# Ignition system for Farm Boy



## simonbirt (Nov 26, 2020)

I am building a Farm Boy hit and miss engine which is progressing OK- huge quantities of swarf so far. 

I am now starting to think about an ignition system, I quite like the idea of building my own. Electronics is not really my thing but I do have a basic understanding and have made a few circuits in the past. It would be useful to learn if others have gone down this route. 

Regards,

Simon


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## deverett (Nov 26, 2020)

If you do want to have a go at soldering up your own module, have a look at Jerry Howell's offerings:








						Ignition Modules - modelengineignition
					






					www.model-engine-ignition.com
				



You won't have wasted too much money if things do go wrong!

Next step if that fails, have a look at the replacement ignition modules sold for the Chinese hi 'n' miss engines:
eBay UK 372664264988.  That is the route I'm taking for my present project.
Or Roy Scholl at S & S, but it looks like you have to be quick: Roy's CDI Ignition Systems

Dave
The Emerald Isle


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## doc1955 (Nov 26, 2020)

Yes I build my own ignition units a good place tostart if you want to do your own is to usr one of Jerry Howells or if you can still get one of Roy's cdi either will work great for what you want. Here is a video showing the ones I build.


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## coulsea (Nov 26, 2020)

deverett said:


> Next step if that fails, have a look at the replacement ignition modules sold for the Chinese hi 'n' miss engines:
> eBay UK 372664264988.  That is the route I'm taking for my present project.
> 
> Dave
> The Emerald Isle


I don't know about that particular chinese ignition but I do know that quite a few cheap ones have problems. I can recommend the rcexl units. ebay uk 173851217006


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## doc1955 (Nov 26, 2020)

I purchased this one to just check it out and see how well it would work. Well the first one did not work at all but after a few e-mail back and forth they sent another that seems to work well. I never did put it on any of my engines I still prefer the ones I build. But anyway you could try one and see if you like it or not. For around $20 it's not a bad price.
PS they have it labeled as a glow plug but it is a cdi unit.









						CDI Glow Plug Igniter for Hit & Miss Gas Model Engine RC Plane Ship Car Model Engine Model - Stirlingkit
					

CDI Glow Plug Igniter for RC Plane Ship Car Model Engine ModelFeatures:.For gasoline internal combustion engine model.The product is used for engine ignition. One end is connected to the spark plug. One end is connected to the engine. One section ...




					www.stirlingkit.com


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## Tim Wescott (Nov 26, 2020)

You could always go with a Kettering (points, condenser & coil)!  That's pretty easy.


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## deverett (Nov 26, 2020)

coulsea said:


> I don't know about that particular chinese ignition but I do know that quite a few cheap ones have problems. I can recommend the rcexl units. ebay uk 173851217006


Have you tried one of these on a hit  'n' miss engine?  Reason I ask is that I note they have auto advance and I was under the impression that this was not suitable for hit 'n' miss engines. (hearsay only, not practical experience).

Dave
The Emerald Isle


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## coulsea (Nov 27, 2020)

deverett said:


> Have you tried one of these on a hit  'n' miss engine?  Reason I ask is that I note they have auto advance and I was under the impression that this was not suitable for hit 'n' miss engines. (hearsay only, not practical experience).
> 
> Dave
> The Emerald Isle


Yes I do have them on hit n miss engines and they seem to work fine. I have found it difficult to find out the specs for the auto advance but some on the plane forums suggest that the spark is constant between 450 and 4000 revs (or maybe 2500). I can start them with a good flick of the flywheel. A hit n miss will only fire in a fairly narrow rev range by design.
I haven't tried any other type of ignition so would be interested to hear what others say.

Andrew


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## bluejets (Nov 27, 2020)

Below is a multi spark kettering ignition, easily used with points.
Problem usually is getting a hold of small kettering ignition coils as most small engines these days use CDI and not suitable for points ignition.

I found the circuit can be used with a Ford BA Falcon coil and quite ok on a single 18650 2500mAh 3.7v Lipo cell.

Doc uses the same board and he uses 6v and a dropping resistor.
He might be able to help you with the type of coil he used and where to get one if you are in the US.
Although just more bits to go wrong, more than likely he is just using what he has on hand.

