An integrated control-unit and power-supply assembly usable on board a bicycle includes a box for containing an electronic control unit, the said box being fixable to the down tube of the bicycle in the area where the bottle cage is fixed, or else underneath the crank case, and being provided with a receptacle-like tubular appendage which receives, by fast-coupling means, the end of a cylindrical battery holder. One end of the cylindrical battery holder carries a sensor device, for example a magnetically operated sensor, which is set at a distance from the crank pin that is substantially equal to the length of the crank arm. The said sensor co-operates with a permanent magnet carried by one of the pedals to emit a pulse at each revolution of the crank arms. The assembly according to the invention can be exploited for carrying one or more sensors, of any type.