Knock sensor and progressive Leds

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Discussion Overview

The discussion revolves around the design of a visual output system for detecting detonation in a spark-ignition (SI) engine using a knock sensor. Participants explore methods to implement a series of LEDs that indicate the severity of engine knock based on the output voltage from the sensor.

Discussion Character

  • Technical explanation, Experimental/applied

Main Points Raised

  • One participant describes using a piezoelectric knock sensor connected to an op-amp, expressing the desire to light up three LEDs based on the severity of knock detected, with specific voltage ranges for each LED.
  • Another participant suggests using a peak detector or peak-to-peak detector with a sample and hold circuit to drive a comparator for lighting the LEDs.
  • A suggestion is made to search for "VU meter circuit" as a potential solution, indicating that the design could extend beyond three LEDs.
  • A later reply provides links to circuits using the LM3914 and LM3916, suggesting these could serve as suitable solutions for the LED implementation.

Areas of Agreement / Disagreement

Participants present various approaches and suggestions, but there is no consensus on a single solution or method for implementing the LED indicators.

Contextual Notes

The discussion does not clarify the actual output voltages from the knock sensor, which may affect the proposed LED activation thresholds. Additionally, the effectiveness of the suggested circuits in this specific application remains unverified.

varnish
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I am detecting detonation in a SI engine using a knock sensor (pizeo element).
What I would really like is to have 3 leds that light up as the knock gets more severe.

I have the knock sensor running into an op amp powered by a 9v battery. I am listening to the output with a pair of head phones, but I would like to add a visual output.

The knock sensor is a pizeo element, so as I understand it the more aggressive the engine is knocking the greater the output voltage will be from the sensor.

I was hoping to do something like this;
First led to light when the output from the op amp is between 1-3 volts, the second to come on at 3-6 volts and the third to light up between 6-9 volts.
(arbitrary values I'm not sure what the actual output voltages are, but you get the idea).

The idea is that when no knock is present no lights are on, and under heavy knock all three lights are on.

Any input would be greatly received.
 
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Probably a simple peak detector or peak to peak detector with a sample and hold on the output. This would drive a comparator to light the LEDs.
 
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