Below are a few pics and some files if you want to build your own or get a mate help you out there.

Of course, the electronics board is not essential as a 3.7v Lipo, a BA coil, a set of points and a condensor would be just as good.
Plenty of basic kettereng system drawings around on the net.
I use a 0.47uF 400v capacitor from any electronics store across the points.

Advantage of the electronics board is, if the engine stops with the points in the coil saturation position, it will time out and shut off after a short period, thus saving your battery power.
Then again, most of these engines run under some sort of supervision so any shut down not really necessary.


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## simonbirt (Nov 27, 2020)

Thank you all for your help and advice. I now have a better idea of what is needed, leaning toward building one. I am in the UK so will see what can be found coil wise. I assume a motorcycle one may do the job?


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## elliot9797 (Nov 27, 2020)

I have used a International Harvester Farmall A,B,C,H,or M coils. Work great, and cheap


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## mrehmus (Nov 27, 2020)

Here is how I mounted my Sage ignition board in the bottom of my GEM-1 box. I triggered in with a reed switch mounted in a brass tube. The coil is a Ford Coil-over-Plug which works fine with 12 volts as in this setup down to approximatelye 6 volts with 4 AA batteries. 12 volt gel-cell is in white 3D printer box under the ignition circuit.


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## doc1955 (Nov 27, 2020)

I use 12v coil packs and step up the resistance. You need to run the resistance over 1.2ohm or you run the risk of frying the 555 timer or the TIP 120 chip. I run mine with 6V and I use the spark saver (2 hall sensors) but it will work fine without the spark saver the spark saver just saves on battery life. I also put a heat sink on the TIP 120 on engines I run at a higher rpm. You shouldn't need it though on a hit miss. 

 I have also used the TIM6 circuit   and step up the resistance in the coil the same only thing with this circuit is if your engine stops on the magnet you run the risk of frying the TIP42 chip.
Anyway I have had good luck with both. Good luck


PS
I order my 555 chip of of ebay just look for 200mA I think I got 10 for around .50 each. I also get my other IC chips there usually can get them for a lot less than at any electronics store.


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## 74Sprint (Nov 28, 2020)

bluejets said:


> Below is a multi spark kettering ignition, easily used with points.
> Problem usually is getting a hold of small kettering ignition coils as most small engines these days use CDI and not suitable for points ignition.
> 
> I found the circuit can be used with a Ford BA Falcon coil and quite ok on a single 18650 2500mAh 3.7v Lipo cell.
> ...



This is probably one of the best small low battery voltage ignitions I have seen. The 555 timer can be modified to work very similar to almost all the electronic HEI ignitions used through out the world of distributor type engines or 1 cylinder, or 2 cylinder wasted spark. For example the GM-Ford-Chrysler HEI works with a inductive pick-up, the coil starts to charge when the pulse voltage starts to rise (going positive) and fires the coil when the pulse starts to go back to zero volts (going negative). No positive going pulse, no coil charging. By using the 555 timer one can adjust the dwell time to suit the coil.

Ray


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## 74Sprint (Nov 28, 2020)

Auto advance can be done in several ways: #1 use the negative going side of the pulse. As the RPM increases the pulse width will decrease but, the start of the pulse will never change. Only the trailing negative going edge changes. If one uses the negative going edge, the timing will advance automatically with increasing RPM but, only to a limit which can be controlled. #2. Some manufacturers use something like a small preprogrammed PIC micro controller with a fixed advance curve. #3. Same as number 2 but with a programming interface to change the advance curve. Of course as the complexity increases so does cost but, each circuit can be modified to suit one's needs and funds available.

Ray


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## simonbirt (Dec 2, 2020)

bluejets said:


> Below is a multi spark kettering ignition, easily used with points.
> Problem usually is getting a hold of small kettering ignition coils as most small engines these days use CDI and not suitable for points ignition.
> 
> I found the circuit can be used with a Ford BA Falcon coil and quite ok on a single 18650 2500mAh 3.7v Lipo cell.
> ...


Have decided to build the electronic version as I don't want to use points. I have or can source all the components, except I am having trouble with the Q3/Q4 transistors, can't find a 3030T. Is there an equivalent or am I looking in the wrong place. I am in the UK.


