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Old 12th May 2020, 11:11 am   #41
chris.oates
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Default Re: Reverse engineering Lumenition optical switch

Useful comments about my device, thanks.

Quote:
Originally Posted by duncanlowe View Post
It looks like what I think is known as a bare die package.
This sounds quite likely.

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Originally Posted by Radio Wrangler View Post
It is possible that this ceramic is simply Alumina, aluminium oxide, which is safe, BUT there is also the possibility that it could be beryllium oxide BeO, which is very dangerous if chipped, cracked, ground or drilled. ..
As an alternative, there are power transistors of the necessary ratings in packages similar to that. David
Warning noted, I’ll put the Dremel away. I was really just curious what this package is called, wasn’t really planning to resurrect this one as I’m not exactly short of working units.
I had unsoldered the brown wire from its central collector connection. It still shows semiconductor activity between the base and emitter.

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Originally Posted by Uncle Bulgaria View Post
We have success! Here's the circuit I've knocked up to test, which fires reliably each time the gap is broken.
Next question: can I make this in a small enough space to fit into the optical switch housing, and what do I pot it in with? Is there anything that is rather more easily removable than the stuff originally there that required some serious time with little drills and scrapers?
Hurrah, please will you post a sketch of the working optical sensor circuit so I can file it away with all my other notes on such things.

As to potting, here’s a photo of a dissected Hall Effect sensor that has to live in the same environment, its encased in a hard clear, epoxy type material, inside a semisoft plastic case, alongside is my working copy soon to be encased. I too am interested in the suggestions.

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Old 12th May 2020, 4:46 pm   #42
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Default Re: Reverse engineering Lumenition optical switch

Farnell has these to show for all silicones, which are foreign to me as they're two-parters. RS has more of the gun-mastic types I was expecting, but it's unclear what is non-acetic. I can't find any GE branded examples, or Plast2000 on suppliers I have accounts with. Loctite 5990 is available but described as a 'copper silicone', whatever that is. I'm loath to throw money at an expensive small tube of something that I haven't got more than one use for at the moment. The 5990 is under a tenner, so that's what I'm leaning towards at the moment!

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Originally Posted by chris.oates View Post

Hurrah, please will you post a sketch of the working optical sensor circuit so I can file it away with all my other notes on such things.
Chris, all I've done is make the patent circuit, with values I measured on my broken board for the resistors. I haven't included R4 or D3 as I can't see them on my board. However, I can't see them on your dissected power module either. It seems either they are not required, or the modules differ from the patent.

I have the collector of Q1 connected only to the blue wire to the power module.

What is the purpose of D3/R4? I'll draw it up when I've got it finalised. I don't think it will be possible to fit it in the optical switch housing with discrete transistors, but I'm going to cut a piece of veroboard and test.

Edit: I've found the reference to D3/R4 in the patent: "It is stated above that the zener diode Z1 provides a stabilized 7.5 volt supply to the Darlington pair Q1 in addition to the infra-red lamp 1 and the photo-transistor 2. Furthermore, it is essential that the diode D3 has a minimum storage time in the base of Darlington pair Q2, and both a minimum forward-recovery time and a minimum reverse recovery time. This is achieved by the zener supply to the resistor R4 in the collector circuit of the Darlington pair Q1. Operated under these conditions the diode D3 together with the circuit consisting of zener diodes Z2 and Z3, the capacitor C and the resistor R5, helps to ensure that there is no radio interference generated on switching the Darlington pairs."

Incidentally, I attach the patent application uploaded in post no. 17, but with OCR text recognition applied so it's now searchable to an extent.

So they're just there for radio interference suppression? I did wonder whether, as I have the 'performance' rather than 'optronic' model, the 'constant energy' coil meant there was some alteration to the circuit.
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Old 12th May 2020, 5:02 pm   #43
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Default Re: Reverse engineering Lumenition optical switch

I have just potted a new hall-effect sensor for a similar application, i.e. in the same type of environment, and I used 5-minute Araldite epoxy which would seem to fit the bill.

My dissection of a power module from the 80's seems to indicate that the Q1 driver from the patent application diagram has been dispensed with. In addition to the thick-film resistors on the substrate and some surface mount and leaded components, I didn't find any evidence of another active device.
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Old 12th May 2020, 8:25 pm   #44
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Default Re: Reverse engineering Lumenition optical switch

Just to comment regarding the none acetic silicone. I am aware of an application from the late nineties where ordinary slicone was used as an anti vaibration component on the PCB of a module (used in cars but not relevant). After a number of years the acteic acid destroys some surface mount resistors in the module and requires repair.

