Big Project Kits (9)
Sound Effects (6)
Measurement Circuit Kits
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We offer 555 IC Tester. The use of Timer IC555 proves its importance in almost most of the circuits. So it becomes necessary to build such a design to test this most popular IC. Although the IC555 is generally very reliable, there are occasions when malfunction does occur. The circuit shown here will provide a simple and effective method of testing suspect devices.
About the Circuit:
The timer to be tested, IC1 is connected as an astable multivibrator. When the push to test button ‘S1’ is closed, capacitor C1 will start to charge up via resistors R1 and R2/P1. As soon as the voltage level on this capacitor reaches the trigger point of the timer, the internal flip-flop is activated and pin7 is taken low to discharge C1. The flip-flop is reset when the voltage on C1 reaches the threshold level of IC1. This takes pin7 high and the charge cycle starts once more. The output of the timer pin3 is connected to a pair of light emitting diodes. When the output is high, LED D2 will be ON and D1 will be off. Conversely, when the output is low D1 will be ON and D2 will be OFF. The LED will flash ON and OFF alternately provided, of course, that the IC under test is a good one.
For readers who may have other application for the circuit and who wish to alter the frequency, the rate at which the LED flash is determined by the values of R1, R2/P1 and C1. The frequency of oscillation can be calculated from the formula
f = 1.44/(R1+2(R2+P1))C1
If, as in this case, the value of R2 is much greater than the value of R1, the frequency can be approximated from the following
f = 0.72/(R2+P1)C1
Many times it is required to test the semiconducting components. This is a simple and inexpensive tester, used to test virtually any kind of semiconducting components such as switching diodes, transistors, power transistors etc. It is also useful in finding functional, short circuited and internally open devices in semiconductor batches.
The circuit uses only one IC as shown in the circuit diagram. Two colour LEDs are used to indicate the testing results.
LED Voltmeter For Battery
This is a simple battery monitor used specially for car batteries. The battery voltage display is in the form of ten LEDs connected to the output of linear voltage display IC1. The voltage display range is from 7.5V to 14V. The lowermost LED D10 lights when battery voltage is 7.5V. The next LED D9 lights when battery voltage is at 8.2V. Thus with a span of each 0.7V, LEDs D10 to D1 glows sequentially or in dot mode by keeping switch S2 open. The uppermost LED D1 glows when battery voltage is at 14V. We can differentiate the glowing of each LEDs as a ‘battery status indicator’. The two lowest LEDs indicate ‘battery low’ condition. The next six LEDs indicate ‘battery well’ condition. And the uppermost two LEDs indicate ‘an overvoltage’ condition.
We can show the display in bar mode also by making S2 on. In this case mode pin9 connected to supply line. At an overvoltage state i.e. when battery voltage range is 13 to 14V, all ten LEDs glows. As the voltage decreases LEDs turns off one by one sequentially.
About the Circuit:
The operation of the circuit is based on linear voltage display IC1, which consists of 11 op-amps as comparators connected internally. The input of IC1 is directly derived from the battery voltage via potential divider R4-R5-P1. This variable input is about 3V for battery potential of 12V. The display range depends on the internal voltage reference and resistors R1-R3.The reference output at pin7, which here is also the upper display level, is always 1.25V higher than the level at reference adjustment at pin8, so that the current from reference output to earth is about 1mA. The potential difference caused by this current across R2 and across R3 determines the lower display level.The lowest LED D10 lights when input voltage is 1.8V, whereas the uppermost LED lights when the voltage exceeds 4V. Since the input signal is divided by four, the display ranges should be multiplied by this figure. Therefore, the actual display range is 7.5-14V, that is 0.7V per LED when P1 is at minimum level.
This simple circuit of temperature monitor uses differential amplifier IC and temperature sensor. The three different colour LED indications are used to indicate different temperatures. The temperature at which LEDs will glow set by preset P1. Generally LED D1 will glow at normal temperature. As the temperature increases LED D2 glows. At highest temperature LED D3 glows.
About the Circuit:
As described earlier circuit uses differential amplifier IC, IC1. The reference voltages are applied to pin2 and pin6, which are set by preset P2 and P3 respectively. The differential voltages developed at pin3 and pin5 according to the voltage produced by R1/P1 and temperature sensor, which gives an output voltage of 10mV/°C. Accordingly output at pin1 and pin7 changes and LED indication changes.
At normal temperature, voltage produced by sensor is smaller than either of the reference potentials. The output at pin1 and pin7 are low: D1 will then light.
When the ambient temperature rises, the output of sensor rises proportionally. When the level of the sensor output lies between the two reference levels, the output at pin1 is high and that of pin7 is low. Diode D2 will then light, showing that the critical temperature has been reached.
At even higher temperature, the output at pin7 also goes high and D3 lights, while the other two LEDs will go out. At the same time, the relay will be energised via T1. Also LED D6 lights which gives visual indication.
Zener diode D4 ensures that T1 does not come on when D2 lights. The temperature at which the LEDs should light can be set with preset P1, P2 and P3. The precaution should be taken that the monitor is intended for normal temperatures between 25°C and 100°C
Infrared Remote Tester
Many times it is required to test our TV remotes. This is a simple, low cost and easy to construct Infrared Remote Tester. The tester is build around an easily available infrared receiver module.
About the Circuit
Normally data output pin 3 of IR receiver module is at a high level and as such driver transistor T1 is in cut off state. Whenever the IR receiver module receives a valid (modulated) infrared signal, its data output pin goes low in synchronism with the received infrared bursts. As a result T1 conducts during negative pulse period and the LED blinks to indicate reception of signals from the remote such as TV remote control. A miniature active buzzer is connected at the collector of T1 for audio indication.The advantage of this tester is no false triggering due to the ambient light or electronic ballast operated tubelights .IC1 is a regulator IC used to give 5V regulated DC supply.
All of us know it is impossible to separate sound effect and light effect. But this simple circuit makes it possible to vary the effect from simple to complex. This circuit is a sort of running light whose rate of change depends on the frequency and intensity of the sound. About the Circuit:
The circuit is build around two counter ICs, IC1 and IC2 as shown in the circuit diagram. The sound signals generated are received by condenser microphone. These signals are amplified by pre-amplifier circuit designed around transistor T1. It should be noted that the amplified level must be high enough to overcome the switching threshold of the counter, while its frequency determines how often counter is clocked. After amplification, the signal is applied to IC1 via P1, which controls the sensitivity of the circuit.
Since audio frequencies are too high for making a good visual effect, the signal frequency is scaled down by IC1 when S1 connects pin11 with pin15 of IC1, when the switch is in other position, pin2 is connected with pin15, the counter then divides by 1 and the effect assumes a completely different character that no longer resembles a running light.
The actual running light is provided by IC2, a counter with integral 1 from 10 decoder, which is clocked by the Q0 output at pin3 of IC1 of the ten output of IC2 each of which is connected to an LED, there is always one ‘high’. The ten LED have a common bias resistor R5, an arrangement that is perfectly visible since only one LED lights at a time.
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