circuit to sense if car is motion

speedometer accelerometer

Hi,


What is the simplest circuit I could use to sense if a car is in motion??

Newtons Laws of motion say that you cannot sense the motion from inside of a body moving at a constant velocity. You have to sense by the ground speed, air speed on the wheel rotation. Wheel rotation seems to be the easiest. The conventional car speedometer uses a cable to bring rotational info to the speedometer. If you can open the speedometer, you can install some sensor inside and get the speed info. Alternately, you can install a non-contact sensor on one of the wheel assembly.

If you need only sense motor run , you can use piezo sensor as vibration sensor or magnetic switch sensor near accelerator paddle

If the car has a speed sensor, just put a schmitt trigger circuit if you wanna know the velocity, or a peak detector if you just know if the car is moving. If it hasn't speed sensor (has magnetic cable), exist some sensors for interface the cable and get the signal.

how about a simple GPS Rx'er. You can get them from w**.sparkfun.com

Vibration. Can use from simple contact alike inertial sensors up to chip accelerometers .

You can tap in to the ABS system where you get a pulse train which is proportional to the speed.

How about the car's speedometer? Can you get the pulses from that?

In a car has two main forms of measure velocity:

1) For older cars exist a cable with a magnetic element that rotate (I forget the name in English, in Doebelin book has) and moves the velocity indicator on dashboard, the magnetic field generated wins the spring force and move the indicator (how can I say it? pointer of velocity)...

2) Newer cars has magnetic pickup on transmission box, that delivers a sine wave proportional to speed ... this signal is differential and get it isn't simple. I have to do it, but in an PMS sensor, it's more difficult because PMS is a crankshaft reference of the motor, and I can't introduce errors... another makers like Volkswagen use electronic sensors, e.g, magnetic pickups with TTL compatible output (0-5V), much more easy to use ...

In cars with ABS each wheel as an teethwheel with a magnetic pick, because ABS unit has to know the velocity of each wheel, to avoid block. In an ABS system when it see a DC signal only in a wheel, or a inconsistent signal, it consider that signal as a error and turn off all the system.

leomecma

GPS doesn't work inside the building or no sky area.