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Input signal for LM3915. need help.


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The opamp that feeds the average detector is a half-wave rectifier because without signal its output is at 0V.
The average detector has its rise and fall times the same and its response is slow so its output is the average of sounds picked up by the microphone.

Peak sound levels must be allowed to be amplified normally without clipping so the average voltage will be much less. Perhaps a voltage of 1.6V should be used for Rhi to allow the peaks to be 10dB (3.16 times) higher than the average voltage.

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Hello, The circuit work very well using the Average detector.

figure bellow show how i supply my Rhi.


When i change the R1 to smaller value (20k), the first 2 LED will lights. When i use 220k, the first 5th LED wont light up (dot mode). It starting on the 6th LED.
Playing with the R1 value can give me a good result without knowing what is the true Voltage or current for the Rhi.

Any comment about the diagram above? how i can supply my Rhi with 1.6v?
btw, the capacitor seem does not affect The Rhi? am i right?

How do i make the LED to discharged slowlly? i meant, the LED suppose to light up quickly(sensitive) but light off slowlly? increase the C8 value will do the job?

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Hello Again. I come up with a new question.

I'm planing to connect the 14th or13th (or 12th) LED to trigger the interrupt on my PIC16F84. I think that we can generate needed voltage for interrupt by connecting the signal form an LED to an logic gate. Here i use an AND

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The circuit work very well using the Average detector.

Good.

When i change the R1 to smaller value (20k), the first 2 LED will lights. When i use 220k, the first 5th LED wont light up (dot mode). It starting on the 6th LED.
Playing with the R1 value can give me a good result without knowing what is the true Voltage or current for the Rhi.

The datasheet says that the resistance at Rhi is typically 28k. You can measure the voltage of Rhi or calculate it. With a 5V reference and 20k in series with the 28k, the Rhi voltage is 2.92V. Using 220k, the Rhi voltage is 0.57V.

how i can supply my Rhi with 1.6v?

The voltage reference pin of the LM3915
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You need to detect when an LED blinks, since your LM3915 is in the DOT mode.
A logic gate or a comparator isn't needed. The LED to be detected operates with current, not voltage.

The LED of an optical-coupler could be connected in series with the LED to be detected and its phototransistor could drive the interrupt of the microcontroller, if the LED "blink" duration is long enough. A monostable might be needed to extend the duration of the "blink".

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