The Crankshaft Timing Signal Wheel Simulator is software from Bowling and Grippo that simulates the signal from a crank wheel. It does this by creating a sound file (.WAV) and playing it back through a computer's sound card, on the 'left' channel. There is an optional cam sync signal playable on the 'right' channel.

Hardware

A typical sound card by itself will only put out about 3 Volts (peak-to-peak) maximum (you can always lower the voltage with the volume control). This may be enough for some purposes, but you may want/need more. There are a couple of ways to increase the output voltage of the signal to usable levels the signal:

1. Use amplified speakers (they will have an AC power adapter) that have a headphone jack (often available for $20 or less, if you don't already have them). These will boost the output to around 13 V (p-p) or more, and require no additional hardware other than a headphone cable. Use the left channel for the crank signal, the right channel for the cam signal. You will get the maximum output with both the Windows volume and speaker volume set at their highest.

2. You can use a transformer to step up the output voltage (the following will give you up to 30 Volts (p-p) on the crank signal). The variable reluctor (VR) output from the sound card requires an 8 Ohm: 1K Ohm coupling transformer to drive the MegaSquirt-II VR input circuit. A suitable transformer is Digi-Key 146KHM-ND ($12.89), however this is a 'non-stock' item. You can find them at Unicorn Electronics. You might have better luck at your local electronics store (RadioShack, etc.)

   Both the VR transformer circuit and cam sync signal circuits are shown below:

   
   The hardware for the VR output looks like this:
   

   The red wire is the signal, the green wire is ground (on the left side of the transformer). The thick black cable is a stereo jack pirated from an old set of headphones.

   The cam sync signal (if you use it) requires an external transistor driver circuit.

   Wire the signal from the sound card to the low resistance side of the transformer, ~1 Ohm (it will be less than eight ohms, which refers to the impedance, rather than the DC resistance), and the output to the high resistance (~50 Ohms DC) side of the transformer.

   You can build the transformer circuit on a small proto board, or solder the leads directly to the transformer.

   

Software

Get the executable file here (right click and 'save as' or run it from the current location):

The source files are here: CWP.zip (7.6 MegaBytes!)

You can specify the number of teeth and the 'missing tooth pattern' from the selection box. An XX-Y pattern means a wheel in which there are XX evenly spaced teeth, Y of which has been removed (for example, 36 minus one means 36 evenly spaced teeth, a 5° tooth with a 5° gap to the next one, with one of these teeth removed, creating a 10° gap). These are the number of teeth per 360 degree revolution (I.e, one crank revolution), so '4 teeth' would be appropriate for V8 with one signal per ignition event.

For the cam sync setting, you can specify the positional location in degrees of the cam sync signal with respect to the first 'missing' tooth.

To use the software:

1. Define the crank wheel by entering the number of teeth/missing teeth, and select whether to use the cam sync signal, and select the angle (0-720°) for the sync to be sent,
2. Set up the engine rpms for the WAV file (vary from the lower rpm to the higher rpm and back over the time you enter.),
3. Set up the WAV file by selecting the sample rate (44100 is more than good enough in most cases) and file length (from 2 to 10 seconds is best in most cases - larger files may be slow to generate on some systems),
4. Generate the WAV file by clicking the button and saving the file.
5. Play the WAV file. You can do this once, or in a repeating loop (which may be convenient for testing - but note that there may be discontinuities in the file when the program it starts each new loop).

Notes:

• v1.001 correctly ends the output at the end of a wheel cycle, meaning it completes a whole crankshaft revolution before restarting the file at the beginning of the revolution. This makes sure there are no discontinuities to mess up the missing tooth code when playing the file in a loop. So the run time is approximate, the actual run time may be slightly longer. Earlier versions did not necessarily do this.
• the possible rpm range is limited by the nominal 20-2000 Hertz range of the sound card. With a 36 tooth wheel, 20000 Hz is 20000 teeth/sec divided by 36 teeth/revolution times 60 seconds/minute = 33333 rpm. For a 60 tooth wheel, because there's 60 teeth and 60 seconds in a minute, it all cancels out and 20000 rpm is 20000 Hertz.
• At the lowest rpms (less than 300 for a 60 tooth wheel), the signal is not so good and clean, and the triggering may not work well (or at all).
• to simulate a non-missing tooth distributor, you can choose 4-0 for the wheel settings (for a V8), 3-0 (6 cylinder), or 2-0 (4 cylinder). In this case, low rpms are a problem as well. For example, 30 Hertz for V8 is 30 teeth/sec / 4 teeth/rev * 60 sec/minute = 450 rpm (but the signal is distorted and the actual limit may be a few hundred rpm above this).