Step 1: structure
This project is very important to have a strong and stable support. The idea is that, when it faced a pothole, or when you decide to have fun and ride in difficult circumstances, the period may be subject to a heavy impact. Further, when the magnet on the wheel through the Hall effect sensor on the carriage, we input. If all the wrong things at the same time, arduino will display the speed of high-speed railway. Also you do not want your best friend because you arduino lazy and decide to use some cheap material falls on the road
So, to be safe, I decided to choose aluminum because they can be easily cut and drilled, corrosion-resistant and inexpensive, it is always beneficial for DIY.
I also used a number of nuts (with washer) on the bolts and secure them to the frame, since they must be securely placed on the chassis. If you put aside the error and must be relocated them, which would also help.
Another important part is made of any metal, if they are made by me, the electronic components must be isolated and the correct holder. I use hot glue is useful, because it also absorbs some of the shock and cushion the display.
Step 2: the sensor and the magnet
And part of the measuring items depend on the input section. The idea is to place a magnet on the cycle wheel and add a Hall effect sensor on the frame, so that each time the magnet passes through the sensor, and Arduino know complete rotation speed and distance can be calculated.
Sensors used here is the classic A3144 Hall-effect sensors. When a particular magnetic pole facing the right direction, the sensor outputs low. Direction is very important, because the outside pole will not affect the output.
The following are some of the pictures show the right direction. Hall effect sensors need a pull-up resistor of 10k. In my project, replaced by a pull-up resistor arduino of 20k.
Carefully place the magnet is important. Placing it may lead to inconsistent readings or far lose rotation and placed very close to the magnet may cause a contact sensor, which is less desirable.
If carefully observed, the wheel will have some inclination of the shaft, which will lead to crusts and troughs. Try a magnet into the slot. I personally do not have that much effort.
Step 3: Display
This display is theoretically optional, but you need something to display speed and distance in real-time and accelerated. Consider using a laptop is completely absurd. I use the monitor OLED display is 0.96 inches, I2C protocol as a communication between the slave and master devices.
Posted picture shows the three modes arduino automatic switching.
1) the lower left corner is a small beginning arduino just started and successful startup.
2) km / hr speed units. This mode is only displayed in the cycle time, and turn off automatically after circulation is stopped.
3) The last in meters (Long live the metric system) as the unit is clearly distance cycling trip. Once the cycle is stopped, arudino switch will display the distance in 3 seconds
This system is not perfect. Even when a circular motion, it will temporarily display the distance traveled. While this show is not a perfect place, but I think this is very good.
Step 4: Power
The project is a bit clunky, not always near a wall outlet for charging. So I decided lazy, just use as a mobile power supply and use mini-USB cable to the USB mobile power supply is connected to the arduino nano.
But you need to carefully choose the power. Important to have a suitable geometry so that it can be easily mounted. I just fell for such a conventional mobile power I and square geometries.
In addition, mobile power must be a little dumb. Things in order to save power, if the current draw is not above a certain threshold, the power pack is designed to close the output. I suspect that this threshold of at least 200-300 mA. Our circuit does not exceed the maximum current consumption of 20mA. Thus, normal mobile will turn off the output power. This might make you believe your faulty circuit. There is such a small current consumption of mobile power when this particular work, it gives me another reason to love this mobile power.
Step 5: Brakelight (completely optional)
As an additional feature, I decided to add brake lights. The problem is that if I broke, how can I find. It turns out that if I brake deceleration cycle. That means, if I calculate acceleration, if the result is negative, I can turn on the brake lights. However, this means that even if I just stop pedaling, the light will light up.
I did not add my transistor in the light, which is totally recommended. If someone did this project and to properly integrate this part, I will be very pleased to see that end and add a picture.
I draw current directly from a digital pin arduino nano's 2
Step 6: Program
I have been writing programs on Arduino IDE. My initial goal is to record the parameters to the SD card. Unfortunately, in this case, I would have to use three libraries, SD.h, Wire.h and SPI.h. these combined with the core accounted for 84% of available memory, IDE warned me stability problem. However, soon after that, every time the poor nano collapse, everything is frozen. Restart lead to repeat history. Read more
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