Saturday, August 31, 2013

Digital AC DC Voltage Tester Circuit

It is always necessary for engineers and technicians to test AC/DC mains voltages and continuity for any given circuit during breakdowns, the above mentioned circuit can be used as and sought of tester and can also check the continuity for you. all one has to do is that to touch the two probes at the required terminal of either live or an dead circuit
The unique design of the tester allows the circuit to work in both AC and DC without any mode selector switch.
When the probes A and B are short circuited voltage pin 1 goes a little below the threshold of the Schmitt trigger due to the voltage divider action of the resistor R1, R2 and VR1 This disables the gate of pin1 and due to this the transistor T2 goes into saturation while the transistor T1 is cut off therefore the green LED glows while the red segment goes off and the display will now glow as “C” 
Circuit Diagram
VR1 is a miniature preset which is to be calibrated before use its calibrations are fairy simple, keep both the probes A and B short circuited and the preset VR1 at its minimum value and slowly increase the resistance value of the VR1 till the red LED glows OFF and only green LED glows 


Digital Remote Thermometer Circuit

 This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensors output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter.
Transmitter Circuit Operation:
IC1 is a precision centigrade temperature sensor with a linear output of 10mV/°C driving IC2, a voltage-frequency converter. At its output pin (3), an input of 10mV is converted to 100Hz frequency pulses. Thus, for example, a temperature of 20°C is converted by IC1 to 200mV and then by IC2 to 2KHz. Q1 is the driver of the power output transistor Q2, coupled to the mains supply by L1 and C7, C8. 
Circuit Diagram:

Transmitter parts:
  • R1 = 100K 1/4W Resistors
  • R2 = 47R 1/4W Resistor
  • R3 = 100K 1/4W Resistors
  • R4 = 5K 1/2W Trimmer Cermet
  • R5 = 12K 1/4W Resistor
  • R6 = 10K 1/4W Resistor
  • R7 = 6K8 1/4W Resistor
  • R8 = 1K 1/4W Resistors
  • R9 = 1K 1/4W Resistors
  • C1 = 220nF 63V Polyester Capacitor
  • C2 = 10nF 63V Polyester Capacitor
  • C3 = 1µF 63V Polyester Capacitor
  • C4 = 1nF 63V Polyester Capacitors
  • C5 = 2n2 63V Polyester Capacitor
  • C6 = 1nF 63V Polyester Capacitors
  • C7 = 47nF 400V Polyester Capacitors
  • C8 = 47nF 400V Polyester Capacitors
  • C9 = 1000µF 25V Electrolytic Capacitor
  • D1 = 1N4148 75V 150mA Diode
  • D2 = 1N4002 100V 1A Diodes
  • D3 = 1N4002 100V 1A Diodes
  • D4 = 5mm. Red LED
  • IC1 = LM35 Linear temperature sensor IC
  • IC2 = LM331 Voltage-frequency converter IC
  • IC3 = 78L06 6V 100mA Voltage regulator IC
  • Q1 = BC238 25V 100mA NPN Transistor
  • Q2 = BD139 80V 1.5A NPN Transistor
  • T1 = 220V Primary, 12+12V Secondary 3VA Mains transformer
  • PL = Male Mains plug & cable
  • L1 = Primary (Connected to Q2 Collector): 100 turns
  • Secondary: 10 turns
  • Wire diameter: O.2mm. enameled
  • Plastic former with ferrite core. Outer diameter: 4mm
Receiver Circuit Operation:
 The frequency pulses coming from mains supply and safely insulated by C1, C2 & L1 are amplified by Q1; diodes D1 and D2 limiting peaks at its input. Pulses are filtered by C5, squared by IC1B, divided by 10 in IC2B and sent for the final count to the clock input of IC5. IC4 is the time-base generator: it provides reset pulses for IC1B and IC5 and enables latches and gate-time of IC5 at 1Hz frequency. It is driven by a 5Hz square wave obtained from 50Hz mains frequency picked-up from T1 secondary, squared by IC1C and divided by 10 in IC2A. IC5 drives the displays cathodes via Q2, Q3 & Q4 at a multiplexing rate frequency fixed by C7. It drives also the 3 displays paralleled anodes via the BCD-to-7 segment decoder IC6. Summing up, input pulses from mains supply at, say, 2KHz frequency, are divided by 10 and displayed as 20.0°C. 
Circuit Diagram:

