![]() Thus, the LM3914 is a linearly-scaled unit, specifically intended for use in LED voltmeter applications in which the number of illuminated LEDs gives a direct indication of the value of an input voltage (or of some parameter that is represented by a proportional voltage). Threshold-point values of the LM6 range of ICs when designed to drive 10 LEDs at a full-scale sensitivity of 10V. Internal circuit of the LM3914, with connections for making a 10-LED 0-1.2V linear meter with dot- or bar-graph display.įIGURE 4. The family comprises three devices, these being the LM3914, the LM3915, and the LM3916 they all use the same basic internal circuitry (see Figure 3), but differ in the style of scaling of the LED-driving output circuitry, as shown in Figure 4.įIGURE 3. They are moderately complex but highly versatile devices, housed in 18-pin DIL packages and each capable of directly driving up to 10 LEDs in either the dot or the bar mode. The LM3914 family of dot/bar-graph driver ICs are manufactured by National Semiconductors. A wide variety of multi-LED LM3914-based graph display circuits are shown in this article. The scale’s resolution depends on the number of LEDs used a 10-LED display gives adequate resolution for many practical purposes. LED ‘graph’ displays have better linearity than conventional moving-coil meters typical linear accuracy being 0.5%. ![]() In a given display, individual LED colors can be mixed to emphasize particular sections of the display, and ‘over-range’ detectors can easily be activated from the driver ICs and used to sound an alarm and/or flash the entire display under the over-range condition. Their scales can easily be given any desired shape. They are immune to ‘sticking’ problems, are fast acting, and are unaffected by vibration or by physical attitude. IC-driven bar-graph displays make inexpensive and, in some ways, superior alternatives to analog-indicating moving-coil meters. The LM3914 family are popular and versatile ICs that can each directly drive up to 10 LEDs (but can easily be cascaded to drive larger numbers of LEDs) and can drive them in either bar or dot mode. However, the first two of these families have now ceased production, and only the LM3914 family remains. For many years, the best known ICs of this type were the U237 (etc.) family from AEG, the UAA170 (etc.) family from Siemens, and the LM3914 (etc.) family from National Semiconductors. Dot-graph indication of (a) 7V and (b) 4V on a 10V 10-LED scale.Ī number of special ICs are available for operating general-purpose LED analog-value display systems. In reality, the ‘0’ position is often indicated on these scales by a separate LED that is permanently active whenever the display is in use.įIGURE 2. Bar-graph indication of (a) 7V and (b) 4V on a 10V 10-LED scale.įigure 2 shows the same meter operating in the dot-graph mode the input voltage value is indicated by the relative position of a single illuminated LED. ![]() Figure 1 illustrates the bar-graph principle, and shows a line of 10 LEDs used to represent a linear-scale 0-10V meter that is indicating (a) 7V or (b) 4V the input voltage value is indicated by the total number of LEDs that are illuminated.įIGURE 1. ![]() Practical graph circuits may be designed to generate either a bar-graph or a dot-graph display. One of the most popular types of multi-LED indicator circuits is the so called analog-value indicator or ‘graph’ display, which is designed to drive a chain of linearly-spaced LEDs in such a way that the length of chain that is illuminated is proportional to the analog value of a voltage applied to the input of the LED-driver circuit, e.g., so that the circuit acts like an analog voltmeter. » Skip to the Extras LED ‘GRAPH’ DISPLAYS
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