Advice on reading car's speed

Hello, I'm trying to make an alert and monitoring system for elderly and those who have health problem (like heart problem, hypertension, etc) and this system will be used when the user is driving a car. So the concept is when the heart rate is too low or too high it will give an alert to the registered number on the server via SMS.

Anyway to minimize the false alert, I want to add the car's speed as another parameter, as if the car speed suddenly drops to zero. But I'm still confused how to measure it with Arduino. :cold_sweat: Are there any ideas out there on how to measure the car's speed using Arduino? I've been searching for such a speedometer but mostly they are meant for bikes.

Any ideas and help would really be appreciated. Thank you! ;)

You may be able to find out how to get the information from the cars computer. Otherwise you may be able to find where the speed sensor comes from in the particular car and hook into that point.

Just be very careful that what you do does not effect the control of the vehicle in any way. (Unless you have a very big insurance policy protecting you!)

The safe way is to fit a non contact sensor that detects rotation of the tail shaft, this way you are making no connection to the control of the vehicle.

This can be done by putting two small powerful magnets on the tail shaft and using a hall sensor to detect them passing when shaft is rotating. The mechanics of mounting is up to you for each particular car.


Research OBD2. Standard connector, communication standards, and on all cars built in the last 10 years I think.