Old CDI Page

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I am constructing an electronic ignition system for model engines.


Update january 25 2005, click here

Planned spec:
Run from a 4,8, 600 mAh battery
Use CDI to get a hot spark, even when starting.
Electronic advance
Minimal part count

Possible extra's;
Ignition on/off by RC control

The ignition will be based on a free running oscillator to generate the CDI voltage, a SCR to control the fiering, and a PIC chip to control the advance. A standard Modelectric coil is used. A hall effect IC reads engine position.

Block Diagram







September 26 2003
First prototype built, crude construction, but it works.

Components used;

1 Transistor  BD242B
1 Thyristor  2N6237
4 Diodes  1N4001
1 Resistor  500 ohm
2 Capasitors 4,7nF and 0,47uF/250V
1 homemade toroid coil, see belov
1 Modelectric coil

Waveform from prototype:

Upper track is the trigger pulses
Lover track is the CDI voltage

Works wery well.
Strong spark, even at 500 Hz (30000 RPM)



Toroid coil
The ferrite core is a very common type; it is taken from an old computer. It was used as an RFI suppressor on the motherboard cables.
It has an outer diameter of 2,5 cm.
The 3 windings is made like this;
L1 20 turns of 0,5 mm
L2 10 turns of 0,1 mm
L3 450 turns of 0,1 mm
All windings must go in the same direction, and must not be too loose on the ferrite core.
Wind L3 first. When done, put on some lacquer to fix them.

The components values are form my prototype, but none of them is critical, use what you have…
To trigger the unit, use a Hall Effect device with logic level output.
Mount a small magnet on the flywheel, and position the Hall Effect device so the magnet will trigger it.

The next step is to make the advance control. I will use a PIC microcontroller for this, probably a PIC12C508/509.

Fell free to send send me a mail, if you have any questions.