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Tuesday, October 20, 2009

20 Segment Meter Circuit with Mode Switch

This is a schematic circuit for ones application for segment meter circuit using mode switch. This circuit is based on LM3914 that is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. This is the figure of the circuit.


The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode. These currents flowing out of the ground pin caused voltage drops in external wiring, and thus errors and oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string (as illustrated) to a single point very near pin 2 is the best solution. In cases where proper wiring and bypassing fail to stop oscillations, V+ voltage at pin 3 is usually below suggested limits. Expanded scale meter applications may have one or both ends of the internal voltage divider terminated at relatively high value resistors. These high-impedance ends should be bypassed to pin 2 with at least a 0.001μF capacitors, or up to 0.1μF in noisy environments. Power dissipation, especially in bar mode should be given consideration.[Schematic source: Linear Technology Corporation].

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