Thursday, May 26, 2011

Hot Water Indicator Using NTC Thermistors

A simple circuit to indicate various levels of hot water in a tank. SW1 is a normally open press button switch which allows you to view the level of hot water in a hot water tank. When pressed the voltage difference at the junction of the thermistor and preset is compared to the fixed voltage on the op-amps non-inverting input. Depending on the heat of the water in the tank, the thermistors resistance will toggle the op-amp output to swing to almost full voltage supply and light the appropriate LED.
Hot Water Indicator Circuit Using  NTC Thermistors

With a full tank of hot water adjust P1-4 so that all LED's are lit. As hot water rises, the sensor at the bottom of the tank will be the maximum level of hot water. "Hot" can be translated as 50C to 80C the presets P1-4 allow adjustment of this range.

  • I have used a quad version of the LM324 but any quad opamp can be used or even four single op-amps.
  • R2-R5 I used 330ohm resistors, but value is not critical. Lower values give brighter LED output.
  • NTC1-4 The thermistors maximum resistance must roughly equal the resistance of the fixed resistor and preset. As negative temparature coefficient (NTC) thermistors are used, then their resistance decreases for increases in temperature. I used a thermistor from the Maplin Catalogue. Cold resistance was around 300K, hot resistance 15k. Alternative thermistors may be used with different resistance ranges, but the presets P1 to P4 must also be changed as well.
  • R7-10 series resistance, only required if your thermistors resistance is several ohms at the hottest temperature.
  • P1 - P4 Chosen to match the resistance of the thermistor when cold.
  • R1 & R6. These resistors are equal and bias the op-amp inverting input to half the supply voltage. I used 100k.
Detail download here

Tuesday, May 24, 2011

Long Delay Timer Using IC 4011 Nand Gates

This following circuit shows a Long Delay Timer Circuit Diagram. This circuit designed mainly to switch off a portable radio after some time:

A very long time constant is provided by R1 and C1. C1 discharges and the near zero voltage at its positive lead is applied to the high impedance inputs of the four gates of IC1 wired in parallel when P2 is momentarily closed. The battery voltage is available at Q1 Emitter since the four paralleled gate outputs of the IC go therefore to the high state.
Long Delay Timer Circuit Using IC 4011 Nand Gates
The circuit will start if P2 is pushed for 1 to 5 second and will switch off after about 35 minutes. The time delay can be varied depends on values of R1 and/or C1. If required, P1 will stop the timer. LED D1 is optional. When the load is placed far from the time, LED D1 can be useful to signal relay operation

List Components of Long Delay Timer Circuit :
R1   : 10M
R2 : 4K7
R3 : 1K
C1 : 220µF/25V
D1 : LED any type
D2 : 1N4148
IC1 : 4011 Quad 2 Input NAND Gate CMos IC
Q1 : BC337
P1,P2: SPST Pushbuttons
RL1 : 12V Relay Switch
Detail download here

3-Phase Pulse Generator Using CMOS Inverters And Shift Register

This is a circuit of a 3-phase pulse generator. This circuit produce 3 phase overlapped output similar with 3 phase  AC powerline, you can say this circuit produce the DC pulse version. This circuit Requires only CMOS 4-bit shift register and two CMOS inverters  as the circuit’s  main components. The shift register is configured as divide-by-6 Johnson counter, providing glitch-free outputs. Square-wave clock signal should be provided by external source to drive this circuit, and this clock source should have frequency 6 times of desired output frequency. 
3-Phase Pulse Generator Circuit
Detail download here

Adjustable Switching Regulator using LM317

A switching voltage regulator circuit shown here can be a low cost solution for your high efficiency requirement electronic circuit design. This regulator circuit  can deliver up to 3A of current. The input voltage range of this circuit is between 8 to 35V DC and the output voltage can be adjusted between 1.8 to 32V DC. The output voltage can be adjusted by using the POT R4
Adjustable Switching Regulator Circuit  using LM317

LM317 Pinout
The circuit uses a standard linear regulator LM317 IC. LM317 regulator IC provide a stable internal voltage reference, and provide the adjustment method. This wide-range output voltage adjustment make it suitable for general purpose power supply in lab application.

When compared to linear voltage regulators the switching voltage regulators are much power efficient. In the case of linear voltage regulators the difference between the input and output voltage is just wasted and for switching regulators there is almost no such wastage and that’s why the switching regulators have great power efficiency ranging up to 85% . In simple words, the switching regulator operates by taking small bits of energy from the input voltage source and then transferring it to the output with the help of a solid state switch and a control circuitry. Since the switching element is either fully open or closed at any moment, no energy is wasted across it. The control circuit controls the duty cycle of the solid state switch which in turn determines rate at which energy is transferred to the output.
Detail download here

Monday, May 23, 2011

Water Level Indicator With Buzzer Circuit Using Transistor

This is a simple water level indicator circuit that is based on few transistors . The circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full.
Water Level Indicator With Buzzer Circuit Using Transistor
Water Level Indicator + Buzzer Circuit Using Transistor
The circuit is very simple and it has a very low current consumption , so you can use a 9 volts battery to powering this water level indicator alarm . This water level indicator alarm electronic circuit can be used even for rain alarm or short circuit alarm , a resistance with a value from 0 to about 1 M ohm will trigger it . The Q1 transistor acts as a switch which applies current to the unijunction relaxation oscillator Q2 . The signal frequency of the alarm circuit is give by the values and ratios of the C1 / R2 .

