For almost one year now, I m going to office by bike, crossing a crazy busy city by bus&cars (Shenzhen, China). When I was young and going to school by bike also, I was used to have small miror on left and right to see any cars overtake me on left or right.

Now, it is difficult to find this and I was thinking to a system, to alert me without loosing my view in front. The natural idea is to use US sensor, capable to give distance from 20cm to 4m.

As the plan is to be low consumption and solar power, I didn t want to use 5V or 3.3v regulator. One US sensor can accept large voltage input, with temperature compensation, US100 or Y401. They are capable of send the data from Rx/Tx or with a signal lengh. this second option will be use here.

So far, I use a uC from Microchip, 12F1512 due to Fix voltage Reference inside, small (8 pins).

2 US sensors, position at 90 degres, will be trigger by the uC. the output goes to the Timer1 gate which count the distance. A simple rule to estimate the distance: duration in us * 34 / 200. this is given the distance in cm.

Then, how to give the alert to the rider ? That's the funny idea. I'm using 2 vibrators (from old mobile phone), put under the seat post of the bike, one on left and one on the right. The number of vibration will indicate if a car is close or far. 3 vibrations means close, 2 medium, 1 far but approaching.

Prototype is finished, code in C with MikroC (free version) as usual. Testing soon.

Laurent