I got screwed on the WB02 purchase

[Brian Dessent]

A70Duster at aol.com wrote:

> Does anybody have a schematic for making a knock detector circuit.  I'm
> guessing the circuit would have a front end band pass filter of 4k to 7k
> Hertz.  Then that signal could be used to trigger a 555 timer that could
> flash a light/LED.

Intersil makes two chips, the HIP9010 and HIP9011, which are designed to
interface the knock sensors and the engine computer.  The chips are
designed with two channels (two knock sensors, one on each bank of
cylinders) and the idea is to use one channel as a reference for the
background noise while sensing knock in the other.  The chips contain
on-board amplifiers, programmable bandpass filters / gain stages, and a
rectifier + integrator to sum the total in-band energy.  It seems like a
very robust and complete solution.  Unfortunately, it comes with the
cost of complexity: they are meant to be interfaced with microprocessors
via the SPI bus to get the sampling information (only listen when knock
is expected) as well as for setting the passbands and gains.  So at the
very least you would need a PIC or Amtel or some other simple processor
to make a functional circuit with these chips, and this may be more than
you were looking for.  I've never used either of these, so I really
can't say what would be involved.  Below are links to the datasheets in
PDF...

Brian

HIP9010: http://www.intersil.com/data/fn/fn3/fn3601/FN3601.pdf
HIP9011: http://www.intersil.com/data/fn/fn4/fn4367/FN4367.pdf

And here's a quote from the 9010 datasheet explaining the basic
operation:

Description of the HIP9010 Operation

This IC is designed to be a universal digitally controlled,
analog interface between engine acoustical sensors or
accelerometers and internal combustion engine fuel
management systems. Two wideband input amplifiers are
provided that allow the use of two sensors that may be of the
piezoelectric type that can be mounted in optimum locations
on either in-line or V-type engine configurations.
Output from these amplifiers is directed from a channel
select switch into both digitally controlled filter and amplifier
channels. Both filter bandpass and gain settings are
programmable from a microprocessor. Output from the two
channels is combined in a digitally programmable integrator.
Integrator output is applied to a line driver for further
processing by the engine fuel management system.
Broadband piezoelectric ceramic transducers used for the
engine signal pickup have device capacitances in the order
of 1100pF and output voltages that range from 5mV to
8V RMS. During normal engine operation a single input
channel is selected and applied to the filters. One filter
channel processes a signal that is used to establish the
background reference level. The second channel is used to
observe the engine during the time interval that preignition
may be expected. This information is compared with the
“background” signal via the IC’s integrator and will tend to
cancel the background noise and accentuate noise due to
engine pre-detonation. Moreover, the bandpass of filter
channels can be optimized to further discriminate between
engine background and combustion noise and
pre-detonation noise.
A basic approach to engine pre-detonation systems is to only
observe engine background during the time interval that noise
is expected and if detected, retard timing. This approach does
not require the sensitivity and selectivity that is needed for a
continuously adjustable solution. Enhanced fuel economy and
performance is obtainable when this IC is coupled with a
microprocessor controlled fuel management system.

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