knock filter and amp - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


ECUs and Tuning Discuss Engine Management, Tuning, & Programming

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 07-06-2011, 10:38 PM   #41
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

y8s is offline   Reply With Quote
Old 07-06-2011, 11:17 PM   #42
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Cool stuff on the windowing.

Matt, the output of my circuit isn't "0-5V". It's a bandpassed, amplified version of the knock signal. You'll need a peak detector or AM circuit after it.
JasonC SBB is offline   Reply With Quote
Old 07-07-2011, 12:02 AM   #43
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,328
Total Cats: 1,926
Default

Quote:
Originally Posted by y8s View Post
ok but the AC is all happening from 0-5V... which sounds like what I'm after.
Quote:
Originally Posted by JasonC SBB View Post
Matt, the output of my circuit isn't "0-5V". It's a bandpassed, amplified version of the knock signal. You'll need a peak detector or AM circuit after it.
Also, the MS's knock input is kind of backwards. +5 indicates no knock, 0v means that knock is occurring.

Also II, this input goes directly into a pin on the microprocessor, so the threshold is pretty damned nondetermenistic. The specs for the '908 only guarantee that the threshold will be somewhere between 0.2 * VDD and 0.7 * VDD, which is pretty typical. And, of course, you need to hold the sample for long enough the the uP has a chance to actually read it. A quick transient is likely to get missed by the processor as it only polls the inputs on a "best effort" basis. The closest thing I've found to an official spec says you need to hold the low state for at least 400ms, which is an eternity for a high-frequency audio waveform. Granted, that spec was written for the MS1, but even the MS3 isn't polling those ports continuously.




Quote:
Originally Posted by y8s View Post
Now that is damned cool.

I may have to build myself another MS and sacrifice the engine in my '90 on the altar of figuring out how to tune that little bugger.

Anybody know were I can buy some 70 octane gas?
Joe Perez is offline   Reply With Quote
Old 07-07-2011, 02:37 AM   #44
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

A rectifier + peak detector + peak&hold circuit to process the output of the bandpass circuit is pretty simple.
JasonC SBB is offline   Reply With Quote
Old 07-07-2011, 12:44 PM   #45
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

Quote:
Originally Posted by Joe Perez View Post

Now that is damned cool.

I may have to build myself another MS and sacrifice the engine in my '90 on the altar of figuring out how to tune that little bugger.

Anybody know were I can buy some 70 octane gas?
5 samples free on that tpic.
y8s is offline   Reply With Quote
Old 07-09-2011, 02:13 AM   #46
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,328
Total Cats: 1,926
Default

It occurs to me that we are all complete idiots, myself included.

The time-window of interest to us can be expressed as either n degrees of crankshaft revolution or n number of milliseconds after the ignition event, right? (I'd need to do a bit of reading to recall which.)

How hard would it be to rig up a little external device to take, as inputs, a one-pulse-per-ignition-event signal and something resembling an RPM signal (which could be as simple as a freq-to-voltage converter, if we're working in the analog domain) and use it to drive a monostable multivibrator to gate the sensor signal?
Joe Perez is offline   Reply With Quote
Old 07-09-2011, 03:55 AM   #47
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Easy. Just use an analog CMOS switch e.g. CD4013B for gating.

You'll need a pulse train that goes 'hi' during said ignition window e.g. from 10* to 90* ATDC to gate the CMOS switch.

Since most knock occurs after the ignition event, just use the actual ignition event to gate the window. And since burn time is 3 ms max IIRC, use a 3 ms monostable.
JasonC SBB is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 12-15-2017 09:00 PM
Garrett Turbo, 1.8 Oil Pan, & Misc. Stuff nbdooey Miata parts for sale/trade 9 08-30-2017 10:50 PM
K&N Intake Filter nbdooey Miata parts for sale/trade 0 09-28-2015 09:46 PM
NB2 Denso Injector Filter Basket Part Number? Neddy Engine Performance 0 09-10-2015 10:42 PM
Annoying little leaks AlwaysBroken Engine Performance 5 09-06-2015 01:53 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 01:27 AM.