Quote:
Originally Posted by dcb
signals can bounce a bit
|
Speaking of signals, I noticed an entertaining side effect of the zener setup: it acts like a floating input when disconnected from the car. If I hold the hookup wire in one hand, it registers a 52.8 MPH speed (with associated odometer crawl). Using my other hand as an antenna, I can get much higher values by reaching toward various electronic devices. For instance, the LED cabinet lights I use at my desk register speeds in excess of 3 miles per second. If I touch my (grounded) computer case, it drops to zero. A 1M ohm pulldown resistor in parallel the the zener seems to fix it. I suppose most cars already have a pulldown in place so it's a non-issue. It's kind of handy for desktop testing actually.