Free electronic circuit design and schematic diagram
Monostable multivibrator circuit produce a fixed pulse-width when the input is triggered. The input is fed to CR1, which should be an open collector source since the TR1 would short the input to ground during the active state appear on this circuit’s output. The output of this circuit is tapped from the collector of TR2. This monostable multivibrator output pulse […]
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NiCd/NiCad battery charger circuit is still needed since some application demanding high current is still rely on NiCd type, since this type is still superior in term of high current output (low internal resistance) and low cost. This battery charger circuit is used to charge 12V NiCd battery at around 74 mA until battery is fully charged. This circuit need […]
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This is a simple circuit of beeper using 555 timer. This circuit can be employed to energize lights, horn, or other signaling device at any desired interval when the mercury switch is triggered. Since the current handling capability of mercury switch is not so high, an SCR is used to handle current drawn by the 555 timer circuit. Chose the […]
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Using this continuity tester circuit, a failure of PCB tracks be examined without looking directly at the tracks routing, which is can be very frustrating. The indication of this circuit is done by an audible alarm (a buzzer). This circuit can be used to indicate continuity below any resistance value up to 35 ohms by adjusting the circuit. To make […]
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This is a transceiver saver circuit that protect a transceiver device (applicable to other device as well) from overvoltage of the power supply. This circuit is used to protect the device by regulating the power supply, avoiding damaging the device if overvoltage occurs. If the transceiver transmits current of above 2A, a heatsink should be used for the transistor. The […]
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This circuit can provide 5,000 VDC from 26 VDC. This circuit has ripple of under 0.01% due to Voltage-doubling capacitors. As sinusoidal oscillator, a 2N217 transistor is used. The diode and the capacitors at the output stage should be of high voltage type. Here is the schematic diagram of the circuit:
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This is a SCR timer circuit. Here, SCR is used to drive the final actuator, the buzzer. The time constanst of this circuit is determined by R1 and C1. The buzzer will sound when C1 charges up to a desired level, it will cause the Q1 to conduct and triggers SCR1. The use of FET for Q1 make the RC […]
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