Design of LED level indicator circuit based on LM324

This paper introduces produced by LM324 two LED level indicator circuit. LED level indicators are often used in the audio circuit and power amplifier circuit output level indicator. LM324 is a four op amp IC

LED, first introduced the 1 level indicator with adjustable gain amplifier, which can be connected to the output end of the audio power amplifier circuit, power amplifier as the output level indicator, also can be connected to the audio output of the amplifiers (before the volume control circuit), as the pre stage level indicator. See the diagram below.

In the circuit, the LM324 amplifier consists of a programmable gain amplification stage, adjustable resistor RP is used to adjust the gain; LED driver circuit consists of a triode V, a capacitor C3, zener diode VS, a resistor R1, a Rn light emitting diode VLl and a diode VD1 VDn VLn.

From the power amplifier or preamplifier of the audio input signal by C2 coupled to LM324 operational amplifier 5 feet by LM324 and transistor amplifier, the triode output signal voltage, the VLl V Ln by light. The stronger the audio input signal, the more the number of light emitting diodes.

Component selection

R01-R05 and R1-Rn use 1/4W carbon film resistor or metal film resistor. RP use ultra small potentiometer or vertical variable resistor.

C1-C3 aluminum electrolytic capacitor with a voltage of 16V was selected. VD1-VDn uses 1 N4148 silicon switching diode or 2AP5VS 1/2W, 3.6V Silicon Zener diode.

VU-V Ln are selected using red 5mm high brightness light-emitting diode.

V selects C8050 or 58050, 3 DG8050 type silicon NPN transistor.

IC type LM324 operational amplifier integrated circuit.

2, the following introduction of the LED level indicator without gain amplification circuit, can be used for audio amplifier output level indicator. However, the level indicator has a moving point light type and progressive lighting two display modes can be selected. Schematic diagram of the circuit shown in figure.

When the level of the input audio signal is less than 0.7 V, Nl output high level VLI light; when the input signal level in between 0.7-1.4V, N2 output high level, on one hand the V L2 light, on the other hand through the V D6 N1 inverting input terminal goes high, the N1 outputs low level the VLI goes out. Similarly, if the input signal level becomes high, then the VL1 and V L4 will be lit, showing a moving point light display.

The diode VD4 - VD7 removed, then the circuit into four level LED level indicator, with changes in the size of the input signal level, the light emitting diode VL1-VL4 light will be lit by type.

Component selection

R1-R5 1/4W carbon film resistor or metal film resistor.

C aluminum electrolytic capacitor with a voltage of 16V.

VD1-V D7 1 N4148 silicon switching diode.

VLl-VIA are selected by the 5mm led.

IC selects LM324 type four operational amplifier integrated circuit.

I made a second circuit diagram, but after all, found four LED lights, and did not reach the level display effect, after careful examination, the circuit of welding is not a problem, so I consider whether there is a problem of circuit design.

Later, I changed a LED, that is, the first, it is less than the resistance of the resistance of some of the smaller, it flashes with the size of the current, but the number two or three LED is still bright, No. four is not bright