We all have probably ridden bicycles at some stage of our life and admired their usefulness. Bicycles are favorites especially among the kids who love not only riding them but also decorating the vehicle with many fancy accessories.
Some children are more tech-oriented and prefer the gadgets attached to make their bicycles look more innovative and futuristic. These gadgets are mostly inspired from the ones which are found with power vehicles like motorcycles, cars, etc. Having some sort of lighting arrangement with bicycles is in fact quite common, rather mandatory equipment in some countries, however, a speedometer is something that’s out of the blue and usually never seen anywhere as far as bicycles are concerned.
The present design of a bicycle speedometer system discussed will certainly impress and intrigue the many techno-freaks.
Let’s learn how we can build and install the device in our existing bicycle.
As the name refers to a vehicle speedometer is a device which indicates the speed at which the particular vehicle is moving, which is directly proportionate to the rotational movement of its wheels. It’s obvious that the system would require some sort of stage comprising a device which would translate the wheels rate of movement linearly to corresponding voltage levels, or alternatively the rate of rotations could be counted through some optical or magnetic device.
The second option is rather more complicated and may involve complex opto-coupler/LED assemblies or costly and much complicated Hall-effect sensor assemblies. Converting the rotations into corresponding levels of voltages looks simpler and feasible, as it could be done using an ordinary bicycle dynamo.
A bicycle dynamo basically consists of coils and magnets arranged in such a way that when the central shaft is rotated, voltage is induced in the coils due to the influence of cutting magnetic fields. The magnitude of this voltage is directly proportional to the speed at which its shaft is rotated.
Generally, these dynamos are claw-poled type of electric generators, designed for low RPM applications. We have seen the use of the sidewall running, bottle-type dynamo being used in bicycles for many years which today have been replaced by much more efficient hub dynamos.
In our design, the specification or type of dynamo is not critical; anything that’s able to generate from 1 to 6 volts of power corresponding to slow and maximum peddling speeds respectively is all that is required here.
The bicycle speedometer design presented here uses the above voltage range, which is processed and fed to an electronic circuit for converting the levels into a visible LED bar graph indications.