View Single Post
Old 03-11-2011, 01:14 PM   #17 (permalink)
EcoModding Apprentice
Join Date: Jan 2010
Location: Newark, DE
Posts: 143

'91 CRX - '91 Honda CRX DX
90 day: 34.91 mpg (US)
Thanks: 0
Thanked 14 Times in 14 Posts
Originally Posted by dcb View Post
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.

Last edited by bobski; 03-11-2011 at 01:22 PM..
  Reply With Quote