• AC-CDI
  • For ONE or TWO* cylinders
  • Microprocessor control unit
  • Wireless and easy programming and the fly via smartphone or laptop
  • Compatible Android, Iphone, Windows, Linux smartphones and/or PC
  • Programming security:
    • Only possible when engine is stopped.
    • Only possible when ignition key is ON.
  • One programmable ignition curve
  • Rev from 200 to 20,000 RPM
  • Adjustable timing in 10 steps from 1000 to 10,000RPM
  • Adjustable timing at very low RPM (~250RPM)
  • Soft rev limiter.
  • 1 input for a inductive pickup
  • Selectable pickup polarity (2 types)
  • 1 output for a capacitive coil type
  • Non volatile configuration
  • Tachometer output
  • Kill switch
  • Power supply voltage DC 8 to 16 volts
  • Current consumption: 60 to 100mA
  • Protected against reverse supply voltage
  • Dimensions: 80|106 x 64 x 25mm (3.15×2.52×0.98inch)
  • Strong grey extruded Aluminum box
  • Made in France


If there is one separate pickup
=> This AC-CDI works.
If there are 2 separate pickups (one for low RPM and one for High RPM)
=> This AC-CDI works.
If there is no separate pickup and the timing is done by using the High Voltage of the stator
=> This AC-CDI will not works
If the engine works with missing teeth
=> This AC-CDI will not works

* Twin-cylinders:
If the engine works with WASTED spark and if there is ONE twin coil.
=> This AC-CDI should works.

If the twin engine doesn’t support wasted spark:
=> This AC-CDI will not work

Remember that ignition coils are different from TCI to CDI system
– CDI coils have low inductance and impedance around 0.5-0.8ohm
– TCI coils have higher inductance and impedance around 1-3ohm

Remember there are AC-CDI and DC-CDI…


– 1 input for inductive pickup with 1 signal per crank rev.
or for 1 inductive pickup with separate output for low and high rpm (XT600)
– Pickup must give 2 to 30Vac
Points, reluctors, Hall sensor, optical sensors can be used as long as they give only 1 pulse per revolution.
– CDI is not compatible with multi-pulses pickup or missing tooth wheel.

Rev Limiter:

There is no “Hard rev limiter” that stop all sparks above a given RPM
but you can drop the timing back far at high end so the engine cannot rev more.

WIFI range:

5 meters distance from the CDI (compared to a regular ISP box at same distance):

10 meters distance from the CDI :

Troubleshoot with LEDs:

In default CDI mode, with KILL SWitch not connected to GROUND:
Blue led blink 2 times, Red led blink 3 times then both led are OFF: mode_CDI
Slow motion: mode_CDI_slowmo

In Access Point mode for wifi programming, when Kill switch is connected to GROUND prior to turn the master key ON:
Blue led blink 1 time, Red led blink 3 times then both led are ON.

A buzzer sound after 5 seconds meaning the CDI is ready to be programmed : mode_AP
Slow motion: mode_AP_slowmo


To proceed to the initial setup

  1. Connect the AC-CDI to
    Wireless Setup video


Work in progress:

January 2018: Prototype is under test for the last debug sessions:

Debug with MPLAB Simulator:

February 2018: First serie being populated:

Soldering done:

16 thoughts on “AC-CDI v9”

    1. Version v9.0.0 is designed for 1 cylinder.

      It should work on a Twin-cylinders if the engine works with WASTED spark and if there is ONLY ONE twin coil.

      ie: It works on BMW as they are opposed twin/4 strokes, and needs only one spark every 360°, the very same as a single cylinder/2 strokes.
      Their twin coil has 2 outputs and fires the 2 sparkplug at the same time.
      (One spark is wasted as one cylinder is on its exhaust stroke.)
      See left part of this animation.

  1. As you mention the ignition can handle wasted spark, I supposed it then can work for a three-cylinder engine with wasted spark and three ignition coils firing in paralell, that gives one real spark for ignition + two wasted sparks per revolution for each cylinder.
    For example a three-cylinder engine that revs 8000 rpm, the ignition need to produce 3×8000= 24 000 sparks/min, or 400 Hz.
    What is the maximum sparks/min the v9 ignition can produce?

    1. You are right. It could theoricaly work… but there are 2 limitations: hardware and software
      Hardware :
      The CDI has one output meaning that it can drive:
      – one coil: fit 1 cyl
      – one twin-coil: fit 2 cyl
      – 2 coils in parallel: fit 2 cyl
      – a distributor to fit 4-8 cyl
      if you drive 3 coils in parallel , their low impedance will be divided by 3 and can destroy the output SCR inside the CDI
      It also mean there are wasted spark during intake and exhaust strokes inside the 2 others cyl.

      Without wasted sparks:
      Number of sparks = ( RPM x cylinders ) / 2
      ex: 3000rpm on twin cylinders: 3000 x 4 /2 = 6000 sparks / minute = 6000 /60 = 100Hz

      With wasted sparks:
      number of sparks = ( RPM x cylinders )
      ex: 3000rpm on twin cylinders: 3000 x 4 = 12000 sparks / minute = 12000 /60 = 200Hz

      AC-CDI v9.0.0 can reach 400Hz but the RPM range that is adjustable is 500 to 10000RPM (then 250 to 5000 on a twin)

  2. Sorry I was unclear about my example about the three cylinder engine!
    I was referring to a two-stroke engine, that ignite the fuel every revolution. My intention was to use the CDI on a two-stroke engine.
    Ok, so essential you are saying that the ignition can handle 400 Hz, but the possible problem with three paralell coils would be the low resulting impedance from them, affecting the SCR!
    – Would it work then if the three coils are in series instead (at 400 Hz), that means adding 3 times impedance, compared to a single coil impedance?
    – If I understand you right the adjustable part of the curve is from 250-5000 rpm if useing the CDI on a two-stroke (without wasted spark). But it will give sparks up to 10000 rpm for a single cylinder two-stroke engine, and sparks up to 20000 rpm for a single four-stroke engine.
    – Is it only a programming issue that make the max limit to 5000 rpm for one spark on every engine revolution, or is it the processor speed that are the limitation?
    – Do you have any possibility to make an alternative PIC-programming for a two-stroke application?

    1. To drive 3 coils your need a CDI with 3 outputs. That’s it!
      Otherwise serial or parallel are just compromises…
      Parallel (high current) is a threat for the SCR depending on its characteristics and need a bigger cap
      Serial (lower current but lower tension) is poorer performances.

      I don’t have experience with 2 stroke as there are rare.
      As I understand it, RPM is divided by 2 for a twin 4 strokes (useful spark each 2 crank rotations) but is not for a twin 2 strokes (useful spark each 1 crank rotation) so this CDI “should” perf the same (adjust until 10,000 and capable of 20,000)

      If your current CDI works, why don’t you check that on yours?
      Plug a scope on each sparkplug and on the main pickup and do the math.

      it’s software limitation for the most part. Processor speed only limit the accuracy at high RPM
      This coming AC-CDI is intend to be sold only 😉

    1. Thanks for your interest !
      It’s plan to be available this month March2018.
      At the same time I change the whole site look.

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