This is Just a Silly Trick to Pass the Time...Actually A Lot of Time!

As you may remember, this project is centered around Chitty-Chitty-Bang-Bang.  She was a car with magical powers.  She was given these powers through the efforts of her inventor/owner, Caractus Potts, who rescued her from behind a barn. The "barn find" classic car has now become an anachronism.  There is a TV show and numerous magazine articles about these rare treasures.  But Ian Fleming, (yes, that Ian Fleming) really captured the magic of bringing a car back to, or beyond, her original powers.

There is no car from 1967 that flared its gauges.  I suppose that was a 90's trick?  But BB does:

There is still some work to do, but those are the original analog instruments driven by a bit of digital magic!

Now, how was that managed?  In a previous post, I detailed the inner workings of these instruments.  The speedometer was the first challenge.  When the previous owner installed the synchronized 1st gear transmission from 1968, he left the original speedometer.  Unfortunately, this meant that the speedometer read 27% too high.  Until I did the cleaning and relubrication, it was also bouncing up and down around 20 mph.  The bouncing is a common problem in 53 year old cars.  I'll be interested to see what issues arise if one of today's cars is kept around for 53 years!

Since I knew that I would be changing the engine and transmission to something that had no mechanical speedometer output, I decided to make a permanent upgrade.  I removed the speedometer cable (which saved about 9 ounces of weight, every little bit counts!) and installed a drone motor in its place.  I connected an ESC (Electronic Speed Controller) and an Arduino with Hall effect sensor on the transmission output.

This allowed me to calibrate the speedometer correctly, after some 50 iterations of software!  I learned long ago that everything that happens in a running car is much more violent than any test bench.  My training involved mechanical systems but clearly electrical suffers just as much.  Talk about noise!

Finally, I established a software which checked 3 times every pulse from the Hall effect sensor to see if it was real or if it was noise.  It was quite primitive but it worked!  So I have one of the few cars from 1967 with a computer onboard.  This may be needed more next year when I install a rotary engine and may need to drive the Tach directly from the Arduino.  

So, the flaring of the speedometer was simple.  I just sent a short speed signal to the drone motor when the Arduino boots up at start.  The tachometer was more difficult.  It uses two of the first production transistors to form a monostable oscillator which is triggered by a small transformer from the ignition coil.  I did some experiments with different ways of jumpering into the circuit directly to drive it but eventually decided on the brute force approach!  I simply wound a few turns of wire around the transformer (which sticks out the back of the tachometer case) and drove it directly with a Mosfet transistor through a 5W power resistor.  All is well that ends well and this car is ending well!

Keep having #funwithcars and see you next post!