Shock Sensor Question

[Jon Snoddy]

Not sure if this will work, but I think is should:  Plug the data recorder
analog output signal into a laptop's analog audio input and record it to an
uncompressed wave file.  View it with an audio editing program.  Audio
editing programs provide a timeline view that will have very accurate time
marks in seconds, fractions of seconds and even samples (44k per second).
Another cool trick is that the input is stereo, so you can record and
display two channels of data at once.  Using one of the many multi-track
recorders, you can view successive recordings on top of one another on the
same time line.  Record audio with a microphone on one channel so you can
hear bumps and engine speed (easy to arrive at RPM from pitch) in time synch
to the shock data. Hmmm.  I'm beginning to like this idea.

You will need to install a "pad" to reduce the signal from 0-4v down to
about 0-1 volt (what is that, 6db?) to keep from overloading the input of
the laptop.  I imagine you can buy a 6db pad at Radio Shack.  Many computers
have low pass filters at the front end that make it impossible to record DC
which means that any movement at a rate slower than 50 to 20 Hz would come
out as a straight line.  There are many audio A/D cards available for
desktop units or with a firewire connector on a laptop, some of which have
defeatable low pass filters.

You will want to make sure the voltage is limited to what ever your line
input can tolerate.

-jon

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On Behalf
Of Bernd Felsche
Sent: Thursday, December 13, 2001 5:18 PM
To: diy_efi at diy-efi.org
Subject: Re: Shock Sensor Question

Steve.Flanagan at VerizonWireless.com tapped away at the keyboard with:

> Don't know how you can record Digital pictures into an analog data
> recorder.

Computer is digital. I wasn't aware of your limitation of an
analogue data recorder. If the camera is digital, use IEEE1394
connection for lossless, digital transfer. You measure the
displacement on-screen on a field-by-field basis.

> I have a multi channel 0-4V analog data recorder,  and am looking
> for a cheap way to monitor the position of my shocks on the launch
> and also down track.

> The expensive way is to use the $180-$200 dollar linear position
> sensors, I am just looking for a cheaper way.  The budget wont
> allow for that expense when the money is needed else where on the
> car.

Rotary encoders are somewhat cheaper, depending on enclosures and
resolution.

Cost really depends on if you already have a camcorder.

> Thanks though.
>
> BW???   The recorder can sample from 1 Hz to 1000 Hz max.

What's the frequency of the thing you're trying to measure?
Normal (road) suspension dampers cannot respond to frequencies much
beyond 100Hz. The suspension relies instead on tyre flexure.


> -----Original Message-----
> From: Bernd Felsche [mailto:bernie at innovative.iinet.net.au]

> Steve.Flanagan at VerizonWireless.com tapped away at the keyboard with:
>
> > Application is to monitor the shocks on our 1/4 mile car.  This
> > way I can determine if I need an adjustment based on how the car
> > is launching and driving down track.
>
> > We can adjust both compression and extension of the shock, so it
> > would be nice to see how the adjustments actually effect
> > performance.  Tuning the start line reaction of a chassis is
> > critical to maximizing the performance.
>
> Consider a high-speed camera. Even a low-end camcorder delivers 50
> or 60 fields per second (depending on video system). Plug the signal
> into a computer (digital camcorder makes that easy) and measure the
> displacement over time, from field to field.
>
> What sort of bandwidth and displacement do you think you'll be
> measuring?

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