R6_____________5K6 1/4W Resistor
R7___________560R 1/4W Resistor
R8_____________2K2 1/4W Resistor
R11____________1K 1/4W Resistor
R12___________33K 1/4W Resistor
R13__________330R 1/4W Resistor

C1___________100nF 63V Polyester Capacitor
C2____________10µF 25V Electrolytic Capacitor
C3___________470µF 25V Electrolytic Capacitor
C4____________47µF 25V Electrolytic Capacitor

D1_____________5mm. Red LED

IC1__________LM358 Low Power Dual Op-amp

Q1___________BC327 45V 800mA PNP Transistor

MIC1_________Miniature electret microphone

SW1__________2 poles 4 ways rotary switch

B1___________9V PP3 Battery

Clip for PP3 Battery

Use :

• Place the small box containing the circuit in the room where you intend to measure ambient noise.
• The 50 dB setting is provided to monitor the noise in the bedroom at night. If the LED is steady on, or flashes bright often, then your bedroom is inadequate and too noisy for sleep.
• The 70 dB setting is for living-rooms. If this level is often exceeded during the day, your apartment is rather uncomfortable.
• If noise level is constantly over 85 dB, 8 hours a day, then you are living in a dangerous environment.

Detail: Room Noise Detector Schematic Circuit

0 Temperature Detector For Fan Controller

The fan controller circuit for the Titan 2000 and other AF heavy-duty power amplifiers, has an output that sets a voltage if the fan controller reaches the end of its range. Since the controller responds to temperature, this signal is seen by the amplifier protection circuitry as an over temperature indication. The disadvantage of this output is that the maximum voltage for the fans is not constant, but depends on the load (number of fans, defective fans) and the mains voltage. This variation is caused by the fact that the supply voltage for the output stage is taken directly from the filtered transformer voltage.

If the fans should fail, for example, the maximum temperature limit would lie at a considerably higher level than the desired value. The accompanying circuit, which compares the magnitude of the fan voltage to a fixed reference value, has been developed to allow the maximum temperature to be reliably detected. This circuit is tailored for 12-V fans. The reference voltage is generated by the ‘micro power voltage reference’ D1 and the FET T1, which is wired as a current source. These components are powered directly from the applied fan voltage. The current source is set up to deliver approximately 50µA.

D1 can work with as little as 10µA. The supply voltage for the IC is decoupled by R10, C3 and C4, with D4 providing over voltage protection. A maximum supply voltage of 16 V is specified for the TLC271. This opamp works with a supply voltage as low as 3 V and can handle a common-mode voltage up to approximately 1.5 V less than the positive supply voltage. Accordingly, 1.2 V has been chosen for the reference voltage. The fan voltage is reduced to the level of the reference voltage by the voltage divider R2–R3–P1. The limits now lie at 11.2 V and 16.7V.

If you find these values too high, you can reduce R2 to 100 kΩ, which will shift the limits to 9.5 V and 14.2 V. The output of the voltage divider is well decoupled by C2. A relatively large time constant was selected here to prevent the circuit from reacting too quickly, and to hold the output active for a bit longer after the comparator switches states. A small amount of hysteresis (around 1 mV) is added by R4 and R5, to prevent instability when the comparator switches. D2 ensures that the magnitude of the hysteresis is independent of the supply voltage. Two outputs have been provided to make the circuit more versatile.

Output ‘R’ is intended to directly drive the LED of an optocoupler. In addition, transistor T2 is switched on by the output of the opamp via R7 and R8, so that a relay can be actuated or a protection circuit triggered using the ‘T’ output. The high-efficiency LED D3 indicates that IC1 has switched. It can be used as a new ‘maximum’ temperature’ indicator when this circuit is added to the fan controller. The circuit draws only 0.25 mA when the LED is out, and the measured no-load current consumption (with a 12.5V supply voltage) is 2.7 mA when the LED is on.

Resistors:

• R1 = 22kΩ
• R2 = 120kΩ
• R3 = 10kΩ
• R4,R6 = 1kΩ
• R5 = 1MΩ
• R7,R8 = 47kΩ
• R9 = 3kΩ9
• R10 = 100Ω
• P1 = 5kΩ preset

Capacitors:

• C1,C3 = 100nF
• C2 = 100µF 25V radial
• C4 = 47µF 25V radial

Semiconductors:

• D1 = LM385-1.2
• D2 = BAT85
• D3 = high-efficiency-LED
• D4 = zener diode 16V/1W3
• T1 = BF245A
• T2 = BC547B
• IC1 = TLC271CP

Miscellaneous:

• K1 = 2-way PCB terminal block, raster 5mm
• K2 = 3- way PCB terminal block, raster 5mm

Detail: Temperature Detector For Fan Controller

0 Versatile Proximity Detector with Auto Reset

Electrochemical processes taking place in our body generate complex sig-nals (hum) that are continuously being passed along the nerve fibres throughout the body. Any physical activity such as muscle movement increases hum.