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## Tim Wescott (Dec 2, 2020)

Don't buy electronic components off of eBay (Sorry @doc1955)  At least not common chips like the 555 -- you can get them cheaply from real mail-order suppliers.  DigiKey, Mouser and Newark in the US, Farnell (I think) in the UK.  Counterfeit chips are a thing, you can trust a distributor, and it doesn't cost all that much more than eBay.
I'm not sure what a 3030T is, but there's plenty of Hall effect sensors out there.  Some of them are even designed so you don't need to make a custom board just to mount them.  Here's a plethora of them from DigiKey, all of which should work.  You want to look for sensors that are: 
Bipolar or omnipolar (works with the magnet pointing either way)
Through-hole mounting (so you can solder wires to the leads)
Open collector or open drain (so it acts like an open switch with no magnet)
Will stand a power supply voltage of 6V or more


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## bluejets (Dec 3, 2020)

simonbirt said:


> Have decided to build the electronic version as I don't want to use points. I have or can source all the components, except I am having trouble with the Q3/Q4 transistors, can't find a 3030T. Is there an equivalent or am I looking in the wrong place. I am in the UK.



KY-003 hall effect modules will work ok.......already mounted on a pc board with an LED and resistor on the collector.
If you want to roll your own , then I use Allegro A1120 but pop a tiny cap right on the base of the hall effect supply pins (0.01uF)
Or use 3144 same as on the board of the KY-003. 
20PCS SENSITIVE HALL-EFFECT SWITCHES SENSOR SIP3 OH3144 3144OH A3144E A3144 3144  | eBay
Contrary to some comments about Chinese electronic clones etc. , never had a problem, mostly old wives tales.


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## simonbirt (Dec 3, 2020)

Thank you all, I am much wiser than before. I will let you know how it turns out.


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## Bernett1 (Dec 3, 2020)

I’m new to this group. I don’t have the expertise or equipment to build engines but I really love the work this group does. I am using converted 2 stroke engines for RC planes and wanted a less expensive CDI system than the rexcl systems. I have purchased a 4 pin dc scooter CDI system and a scooter coil. I anticipated the same issues of using a standard hall sensor and not being able to trigger the CDI unit. I did some searching and located some inverted hall sensors. There aren’t many of them. I purchased some melexis us5683 hall sensors. They are unipolar inverted hall sensors. They should be low to high when they come in contact with the magnet. I don’t have all the components so I haven’t been able to test the system. My question is do you think thes inverted hall sensors will work and if I’m using a 3s lipo battery to power the CDI system can I use the same battery to power the hall sensor. I’m thinking the CDI trigger is just looking for positive voltage and it doesn’t matter if it’s .5v, 5v, or 12v. Do you think I am correct in my assumption?  Thanks.


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## bluejets (Dec 4, 2020)

Bernett1 said:


> I have purchased a 4 pin dc scooter CDI system and a scooter coil. I anticipated the same issues of using a standard hall sensor and not being able to trigger the CDI unit.



I did a write up on this same approach......
Model engine CDI easy and cheap


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## Bernett1 (Dec 4, 2020)

I saw your other post but the hall sensor I purchased is different than the one you used.  I’m hoping that because it’s an inverted sensor that I can eliminate the transistor circuit you added. I’m just wondering if you think the inverted hall sensor will work?  Thanks


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## Bernett1 (Dec 10, 2020)

I’m new to this group. I don’t have the expertise or equipment to build engines but I really love the work this group does. I am using converted 2 stroke engines for RC planes and wanted a less expensive CDI system than the rexcl systems. I have purchased a 4 pin dc scooter CDI system and a scooter coil. I anticipated the same issues of using a standard hall sensor and not being able to trigger the CDI unit. I did some searching and located some inverted hall sensors. There aren’t many of them. I was able to get the dc CDI unit to spark using the inverted hall sensor. They are so small that mounting them is a challenge.


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## simonbirt (Dec 13, 2020)

A quick update on the ignition circuit. I have built one on a bread board and it worked fine. A bit temperamental as the connections are not that good. Next step is to make one up on using proper joints, I may even have a go at designing a PCB with one of the free cloud based apps and ordering a couple of boards. I am using a 6V motorcycle coil, could perhaps do with something a bit smaller but it is what I could find.


