A new 3-mode Precision Ignition Module

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Oct 12, 2009
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Hello All.

Please see the attached schematic for a new 3-mode small engine ignition module I have developed.

Running on 6-9 volts, this circuit is based on the 555 Timer which allows precise energizing of the coil. It supports three modes 1) single shot with timeout, 2) buzz with timeout, and 3) buzz without timeout. The coil is energized for just 2-3 ms at a time and thus in auto-timeout mode 1) eliminates any “dwell” setup requirements 2) increases efficiency of the coil which prolongs battery life and, 3) minimizes chances of overheating the module or coil. It currently has about 20 components including two terminal blocks and two jumpers to set the operation mode.

Jerry Howell (Dad) offered the TIM6 and BuzzCoil ignition modules along with his engine plans because he felt they were much better than mechanical “points”. He sold these kits with permission from their designer, Floyd Carter of Los Altos, CA. Jerry’s focus was designing and building engines, not ignitions, so inherent flaws in these ignition modules were tolerated and generally compensated for, i.e. intricate “dwell” setup, bigger batteries, short engine run time, etc.

The PICTIM resolved most of the problems, but the PIC chip was vulnerable to EMP/EMI from the coil, sometimes causing rebooting while running, or worse, altered the software on the PIC. With a little time on my hands now, I thought I would try coming up with something more versatile and reliable. I think this new 3-mode Precision Ignition (3PI) fits the bill as a do-it-all module, and hopefully I can retire the TIM6, BuzzCoil, and PICTIM.

I am NOT an electronics engineer, but rather, an electronics tinkerer. I have gleaned over the designs of other ignition modules, along with some original ideas, into the 3PI. I was a software engineer by trade, so I like to break systems down into “functions” and “procedures” and have followed this methodology in the attached 3PI schematic, hopefully making it easier to understand.

I have modeled the 3PI circuit in the falstad.com circuit simulator. This is an amazing website, and was a huge help in the design and testing. I have tried to tweak resistor values to minimize current waste without compromising stability, and my breadboard setup works great, however, I am sure there is room for improvement. I covet any advice and suggestions from electronic experts here. I can email the Falstad schematic data to anyone interested. My email address is in the schematic.

Thanks in advance for your thoughts and suggestions.

Allen Howell


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