Make a Digital Stop Watch

Description

A digital stop watch built around timer IC LM555 and 4-digit counter IC MM74C926  with multiplexed 7-segment LED display.MM74C926 consists of a 4-digit counter, an internal output latch, npn output sourcing drivers for common cathode,7-segment display and an internal multiplexing circuitry with four multiplexing outputs.The counter advances on negative edge of the clock. The clock is generated by timer IC LM555.The circuit works off a 5V power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in a metal boxvwith provisions for four 7-segment displays, rotary switch S1, start/stop switch S2 and reset switch S3

Testing

First, reset the circuit by pressing S3 so that the display shows ‘0000.’ Now open switch S2 for the stop watch to start counting the time. If you want to stop the clock, close S2. Rotary switch S1 is used to select the different time periods at the output of the astable multivibrator (IC1).

Digital Timer Circuit Diagram .

Digital Timer Circuit

You may also be interested in other Timer circuits we have in our website:

1. Long Duration Timer Circuit

For more circuits, please check our category on Clocking and Timer Circuits

Read more: http://www.circuitstoday.com/category/clocking-timer-circuits#ixzz1N9RBsI8V
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Long duration timer circuit.

Description.

This timer circuit can be used to switch OFF a particular device after around 35 minutes. The circuit can be used to switch OFF devices like radio, TV, fan, pump etc after a preset time of 35 minutes. Such a circuit can surely save a lot of power.

The circuit is based on quad 2 input CMOS IC 4011 (U1).The resistor R1 and capacitor C1 produces the required long time delay. When pushbutton switch S2 is pressed, capacitor C1 discharges and input of the four NAND gates are pulled to zero. The four shorted outputs of U1 go high and activate the transistor Q1 to drive the relay. The appliance connected via the relay is switched ON. When S2 is released the C1 starts charging and when the voltage at its positive pin becomes equal to ½ the supply voltage the outputs of U1 becomes zero and the transistor is switched OFF. This makes the relay deactivated and the appliance connected via the relay is turned OFF. The timer can be made to stop when required by pressing switch S1.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
  
• The circuit can be powered from a 9V PP3 battery or 12V DC power supply.
  
• The time delay can be varied by varying the values of C1&R1.
  
• The push button switch S2 is for starting the timer and S1 for stopping the time.
  
• The appliance can be connected via contacts N1 & N2 of the relay RL1.
• The IC U1 is 2 input quad NAND gate 4011.

Read more: http://www.circuitstoday.com/category/clocking-timer-circuits#ixzz1N9R0PrdY
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Water Level Indicator

Description

This is the circuit diagram of a simple corrosion free water level indicator for home and industries.In fact the the level of any conductive non corrosive liquids can be measured using this circuit.The circuit is based on 5 transistor switches.Each transistor is switched on to drive the corresponding LED , when its base is supplied with current through the water through the electrode probes.

One electrode probe is (F) with 6V AC is placed at the bottom of tank.Next probes are placed step by step above the bottom probe. When water is rising the the base of each transistor gets electrical connection to 6V AC through water and the corresponding probe.Which in turn makes the transistors conduct to glow LED and indicate the level of water.The ends of probes are connected to corresponding points in the circuit as shown in circuit diagram.Insulated Aluminum wires with end insulation removed will do for the probe.Arrange the probes in order on a PVC pipe according to the depth and immerse it in the tank.AC voltage is use to prevent electrolysis at the probes.So this setup will last really long.I guarantee at least a 2 years of maintenance free operation.That’s what I got and is still going.

Components

T1 – T5 BC 548 or 2N2222 Transistors

R1-R5 2.2K 1/4 W Resistors

R6-R10 22K 1/4 W Resistors

D1 – D5 LED’s ( color your choice)

Notes:

Use a transformer with 6V 500 mA output for power supply.Do not use a rectifier! we need pure AC. Use good quality insulated Aluminum wire for probes.If Aluminum wires are not available try Steel or Tin.Copper is the worst.Try the circuit first on a bread board and if not working properly, make adjustments with the resistance values .This is often needed because conductivity of water changes slightly from place to place.The type number of the transistors used here are not critical and any small signal NPN transistor will do the job. Few other suitable type numbers are BC546, BC107, PN2222, BC337, BF494, ZTX300, BEL187 etc. The circuit can be enclosed in a plastic box with holes for revealing the LEDs .

