Tachometer Adapter For Motorcycles

Well, I know that another user on the board had asked for some help building a signal filter for a automotive tachometer, but I have something a little different that I am trying to build. Actually I have no idea where to get started, but here goes. I have a two cylinder engine on my motorcycle. I have a tachometer that uses a ground switching signal from the ignition coil for the display. Unfortunately this specific tachometer was only designed to be used on a 4, 6, or 8 cylinder engine. I need to take the pulses from my ignition coil and double the signal output for the tachometer to read correctly. Apparently this has never been mass produced. The gentleman in the other post stated that he used a decade counter that dropped pulses. He was going in the opposite direction that I need to. Does anyone have any ideas on what I could build to make this work? I have basic electronics knowledge and can solder pretty well. I have built a Megasquirt in the past. Thanks for any help, and I apologize if I posted this in the wrong area.

You could use an exclusive-or circuit (XOR) to generate a double-frequency signal of a digital signal such as this. You can adjust the values of R1 and C1 to change the value of the output pulse-width if you need to.

So long as the signal is doubled, it should be exactly what I need. Thank you, this looks like a fairly simple little adapter to build. Radio Shack here i come.

If you have 2 separate coils for the 2 cylinders, you can use 2 1N4007 diodes on the coils (points input), and a resistor of 270 ohms to +12v. That will give you 2 LOW pulses for the 2 times the coils fire.