FLASHING TWO LEDS
These two circuits will flash two LEDs very bright and consume less than 2mA average current. They require 6v supply. The 330k may need to be 470k to produce flashing on 6v as 330k turns on the first transistor too much and the 10u does not turn the first transistor off a small amount when it becomes fully charged and thus cycling is not produced
1.5v LED FLASHER
This will flash a LED, using a single 1.5v cell. It may even flash a white LED even though this type of LED needs about 3.2v to 3.6v for operation. The circuit takes about 2mA but produces a very bright flash
LED on 1.5v SUPPLY
A red LED requires about 1.7v before it will start to illuminate - below this voltage - NOTHING! This circuit takes about 12mA to illuminate a red LED using a single cell, but the interesting feature is the way the
LED is illuminated. The 1u electrolytic can be considered to be a 1v cell. (If you want to be technical: it charges to about 1.5v - 0.2v loss due to collector-emitter = 1.3v and a lost of about 0.2v via collector-emitter in diagram B.) It is firstly charged by the 100R resistor and the 3rd transistor (when it is fully turned ON via the 1k base resistor). This is shown in diagram "A." During this time the second transistor is not turned on and that's why we have omitted it from the diagram. When the second transistor is turned ON, the 1v cell is pulled to the 0v rail and the negative of the cell is actually 1v below the 0v rail as shown in diagram "B." The LED sees 1.5v from the battery and about 1v from the electrolytic and this is sufficient to illuminate it. Follow the two voltages to see how they add to 2.5v
These two circuits will flash two LEDs very bright and consume less than 2mA average current. They require 6v supply. The 330k may need to be 470k to produce flashing on 6v as 330k turns on the first transistor too much and the 10u does not turn the first transistor off a small amount when it becomes fully charged and thus cycling is not produced
1.5v LED FLASHER
This will flash a LED, using a single 1.5v cell. It may even flash a white LED even though this type of LED needs about 3.2v to 3.6v for operation. The circuit takes about 2mA but produces a very bright flash
LED on 1.5v SUPPLY
A red LED requires about 1.7v before it will start to illuminate - below this voltage - NOTHING! This circuit takes about 12mA to illuminate a red LED using a single cell, but the interesting feature is the way the
LED is illuminated. The 1u electrolytic can be considered to be a 1v cell. (If you want to be technical: it charges to about 1.5v - 0.2v loss due to collector-emitter = 1.3v and a lost of about 0.2v via collector-emitter in diagram B.) It is firstly charged by the 100R resistor and the 3rd transistor (when it is fully turned ON via the 1k base resistor). This is shown in diagram "A." During this time the second transistor is not turned on and that's why we have omitted it from the diagram. When the second transistor is turned ON, the 1v cell is pulled to the 0v rail and the negative of the cell is actually 1v below the 0v rail as shown in diagram "B." The LED sees 1.5v from the battery and about 1v from the electrolytic and this is sufficient to illuminate it. Follow the two voltages to see how they add to 2.5v
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