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The simplest LED sound level indicator

     This is a very simple stereo LED sound level indicator (meter) for amplifier or other audio equipment. It is controlled by the Atmel AVR ATtiny24A or older ATtiny24 or ATtiny24V. A single integrated circuit provides an indication of both audio channels. The indicator has a total of 7 divisions per channel, 1 division corresponds to 5 dB. Display range is -30 to 0 dB. Basic 0 dB corresponds to the voltage of 0,775 V RMS and is indicated by highest (seventh) LED. Thus, if the highest LED shines or blinks, the overdrive occurs. The display uses 5x7 dot LED matrix display, such as TA07-11SRWA. The sound level scale consist of pairs of dots, the middle column is not used. However, individual LEDs (eg 2x7 rectangular LED) can also be used. The display is controlled by line multiplexing, frequency of multiplexing is 100Hz. Columns are anodes, rows are cathodes. The resistors R1, R2 determines the brightness of the display. The signals of left and right channels are connected to the inputs of the AD converter ADC0 and ADC1. Fade out (fall) time of whole scale is about 500ms (in the program, it can be adjusted on the 4th line from the bottom). This sound level indicator is powered from a 5V supply and maximal consumption is about 30 mA when all LEDs are lit. Put C1 close to AVR.
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     The AVR program for download:
source code in Assembly (ASM)
compiled HEX file (274 Bytes)

I can send you the programmed microcontroller. For more info click here.

The schemtic with the simple sound level indicator with ATtiny24A / ATtiny24 / ATtiny24V.

Configuration bits setting.

LED sound level indicator operating.

Video - testing the LED sound level indicator.

Added: 24. 6. 2013