legacycentral bbs

How to make a cheap knock light?

Something that lights up when you get knock?

Best would be just to tap the stock knock sensor, but if needed, we could stick another sensor in.

What do you think?

They are out there, but spendy.

And we Legacy Folk are cheap as shit.......

douglas vincent wrote:And we Legacy Folk are cheap as shit.......

WORD!!

Why not just use the stock sensor and tap that into an AUX port on a head unit? Then you can LISTEN to knock .

The TurboXS Tuner has a port that taps your knock sensor, and you can listen to knock through headphones (for tuning purposes). On a few cars, we've just jumped the output there to the AUX input on their headunit and listened for knock through the car's speakers

tapping into the stock senor really wouldn’t work to well as scoobies use a flat response type sensor. You would amplify the signal from the flat response sensor to make it work... though the speakers you'd hear nothing at all then something like a little pop when there was knock. I use a regular Toyota knock sensor that works like more typical sensors. They are just small microphones and you could tap it into your stereo to listen. I run mine to my R-500 as I don’t have any aux inputs in my stereo (late model outback head unit)... I do hook it up to my laptop though when I'm datalogging

As far as I know the Subie Knock Sensor is just a grounding one...so for the light, just tap into the sensor wiring loom and run a +12v always on to the light and make the might ground through the sensor...

Unless you really know what you are doing, I would advise against tapping the stock sensor. It would be much safer to add a sensor and leave the stock system undisturbed.

Anytime you tap that line and run it to something else, you're adding load to that sensor. I don't know much about knock sensors, but I think they're piezo-based. Tee-ing off could reduce that output of the sensor, in which case your engine would obviously no longer be as sensitive to detect knock/pull timing.

You can theoretically tee off the stock sensor lines, and some aftermarket companies probably do, but you just have to make sure the electronics have high-enough input impedance to avoid changing what you're measuring. So, I wouldn't even do it with an aftermaket system unless I really trusted it was a quality company and my wiring job was quality too.

Seems like the right way to do it is tap another hole for a completely separate sensor.

I know Vikash is going to agree with that

Sam, the Selectmonitor can read knock sensor activity.

That's all you really need, right? Know knock sensor activity. So surely you could simply tap the diagnostic system and have a simple circuit tell you when there is a signal from X.

Leave the stock system alone, and just rely on the ECU OUTPUT which is meant for diagnostic readings.

Signal occurs, switch ground on a light, and turn it on.

But I may be oversimplifying....

make the thing even easier... grab a GM knock sensor, and a knock module out of an early 90s GM (mostly 60 degree v6s) hook it up, the module as a simply voltage output corresponding to the knock level. hook it up to a cheap A/F meter and you have no knock/knock instead of lean rich

BAC5.2 wrote:Sam, the Selectmonitor can read knock sensor activity.

That's all you really need, right? Know knock sensor activity. So surely you could simply tap the diagnostic system and have a simple circuit tell you when there is a signal from X.

Leave the stock system alone, and just rely on the ECU OUTPUT which is meant for diagnostic readings.

Signal occurs, switch ground on a light, and turn it on.

But I may be oversimplifying....

Yeah, I think that would theoretically work and that would be the best option because you could see what the ECU sees. But to get the data , you need a whole select monitor or some chip or some PC running Vikash's code to do serial communication with the ECU and pull the data out. Then, how do you hook a light up? Maybe if we buy Vikash a pizza he will re-write his code so that the whole laptop screen flashes in your face when you get detonation.

The other problem is that Vikash said that the ECU doesn't always report information when it gets busy, so it might miss pings. Dunno how badly it misses data, though.

"Danger to manifold"!

I just want a dash mounted light that flashes.

rallysam wrote:The other problem is that Vikash said that the ECU doesn't always report information when it gets busy, so it might miss pings. Dunno how badly it misses data, though.

That is correct....the ECU basically says fuck off, I'm busy.

You'd be better off using a separate knock sensor.

Yea, but would you be able to mount another sensor in a position that would read exactly the same as the ECU sees?

Maybe, maybe not.

My understanding is that most aftermarket knock detection dealies are very very simple -- they just threshold the signal from the knock sensor. It'd be very easy to rig something up to do this -- just an op amp to serve as a comparator and then a one-shot timer or some type to extend the pulse so it's long enough to see. A good op amp should have a high enough input impedance to prevent it from interfering with the ECU's reading of the signal.

Good OEM setups are much more sophisticated because they watch for noise at the correct frequencies. This means gains can be higher so they're both more sensitive and more immune to noise. It would be possible to make something like this out of a chip like TI's TPIC8101, or to just put together an amplifier and band-pass filter, threshold the output, and extend the pulse width as above. The hard part would be matching the characteristics of the filter to the sensor and engine.

Want me to draw up the first one?

yes please.

also. would it be possible to hook up a oem sensor identical to a light, be it led or a shift light. so ya dont have to design a whole new sensor

Okay. Give me some time, though -- bump this thread if I haven't done it in a week.

ok its been a week so bump

Gimme another week...

http://www.turboxs.com/shop_prod.php?what_category=7

Half way down the page.

How hard would it be to splice the knock sensor wire? when I removed my engine i noticed that the wire on the computer side of the harness had come out of the connector so i was thinking of cutting the part off of a legacy at the junkyard and splicing it together to get it hooked up again. I did notice that the wire is shielded tho.

Good feature... adding to list of signals the LegacEBC will monitor and respond to.

Not only a knock light, but optional immediate boost reduction if knock is detected. And a snapshot of the other readings that generated the knock conditions for later review. Excellent.

remember, if you're going to use the factory knock sensor, it's a flat response type, not just a microphone like most other knock sensors are. That might actauly make the circut easier. The way it works would be very different than a device that uses a regular knock sensor.

Can you explain more, Junior? What's a flat response type knock sensor?

flat response is a non resonant sensor. It's more accurate but seems to require more application specific design. They are found in Audis, Porches, the new EVOs and of course Subarus.


everything you ever wanted to know about knock sensor types and their output
http://deviantmethods.com/bigmoose/pages/knock.htm

Oh. You just mean it's not tuned to any particular resonance. Do you have a source on that? I'm curious -- I've always wondered, though I had a hunch because Subaru specifies the same sensor for early EJ22s and EG33s.

Isn't a flat response sensor more like a microphone though?

By "more application specific design" you mean more sophisticated signal conditioning, right? So wouldn't that make the circuit harder?