If you don’t have the transistors marked on the schematic diagram you can replace them almost with any similar types.
Detail download here

74LS90 Counter With 7 Segment Display

Here is the circuit diagram of a seven segment counter based on the counter 74LS90 IC TTL.This circuit can be used in conjunction with various circuits where a counter to display the progress adds some more attraction. This circuit accepts any TTL compatible logic signal, and can be expanded easily.
74LS90  Counter Circuit With 7 Segment Display

 7 Segment Common anode
  • All pulses to be counted are to be TTL compatible. They should not exeed 5V and not fall below ground.
  • You can add more digits by building a second (or third, or fourth, etc...) circuit and connecting the pin 11-6 junction of the 74LS90 and 74LS47 to pin 14 of the 74LS90 in the other circuit. You can keep expanding this way to as many digits as you want. 

List Component:
R1-R7 : 470 Ohm 1/4 Watt Resistor
U1 : 74LS90 TTL BCD Counter IC
U2 : 74LS47 TTL Seven Segment Display Driver IC
DISP1 : Common Anode 7 Segment LED Display
Detail download here

Monday, May 9, 2011

Temperature Controlled 220v AC Fan

This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain
Temperature Controlled 220V AC Fan
R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage, P1-R1 generate a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector. P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.

This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.

This Circuit From:
Detail download here

Delayed Turn-On Relay Circuit Using NOR Gate 4001

This is a delayed turn-on relay driver and can produce time delays for up to several minutes with reasonable accuracy. The 4001 CMOS gate here is configured as a simple digital inverter. Its output is fed to the base of a regular 2N3906 transistor, Q1, at the junction of resistor R5 and capacitor C2. The input to IC1 is taken from the junction of the time-controlled potential divider formed by R2 and C1. Before power is applied to the circuit, C1 is fully discharged. Therefore, the inverter input is grounded, and its output equals the positive supply rail; Q1 and RY1 are both off under this circuit condition. When power is applied to the circuit, C1 charges through R2, and the exponentially rising voltage is applied to the input of the CMOS inverter gate.

After a time delay determined by the RC time constant values of C1 and R2, this voltage rises to the threshold value of the CMOS inverter gate. The gate's output then falls toward zero volts and drives Q1 and relay RY1 'ON'. The relay then remains automatic turn-off relay driveron until power is removed from the circuit. When that occurs, capacitor C1 discharges rapidly through diode D1 and R1, completing the sequence. The time delay can be controlled by different values for C1 and R2. The delay is approximately 0.5 seconds for every µF as value for C1. The delay can further be made variable by replacing R2 with a fixed and a variable resistor equal to that of the value of R2. Taken the value for R2 of 680K, it would be a combination of 180K for the fixed resistor in series with a 500K variable trim pot. The fixed resistor is necessary.
Detail download here

Sound Activated Relay Switch Using Op-Amp LM741

Sound Activated Relay Switch  Using Op-Amp 741

Sound Activated relay. The relay remains dormant until the op-amp activates upon sound via the electret-microphone. The input stage is a regular off-the-shelf 741 operational amplifier and connected as a non-inverting follower audio amplifier. Gain is approximately 100 which you can raise by increasing the value of R2. The amplified signal is rectified and filtered via C3, D1/D2, and R4 to an acceptable DC level. Potentiometer R5 is used to set the audio level to a desired sensitivity value to activate the relay via transistor Q1. Diode D3 is mounted over the relay coil to absorb sparks. The op-amp configuration in this particular drawing needs a dual voltage power supply which can be made from two 9-volt batteries.
Detail download here

Sound Activated Relay

Here is a circuit that allows you to control a relay in response to sound from a non-amplified sound source (computer, CD player, or my Digital Sound Recorder board).

This circuit accepts audio input from any non-amplified sound source and when the volume reaches a certain level, it actuates a relay. This relay can be used to switch another device (light bulb, etc.) on and off in sync with the volume of the input.
Sound Activated Relay Circuit
The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used. When you first connect the supply voltage to the sound activated switch circuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 μ F.

Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error.
Detail download here

Thursday, May 5, 2011

19 LED Bar/Dot VU Meter Using LM3915-LM3916 ICs

This 19 LED VU Meter circuit was designed by two monolithic integrated circuits to measure the level of audio signals whose unit of measurement is known as volume unit. The circuit round the IC1 makes input adaptation and amplification with the trimmer TR1 [GAIN]. The circuit round the IC2 makes half-wave rectification of acoustic signal. With switch S1, we select the type of indication, that we will have from the LED. With the prices in resistances R6 and R7 that exists in the circuit, the level of signal, in the entry is 7.8V (gain of first stage IC1, is one), and the difference of level between the LED D10-11, should are 3 db. The positive department of supply, should have the possibility of giving more current, one and it is overloaded with the current of LED.
19 LED Bar/Dot  VU Meter Circuit Using LM3915-LM3916 ICs

list componet
R1-2   : 10Kohm      C1   : 100uF/25V       D1-19 : LED 3 or 5mm any colour. 
R3-4 : 10Kohm C2-5 : 10uF/25V D20-21: 1N4148
R5-8-9 : 1Kohm C3-4 : 100nF IC1 : TL 072
R6 : 330Kohm C6 : 1uF/25V IC2 : LM3915
R7 : 62Kohm S1 : mini Switch IC3 : LM3916
TR1: 47Kohm Trimmer

This 19 LED Bar/Dot  VU Meter circuit from
Detail download here

Wednesday, May 4, 2011

10 LED VU Meter Using LM3915 IC

This circuit is a very simple circuit-level indication, with 10 Led. LM3915 IC is used to control the led, as an indicator VU Meter. This circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V.

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs. The whole display system can operate from a single supply as low as 3V or as high as 25V.
10 LED VU Meter Circuit Using LM3915 IC
The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.
Detail download here