Another Cam Sensor
Turbo Mini Forums

I've just had delivery of the new cam sensor from DigiKey.



This is a hall sensor made by Hamlin:

http://www.hamlin.com/specsheets/55075%20IssueAF.pdf

This is going in the fuel pump hole in the block and will use the fuel pump lobe as the "tooth". Hopefully it will work.

EDIT: Decided to try it on the cam wheel first.

Obviously if you are using the fuel pump hole for your turbo oil drain, then this is not an option. OK for remote mounted turbo and NA applications though.

I can remember that when I built my first cam sensor, some very helpful people on here showed me how to make a circuit with an LED to test it. I can't find the thread however.

So how would I go about making a circuit to test the switching points?

Edited by Paul S on 7th Feb, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Wire it up exactly the same as your circuit for your exixting Hall switch on the Megasquirt except put an LED where U3 would be.....

U3 is an LED anyway, you just can't see the light !!!

Make sure the LED polarity is the right way around.

This hall switch is rated at 20mA so I would probably use a 680ohm resistor rather than 470 (assuming you are going to run it at 12V).

Schrödinger's cat - so which one am I ???

Another led on the side of the case might be good for this then, that way if we have any problems we can rule it out straight away.

:cool:

Yes i moved to the darkside

Instagram @jdm_brett

Schrödinger's cat - so which one am I ???

Thanks Rod, I did a search on U3 and the original thread came up.

http://www.turbominis.co.uk/forums/index.p...tid=201921&fr=0

I was actually looking for a circuit to test it without the MS. Just a manual check of the LED going on and off against a degree wheel.

If I take 12v through a 680k resistor to an LED connected to the sensor output, would this work?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Put them in series then.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

Edited by Rod S on 27th Jan, 2010.

Schrödinger's cat - so which one am I ???

On 27th Jan, 2010 Rod S said:
I've just read the rather old thread you linked...... where I said I think a cam sensor might become usefull in the future

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

It occurred to me this afternoon, that this particular style of sensor could be used on the cam wheel.

Just a 12mm hole though the timing plate, a screw fitted in the cam wheel to provide a "tooth", plenty of sealant and jobs a goodun.

Added advantage that it would be easier to set at the optimum point.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

No reason why not so long as your "screw" tooth is a reasonably different "height" to the rest of the wheel.

Only issue might be finding a plain enough part of the wheel for the remaining 355 degrees of the sensor path - standard wheels have holes in them, verniers have bolts etc, all of which could produce noise if they were passing anywhere near the Hall switches path - you ideally need a totally clean path beneath (and near to) your switch so it only sees your "tooth" and nothing else.

Schrödinger's cat - so which one am I ???

My wheel has holes at the radius that I plan to fit the screw. So if the sensor is too close to the wheel then it will see the holes as well.

I may need to space the screw away from the wheel with some washers and fit the sensor at minimum depth so that I get a clean signal.

I'll also need to put another screw, diametrically opposite, but on the front of the wheel, to maintain balance.

I'll do some testing.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I'm making up this circuit to test this sensor.

So flat side of the LED towards the sensor?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Try this
http://www.tonystrains.com/technews/img/in...tall-led-01.gif

Schrödinger's cat - so which one am I ???

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Well, the circuit works.

The LED lights when it gets within 1.5mm of anything ferric, then stays on until you move it about 10mm away.

Tomorrow I'm going to set the cam wheel up in the lathe chuck and the sensor on the toolpost and see if it will work with a screw in the cam wheel.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

that'll work a treat Paul,

I'm running a hall sensor on my trigger wheel, straight into the opto isolator on the MS.

Schrödinger's cat - so which one am I ???

Now it's me getting obsessive about the cam sensor timing.

Borrowing Rod's picture:


The cam sensor signal ideally should be 150 degrees before No.1 cylinder at TDC before the firing/expansion stroke.

Hence my question elsewhere about the stroke at TDC.

So if I set the cam at TDC setup position, I then need to rotate the engine through 360 degrees, then back 150 degrees to set the sensor screw location.

Is that right?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

From the way I understood Jean's answer when I asked this, the cam sensor should be a reasonable distance before the missing tooth which itself is 90 degrees BTDC on the firing stroke of No 1.

Hence my plot above.

I treated the cam timing completely by itself, ie, set the cam timing up with the marked wheel on the crank and DTI on the pushrod and then did the phase sensor independantly just counting the teeth on the 36:1 wheel and making sure it was No1 firing that I was counting the teeth before.

Schrödinger's cat - so which one am I ???

Just the job:


Watch it in action:
http://www.youtube.com/user/PaulSturbo#p/a/u/0/86LAN0zhXyc

The youtube video seems to have lost some of the resolution and it's not flashing anything like it really does.

Edited by Paul S on 7th Feb, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Seems fine, the only thing I would suggest is on the final version, get rid of that washer or somehow make it the same diameter as the bolt head. Otherwise the sensor has two square edges it could pick up from and with the 10mm switch off distance you've already measured you won't know which is switching just from an LED and it might be so close to the cutoff point that it could be either at random.

If that makes sense.....

Schrödinger's cat - so which one am I ???

The washer is only temporary for the purpose of the test, as the holes are bigger than the screw head.

Once I know exactly where to fit the screw I will drill and tap it M6 and locktight a short length of the screw in. I'll also do the same diametrically opposite, but with the bolt head on the opposite side to balance it up.

That cam wheel does not have the "dots" to line it up, so I will need to get the crank and cam in the block and set it all up with the DTI and degree wheel before I can identify where to fix the screw.

I think this solution is better than trying to pick up a signal off the fuel pump lobe. It can also be used if you are using the fuel pump hole for oil drain.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Schrödinger's cat - so which one am I ???

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."