This is the pin that allows us to have the LM in bar mode or in dot mode. All three devices of the LM family use the same basic internal circuitry, and Figure 3 shows the specific internal circuit of the linear-scaled LM, together with the connections for making it act as a simple LED You have the choice: So we plug 5V into this formula. The pinout of the LM is shown below. The IC responds only to the positive halves of such input signals, and the number of illuminated LEDs is thus proportional to the instantaneous peak value of the input signal. As we increase voltage, more LEDs turn on.

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The other formula is to calculate the second resistor value R2. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge dksplay you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

This is the pin that allows us to have the LM in bar mode or in dot mode.

LED bar graphs are used often in VU meter circuits, in which the LED bar graph can be lit up in proportion to the amount of voltage a device is outputting. The internal voltage reference of the IC produces a nominal output of 1. With varying voltage, we get varying LEDs lit.

An over-range alarm-driver circuit, for use with bar-type displays. The LM, on the other hand, has a log-scaled output designed to span dB to 0dB in 10 -3dB steps, and is specifically designed for use in power-indicating applications, etc.


Finally, note that the major difference between the three members of the LM family of ICs lies in the values of resistance used in the internal stage potential divider.

How to Build an LM3914 Dot/Bar Display Driver Circuit

In the LM, the resistors are weighted in semi-log fashion and produce a display that is specifically suited to VU-meter applications. They are moderately complex but highly versatile devices, housed in pin DIL packages and each capable of directly driving up to 10 LEDs in either the dot or the bar mode.

Recheck the settings of RV1 and RV2.

This basic VU-meter circuit gives a bar-type display, with a dot-type current drain. Here, the LEDs are lm3941 wired in series, but with each one connected to an individual output of the IC, and the IC is wired for dot-mode operation. Views Read Edit View history. The Figure 17 circuit is that of a simple LMbased audio power meter that is used to indicate instantaneous output voltage values from an external loudspeaker.

Using the resistor R1 value we calculated before of 1. In Figure 16the C2 value of 22n is the optimum value for a full-scale range of 10, RPM on a four-cylinder four-stroke engine.

How to Build an LM Dot/Bar Display Driver Circuit

When the input reaches the 0. The IC also contains a logic network that can be externally set via pin 9 to give either a dot or a bar display from the outputs of the 10 comparators. In the LM, all resistors in the chain have equal values, and thus produce a linear display of 10 equal steps. When a particular output is active the internal chip transistors will pull the output pin towards ground. How the Circuit Works The potentiometer is the mainstay of the circuit.


Since the reference voltage is 5V and there are 10 LEDs, each 0. The LM is an pin chip. Use either hex CMOS inverters or built simple pnp inverter for every channels.

LED ‘Graph’ Circuits | Nuts & Volts Magazine

For many years, the best known ICs of this type were the U etc. In this case, the 1mA current determined by R1 of the floating 1. Home Questions Tags Users Unanswered.

Pin 5 is a very important pin. Figure 19 shows an alternative way of using the LM as a VU-meter with a bar-type display.

LED ‘Graph’ Circuits

I guess the LM must have all outputs low when it starts? It’s not a big deal.

This includes the pinout and all the details of how to connect the LED Bar graph. Depending on the its resistance affects the voltage directly. Finally, the LM has a semi-log scale that spans 23dB, and is specifically designed for use in VU meter applications.