Rev Counter

[bob46320]

I am coming to the final stages of a temperature measuring, rev counter and stop watch display which is run from an ARDUINO micro computer.  I am measuring 5 different temperatures around the carburettor, manifold, fuel line and ambient in an aid to find out why the carb seems to "vaporise" under certain conditions.  All going OK so far and am about to try to measure engine speed using a Hall Effect sensor with its 5 gram magnet attached to the inside of the camshaft pulley.
Any comment as to wether this would cause any undue inbalance.  I could mount a second magnet opposite which would help to balance things I suppose.

A final stage of development is to add a similar device to the rev counter onto the prop shaft to get road speed.
BobH

[John Cornforth]

Hi Bob

I have "played" with both Austin Sevens and Arduino based systems. Must make me a minority of a minority !   I doubt if a 5 gram imbalance at such a small radius will have any detrimental effect.  However, using two magnets will of course double the pulse rate and allow you to measure RPM with less need for smoothing.  You will need a good magnet adhesive to withstand heat and vibration.

Given the fairly low speed of camshafts and propshafts, you might consider measuring RPM indirectly, i.e. by measuring the time interval between shaft pulses (gate a fairly fast clock and count the clock pulses) and then calculating the reciprocal.  This "reciprocal counting" gives a much quicker responding measurement of RPM with good resolution.  Apologies if you have already thought of this.

Let us know how you get on

Cheers,  John

[bob46320]

John, thanks for that. I was going to use one of those "metal" epoxy glues and because the magnets will be on the inside of the pulley, they are being 'flung' against the mating surface. I just hope I don't drop a nut or some other small object near the magnets in the future.

[David.H]

for what it is worth the MGCC  did a lot of research on vaporisation of modern fuel in old (XPAG) engines and as I recall one of the (surprising) findings was that the heat from combustion going back up the inlet tract was a really significant factor. Their findings are in the TR Register "TRaction" magazine I believe. I don't have a link I'm afraid.

[jansens]

Why not get RPM direct from the coil? You need a suitable filter to cut the signal down and maybe use an opto isolator on the input to the Arduino.

I've been considering using an ESP32 with a camera to see if you could measure the needle lift on an SU carb and link that to throttle position, RPM and O2 reading. In theory you could tell if the needle is the correct one across the entire range. In practice would take a lot of fiddling I think.

I have ordered a ESP32 to play with but don't think I get will get beyond that. The time it would take to get such a system working reliably I can better spend manually turning the car then getting it finished so I can drive it!

I did start playing around with emulating the Innovate serial protocol (ISP2) using an Arduino so I could use their data logger software to measure things but then I bought a proper Innovate unit so that need went away.

Simon

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I should add that's tapping off the LT side of the coil of course, where it connects to the distributor. Looking at how the Megasquirt people do it might help: http://www.bgsoflex.com/v22/msv22.html

Of course this is no help if the car isn't a coil one!

Simon

[bob46320]

I looked at coming off the coil, but my electronics knowledge is not up to that, saw several circuits, but decided for non contact system ie: hall Effect.
This weekend, we are out with the local club, so hope to get some results from that run so long as the weather is hot enough to cause a problem.

[jansens]

Fair enough, non contact is certainly safer for the Arduino! There are a lot of bad examples of how to do it directly out there. Just remember (and I am sure you know this) when measuring off the cam it's only going half the crank speed. Also when running any wires to your remote sensors use shielded cables. It will help prevent noise upsetting the Arduino side of things. Years ago I made an optical tach using an Arduino to measure the RPM of a home made jet engine. That would go over 100 000 rpm so you shouldn't have a problem with an Austin 7 engine!

Another possible non contact way to do it (and I haven't tried this so no idea if it would work on a car) is using a neon bulb off the high tension side. I have once built a sort of simple opto isolator doing exactly that with a neon bulb and a LDR or photo transistor in a tube. The neon is on the output of a dynamo in an old wind up telephone triggering an Arduino to play old fashioned music. It works very well.

Simon

[Dave Wortley]

Is anyone going to say it? I am completely out of date and can’t make any sense out of this conversation. It’s good that people can use 21st century solutions in 80plus year old vehicles.
Cheers,
Dave.

[bob46320]

Dave W, don't worry about it, a bit more 'noise' for a 7 won't make much difference to my RN.

[Paul N-M]

As the TV add for a certain flat pack furniture retailer says, 'The Wonderful Every Day'  Thats the A7FF for you!

Paul N-M