Building your own knock sensor headphones

[Matt]

Currently putting together some headphones. Thought I would share:

From PL:

Link Knock Box ($1100) They use a commercially available active noise cancelling headset “Noisebuster PA4000”. Pretty decent. Considering trying a set myself. They use a standard audio jack (which is unfortunately their weak point) for input. Bit pricey though:
http://www.ebay.com.au/itm/New-NoiseBus ... 1128437795

Naturally there are cheaper ones around. You just need an ear muff that has aux input. Active noise cancelling is nice to have but not entirely necessary as long as the ear muffs are good quality. Avoid things like domestic headphones as these don’t physically keep enough noise out and their noise cancelling is only designed for light background noise.

These might work:
http://www.ebay.com.au/itm/EAR-MUFFS-BU ... 2ed4c2cc73

These are also worth a look. Not active or noise cancelling. But they’re a Class 5 ear muff ( = highest rating) so should be good - with speakers in them.
http://www.ebay.com.au/itm/Howard-Leigh ... 2c8bd178f0

3M/Peltor make the good stuff in ear muffs world, so these may also be OK:
http://www.ebay.com.au/itm/3M-tekk-Work ... 19f41a0e35

Matts build list:

- Earmuffs with headphones. The ones I used are Howard Leight Sync headphones $55 plus postage from ebay link above

- Amplifier
Prechamp (Jaycar KC5166 $8.92) or
The Champ Amplifier (Jaycar KC5152 $7.95) which will require a dropping resistor on the mic input

- Standard microphone insert (Jaycar AM-4010 $2.35)

- Power switch (Jaycar ST0335 $2.95)

- 9V Battery snap (Jaycar PH9232 $0.70)

- LED + about 300ohm resistor (power indicator)

- 2 core shielded cable (Jaycar WB-1530)

- Lead with 3.5mm plug at end to connect headphones to amplifier output

- Small plastic box to fit amplifier, battery, switch and LED

- Length of rubber / plastic hose about 15cm in length which fits condenser mic

- Hot melt glue or similar behind condenser mic to stop wires breaking off

[Matt]

Pictures so far. Initial testing had too much noise with standard headphone cable so grabbing the shielded stuff today and will try again

Also the tube pictured was too short and will pick up more noise. Longer tube PL mentioned will help with differentiating knock

[Drift]

Hi there.
Awesome Matt!
Love to hear what sort or feedback your getting from your mic.
The z32 sensor still gets a good pick up but I'm yet to try the mic later today.
I love how they charge the earth for these things when really its not that hard to make your own on a budget.
I used the little bear mini guitar amp off AliEx---- nice and small board fits almost anywhere. May be hard to find at this time of year ( Chinese new year ).
Runs on 9v battery also.
It was suggested to me to use a shielded wire to stop electrical noise from the engine and other equipment used in today's cars.
I found a jaycar catalogue I had laying around and found a shielded cable that says eliminates just about all interference but it is a RCA line level cable for amplifiers WB-1506 but needs stripping down to 2 cores as its a 5 core cable.
From what I can see this (maybe) the best cable but Matt may have a better cable for this type of install as he's a real brain!


I was looking at high pass filters.
Maybe one could be used in line from the mic/sensor and only pick up fro say 5000hz and up to 20,000hz.
Knock on a rb is at a range of 7000hz if I'm right so should cover the start of knock maybe.


Another thing I had trouble with is the removable sensor/mic cable which I may just keep soldered.
I used RCA panel mount socket and connector and seemed to pick up a lot more noise, even when you put your finger near the unshielded part of the plug.
There are also car amp rca inline noise filters that may help here if noise is a problem but I'm nothing close to a electrical engineer.

[unex]

I dont want to hijack thread, but had some experience in building my own knock detection. Long story short: for me more convenient is visual alarm not the headphones, because with cheaper headphones you hear a lot of environment noise (especially when car is without exhaust). If you make a lot of sound volume, you are unable to talk with driver (when tuning), so personally for me, with visual alarm was easier to work. So, I made knock box with few small LED's when small knock or noise occurs, and one big LED which you wont miss when it lights. At first I made it just for my self, but because visual knock alarm you can install permanently, so now I am making such kits for my clients:



I dont know if I can say price on this thread, but knock box by it self is very cheap. If you Matt, or Pete would be interested to try it, just let me know.

[Drift]

Ok I used the same cable as Matt the other stuff was not shielded as good as the 2 core. but helps a lot for noise as does a few feet of extra cable looped up on the fire wall near the big grommet on r33 gtst. I used about 3 loops roughly 120mm and cable tied to the existing spaghetti. I did really help on my car.
I added another input with a guitar socket and plug, power and capacitor for the mic, I just used power from the 9v battery and added in line + side a 5k resistor to drop voltage to the mic.
So now I have both inputs z32 and the mic but yet to test the mic on the car.


Also thumbs up to Unex mate well done!

[Matt]

Yeah listing price is fine. Open discussion for different knock sensing types. I've just replaced my cable tonight, and built a second kit using the "champ" amplifier. Slight modification to the existing circuit required (pictures to follow)

How much were you looking for your particular ones? Do you use a narrowband filter for displaying the "knock" LED at the end similar to how the ECU uses it?