Receiver Parts:
  • R1 = 100K 1/4W Resistor
  • R2 = 1K 1/4W Resistor
  • R3 = 12K 1/4W Resistors
  • R4 = 12K 1/4W Resistors
  • R5 = 47K 1/4W Resistor
  • R6 = 12K 1/4W Resistors
  • R8 = 12K 1/4W Resistors
  • R9-R15=470R 1/4W Resistors
  • R16 = 680R 1/4W Resistor
  • C1 = 47nF 400V Polyester Capacitors
  • C2 = 47nF 400V Polyester Capacitors
  • C3 = 1nF 63V Polyester Capacitors
  • C4 = 10nF 63V Polyester Capacitor
  • C7 = 1nF 63V Polyester Capacitors
  • C5 = 220nF 63V Polyester Capacitors
  • C6 = 220nF 63V Polyester Capacitors
  • C8 = 1000µF 25V Electrolytic Capacitor
  • C9 = 100pF 63V Ceramic Capacitor
  • C10 = 220nF 63V Polyester Capacitors
  • D1 = 1N4148 75V 150mA Diodes
  • D2 = 1N4148 75V 150mA Diodes
  • D3 = 1N4002 100V 1A Diodes
  • D4 = 1N4002 100V 1A Diodes
  • D5 = 1N4148 75V 150mA Diodes
  • D6 = Common-cathode 7-segment LED mini-displays
  • D7 = Common-cathode 7-segment LED mini-displays
  • D8 = Common-cathode 7-segment LED mini-displays
  • IC1 = 4093 Quad 2 input Schmitt NAND Gate IC
  • IC2 = 4518 Dual BCD Up-Counter IC
  • IC3 = 78L12 12V 100mA Voltage regulator IC
  • IC4 = 4017 Decade Counter with 10 decoded outputs IC
  • IC5 = 4553 Three-digit BCD Counter IC
  • IC6 = 4511 BCD-to-7-Segment Latch/Decoder/Driver IC
  • Q1 = BC239C 25V 100mA NPN Transistor
  • Q2 = BC327 45V 800mA PNP Transistors
  • Q3 = BC327 45V 800mA PNP Transistors
  • Q4 = BC327 45V 800mA PNP Transistors
  • PL = Male Mains plug & cable
  • T1 = 220V Primary, 12+12V Secondary 3VA Mains transformer
  • L1 = Primary (Connected to C1 & C2): 10 turns
  • Secondary: 100 turns
  • Wire diameter: O.2mm. enameled
  • Plastic former with ferrite core. Outer diameter: 4mm.
  • D6 is the Most Significant Digit and D8 is the Least Significant Digit.
  • R16 is connected to the Dot anode of D7 to illuminate permanently the decimal point.
  • Set the ferrite cores of both inductors for maximum output (best measured with an oscilloscope, but not critical).
  • Set trimmer R4 in the transmitter to obtain a frequency of 5KHz at pin 3 of IC2 with an input of 0.5Vcc at pin 7 (a digital frequency meter is required).
  • More simple setup: place a thermometer close to IC1 sensor, then set R4 to obtain the same reading of the thermometer in the receivers display.
  • Keep the sensor (IC1) well away from heating sources (e.g. Mains Transformer T1).
  • Linearity is very good.
  • Warning! Both circuits are connected to 230Vac mains, then some parts in the circuit boards are subjected to lethal potential! Avoid touching the circuits when plugged and enclose them in plastic boxes. 
Source -

Friday, August 30, 2013

32W Hi Fi Audio Amplifier Using TDA2050

Here is a Hi-Fi power amplifier circuit, built with a power IC TDA2050. This circuit will produce a power output up to 32watt. With good sound quality, high power and very low distortion feature, this circuit will be very suitable for simple and cheap audio systems.

32W Hi-Fi Audio Amplifier Circuit Diagram

TDA2050 Amplifier PCB Design:

 About TDA2050:

The TDA 2050 is a monolithic integrated circuit in Pentawatt package, intended for use as an audio class AB audio amplifier. Thanks to its high power capability the TDA2050 is able to provide up to 35W true rms power into 4 ohm load @ THD =10%, VS = ±18V, f = 1KHz and up to 32W into 8ohm load @ THD = 10%, VS = ±22V, f = 1KHz. Moreover, the TDA 2050 delivers typically 50W music power into 4 ohm load over 1 sec at VS=22.5V, f = 1KHz.

The high power and very low harmonic and crossover distortion (THD = 0.05% typ, @ VS = ±22V, PO = 0.1 to 15W, RL=8ohm, f = 100Hz to 15KHz) make the device most suitable for both HiFi and high class TV sets.

Simple SWR and PWR Meter

Many SWR / Power meter used by amateurs to the extent reasonably accurate continuous average power with a CW key-down signal, but can not reliably be used with other (modulated) signals PEP or average power measurement. These laws seek to show why the power measurement can be a sensitive issue, and because the interpretation of a yardstick of power can be a lot of attention and knowledge of construction and the characteristics of the instrument.

A reflectometer-type SWR meter can be calibrated to give power back and forth (PF, Pr) on a power supply. A classic example is the 1943 Bird Series power meter, which is a directional coupler is used to obtain a sample voltage proportional to the voltage wave or forward or backward on the feeder (VF, VR). Other systems, perhaps more suitable for HF, then use a bridge circuit to perform the same function.

 Simple SWR and PWR Meter Circuit diagram 

The sample voltage is then rectified and displayed on a meter that is calibrated in watts. If the counter is typically a coil, the scale, so the numbers on the scale, representing the power, are proportional to the square of the applied voltage or the current calibration. The theory of this type is very simple and is based on the concept represented by PF = Vf2/Zo. Note that if the power supply has an impedance that differs from the value of how the instrument is calibrated, there will be a mistake. The output voltage of the rectifier is a solid phase of VF or VR, and this is expected in the calibration of the meter.

Examples of directional coupling, and bridge-type reflectometers are shown in Figures 1 and 2, while the bird directional coupler means 43 is illustrated in Figure 3. Note that in all cases the measurement circuit, a combination with a small RC time constant, making the system unsuitable for the measurement of PEP, and the absence of a specific device quadratic, making them unsuitable for measuring the average power .