Building Blocks for Designing Speedo-Odo-Meter
Lets first roughly design the building blocks for this device. I just want to keep the device as simple as possible for this iteration.
Here is the block diagram.
To detect the rotation of the wheel of the bicycle, I am using a reed switch and magnet. Will come to working details of reed switch later.
Few switches are used for configuring/ setting parameters such as wheel diameter, getting distance or speed, etc.
A small Display will show current speed and distance covered. It also help you configure you device.
All these input and output devices are connected to a microcontroller, Here i am using 8-pin, 8-bit ATTINY 85. You can also use Arduino nano or Pro mini for small form factor and also any other microntroller or board.
Lets see how all of these components look like:
|ATTiny 85 or Arduino nano or Arduino pro mini or Arduino Uno||1|
|Oled 128 x 62 I2C display||1|
|Jumper Wires Male to Female||20|
|Jumper Wires Female to Female||20|
|Jumper Wires Male to Male||20|
|AA/AAA Battery (1.5V)||(for 3v operation) 2 and (for 5v operation) 4|
|AA/AAA Battery Holder||(for 3v operation) 2 cell holder and (for 5v operation) 4 cell holder|
|Reed Switch or Door Lock Sensor pair||1|
|Small plastic box for enclosure||1|
Try to identify the componets as block diagram and feel free to ask any query.
This is all we need for our primary function (to measure speed and distance covered), but you may also think for more features for you cycle computers.
Let us know what all features you want to add to your cycle computer and how you have designed your block diagram.
Know Your Bicycle
Here is the image of bicycle with labelled parts.
So try to identify parts on your bicycle and mention any missed part in the above image? We love to hear from you.
But wait, why should i choose the front wheel for calculating the speed and distance covered but not the rear one or is it not the case? Help me to understand this by replying to this post.
Ashish, as a cyclist, maybe I can help answer some of your queries.
Technically, the magnet + reed switch (or hall sensor) can be installed on either wheel.
If the speedometer is of the single sensor type (only speed measurement), it is usually fitted on the front fork for convenience.
If the speedometer also includes a second sensor (for cadence measurement), then the speed sensor is usually mounted on the rear wheel as it makes wiring easier. Both sensors are mounted on the non-drive side (left side) chain stay, with one magnet attached to a rear wheel spoke, and another magnet attached to the left side crank arm.
If the speedometer is wireless (sensors communicate with head unit via - not too sure - but some form of radio or bluetooth link), then the speed sensor goes on the front fork, and cadence on the left chain stay.
Also, remember that your device will need some kind of internal look up table for selecting the correct wheel diameter based on tyre size.
For example, for MTB bikes, the wheel size is usually 26" (or 29" for 29’ers). However the tyre width can range from 1.5" to 2.5", and this changes the overall diameter of the complete wheel.
Same applies for road bikes, with the wheels usually being 700mm, and widths ranging from 18mm to 35mm.
Commercial speedometers will have a SETUP function for selecting the precise wheel size.
This is great help @Anool. I will keep seeking for other curious questions also.
Lets Rotate a Wheel
Well, you can read about bicycle wheels in more details. Here is the link: Bicycle Wheel.
Other than Bicycles or vehicles, one can also play with wheels, just look at this image.
What you think can your under development speedo-odo-meter will help this little boy to measure speed and distance covered by his wheel toy?
2D Geometry of Wheel
Lets get into the simple 2D geometry of bicycle wheel. It is a shape of Circle.
A Circle with centre ( O ) measured by its radius ( R ), diameter ( D ) and circumference ( C ).
radius ( R ): a line joining the centre of a circle with any point on the circle.
diameter ( D ): a line joining two endpoints on the circle that passes through the centre. It is twice the radius.
circumference ( C ): the distance around the circle or the length of the circle.
Cool so we have seen these geometry, now lets imagine we want to rotate this circle or wheel.
In the above image the pink color wheel was stationary at plane surface represented by grey line and the green color mark on plane surface represent the initial contact of wheel with respect to it center of axis of wheel.
In this above image we rotate the wheel in such a manner that green point on the wheel come again to the plane surface and thus completing the one rotation.
Now we have two green mark on this plane surface.
So what do you think what is this distance between these two green mark?
In fact does it telling the distance covered in one rotation?
As @Anool also helped us in great details by letting us know range of wheel diameters of different bicycle, the different wheel diameter will cover different distance in one rotation.
So let us know what is the diameter of your bicycle wheel and try to find out the distance covered by it in one rotation.