Digital Voltmeter Circuit

Posted by Micro System

on Tuesday, September 14, 2010

This is a circuit for digital voltmeter circuit. This circuit is based on ICL7107 is a 3-1/2 digit LED A/D converter. It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers. The auto-zero adjustment mechanism ensures zero reading for 0 volts input. The circuit is classic design and you can be sure that it will work fine. However, for better result, it is recommended to design a proper PCB for minimum voltage drift and noise. This is the figure of the circuit;

Connect the positive and negative probes PLG1 and PLG2 to two points of the electric circuit you would like to know their electric potential difference or simply voltage. You have to set the selector switch S2 to proper voltage range you expect those two points would have. To calibrate the volt-meter, use the potentiometer P1. Adjust it to read correct voltage on the display by connecting probes to a known voltage source. You may need to use another calibrated volt-meter in this case.

Digital Step Counter Circuit

Posted by Micro System

on Wednesday, August 4, 2010

This is a circuit for calculate the range that can be used in your vehicle. This is a simple form circuit. This is the figure of the circuit;


IC1A & IC1B form a mono stable multi vibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divides by 64. Q2 drives the LED dot-segment of D1 every 32 pulses counted by IC2. Either IC3 & IC4 divide by 10 and drive the displays. P1 resets the counters and P2 enables the displays. IC1C generates an audio frequency square wave that is enabled for a short time at each mono stable count. Q1 drives the piezo sounder and SW2 allows to disable the beep.

Part;
R1,R3____22K 1/4W Resistor
R2________2M2 1/4W Resistor
R4________1M 1/4W Resistor
R5,R7,R8__4K7 1/4W Resistor
R6_______47R 1/4W Resistor
R9________1K 1/4W Resistor
C1_______47nF 63V Polyester Capacitor
C2______100nF 63V Polyester Capacitor
C3_______10nF 63V Polyester Capacitor
C4_______10µF 25V Electrolytic Capacitor
D1_______Common-cathode 7-segment LED mini-display (Hundreds meters)
D2_______Common-cathode 7-segment LED mini-display (Kilometers)
IC1______4093 Quad 2 input Schmitt NAND Gate IC
IC2______4024 7 stage ripple counter IC
IC3,IC4__4026 Decade counter with decoded 7-segment display outputs IC
Q1,Q2___BC327 45V 800mA PNP Transistors
P1_______SPST Pushbutton (Reset)
P2_______SPST Pushbutton (Display)
SW1______SPST Mercury Switch, called also Tilt Switch
SW2______SPST Slider Switch (Sound on-off)
SW3______SPST Slider Switch (Power on-off)
BZ_______Piezo sounder
B1_______3V Battery (2 AA 1.5V Cells in series)

Simple Sonar Tester Circuit

Posted by Micro System

on Tuesday, July 27, 2010

SONAR stands for Sound Navigation Ranging. It is a technique which is used to determine the distance and direction of objects by acoustic means usually in water, but also in air. The SONAR described here has the most basic functionality it simply reports the existence of an object up to a few meters’/yards’ distance. This is the figure of the circuit;


It would, for example, shriek when a reversing vehicle approached a wall (X1 and X2 would be mounted just far enough apart NOT to shriek until the vehicle was near the wall). Or X1 and X2 would be mounted on opposite sides of a closed door -- thus the circuit would shriek when the door was open. Or X1 and/or X2 could be placed underneath an item, to shriek when the item was lifted. OBSERVATION: The circuit relies on acoustic feedback. IC1 is a sensitive amplifier. Both X1 and X2 are piezo sounders (discs, mounted in plastic housings) without internal electronics. X1 functions as a "microphone", X2 as a "speaker". Ideally, X1 and X2 will be identical, to encourage feedback at their resonant frequencies. Piezo tweeters may also be used, although these are expensive. C2 determines gain (amplification). First try the circuit without C2. If C2 is, say, 10μ, the circuit’s sensitivity will be greatly increased. C3 is necessary to limit output current. The circuit would ideally be run off a 12V DC plug pack power supply.

Checker Transistor Tester Circuit

Posted by Micro System

on

This is a simple circuit for has helped me out on many occasions. It is able to check transistors, in the circuit, down to 40 ohms across the collector-base or base-emitter junctions. It can also check the output power transistors on amplifier circuits. This is the figure of the circuit;


Circuit operation is as follows. The 555 timer (IC1) is set up as a 12 Hz multi vibrator. The output on pin 3 drives the 4027 flip-flop (IC2). This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LED's are arranged so that when the polarity across the circuit is one way only one LED will light and when the polarity reverses the other LED will light, therefore when no transistor is connected to the tester the LED's will alternately flash. The IC2 outputs are also connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will turn on and produce a short across the LED pair. If a good NPN transistor is connected then LED1 will flash by itself and if a good PNP transistor is connected then LED2 will flash by itself. If the transistor is open both LED's will flash and if the transistor is shorted then neither LED will flash.

9v Battery Voltage Monitor Circuit

Posted by Micro System

on

This is a simple form circuit for monitoring battery. This circuit is based on LTC 1440. This is the figure of the circuit;


Nine voltage batteries are used in a wide variety of electronic devices. But, you often don’t know when it is time to change the battery until the device stops operating. The hobby circuit below provides a visual indication when the battery needs to be replaced. It uses a neat IC from Linear Technology, which contains a very low power voltage reference and a voltage comparator. The circuit is designed to turn on a LED indicator light when the battery voltage drops below 7.2 volts.

Room Thermostat Circuit

Posted by Micro System

on Sunday, July 25, 2010

This is a circuit of room thermostat which is used to control heating or cooling system in air conditioning and heating system has been one of the common device used in residential and industrial buildings to control the temperature of a space in a warehouse, a room, a hall or an office. This is the figure of the circuit;


The circuit diagram shows the configuration of the Room thermostat. The LM358 Op Amp is used as a comparator to sense the inputs of the reference voltage (PIN 3) and room temperature (PIN 2). The thermistor used is a NTC (negative temperature coefficient) type where its resistance will drop when the temperature increases and vice versa. It has a resistance of of 20K ohm at 25 degree Celcius. When the room temperature increases, the thermistor resistance will drop and hence the output of the operational amplifier will be high. This cause transistor Q1 to turn ON and the relay is turn ON. The COM position of the relay contact will switch to NO and ON the chilled water valve which allow the cold water to pass through the coil. The cold air from the coil is transferred to the room by the fan until the temperature of the room goes down to its setpoint again.