VM-AI1i User guide

VM-AI1i is a useful VU-Meter/Audio meter that has several features. This page shown these features.

Mode Setup

This section show how setup the function mode of VM-AI1i.

Display Mode (DM)

Display Mode indicates how VM-AI1i “show” current audio level. VM-AI1i has two display modes:

  1. Bar – turn on all leds from first to current-level led;
  2. Dot – turn on only current-level led and previous;

The default DM value is Bar.

Peak Mode (PM)

Peak Mode indicates how VM-AI1i treat and “shown” the temporary maximum audio level (aka peak). There are four modes:

  1. Peak Off – Simply don’t show the peak;
  2. Peak Fall – Show the peak. After a hold time (800ms) the peak “fall” in automatic (95ms @ point);
  3. Peak Hold with auto reset – Show the peak. After a hold time (3sec) the peak is reset in automatic;
  4. Peak Hold with manual reset – Show the peak. The peak is reset only by pressing the button S2;

The default PM value is Peak Fall.

Meter Scale (MS)

Meter Scale indicates which measuring scale is used by VM-AI1i. There are four scales:

  1. Scale N1 – (Extended) ANSI VU-Meter specification. It’s the classic VU-Meter scale and has 45dB of dynamic.
  2. Scale N2 – 1dB @ Point; Useful for fine audio measuring. Has 24 dB of dynamic.
  3. Scale N3 – 2dB @ Point; Useful for audio measuring. Has 48 dB of dynamic.
  4. Scale N4 – Mectronics’s custom scale;

The default MS value is Scale N1. In the following table there are the specification of scales:

Nr. Led Scale N1*
(Ansi VU-Meter)
Scale N2
(1 dB @ Point)
Scale N3
(2 dB @ Point)
Scale N4
(Mectronics Scale)
24 0 dB 0 dB 0 dB 0 dB
23 -1 dB -1 dB -2 dB -1.5 dB
22 -2 dB -2 dB -4 dB -3 dB
21 -3 dB -3 dB -6 dB -4.5 dB
20 -4 dB -4 dB -8 dB -6 dB
19 -5 dB -5 dB -10 dB -7.5 dB
18 -6 dB -6 dB -12 dB -9 dB
17 -7 dB -7 dB -14 dB -10.5 dB
16 -8 dB -8 dB -16 dB -12 dB
15 -9 dB -9 dB -18 dB -13.5 dB
14 -10 dB -10 dB -20 dB -15 dB
13 -11 dB -11 dB -22 dB -16.5 dB
12 -13 dB -12 dB -24 dB -18 dB
11 -15 dB -13 dB -26 dB -19.5 dB
10 -17 dB -14 dB -28 dB -21 dB
9 -19 dB -15 dB -30 dB -22.5 dB
8 -21 dB -16 dB -32 dB -24 dB
7 -23 dB -17 dB -34 dB -28 dB
6 -26 dB -18 dB -36 dB -30 dB
5 -29 dB -19 dB -38 dB -33 dB
4 -32 dB -20 dB -40 dB -36 dB
3 -35 dB -21 dB -42 dB -39 dB
2 -38 dB -22 dB -44 dB -42 dB
1 -41 dB -23 dB -46 dB -44.5 dB

*Note: the scale is implemented in the respect of “delta” between the divisions. Assuming 0dB as “+3dB” (full scale of VU-Meter), the ticks are: +3dB, +2dB, +1dB, 0dB, -1dB, -2dB, -3dB, -4dB, -5dB, -6dB, -7dB, -8dB, -10dB, -12dB, -14dB, -16dB, -18dB, -20dB, -23dB, -26dB, -29dB, -32dB, -35dB, -38dB. So user must set 0dB as level to turn-on the 21th led.

VM-AI1i - Meter Scales

VM-AI1i – Meter Scales

Decay Speed (DS)

Decay Speed indicates how many “fast” are the “falling” (also called “release”) of bar (dot). Fast releases speeds are useful to monitoring fast peak and spikes; slow speed instead are good to measure the average of audio signal. VM-AI1i has up to 7 decay speeds:

  1. UltraFast – 8ms @ point, that is about 190ms for the complete bar;
  2. SuperFast – 16ms @ point, that is about 385ms for the complete bar;
  3. Fast – 30ms @ point, that is about 720ms for the complete bar;
  4. Normal – 56ms @ point, that is about 1.34sec for the complete bar;
  5. Slow – 60ms @ point, that is about 1.44sec for the complete bar;
  6. SuperSlow – 76ms @ point, that is about 1.82sec for the complete bar;
  7. UltraSlow – 96ms @ point, that is about 2.3sec for the complete bar;

The default DS value is Fast.


