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+/- Voltage on bargraph display

+/- Voltage on bargraph display
The LM3914 is a truly versatile component. Besides LEDs, only a few other components are needed to make the ‘bidirectional’ bargraph voltmeter shown here. The circuit is similar to a conventional bar display, but it offers a possibility to change the direction in which the LEDs are switched on. This may be useful, for example, when positive and negative voltages are measured. For a positive input voltage, the LEDs are switched on in the usual manner, that is, from D3 to D12, while for negative voltages, the LEDs are switched on in the opposite direction, from D12 to D3. Obviously, the negative voltage must be ‘rectified’, i.e. inverted, before the measurement. A suitable circuit for this purpose is presented in the article ‘Absolute-value meter with polarity detector’ (reference number 994020-1) elsewhere in this issue.
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