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## Tim Wescott (Dec 13, 2020)

A couple of suggestions from a professional circuit designer:

First, check to see if you need heat-sinking on that TO-220 case transistor.  The best way to do this is probably to run the circuit at full speed or more, under load (i.e., with a spark plug), for a few minutes.  Then shut it down and feel the tab on the thing -- carefully.  If it's too hot to touch, it needs a heatsink.  If you're left with a transistor-shaped blister, you weren't careful enough!

The rule of thumb is that if you can hold your thumb on it, it's less than 50 degrees C.  If you're in a typical 25C ambient room, that means 25C of temperature rise, which should make the circuit good for operating in a hot engine bay.

Second, if you're in the US, consider buying your boards from OshPark -- they're a very nice circuit board aggregator.  I don't have recommendations if you're outside the US -- I'd do a web search on "circuit board aggregator" and see what popped up.  If you're someplace that's in tight with the EU there are some really good ones out of the former Soviet Bloc; if you're somewhere that's in tight with Asia there's good ones in India and China (there's also some appallingly bad Chinese ones -- so ask around if you go there).  You'll need to check to make sure that your online tool will generate Gerber files.  Or you can just get KiCad or Eagle and learn a whole new set of skills .

Make your tracks wide enough.  The default track width for any program is going to be pretty small -- this is a power circuit, so you want to think about how much current the tracks will be carrying and size them accordingly.  Probably anything that's not associated with the collector or emitter of that power transistor will be fine at the default trace width, but the current through that transistor is going to be significant.  There's circuit board track size calculators out there that you can use -- or just make sure that anything that's in the path from the final transistor's collector to ground is 1/8" wide and call it good.  If it burns up, make the traces wider on the next board!


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## bluejets (Dec 14, 2020)

simonbirt said:


> A quick update on the ignition circuit. I have built one on a bread board and it worked fine. A bit temperamental as the connections are not that good. Next step is to make one up on using proper joints, I may even have a go at designing a PCB with one of the free cloud based apps and ordering a couple of boards. I am using a 6V motorcycle coil, could perhaps do with something a bit smaller but it is what I could find.



Good for you....and as you've already found, breadboards are not the best especially for any device pulling some decent current.
As for the board design, take a peek at Doc's submissions for some idea as his works fine.

Youtube video here.......


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## simonbirt (Dec 15, 2020)

Tim Wescott said:


> A couple of suggestions from a professional circuit designer:
> 
> First, check to see if you need heat-sinking on that TO-220 case transistor.  The best way to do this is probably to run the circuit at full speed or more, under load (i.e., with a spark plug), for a few minutes.  Then shut it down and feel the tab on the thing -- carefully.  If it's too hot to touch, it needs a heatsink.  If you're left with a transistor-shaped blister, you weren't careful enough!
> 
> ...


Thanks all useful stuff.

Simon


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## AndrewW (Dec 15, 2020)

Looking really good Simon.
Cheers
Andrew


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## Mago (Dec 16, 2020)

Attached is a photo of a circuit board I milled on my cnc machine It is 70mm by 50mm so large enough for fat fingers are able to do the wiring with ease.
It takes "normal" electronics and soldering up is no problem.
The other attachment is the circuit. I did this some 10 years ago but I don't expect much has changed since.
I have used it on a number of models.
When using this type of ignition using a magnet always be aware that it won't work if the incorrect pole is presented to the pickup.
I always mark the correct face of the magnet so it shows after fixing. 3mm magnets shave a habit of reversing pole without warning..
The circuit drawing as below.

Mago


file:///C:/Users/user/Documents/6v%20Transistor%20ignition%20circuit..docx


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## L98fiero (Dec 16, 2020)

Mago said:


> file:///C:/Users/user/Documents/6v%20Transistor%20ignition%20circuit..docx


The link didn't work.


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## Tim Wescott (Dec 16, 2020)

L98fiero said:


> The link didn't work.



That ended up being a link to the file on Mago's computer -- which will work fine for Mago.  It just won't work for the rest of us.