Here’s a circuit that operates when it detects hum generated by the human body in proximity. Its versatility lies in the fact that you don’t need to touch the metal plates for detection. Just the presence of your hand/body within 1 cm of the sensing loop triggers the circuit. The activation of the circuit is indicated by the glowing of an LED and an audible beep. The circuit continues to glow and beep until the hand is within 5 cm of the loop. Beyond 5 cm, it resets automatically.

Here IC2 (555) simplifies the circuitry otherwise needed to achieve this. Regulator 7809 (IC1) supplies 9V DC to the circuit.

Versatile Proximity Detector with Auto Reset Circuit Diagram

When power is turned on, capacitor C3 (47 kpF) charges through resistor R1 (1 mega-ohm). Output pin 3 of IC2 remains high as long as the voltage at its pin 2 is below 2/3Vcc; the buzzer beeps for this period. Beyond that voltage, the output resets (goes low).

Transistors T1 and T2 (each BC548) form a Darlington pair. As long as T1 and T2 remain in cut-off condition, capacitor C3 retains the charge and the buzzer is off. When you take your hand within 1 cm of the loop wire, T1 conducts due to the noise picked up by its base. So capacitor C3 gets a discharge path, and the voltage at pin 2 of IC2 going below 1/3Vcc sets output pin 3 high. As a result, the buzzer sounds.

The beep continues until C3 charges to 2/3Vcc due to gradual withdrawal of the hand from vicinity of the loop wire.  The series combination of capacitor C5 and resistor R3 within dotted lines is optional and reduces hum at the base of T1. The values of C5 and R3 to be used for varying the sensitivity of the circuit are given in the table.

For calibration, wire the circuit and use a 7cm hook-up wire at the base of T1. When you place your hand over the wire insulation, the buzzer should beep. If it doesn’t, check connections. Now connect the loop wire. If beep continues even when there is no person within 20 cm, use a suitable combination of C5 and R3 from the table to reduce the circuit sensitivity.

The suggested PCB size for the circuit (excluding power supply) is 4 cm×3 cm. Solder the loop wire directly. A small hook-up wire was used in the prototype.

Do not remove insulation of the wire. Keep the circuit away from mains wiring and large metal objects.

Sourced by: EFY. Author:  Kaushik Hazarika

Detail: Versatile Proximity Detector with Auto Reset

0 Simple Electromagnetic Field Detector Schematic

This circuit is sensitive to low frequency electromagnetic radiation and will detect for example hidden wiring or the field that encompasses a transformer. Pickup is by a radial type inductor, used as a probe which responds well to low frequency changing magnetic and electric fields. Ordinary headphones are used to for detection. The field that surrounds a transformer is heard as a 50 or 60Hz buzz. The circuit is below:-

Electromagnetic Field Detector Circuit Diagram

Notes:

I threaded a length of screened cable through an old pen tube and soldered the ends to a radial type can inductor. I used 1mH. The inductor fitted snugly into the pen tube. The opposite end of the cable connects to the input of the op-amp. Any op-amp should work here, possibly better results may be achieved with a low noise FET type such as the LF351. The 2M2 potentiometer acts as a gain control and the output is a pair of headphones. Stereo types can be used if they are wired as mono. I used an 8 ohm type, but the circuit should work equally well with higher impedance types. The probe (shown below) may be connected via screened cable and a 3.5mm stereo plug and socket.

Detection:

The sensitivity of this circuit is good. Mains wiring buried an inch in plaster can be detected with precision. A small load on the electric supply is all that is needed; a 20 watt desk lamp or similar will suffice. The hum field surrounding a transformer can be detected oat over 7 inches. Domestic appliances such as videos and alarm clocks all produce interference which can be heard with the probe. The electric field surrounding a loudspeaker or earpiece can also be heard. Try lifting a telephone and place the probe near the earpiece. A telephone pickup coil can be used in place of the inductor if desired. I will make an improved version of this circuit with a meter output later. link

Detail: Simple Electromagnetic Field Detector Schematic