Defi Basis CMOS Speed Signal Adapter Circuit

The ProblemAs mentioned in my previous post, the input to the Defi Control unit to determine speed requires a pulse between 20 and ~270 pulses while the car is traveling 40 mph. The wheel sensor on my 2003 E30 M5 generates 10 pulses / MPH. At 40, the number of pulses sent by the E39 wheel sensor is out of range at ~400. I decided to build a circuit that would divided the pulses generated from the wheel sensor by 2. This would allow me to calibrate the Defi at 40 mph as required.
After calling around town and checking local area shops, I ended up ording the parts I needed from Mouser. I ordered a bunch of cmos parts so I'd have some extras. I used a socket and a small breadboard to wire the thing up.

Here's a shot of the circut after I completed the basic wiring. It's simply a cmos 4013 configured to divide by 2. I added a 47uf/50V cap to decouple and glitches that might be present on the supply line and a small driver to make sure the signal can toggle the flip-flop.

Schematic

R1 - 10K 1/4 watt
R2 - 100K 1/4 watt
Q1 - 2N2222 or equivalent
C1 - 47uf / 50V
4013B CMOS Dual D-Flip Flop
This took me about an hour to do using a socket and some wire wrap. There are two outputs S(out) divides the input signal by 2. S(out-1) divides the input signal by 4. Using this circuit, the Defi should be capable of working with a much wider range of vehicles.



I tested the circuit out by driving it with a simple square wave to make sure I didn't make any wiring mistakes. No sense pulling the car apart and installing this if it won't work on the bench As you can see the inside wave-form is half the frequency.




Now that I'm sure I didn't make any mistakes, I just packaged the thing up in a film canister so I can tuck it away under the dash. The plan is to connect this between the BMW DWS Wheel Speed Sensor and the input to the Defi Control Unit.



Now I just need to wait for it to warm up a bit and I'll install it in the M5. It's only 30 deg here in Ithaca and it's too cold in the garage today to do any work today.