And you can switch easily between bar and graph mode by switching the toggle switch. In most practical applications, however, these particular ICs are used to indicate the value of an AC input signal, and the simplest way of achieving such a display is to connect the AC signal directly or via an attenuator to the pin 5 input terminal of the IC, as shown in Figure We ground pin 4 wihtout a capacitor because the leads of the LEDs we use are less than 6″. When the input voltage reaches the 0. It may vary by a few tenths of a volt depending on the tolerane of the resistors and if you used the same exact resistances offered.

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In this case, the LEDs are split into two chains, and the transistors are used to switch on the lower LEDs 1 to 5 chain when the upper chain is active; the maximum total LED current equals twice the current of pm3914 single LED. The potentiometer we will use can really be of any value. Bar mode is a mode in which if full voltage is going to the chip, all 10 LEDs will be lit up. For example, if we replace the potentiometer with a resistor and photoresistor in series, we can build a light-sensing device and then the LED bar graph and light to show the light intensity that the photoresistor is detecting.

Resistor values may vary. Use either hex CMOS inverters or built simple pnp inverter for every channels.

20 LEDs 0 To 20V Bar-Graph Voltage Meter Using LM3914

This is the signal pin. The circuit is shown connected for bar-mode operation, using separate supply voltages for the LED display and for the actual IC, and with the component values shown, gives a current drive of 10mA to each active LED.

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Finally, the LM has a semi-log scale that spans 23dB, and is specifically designed for use in VU meter applications. By fitting potential divider Rx-RV1 to ggaph input of the circuit, this range can be amplified to say V, or whatever range is desired.

Sign up using Facebook. That or call it the “LED Test” function: If 1 or no LEDs are lit, displwy can mean the battery is dead. The doesn’t care if you gdaph such tricks on it. Pin 9 is left open-circuit to give dot-mode operation, and R1 has a value of R to give an LED current of about 30mA, thus giving a clear indication of brief instantaneous voltage levels.

As we turn the potentiometer, increasing its resistance, more and more LEDs will be turned on until a full 5V is fed into pin 5, in which all the LEDs will be on.

LMN – LM Bar-Graph Display Driver

Next in pins 6,7, 8, we place our biasing resistors R1 and R2 to obtain the current of 10mA. The LM 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 risplay.

The IC has a maximum power rating of only mW, however, so there is a danger of exceeding this rating when the IC is used in the bar mode.

So uses such as this are many times what LED bar graphs are used for. Meanwhile, in bar mode, all eight LEDs will be on. Since we are using LEDs with such long leads, we simply connect pin 4 to ground. A similar kind of action is obtained when the LM logic bat set for dot mode operation, except that only one LED is on at any given time; at zero volts no LEDs are on, and at 1.

If, for example, the top of the chain is connected to a 10V source, the IC will function as a V meter if the low end of the chain is ggaph, or as a restricted-range V meter if the low end of the chain is tied displat a 5V source. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.


The input pin 5 to the IC is fully protected against overload voltages up to plus or minus 35V. 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. Recheck the settings of RV1 and RV2. If pnps are used, connect the output of LM to the transistor base, link the emitter to Vcc through 10K resistor. At 3V, 6 LEDs turn on.

,m3914 An alternative variable-range 1. Figure 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.

Vehicle tacho conversion circuit for use with a LED voltmeter. RV1 thus enables the pin 7 voltage connected to the top of the internal divider to be varied from 1.

LED ‘Graph’ Circuits

Again no current-limiting resistors are necessary because the resistor R1 acts as the current-limiting resistor. Using the resistor R1 value we calculated before of 1. My premise is to connect the output pins of the LM directly to the ULN see crude illustration Is this going to be possible?