Sorry I wasn't aware of this thread or I would have chimed in earlier to defend (as it were) my circuit. But it seems John (jgedde) has done a good job since his circuit is almost the same. Albeit he chose to add a bit more protection ( no harm done with a few extra parts). I haven't found any of it necessary. Read on...
The only thing I wish is that people would link to the original post and not take things like the schematic out of context and paste it without the original comments on it. I think it was properly linked a couple of posts back but if not here it is (I hope I have it right myself)
http://www.homemodelenginemachinist.com/f26/ignition-circuit-help-19673/index2.html
POST #17
You will note that #6 in the list states that the hall sensor CAN
but need not be supplied from the same supply as the coil.
LUC there IS a supply stated for the Hall sensor and you in fact circled it a few posts back it's +VE just like the rest of the stuff connected to the same point on the left side.
I guess to be more clear (and conventional) there COULD have been another line marked +VE up at the top shown feeding the whole left side but it would be somewhat redundant since the hall sensor is connected there already and it's marked clearly +VE which is somewhat standard notation for a logic power supply (well, for me anyway).
As for the Hall sensor, I suppose a part number would have been useful but most of the ones folks use are pretty much the same. There is very little current requirement for the sensor so I can't imagine one that wouldn't work. Read on....
The coil supply is marked separately as +12v ignition supply. On purpose to show that it need not be the same as +VE.
The circuit was designed so you can drive it from any logic circuit not just a hall sensor. You could substitute any 5v logic device even a microprocessor output to the driver input. Of course +Ve would be the supply used for that circuit. In the case of a micro +Ve would be 5v.
*** I did state in the original post that the only important thing is to be sure the grounds (negatives) of the two supplies are connected together.
I also have a version with the front end driven by a 555 timer to create a "buzz" coil" multi-spark ignition. I have the ignition coil and the 555 running from the same 12v battery as well READ ON...
I find in a lot of cases problems are self-inflicted. A lot of folks don't follow proper grounding procedures interconnecting the various pieces so it's not a problem with the circuit per se but an interconnecting wiring issue.
I think Steve touched on it when he said when he grounded something properly he had no more problems.
This is just something you learn after 38 years experience (like me). You can't really put it in a schematic.
Addition of extra components to cure whatever problems one experiences in their particular situation are certainly allowed but don't be afraid to look at the wiring to see if the problems are being caused by other issues. I admit finding these things is a bit of a black art. One that I don't even understand most times. But attention to grounding detail is important.
The suggestion of resistor and capacitor on the +VE to the Hall sensor (a filter of you wish) if you are going to use a common supply for the logic and ignition is a good suggestion. Although you have the biggest filter in the world right there in front of you connected to exactly the same place. It's called the battery. Having said that the battery does have some impedance so it may not pass spikes well. So go ahead and use the resistor/capacitor filter or what ever makes you happy.
Sorry if you blow a Hall sensor figuring out that you may need that. I never did.
More important is that you have a good short heavy ground lead from the battery negative to the engine block and ground everything to the same point. No long wires.
Re the high voltage circuit:
Coils only have three leads so the negative of the coil is connected to one side of the HV side of the "transformer". As shown the connection is
inside the coil.
Someone stated that with the circuit drawn the way I have it that HV current path is made through parasitic capacitance or some such crap. To that I say draw the WHOLE circuit including the battery. You will see that the HV current comes from the HV lead, jumps the spark plug gap to ground. The HV current flows through the (very low resistance) battery back to +12v where it is connected to the primary side of the ignition coil. It then it flows through the low resistance primary winding to the junction I've shown inside the coil to the HV side to complete the HV path. (just the way it's done for as long as the kettering ignition has been around). The various low resistances along the way have no effect. In fact they can enhance the spark.
So, this brings up another point. If you have a CRAPPY battery with high resistance, and not a nice Gel Cell made with proper connections (mentioned briefly above) spikes created by the HV current through the battery are more likely to develop across it causing problems with other things connected to the battery i.e. the driver circuit. So go ahead and add the filter.
Like I said I can't allow for everyone's self-inflicted problems. Add whatever components you need to to make it work for you.
I have no intention of sounding "snippy" here. Upon re-reading it comes across that way. Sorry for that. Just trying to clarify a few things
Sorry for such a long post.
Now let the arguments begin. :fan:
Sage
and I understand that we are all trying to help.