Mago said:


> file:///C:/Users/user/Documents/6v%20Transistor%20ignition%20circuit..docx



You need to use the "Attach files" button, below and at the left side of the screen where you enter text.


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## simonbirt (Jan 8, 2021)

As promised here is an update on the ignition module. I have made a short video as it shows the beast in action.


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## AndrewW (Jan 8, 2021)

Hi Simon
You've made a very professional job of that. Very impressive!
I'm looking forward to trying it out on the Jerry Howell Hit n Miss engine I'm currently building.
Cheers
Andrew


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## Tim Wescott (Jan 8, 2021)

Excellent job for a first-time PCB layout.  In fact, it's pretty good leaving out the fact it's your first.  I have two nits for you, if you ever do a board turn.

First:

While you did good with nice generous trace widths on the power path, it wouldn't hurt to bump up the default tracewidth for everything else.  It looks like you're using about .01"; you could go up to 0.02" or possibly even 0.05" -- basically, just make them as wide as you can without losing convenience.

Second:

With all that room on the board you could put a big copper ground pour on the top side to the left of the power transistor, bend the legs, and screw it to the board for a heat sink.  Solder mask is epoxy, so you could probably leave off any insulating pad and just use thermal paste, or you could use a pad for convenience.  Then if someone _did_ need a heat sink, it'd be built in.  You'd crowd the other components a bit, but you've got acres of extra space on that board.


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## simonbirt (Jan 8, 2021)

Tim Wescott said:


> Excellent job for a first-time PCB layout.  In fact, it's pretty good leaving out the fact it's your first.  I have two nits for you, if you ever do a board turn.
> 
> First:
> 
> ...


Thanks Tim for the advice, not really my forte but I thought I could do with learning a new skill. For some reason I've had plenty of time at home of late. If there is a V2 then I will incorporate the ideas, I will also put the diode to protect the LED on the board, I only discovered I needed it after I had ordered them.


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## bluejets (Jan 9, 2021)

Well done Simon.
The old original drawing probably caused a bit of confusion so I drew up what I think should be a clearer drawing.
I only redrew the section in question as the rest remains as is, except for your added zener diode.
What value did you use here...? I'm guessing almost any would do around 6v2..??

I tend to use the small pre-made boards these days off Ebay (KY-003).
Anyhow, drawing below shows the connections with the 2 hall effect in series, Q3 being the normal ignition timing and Q4 (if so desired) on the closed exhaust for a hit and miss engine.
Points are self explanitary so no need to redo that.
Operation is fairly simple in that both are required to be closed for the unit to fire.
Remembering here that closed points are for firing. (opposite to kettering system)

Cheers Jorgo


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## Rudy (Jan 10, 2021)

Thought I could throw in my own designed Farm Boy ignition circuit. It is a "Buzz Box" type. It makes several sparks for a given time. So if used on a higher reving engine the number of sparks will decrease as the revs increase. Haven't tested it on higer reving engines though.
I'm a pro hardware development engineer, but I'm not all that familiar with the quarks of the 555 (I use a dual 555, the NE556). I would like a second opinion on the design. The case is that even if it works grate at 6V, it shuts down on 6,5V or more. Something is not optimal.
Maybe you Tim Wesckott has a tip?
Here you can see it running:  
Rudy


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## simonbirt (Jan 10, 2021)

Just goes to show how many ways there are to skin a cat. 
You have also given me an idea for the base, I like the fact that it is all self contained with everything hidden.


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## simonbirt (Jan 10, 2021)

bluejets said:


> Well done Simon.
> The old original drawing probably caused a bit of confusion so I drew up what I think should be a clearer drawing.
> I only redrew the section in question as the rest remains as is, except for your added zener diode.
> What value did you use here...? I'm guessing almost any would do around 6v2..??
> ...





bluejets said:


> Well done Simon.
> The old original drawing probably caused a bit of confusion so I drew up what I think should be a clearer drawing.
> I only redrew the section in question as the rest remains as is, except for your added zener diode.
> What value did you use here...? I'm guessing almost any would do around 6v2..??
> ...


