Peak Hold VU meter circuit

This VU-meter can show peak signal on 12 LEDs stereo system and use L1424 as main so easy to build.

The importance of the VU-meter, In addition to shows the level of signal and add colorful on the audio system or others tools.

The Peak-hold VU-meter have 2 channel or stereo. The main goal of this project is to show the high point (Peak) hold point for 1-2 seconds.

The normal VU-meter circuits, Most use IC-numbers LM3915 or LM3916 or Lbxxxx series of Sanyo. But this projects use the L1424.

How it works
The heart of this circuit is IC1-L1424. In Figure 2 will see that the parts connected to IC1 with the least amount. Almost everything seems to work completely within the IC1. This is the internal structure of the L1424 Shows a block diagram inside the IC. and various pin positions in Figure 2.

block diagram and pins of L1424
Figure 1 the block diagram and pins of L1424

schematic diagram of the peak-hold LED stereo VU meter
Figure 2 the schematic diagram of the peak-hold LED stereo VU meter

1. Pin 1 and Pin 3 : pins of the input signal, of channel 1 and channel 2, respectively.
2. Pin 2 and pin 4 : pins to set the inside booster circuit, by connects the resistors and capacitors
3. Pin 5 (DC IN) : pin DC input
4. Pin 6 (AC/DC) : pin selector the DC or AC input
5. Pin 7 (MUTE) : the muting pin
6. Pin 8 (P.H.) : The selected pin function Peak-Hold.
7. Pin 9 : pin connected to resistors and capacitors that set the frequency of inside oscillator circuit.
8. Pin 10 and pin 11 (GND): Pin to the ground
9.Pin 12 ??? pin 21 : Pin of driver of display section
10. Pin 22 : Vss pin of positive power supply

L1424 is IC that built to show the signs or called VU 2-channel or stereo. Input signal can be either DC or signal loss (AC) display with 12 levels per channel. The display is trading at its highest point for 1-2 seconds (peak-hold).

The working of figure 1, the input signal channel 1 and 2 will through to C1, C2 and VR1, VR2 respectively. Both VR1 and VR2 will be to adjust the strength of the two input signals. Before entering the inside amplifier circuit. At pin 1 and pin 3 the amplifier circuit, You can adjust rate of increase of resistors that connected between pin 2 and pin 4.

The signal from the some amplifier circuit will is toke to make as the reference voltage circuit (Vref) and others will pass to the switcher. Which it act as on-off the the reference voltage signal and the voltage from the switcher Will be compared to the maximum voltage (peak) and send it to Peak Holding logic again.

The input interface will act on orders from outside. By the pin 5 is input DC, pin 6 is selector pin input DC or AC. If connect to ground will be input DC and if connected to Vss input AC.

The pin 7 to choose working in Null working or no null working. If connected to Acc will “On” and if connects to ground will “Off”

The pin 8 is used to selects between the peak-hold or normal. If connect to ground will working on the peak-hold mode, if connect to Vcc will be normal.

The pin 9 is setting the inside oscillator. The frequency of oscillator will be connected to the switcher and some from frequency divider circuit, then send to the peak-hold logic. Which is scheduled to hold a very long time – at least from the peak-hold logic, it is sent to the driver section, have Q1-Q4 to the signal driver circuits.

How to builds
First of all,prepare the devices available. Then make the PCB 2 pcs. As Figure 3 the main PCB layout. And

the main PCB layout of peak-hold VU meter project
Figure 3 the main PCB layout of peak-hold VU meter project

the display PCB layout
Figure 4 is the display PCB layout

Next step, All devices assembled on both PCBs.

the main components layout of the peak-hold VU meter
as Figure 5 the main components layout of the peak-hold VU meter

the components of display section
and Figure 6 the components of display section.

More detail I think you still know and can builds it with happy.

Parts will you need
Resistors 0.25W +5%
R1, R2________47K
R8-R13_______330 ohms
VR1, VR2_____100K small volume
C1, C2____1uF 25V__electrolytic
C3, C4____22uF 16V__electrolytic
C5_______0.01uF 50V___Ceramic
C6_______100uF 16V__electrolytic
LED1-LED7____LED Green
LED8-LED12___LED Red
PCBs, and more parts…


  1. Tanvir June 20, 2015
  2. momename June 20, 2015
  3. Roger July 2, 2015
  4. Tito August 14, 2015
  5. ma.kader.jibon November 20, 2016
  6. dimuthu champika January 9, 2017

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