Some years later, I was required by an employer to make a modification to product and secure it with silicone. They were less than happy with me purchasing a non acetic silicone, and when I recounted my experience dismissed me with 'that's a new one on me'. I didn't linger there......
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Old 13th May 2020, 9:21 am   #45
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Default Re: Reverse engineering Lumenition optical switch

Here is a simple overview of the types of silicone sealants, acid cure, neutral cure, high and low modulus.

https://blog.univarsc.com/how-to-cho...icone-sealants

Chris
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Old 14th May 2020, 6:50 pm   #46
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Default Re: Reverse engineering Lumenition optical switch

Thanks for those titbits. The non-acetic is the winner so far! Richard - I was concerned that an epoxy would be as difficult to dig out in case repair or alteration was required as the original hard material was!

I have a little vial of neutral silicone on order from Farnell, along with some BJT darlingtons and IR emitters/receivers.

Chris - do any of your power modules contain D3/R4, or do we think it's peculiar to a certain type of optical switch, perhaps the 'optronic' version?

Can anyone explain what article I need to read, or what the circuit subsection is called, to understand how D3 and R4 affect the "minimum recovery time" of darlington Q2?
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Old 15th May 2020, 8:37 pm   #47
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Quote:
Originally Posted by Uncle Bulgaria View Post
Chris - do any of your power modules contain D3/R4, or do we think it's peculiar to a certain type of optical switch, perhaps the 'optronic' version?
I only own 3 lumenition modules, and two sensors. The working module and sensor have not been opened.
The module I pictured at post 14, a Mk 12, does seem to conform to the circuit diagram in that patent and does have a diode between the collector of Q1 and the base of Q2 and a resistor of about 120R between the collector of Q1 and the red +7.5v wire to the sensor. This makes me think that the sensor I pictured at post 14, picked apart, may not be the one for the mk12 module as it contains lots of components, however I am still studying it. I couldn't resist replacing the darlington Q1 as it had a corroded and snapped collector lead, the markings were not readable so I used a MPSA13, it now sparks if the blue sensor lead is grounded, or if connected to the working sensor.

My electronics knowledge is more basic than yours but last night while trying to work out the Darlington unit I pictured at post 21 I came across a Lumenition patent over adding a 4th lead to a Darlington package and wondered if this is what I have, a modified device. Under my old optical microscope I thought one of the marks on the surface could be a welding mark, this area is now shorted to the collector lead. In this patent the purpose seems to be to allow a very high frequency of sparking for performance systems, there is a lot of technical details, and I wonder if that is also something to do with "minimum recovery time" also.

link to that patent, https://worldwide.espacenet.com/publ...4&pageNumber=4

Chris
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Old 15th May 2020, 11:26 pm   #48
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Default Re: Reverse engineering Lumenition optical switch

For what it's worth, this is the label attached to mine. Ignore the advert for their own coil!

Quote:
Lumenition/Microdynamics units design is specifically for use in negative
earth vehicles. Units are fully encapsulated for reliability and protection
from moisture and vibration. This renders units irreparable by the user.
wrong connection may result in permanent damage to the circuit and we
cannot accept responsibility for damage so caused. Installation by a com-
petent Auto Electrician is recommended.
These units will be damaged beyond repair if connected to an ignition coil
with a static primary current greater than 6 amps. (ie electronic ignition
types) Coil and ballast combined resistance must be 2.5 ohms or more and
the coil itself must have a resistance of at least 1.5 ohms. To be safe always
use a Micro Dynamics Mega Spark coil.
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Old 16th May 2020, 12:27 am   #49
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Default Re: Reverse engineering Lumenition optical switch

Quote:
Originally Posted by Uncle Bulgaria View Post
Chris - do any of your power modules contain D3/R4, or do we think it's peculiar to a certain type of optical switch, perhaps the 'optronic' version?

Can anyone explain what article I need to read, or what the circuit subsection is called, to understand how D3 and R4 affect the "minimum recovery time" of darlington Q2?
R4 is pretty important, it's the resistor that turns on the second darlington. Without it or something doing the same job, the current in the coil will never be turned on.

When the coil current is to be turned off (the move that makes the spark, which is the time critical thing for the engine) the first Darlington is turned on. This robs all the current coming down R4, D3 turns off and the second darlington loses all base drive which turns it off.

That's the easy bit.

Darlingtons are a bit sluggish.... especially at turning off. Unfortunately turning off is the critical operation for the seconf Darlington, the big one. The faster it turns off, the higher the HT the coil makes.

The inclusion of D3 is a bit iffy. It sort of helps because it allows the base voltage of the second darlington to go a bit lower than the collector of the first one. It isn't very good though.

The real problem is stored charge in the base region of the second transistor in the darlington. If that transistor were driven by an ordinary switch circuit, with a resistor pull-up and a transistor pull-down, that transistor when turned on would suck charge out of the big transistor base, turning it off a bit quicker.

