LED Chaser

Posted on Oct 28, 2012

General There are many 9V chaser circuits that seem to waste about 7V when driving LEDs that are only about 2V. This project is unique, because it uses only two inexpensive alkaline battery cells totaling 3V for power. Since most of the waste is eliminated, the cells last a long time.

LED Chaser
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Unlike the other circuits, this one flashes the LEDs for only about 30ms each, further extending the battery life. For user convenience, it has a stepper speed control and a brightness control. At slower speeds and with reduced brightness, the battery life is further extended considerably. Specifications · Battery: Two alkaline cells (AA size were used in the prototype) · Pulse Width Modulation frequency: 1.4KHz very bright to 6KHz very dim · LED current: 15mA pulses, reduced to 10.5mA at maximum Pulse Width Modulation · LED voltage drop: 1.76V (measured, not rated) @ 10.5mA · Minimum battery voltage (total of both cells): <1.24V, circuit is running but LEDs are not lit 1.6V, LEDs are very dim at maximum brightness 2.0V, LEDs reach almost full brightness, battery replacement is recommended. · Radio interference: None Circuit Description The 74HC Cmos ICs are rated for a 2V to 6V power supply for high-speed logic circuits. They continue to operate at a much lower voltage but no longer meet high-speed logic specifications. To reach high speeds, their output current can momentarily exceed 400mA (low voltage drop) but thermal considerations limit maximum continuous output current to 20mA. Perfect for driving LEDs! · IC2 is a 10 stage Johnson counter/decoder. On the rising edge of each clock pulse its outputs step one-at-a-time. It drives the anode of each conducting LED...

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