VU meter or a volume unit meter circuit is a device used for indicating the music volume output from an amplifier or a loudspeaker system. It may be also considered as a device for displaying the PMPO of the amplifier at a particular volume setting.
Though the unit looks quite technical, which is applied as a measuring device of audio power, in real terms these are more like decorative ornaments of an amplifier.
Without such devices attached, an amplifier system would look quite dull and without any juice.
The varying response from a VU meter certainly gives a whole new dimension to a sound system making it more dynamic with its features.
Prior to the days when LEDs were not so popular, moving coil meter type of displays were commonly incorporated as VU meters and surely these units with there back lights ON produced a distinctive visual effect as their needles deflected from left to right displaying the varying pitch of the connected audio system.
With the advent of the LEDs, the moving coil displays slowly got replaced with the ones which incorporated LEDs.
With color effect at its disposal, LEDs became the HOT favorites as far as VU meter were concerned, even today amplifiers employ a LED VU graph for displaying the music power in an amplifier.
For electronic hobbyists who are rather more interested in building a particular required gagdet right at home instead of buying a commercial piece, this cool VU meter circuit will interest them if they are intending to make one for their music system.
Using the IC LM3915
The circuit of a simple LED VU meter explained here uses the outstanding chip LM3915 from TEXAS Instruments.
The circuit diagram shows a very simple configuration employing two of the above ICs in the cascaded form for producing a good 20 LED sequencing bar type indication.
The music input is applied across pin #5 and ground of the IC. The music input can be directly derived from the speaker terminals of the music system.
R3 has been stationed for adjusting the typical dB levels between the LEDs for enabling visually more enhanced sequencing pattern in response to the fed music input.
The diagram shows a separate power supply being used for the circuit, however if the amplifier supports a 12 volt stabilized power supply, can be used for powering the circuit as well, this would help to get rid of the extra bulk involving the transformer and the associated rectification circuitry.
The color of the LEDs may be selected as indicated in the diagram or may be altered as desired by the user.
Everything is pretty straight forward and can be simply built over a general purpose board.
Assemble the IC first and then go on fixing the rest of the components and connect then to the relevant pin outs of the IC.
The LEDs should be soldered at the end, such that all of them are arranged in a straight line, preferably at the edge of the PCB.
An external enclosure may be used for housing the assembled circuit or possibly the circuit may be installed in the amplifier dashboard itself, if situation permits the required drilling and fittings.
Simplified VU Meter Circuit
If you are not interested to have a 20 LED VU meter circuit rather satisfied with a 10 LED VU meter, then the following design using LM3915 can be very handy.
Please refer to the comments posted by Kieth Russel and me in order to understand the following diagram VU meter circuit application:
VU Meter using DC Voltmeter
The next VU meter will also show the music level but will indicate it through an ordinary moving coil voltmeter, as shown in the following diagram.
The VU meter circuit indicated in the above diagram consists of a 2-stage voltage amplifier which operates a connected a level meter. The inpu music AC signal is first amplified, and then rectified, and finally the resulting DC potential equivalent to the music level is displayed on the connected voltmeter.
The VU circuit using a voltmeter can be used with any amplifier, music system, audio mixer etc and must be connected from an early stage of the pre-amp. The current intake of the circuit in the absence of an input signal is around 2.8mA. The 12K preset can be used for adjusting the sensitivity of the circuit.
The meter can M be any general purpose moving coil voltmeter.