The diode is just a 1N4003 (what I had) seems to do the trick. I only have a limited understanding of electronics so rely on people who know better. The diode inclusion was worked out from first principles and some help from the web. 

Regards,

Simon


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## bluejets (Jan 10, 2021)

Rudy....the ignition Simon is using is a buzz unit also with cut out if no pulse detected.

Simon...you show the diode in series with your LED as a zener diode but quote as a 1N4003 which is a standard diode.(D1)
Connection you show as a zener i.e. reverse which is correct but a standard diode will not conduct in that configuration in normal operation.
Do you have a clear photo of your completed circuit and of the finished pc board, just to clarify what you have done.

Cheers Jorgo


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## 74Sprint (Jan 11, 2021)

Rudy the problem with your circuit cutting out at higher voltages is that you are grounding out the signal output with the points. I have and use the A1120EUA so I have some experience with it. The A1120 has a built-in voltage regulator and short circuit protection control, the 2 are seperate. The circuitry can provide up to 25ma of current continuously and will trip at 30ma according to the data-sheets. The signal out was never designed to be grounded out, this would put it into a short circuit condition. Like most over current protection it is a latching design and will not reset until the power has been removed and turned back on but, if the condition remains it will lockout again. I don't know the reason for using both a Hall-Effect and points, it should be one or the other.

If your going to use the circuit the way you have it then add a resistor between the points and the Hall-Effect signal as a pull-down resistor that limits the current also then use this formulae V/I=R or properly E/I=R which is 12/0.025 = 480 ohms, 6/0.025 = 240 ohms and so on. I haven't looked at the rest of the circuit I'll do that later and get back to you.

I found if your going to use 555 timers and make a buzz coil and have it work properly you need 3 x 555 circuits. 1 to work as a variable oscillator and the other two to work as what is know as a one-shot mulivibrator. The one-shot circuit can be set up as a non-retriggerable so it gives one pulse out for one pulse in and will not except another in until the first is done, good for debouncing points at high RPM. It will not stay on because you can set the pulse wide to the coil circuit.

I'm making a line of small ignition systems soon and at a price point that I think everyone will like in kit or assembled. The buzz coil is the next design I'm working on. I need to make money so I can buy equipment.

Gnite

Ray


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## Rudy (Jan 12, 2021)

74Sprint said:


> Rudy the problem with your circuit cutting out at higher voltages is that you are grounding out the signal output with the points. I have and use the A1120EUA so I have some experience with it. The A1120 has a built-in voltage regulator and short circuit protection control, the 2 are seperate. The circuitry can provide up to 25ma of current continuously and will trip at 30ma according to the data-sheets. The signal out was never designed to be grounded out, this would put it into a short circuit condition. Like most over current protection it is a latching design and will not reset until the power has been removed and turned back on but, if the condition remains it will lockout again. I don't know the reason for using both a Hall-Effect and points, it should be one or the other.
> 
> If your going to use the circuit the way you have it then add a resistor between the points and the Hall-Effect signal as a pull-down resistor that limits the current also then use this formulae V/I=R or properly E/I=R which is 12/0.025 = 480 ohms, 6/0.025 = 240 ohms and so on. I haven't looked at the rest of the circuit I'll do that later and get back to you.
> 
> ...


Ray, thanks for your useful input! I'll test it. I use hall sensors and just put the point in there for I guessed it would be the same. However, I will put in the resistor as you point out.
Like your idea of making ignition products. I did this on the corner of my lab bench. I do make a living out of hardware development and there is a huge gap between a on time hobb project and a commercial product.
Rudy


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## simonbirt (Jan 12, 2021)

bluejets said:


> Rudy....the ignition Simon is using is a buzz unit also with cut out if no pulse detected.
> 
> Simon...you show the diode in series with your LED as a zener diode but quote as a 1N4003 which is a standard diode.(D1)
> Connection you show as a zener i.e. reverse which is correct but a standard diode will not conduct in that configuration in normal operation.
> ...


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## bluejets (Jan 13, 2021)

Possible to show the schematic you have there,,?
You say you have corrected the drawing to show a "normal" diode....just curious what you have actually done.
I do not see any band or other marking on the device you have in series with the LED.
Others may be interested in your pcb file as well.


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