Model engine CDI easy and cheap. Many years ago, I started making transistor assist ignition for model engines running rather large coils from motorcycles operating on the Kettering system (points,condensor, battery and coil). These changed through the years as the learning curve advanced. I built transistor assisted Kettering, hall effect, and small basic cdi units, adding microcontrollers etc. etc. all labour intensive and requiring differing levels of learning. I saw these small motorcycle coils years ago (GY6 style) and this removed any need for building homemade coils. GY6 is 30mm dia x 50mm long weight approx 50g. Cheap too, a bonus at around $7.00 and the only mod was to remove the large HT lead and replace with something more scale-like but still practical. The cable used is around 4mm diameter, rubber insulation, Belden 8899-010 Black. These ignition coils were not designed for Kettering style so started the road to CDI. Making one's own CDI units does work but they have limitations, namely getting enough power into the capacitor in an ever-decreasing time, increasing rpm. plus of course the time involved in building, programming etc. etc. One's I built here were successful for single cylinder engines turning around 8,000 max. which even had electronic advance map built in to the microcontroller. I like to build engines primarily. With electronics, if nothing is available it can be built quickly using modules. The latter is a great thing these days being cheap and relatively reliable into the bargain. I noticed the "DC CDI units" a couple of years back. These are the type that makes use of power from a 12v battery and the high voltage energy required to charge the internal capacitor is generated within the unit. Also cost $7.00 approximately. (and that, in Aus at least, is delivery included, unbelievable really). Small totally encased box 70 x 40 x 25mm weight around 120g (4 oz.). I knew they were triggered by a pickup coil generating basically a sine wave (ac signal) in which the first rising wave was used (eventually) to trigger the internal SCR. As the commercial pickup unit was LARGE for model use, I began to experiment with the use of a very small relay and modified it to give the correct trigger. This worked a treat and even though the size was now acceptable at around 15x15x15mm, it still required some refining. That was over 1 year ago and the other day, dragged everything out once again for another "go". Hall effect is a great thing BUT as it stands it will not trigger as required. It turns out that by adding a simple single inverter transistor circuit with a small modification to allow a "one pulse signal" was the key to the problem. If one wants to use the old points approach, I have another add-on for that as well in the form of another single transistor and a slightly larger pc board. In this version, the points with a grounded frame as original, on opening will give the one pulse required to the CDI unit trigger input. The last couple of weeks have been spent making the modification as simple as possible with as simple as possible parts. Strip type Veroboard seemed the logical approach and most should either have no problem working with it or at least know someone who can help. I have also been using a hall effect module available on eBay at 5 for $3.00 approx. which saves a lot of mucking around. George has made a 3D plastic casing/mounting for the hall effect module so I imagine the files will be available if required. Testing the unit at this stage has been done using a test bed I made up many moons ago, but final proof will be testing on an engine. George almost has a3-cylinder I.C. ready for such a test so fingers crossed. I cannot foresee any real problems given they were designed initially for the small motorcycle market. Total cost for the complete system is around the AU$20.00 mark which is pretty good for any ignition system, let alone a CDI. I have an idea there may also be an amount of electronic advance built in to these units but only further tests will prove if this is the case. The pre-built parts are easily obtained and cheap with the small modification pc board easy for most to build. So, if interested, I'll post more detail in the form of a pdf file on the build. Any testing we do I can add later.