Will it work the same on the SR20 (donut) and RB sensors?

[unex]

How much were you looking for your particular ones?

110eu with new bosch knock sensor, or 70eu without sensor but including all harness. Also, sensitivity is adjustable from the backside (you can see the hole near the plug for the screwdriver):

Do you use a narrowband filter for displaying the "knock" LED at the end similar to how the ECU uses it?

I am not sure how ECU uses it, because I did not spent my time on that, but my experience was, that if you use very very strict and nice narrowband pass filter for example on 6.7-7.5khz, it will be difficult, or almost impossible to calibrate sensing on different engines (I do tune not only nissan engines), because all engine noise is removed at the other Hz range. Different engines makes different noise level while still not knocking, so you have to "hear" engine noise to be able to calibrate it. If you understand what I am trying to say

Will it work the same on the SR20 (donut) and RB sensors?

I did not tried RB or CA sensors, because I have seen some dead SR sensors and now I am always using only new donut type sensors. BTW, you cant use the same sensor for the ecu and for the knockbox, because ECU will raise fault.

[Matt]

Just an update. I purchased another amplifier board called the "Champ"

It requires some modification to the input. Thanks to PL for this info:

- Add a 10K resistor from power (9V) to the microphone input line.
- Cut the track from the microphone input line to the circuit input
- Use a 1uF capacitor in place of the track (from microphone input line to amp circuit input)

We needed to turn down the volume trim pot a bit on this one (the Pre Champ does not have this). Seems to work fairly well with the well shielded cable with no noise now

Shield the cable to the negative (-) side of the circuit in the box, but not to the condenser mic at the other end

[Matt]

completed

[Tengis]

I may try this using some aviation headphones that also double as ear defenders (noise reduction). I have a few pairs since I work on aircraft in my day job.

Looks good! Matt, is it easy to discern knock from other noise with your setup?

[Tengis]

One more question... is there a benefit to using the mic listed in this thread over doing a setup with an actual OEM knock sensor?

You piqued my interest with this post so I did some googling and a lot of other setups seem to use knock sensors. I actually found a post on a Nissan forum where someone said they literally got a knock sensor and then wired up a shielded audio cable to it... and then plugged it into the aux port of their headunit.

[Matt]

Yes it is easy to work out knock noise from engine noise. A longer tube around the mic tends to help with filtering it out

Pete uses aviation headphones also

I haven't tried an actual knock sensor to compare to answer your second questing

[RomChip200]

double post

[RomChip200]

I also prefer visual indicator of knock, and also useful in daily driving.
Personnally I rely on the OEM knock sensor on Z32 and monitor the evolution of the variable in an add-on
timing_offset2 EQU 0x1614 15

MIL (engine check light) is toggled when knock is detected:

Code: Select all

;----------------------------------
accel
	ldaa timing_offset2       instant knock situation and then, timing pulled ?
	beq miloff_knock	
	cmpa #254	          >= 3° of retard ?
	bcc miloff_knock	          otherwise, came back to normal situation i.e. >=254 ?         
knock_detected
	tst kd_count
	bne milon_knock
kd_save
	sei
	inc kd_count      	  allow to track the latest occurence of timing pulled i.e. <=253
	ldaa tp1
	staa kd_tp		   	
	ldaa timing_offset2
	staa kd_kvalue
	ldd rpm
	std kd_rpm
	ldaa timing
	staa kd_timing
	ldaa engine_temp
	staa kd_temp
	cli
	bra milon_knock

;-----------------------------------------------------------
miloff_knock
	tim %00000001,MILstatus
	bne miloff_knock_cont
	rts
miloff_knock_cont
	aim %11111110,MILstatus
	bra milonoff_cont

miloff_afr
	tim %00000010,MILstatus
	bne miloff_afr_cont
	rts
miloff_afr_cont
	aim %11111101,MILstatus
	bra milonoff_cont

milon_knock
	tim %00000001,MILstatus
	beq milon_knock_cont
	rts
milon_knock_cont	
	oim %00000001,MILstatus
	bra milonoff_cont

milon_afr
	tim %00000010,MILstatus
	beq milon_afr_cont
	rts
milon_afr_cont	
	oim %00000010,MILstatus
	
milonoff_cont	
	ldaa MILstatus
	staa MILsecondstatus
	bra compute_mil_patch

; --------------------------------------------------------------------------------------------------
        org 0xE200
compute_mil_patch
	sei
	ldaa port6_copy               ; PORT6 copy in RAM
  		                      ; Bit 4: Fuel pump relay
			              ; Bit 5: FICD solenoid
	                              ; Bit 6: MIL
	anda #%10111111
	ldab mil_var13
	andb #%01000000
	aba
	tst MILstatus
	beq cmilp1
	oraa #%01000000		      ; MIL needs to be forced on for knock or AFR !
cmilp1
	staa port6_copy               ; PORT6 copy in RAM
                                      ; Bit 4: Fuel pump relay
                                      ; Bit 5: FICD solenoid
                                      ; Bit 6: MIL
	staa PORT6                    ; Bit 1: Throttle switch (1=idle)
	cli
	rts

[Matt]

Be interested to try this. Its not a portable solution (moving from ECU to ECU) but would be nice to have