But instead, the darlington circuit drives it with its first transistor, an emitter follower. THe B-E junction of that emitter follower can source current, but it can't pull it back.

Good quicker Darlingtons incluse a resistor from B to e of their second transistor, to help charge decay quickly in the base region, speeding up turn-off.

Z2 Z3 are voltage clamps. When the coil current is turned off, the inductance tries to make a large positive going spike. If it goes too high the idea is for these two zeners to torn on and thus turn Q2 darlington on a bit, momentarily. to fight and clamp the transien so it doesn't destroy Q2.

D3 also acts to prevent transients form the coil and output stage getting back to Q1 and wrecking it. D2 stops the base of Q2 being driven negative by transients via the capacitor C and the capacitance of the diode. I think this is the real main purpose of D3.

This circuit has to be bomb proof. Engine compartments get ot, get freezing, get wet and this thing has to keep going On top of all that there are huge transients from ignition operation which can get anywhere, especially in fault conditions.

Lumenition recognised that there is more voltage drop in that power darlington (a couple of volts) than in a pair of points. So they did a coil with a larger ratio to keep the HT voltage up. The marketing of the coil was a bit gung-ho and the price bordered on racketeering, but there was an engineering reason until cars started using 9v coils with a dropper resistor... (they shorted the resistor when the starter motor was running to avoid drop in HT just when you needed it.)

David
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Old 18th May 2020, 11:04 pm   #50
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Originally Posted by AC/HL View Post
For what it's worth, this is the label attached to mine. Ignore the advert for their own coil!
I wonder if the 'Constant Energy Coil' that is supposedly required by the 'Performance' system is similar. When the difference is £50 they are likely to be coy about exact differences.

Quote:
...This renders units irreparable by the user.
I hope to gainsay this, Lumenition!

Quote:
Originally Posted by chris.oates View Post
My electronics knowledge is more basic than yours...

...link to that patent, https://worldwide.espacenet.com/publ...4&pageNumber=4

Chris
I think you overestimate my knowledge, Chris! That patent is very interesting though, and I almost understand it. Presumably a more modern Darlington type can be substituted to attain the same effect (though I can't really see myself engaging in engine speeds over 10,000rpm!).

Quote:
Originally Posted by Radio Wrangler View Post

R4 is pretty important...
David, lucid and thoughtful as ever. Thank you - that makes sense in conjunction with the patent above. Of course, Q1 needs to source current from somewhere!

I think R4 and D3 are present in the power module as the 7.5V supply from R3/Z1 arrives at the optical switch, so although the circuit diagram makes it look as though everything associated with Q1 is of a parcel, it could well be elsewhere. There is no R4 or D3 on my optical switch circuit board.

In my test circuit, the open collector of Q1 goes straight to the blue wire and everything fires, so there must be current there.

Some Darlingtons have arrived, and new IR bits. Let's see what I can squeeze into a small space...
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Old 18th May 2020, 11:45 pm   #51
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Inside an ordinary coil is a bar made up of iron wires or iron laminations. A solid iron bar would lose energy in eddy currents, so dividing it up is sensible, just like the lams in a transformer.... Hey that coil IS a transformer, so why the crappy single bar-shaped core?
Why not a full loop?

Cast your mind back to the induction coil they had at school in the physics lab. A single bar shaped core, some primary winding turns on it, a heck of a lot of secondary turns on it and at the end, the armature that drives a pair of contacts turning the battery, the primary, the core and the contacts into a whacking great buzzer.

It's always been like this, ever since Heinrich Ruhmrorff built the first one. No-one's ever questioned it. He even got name-checked by Jules Verne in Journey to the Centre of the Earth. You can't argue against something with those credentials.

So these things turned into trembler ignitions. An improvement on hot-tubes and blowlamps, just. Then Kettering came along and decided to link the contacts to the rotation of the engine. Brilliant idea, but he was following on from the idea of the magneto, a generator with a pair of contacts to synchronise a high voltage pulse to the rotation of the camshaft or crankshaft. Anyway, Kettering must have looked at the trad induction coil and thought 'If it ain't broke, don't fix it' and consequently everybody got a little induction coil under their bonnet. Sometimes multiple ones.

Tell me again why it's a single bar and not a complete magnetic circuit, like a little proper transformer? Think of a line output transformer in a TV. It wouldn't be very effective on a straight ferrite rod rather than the usual gapped U and I cores. The straight core gives less inductance and needs a lot more turns. Think of the mag flux getting from one end back to the other as a damned great gap. A smaller gap would be better.

