LM3914 Bar-Graph Display Driver

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The LM3914 is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. A single pin changes the display from a moving dot to a bar graph. The current drive to the LEDs is regulated and programmable, eliminating the need for resistors. This feature is one that allows the operation of the whole system from less than 3V. The circuit contains its own adjustable reference and accurate 10-step voltage divider. The low-bias-current input buffer accepts signals down to the ground, or V−, yet needs no protection against inputs of 35V above or below ground.

The buffer drives 10 individual comparators referenced to the precision divider. Indication non-linearity can thus be held typically to 1⁄2%, even over a wide temperature range. A 1.2V full-scale meter requires only 1 resistor and a single 3V to 15V supply in addition to the 10 display LEDs. If the 1 resistor is a pot, it becomes the LED brightness control. The simplified block diagram illustrates this extremely simple external circuitry. When in the dot mode, there is a small amount of overlap or “fade” (about 1 mV) between segments. This assures that at no time will all LEDs be “OFF”, and thus any ambiguous display is avoided. Various novel displays are possible.

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LM3914 Pinout

LM3914 Pin Configuration

Pin No	Pin Name	Description
1	LED NO 1	Led No 1
2	V-	-ve Voltage Pin
3	V+	+ve Voltage Pin
4	DIVIDER (LOW END)	Divider (Low End)
5	SIGNAL INPUT	Signal Input Pin
6	DIVIDER (HIGH END)	Divider(High End)
7	REFERENCE OUTPUT	Reference Output Pin
8	REFERENCE ADJUST	Reference Adjust Pin
9	MODE SELECT	Mode Select Pin
10	LED NO. 10	Led No10 Pin
11	LED NO. 9	Led No 9 Pin
12	LED NO. 8	Led No 8 Pin
13	LED NO. 7	Led No 7 Pin
14	LED NO. 6	Led No 6 Pin
15	LED NO. 5	Led No 5 Pin
16	LED NO. 4	Led No 4 Pin
17	LED NO. 3	Led No 3 Pin
18	LED NO. 2	Led No 2 Pin

LM3914 Features

Drives LEDs, LCDs or vacuum fluorescents
Bar or dot display mode externally selectable by user
Expandable to displays of 100 steps
Internal voltage reference from 1.2V to 12V
Operates with single supply of less than 3V
Inputs operate down to ground
Output current programmable from 2 mA to 30 mA
No multiplex switching or interaction between outputs
Input withstands ±35V without damage or false outputs
LED driver outputs are current regulated, open-collectors
Outputs can interface with TTL or CMOS logic
The internal 10-step divider is floating and can be referenced to a wide range of voltages