Water Level Indicator Circuit Diagram and Sensor Arrangement.

Water Level Indicator

If you need a fully automatic water level controller circuit then try this circuit  Water level controller. The circuit is fully based primarily on transistors. The sensing section is somewhat similar to this circuit but there is additional circuitry for switching the pump ON when the water level falls below a set level and the pump will be switched OFF when the tank is full. Few transistors , one 555IC and an electromagnetic relay is used for realizing the control section. The circuit is very simple cost effective , reliable and many guys have successfully assembled it.I am also working on a float type water level indicator/controller using the float type fuel gauge mechanism used in motor cycles.The level sensor section is  finished and now I am working on the control circuitry. I will add the circuit here as soon as it is finished

Read more: http://www.circuitstoday.com/simple-water-level-idicator#ixzz1N9PzvrjF
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Water level controller circuit.

Description.

A simple but very reliable and effective water level controller circuit diagram is shown here. The circuit uses 6 transistors, 1 NE555 timer IC, a relay and few passive components. The circuit is completely automatic which starts the pump motor when the water level in the over head tank goes below a preset level and switchess OFF the pump when the water level in the over head tank goes above the full level.

Probe D is positioned at the bottom level of the tank while probes A, B and C are placed at full, half and medium levels of the tank respectively. The level sensing part of the circuit is built around transistors Q1, Q2 and Q3. When water level is below the quarter level probes A, B and C are open and the transistor Q1, Q2 and Q3 remains OFF. When the water level rises and touches the probes the corresponding transistors gets biased and switches ON. Resistors R1, R2, R3 limit the bases current of corresponding transistors while resistors R4, R5, R6 limit their collector current. LEDs D1, D2 and D3 provide a visible indication of the current water level.

When the water level goes below medium, transistor Q2 gets switches OFF and its collector goes positive. Collector of Q2 is connected to the base of transistor Q6 and as result transistor Q6 gets switched ON. Transistor Q5 will be also ON because its base in connected to the collector of Q4 which is presently OFF. As a result when the water level goes below medium relay K1 gets energised and the pump is driven. The relay is wired in the latching mode so that even if the water level goes above medium level the pump remains ON so that the tank gets completely filled. For wiring the relay in latching mode one set  of N/O contacts is used. When relay is activated these contacs close which forms a short across collector and emitter of Q6. This makes the state of Q6 irrelevant to the opertion of the relay and the relay remains ON as long as the transistor Q5 is ON. The only way to make the relay OFF is by switching OFF Q5 and it is done automatically when the water level reaches the full level.

Collector of transistor Q1 is connected to the trigger pin (pin2) of IC1. When the water level reaches full level the transistor Q1 gets switched ON. As a result its collector goes to ground level which triggers the IC1 which is wired as a monostable. The output of IC1 goes high for about 1S. This makes the transistor Q4 ON for the same time and transistor Q5 whose base is connected to the collector of Q4 is switched OFF cutting the supply to the relay. This makes the motor OFF and it remains OFF until the water level again goes below the medium level.

Resistor R8 is a pull up resistor for the trigger pin of the NE555. Capacitor C3 couples the collector of Q1 to the trigger pin of NE55 and facilitates edge triggering whenever the transistor Q1 goes ON. A monostable circuit can be made edge triggered by connecting the trigger signal to the trigger input pin through a capacitor. The capacitor blocks DC and passes sudden changes. The circuit used here is termed as negative edge triggered because the monostable is triggered when ever the trigger input signal falls. R10 and R12 limits the collector current of Q4 and Q5 respectively while R9 and R11 limits their base current. R13 limits the base current of Q6 while D4 is a freewheeling diode which protects the switching transistors from voltage transients.

Circuit diagram.

Water level controller circuit diagram

Probe arrangement diagram

The probes can be arranged as shown in the diagram above. Insulated Aluminium wires can be used as the probes. The probes can be binded on a plastic rod and should be erected vertically inside the tank. The length of the probes wires and the supporting plastic rod must be chosen according to the depth of the tank. Since DC is used in the level sensing section electrolysis will occur in the probes and so the probes require small maintinances in 1 or 2 month intervals. Using AC in the sensing section will completely eliminates the chance of electrolysis and I am presently working on such a circuit. You can expect it soon.