The first proper core I saw was on the first Vauxhall Cavalier, the rear wheel drive one with an Opel engine... well, it was an Opel with the badges swapped. An ignition coil built as a U and I transformer core out in the open. The windings were moulded up in plastic, but the iron lams were there for all to see.

It looked wrong. My eyes were used to the ouvres of Robert Bosch and Joe Lucas. But when I stoped to think about it, it made sense. It had a proper magnetic circuit instead of just relying on hope. It ought to be significantly more efficient.

The only drawback was that the straight rod core ones were a handy shape to dunk in a canister filled with transformer oil, to keep out the nasty environment, and to dissipate the heat from its lousy efficiency. This may be why I haven't seen a full core coil like it since. Think of trying to operate a line output transformer in the same compartment as a glowing turbocharger with puddles getting splashed up in season. You're trying to make the same sorts of voltages.

So can the trad ignition coil be improved? Oh yes!

Maybe you'd want to make a transformer shaped one, but you'd need an odd shaped can to seal it in with its oil. And that would look wrong to car type people. THey're easily frightened.

David
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Old 19th May 2020, 12:43 am   #52
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I have used a modern pencil coil from an ECU engine for some non automotive things.
It has a full magnetic circuit like those 1970s Opal coils.
The lams are welded like a microwave oven transformer.
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Old 19th May 2020, 1:09 am   #53
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Default Re: Reverse engineering Lumenition optical switch

The full magnetic circuit allows a lot fewer turns to be used of course, and that saves space, allowing for the one-coil per plug arrangements.

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Old 24th May 2020, 4:36 pm   #54
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Removing the receiver, I discovered it's an OP804SL with one of the three legs cut off. What's the advantage of doing this rather than using one of the two-leg devices? If the base is being activated by the light, what can be done connecting it electrically?

I've made up the circuit on veroboard much smaller than before in an attempt to fit it inside the switch with through-hole components, but have discovered the IR receiver I got is too small for the housing. I will probably get another OP804SL as they must have chosen it for a reason...
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Old 24th May 2020, 4:41 pm   #55
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Bonding up a base connection to a pin isn't necessary in many uses BUT it's handy for the manufacturer for testing them because he can measure both the quantum efficiency of light detection and the gain of the transistor separately.

Some designers use the base as a place to apply feedback to make the amplification function better controlled for light measurement accuracy.

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Old 25th May 2020, 8:38 pm   #56
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I see! Thanks, David.

I put the switch temporarily back in and have had the engine running for half an hour without conking out yet! It might just fit in the new configuration I've made to squeeze in the circuit. I've put a trimmed mica insulator against the metal body to avoid contact, and will tomorrow attempt to pot the thing.
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Old 30th May 2020, 12:20 am   #57
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Silicone went in. I discovered the fit was very tight so I endeavoured to get the components to tesselate better. I managed to break two darlingtons trying to rearrange the layout and get the legs into odd holes, also lifting a few (luckily unnecessary) copper rings. It was very hard to get the silicone to go smooth, so it's a pretty mucky job but has at least made a seal.

My trip to the refill shop today encompassed some classic Cornish lanes and steep inclines and it was jolly hot, but I made it there and back without anything untoward happening. I'd like to think the problem eradicated, but there's a nagging sense of unease when no warning was given before the previous conk out!

The Pimm's has flowed in celebratory libation (and imbibation) so I shan't post the sketch Chris requested earlier until tomorrow. It may have taken a few months to get around to it, but it's quite pleasing if with all your wonderful help I've managed to avoid buying a new £100+ switch made from a casting and a fiver's worth of parts.
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Old 30th May 2020, 7:34 am   #58
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Excellent! A fine achievement.
Just a side note, the most usual cause of trouble with that system is the 3-pin connector between the sensor head and the control box - the contacts loosen and become dirty. An easy fix, but not everyone knows that!
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Old 30th May 2020, 12:13 pm   #59
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Thanks! My heart did sink when I put it all back together and it didn't start, before I realised I hadn't put the cables back into the connector housing in the right order. Then I hadn't pulled them through enough to make contact with the socket... I have one of those shoddy sets of contact pin removers from eBay. They sort of work but seem on the point of breaking all the time. I wondered if they'd last the course if I had to take the contacts out again! I looked and looked for something of a higher quality but they don't seem to exist in my usual haunts.
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Old 5th Jul 2020, 9:44 pm   #60
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Chris.oates - here's the final circuit with the parts I used. I tried to do a sketch of the veroboard layout I used, but it really is about on the limit of how small these through-hole component circuits can be, and probably not worth copying. I used the basic layout of the PCB I extracted - zero bus around the top, and the rest fitting in where they could.

It's still running and I'm gradually getting over the fear of it conking out with the shopping in the back...
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