This new feature allow user to select up-to 10 level of brightness of the leds. Brightness varies from 100% to 10%, in 10 steps. The default brightness is 80%.

Connections and adjustment

This section shows how to connect power supply and signals to the VM-AI1i and adjust it.

Power supply connection

To work properly, VM-AI1i requires a (minimum) 9VDC power supply (maximum 15V). In the kit a 2-way header is provided to connect the power supply source, but the PCB can accept also a classic DC Jack (positive tip, like this: KLDX-0202). NOTE: This jack is not provided with the kit. A Schottky barrel diode prevent accidental polarity inversion, and on-board charge pump IC provides the negative voltage for the operational amplifiers. Power supply connections are located near IC4 (TC1044S): the positive connection is internal, the negative external. Figure 3 shown how connect the power supply source to VM-AI1i.

Signal connection

Signal input connections are located near the two input trimmer (R1, R2). As shown the top silk, R-input is external, Common (Ground) central, L-Input is internal. In the kit a 3-way header is provided to connect the signal sources, but the PCB can accept also a classic 3.5mm stereo audio jack (like this: 35RAPC-HN2). NOTE: This jack is not provided with the kit.


VM-AI1i has an high sensitivity, indeed is possible turn on all led with a very low audio signal: 220mVRMS. (This mean that the minimum signal needed to turn-on the first led, using the MS = Scale N3,  is only 1mVRMS!). Using a 50k trimmer as input attenuator is also possible drive the VM-AI1i with high powers, up to 50-60VRMS (that corresponds to about 300-450WRMS @ 4Ω). Adjust these trimmers for desired “0dB” level.


VM-AI1i has a user-friendly and very simple setup interface that consist in only two buttons:

  • S1 – Enter in Setup Mode / Change meter parameter / Store configuration
  • S2 – Reset configuration / Change parameter value / Reset peak (when VM-AI1i is in PM = Peak Hold with manual reset)

To enter in Setup Mode, press the S1 button for at least 1sec. The display are automatic cleared and first meter parameter (DM) and his value are shown. How? Simply! The L-Bar indicates current parameter (DM, PM, MS, DS) and the R-Bar indicates the value of this current parameter (for more information, see next section Setup Visualization). Setup of Brightness instead turn-on all leds.

To navigates through the meter parameters press the S1 button (for at least 0.2s and less of 2sec). The sequence are:

Setup: meter parameters navigation.

Setup: meter parameters navigation.

Once entered in setup mode, using S2 button it’s possible navigate through the values of current parameter, starting from current value. With S1, pressed for a time greater than 2sec, it’s possible save and store (in the MCU’s EEprom) the configuration.

Finally, to reset VM-AI1i, is necessary to press S2 (when VM-AI1i is not in Setup Mode) for a time greater than 3secs. Reset restore the default configuration.

In the following picture is shown all the VM-AI1i setup workflow.

VM-AI1i Setup workflow.

VM-AI1i Setup workflow.

Setup visualization

In following pictures are shown how VM-AI1i displays the current setup parameter and its values. The L-Channel bar show the current parameter (DM, PM, MS and DS) and the R-Channel bar the value of parameter. When the parameter is the Brightness, all leds are turned on.

Display Mode
Display Mode - Bar

Display Mode – Bar

Display Mode - Dot

Display Mode – Dot

Peak Mode
Peak Mode - Peak Off

Peak Mode – Peak Off

Peak Mode - Peak Fall

Peak Mode – Peak Fall

Peak Mode - Peak Hold (Auto reset)

Peak Mode – Peak Hold (Auto reset)

Peak Mode - Peak Hold (Manual reset)

Peak Mode – Peak Hold (Manual reset)

Meter Scale
Meter Scale - Ansi VU-Meter

Meter Scale – Ansi VU-Meter

Meter Scale - 1dB Step

Meter Scale – 1dB Step

Meter Scale - 2dB Step

Meter Scale – 2dB Step

Meter Scale - Mectronics's Scale

Meter Scale – Mectronics’s Scale

Decay Speed
Decay Speed - UltraFast

Decay Speed – UltraFast

Decay Speed - SuperFast

Decay Speed – SuperFast

Decay Speed - Fast

Decay Speed – Fast

Decay Speed - Normal

Decay Speed – Normal

Decay Speed - Slow

Decay Speed – Slow

Decay Speed - SuperSlow

Decay Speed – SuperSlow

Decay Speed - UltraSlow

Decay Speed – UltraSlow



Learn how setup interface works: VM-AI1i Simulator

Download the user guide: VM-AI1i User Guide – V1.2