Notes.

• Use 12V DC for powering the water level controller circuit.
• The relay I used was a 5V/220 ohm relay and that’s why the current limits resistor R12 was added in the circuit. If you use a 12V relay then the R12 can be shorted.
• Do not use a relay that consumes 500mA. Maximum collector current PN2222 can handle is 600mA.
• Use insulated single strand aluminium wires for probe and they can be arranged in the tank as per the probe arrangement diagram.
• Use a holder for mounting NE555.
• The circuit can be assembled on a Perf board.
• K1 must be a double pole relay.
• The load current, voltage ratings of the relay must be selected according to the ratings of the pump motor.
• The type number of the transistors used here are not very critical and you can do suitable replacements if any type number is not availble.
• Most of the components required for this project can be found inside your scrap box.

Power supply for this circuit.

12V DC power supply

A classic 12V regulated DC supply based on 7812 is shown above. A power ON indicator LED is also added in the circuit.Resistor R13 limits the LED current. A small aluminium heatsink can be fitted to the 7812 for better saftey.Small Al heatsinks for TO-220 package are readily available in the market.

Read more: http://www.circuitstoday.com/water-level-controller#ixzz1N9PrOwpH
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DATA SHEETS

Transistors BPW77NA BPW85 BD135 2N3055 2N2222 2N2907 BC548 BC107 BC177 BF494 BF495

ICs MAX660 LM324 NE555 uA741 L200 LF351 LM383 LM386 CD4047 LM3915 TDA4935 UM66 DS1669 RF600D RF600E

Diode 1N4001 1N4002 1N4003 1N4004 1N4007 1N4148 BY127 BY133 EM513 EM516 OA79 FFH50US60S RURG1520CC

Triac BT136

SCR TYN612 TYN100 TYN606

Read more: http://www.circuitstoday.com/datasheets#ixzz1N9PC0qDL
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ir blaster

IR Blaster

Introduction

An IR Blaster is a device that functions or imitates an IR Remote Control in its features. This device is used to control other devices. If this device is connected to a PC, it can be used to control all the other IR devices that are present in the room with the help of that PC. The deice is relatively small compared to other IR devices and can be self-powered by just plugging them to the device that is to be controlled.

How IR Blaster Works?

The working of IR Blaster is pretty much the same as that of a remote control except that there is a digital to IR light converter in the IR Blaster. The digital signals produced by the up and down pulses of electricity while IR light is completely invisible. They are used because they have a better transfer rate and can travel through air without causing any threat to anyone.

If the system is neatly configured, the beam generated by the IR Blaster can be used to control devices such as TV’s and computers while, at the same time, control devices such as VCR or DVR using an IR remote control.

Applications

The main use of an IR blaster is to control a secondary device through a primary device with the help of an infrared remote control. IR blasters can be used for many electronic devices and there is no limit to its extent. The devices vary from TV’s, PC’s, VCR, home theatre, big screen projectors and so on.  Another application of the device includes the extending of the range of the IR remote by keeping the blaster in a closed area, in hiding, or even at an angle that the remote cannot “see”. There are also USB IR blasters which can be connected to computers. Through this device all the other IR devices in the room can be easily controlled.

Advantages

• User friendly
• The user can sit still in one place and handle all the devices in the room.
• Can be configured to work with special devices and also paired with computer applications like EyeTv and RealBasic.
• No need of an external power supply for the device as it gets self-powred from the device it is connected to (computer).

Disadvantages

• Configuring the device at the beginning is difficult and confusing.
• The cost of the device is considerably low, but may go up according to the sensitivity, output power levels, and other factors chosen.

Read more: http://www.circuitstoday.com/infrared-ir-blaster#ixzz1N9OaydGV
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100 Watt sub woofer amplifier.

This is the circuit diagram of a fully transistorized sub woofer amplifier that can produce an output of 100W.There are seven transistors including four in the output stage. The transistors Q1 and Q2 form the preamplifier stage. Transistors Q4 to Q7 form the output stage. Since no ICs are used the circuit is very robust and can be easily assembled on a general purpose PCB.
Circuit diagram with Parts list.



Read more: http://www.circuitstoday.com/100-watt-sub-woofer-amplifier#ixzz1N9OKmY00
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