Hi guys! I need a new tool that tool is an engine stethoscope or digital det
can. In this episode I'm going to show you how to make one from cheap DIY components
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In the description there's a timestamp break down of this episode. Also
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subscribing. What Built On Purpose is about it is it's all about DIY and I
have enough knowledge to be dangerous. I don't know everything but I want to
share that with you guys. So if that's up your alley consider subscribing. So a bit
of background behind this episode. I've recently changed the ignition on this
Datson 240 Zed with the L28 stroker motor in it. I've made up a megasquirt
MS1 computer configured it in ignition only. Um, if you feel like it
have a look at the cards. I'll throw up some videos for you to look at. What has
happened I've put the ignition table together went to drive it a bit and I've
had some strange behaviour where the engines not tolerating as much
ignition advance as it previously had which prompted me to think that
maybe something else is going on. Normally you can hear the knock in this
engine in the cabin but, I mean, what if there's something going on that I'm not
aware about. So what is...that's the driver for this, this build. This, what I'm
doing is not new. I remember reading articles in the early noughties from
Autospeed who are an Australian based online journalism, motor journalism type
website. I don't know if they still exist but they wrote some really good articles
and I remember reading one where they pulled apart a Dick Smith electronics
hearing aid to do the similar function. So the concepts not new.
I believe you can buy more professional setups as well. I think the knock box is
one and it's it's a fairly flash robust looking unit. I will be using
this for detecting detonation but that's not it's only use. I think you could use
it for hearing any other engine noises. Rod nock. If there's a tappet you could, I
think because the the microphone will be movable you probably be able to put it up
and down the engine here close to which rocker might be loose and
needs adjustment...the lash. I don't know. I could put a knock sensor on that but
from my understanding most knock sensors are tuned to a specific waveform and I'm
unsure if they'll actually detect that signs of detonation at low load
particularly around the cruise map which is where I think I'll primarily use this
device. You can get good benefits from fuel economy from winding in
more advancing in your low load and cruise areas. I'm not sure if a knock sensor
will be able to pick that up particularly if those knock indications are low...low in
volume compared to the rest of the rest of the engine noise. So the kit I'm
using, if you're Australian based you'll be familiar with Jaycar. Um, Jaycar....well I
hope I can assemble this because this kit is part of the "Short Circuit" series
which is aimed at children. But this is called the "Bionic Ear" it's part
number KJ8226. But it's basically has just about everything we need in it.
It's got an amplifier, potentiometer to adjust the gain and
needs a 9V battery to run it's got an electret microphone but if you're
doing a kit you can use a piezo transducer does the same thing...kind of.
They produce a wave form without voltage but yeah. So that's the kit fairly simple.
This cost less than ten bucks. I've got a bit of shielded wire to extend the
microphone. I've got a battery clamp to to fix the microphone to so i can clamp
it anywhere on the engine and just need a set of headphones. A jiffy box to
to mount it all in and a few other things but i mean it's a fairly simple
kit. I think it'll go well. Might as well head over to the bench and start putting
this thing together.
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This is the finished box. See this is the that's the Jaycar kit. It's got the potentiometer
through it. I used some single core shielded wire to extend the
microphone. There's the the headphone jack and just to switch to turn it on
and off and the 9V battery battery connector. What I did do was I spaced
the board off the base of the jiffy box using some...some...some bolts with...there's
another nut underneath the PCB and then the PCBs on there. Connecting the
microphone to my terminal it's just simply hot melt glue in for now. I'll
have to see how well that lasts. I think I'm gonna call this just the the mark
one iteration. There's a few things I might might alter eventually. Things
I gotta do it is put a bit of a zip tie on the microphone cable so it doesn't pull
it any further and maybe some means to hold down the 9-volt battery. But yeah I
mean all up it took half an hour to do and this this is this kids kit. The
hardest thing to do is figure out the...
make sure your polarized capacitors are in the right orientation. So it's not too
hard it'll do for a first round iteration. So I think we'll give it a
quick test and maybe see if it actually works first cause I haven't tried it out
yet so but yep do that now.
[THUD}
[amplified tapping sounds]
[really amplified tapping sounds!]
I was chuffed that it work first time which wasn't unexpected though that is a kids
kit and it's not exactly rocket science to do. What I haven't filmed and what I
won't...I don't think I'll edit in is I got a all excited that it worked and I
thought well I'll give it a trial on an engine. Now I've got a Defender TD5 Land
Rover with a diesel. I thought if there's any engine I'm gonna be able to hear the
inner workings up it would be a diesel motor. So I went through it on the td5
and you can hear a lot but and I think to be functional
I'm gonna have to train my brain to pick the noises. It is acting as just an
amplified stethoscope so it's not isolating one sound and it's hearing
everything. So I'm gonna have to train my brain to pick the detonation when it
does occur. But it was interesting. You could hear a lot of stuff going on there
and I'm wondering if I could do things like attach it to the sump and turn the
engine off and see if I could hear the oil pooling around. I don't know it was just it was
just very interesting to those do to listen to so. Yeah happy with the first
friend iteration. Um yeah. I have to see how it goes I think there will be a few
tweaks to be made. One modification I think I will have to make before I hit
the road is some means how to record the sound from the box into my laptop that
I'm going to use to data log. I think I might have to modify a 3.5 mm cable, mono
cable because it only produces mono sound and turn that into a microphone
um and somehow have an output so I can hear it while I'm using it. I think that
will benefit particularly I get some good sound recording software to isolate
the information and to see, I don't know, I've got to demonstrate you guys that it
actually functions and the only way I can think of doing it are actually
recording the sound and playing it back to you. I think the only thing holding me
back from actually doing some more Road tuning on this car is bleeding the
brakes. it has been exceptionally difficult to try and get my my favourite
pen right brake fluid in the region I in. It seems to be an order only
type item. So once I get hold of some brake fluid I'll bleed the brakes and
we'll go go for a drive and that start tuning! Lesson learn for me is it's fun
to prototype. I forgot how much fun it is to make up a kit and the satisfaction
that it is to actually have a function. So I don't know if this interests anyone?
If anyone is interested in doing their own or similar what I might do is in the
future I might even try and make a bit more of a robust kit and run a series of
videos or something that shows a bit more in depth how to do it yourself.
I dunno. if that interest is anyone yeah let me know in the comments. I'd be
be keen to know that. Thanks for watching. if you thought this video was of
interest like it and also share it with your mates if you think someone might be
interested or find the information valuable. Have a look at what YouTube recommends
to watch next as well as just the megasquirt playlists for this car,
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the next episode. Thanks for watching!