Bill of Materials

Sl.No	Part Name	Source	Quantity	Total Amount (in INR)
1	Main Housing	3-D printing	64gm of ABS	500
2	Magnet Mount	3-D printing	16gm of PLA	100
3	LCD Holder	3-D printing	40gm of PLA	200
4	Neodymium magnet	Fab Lab Inventory	1	2
5	3mm Acrylic (Black)	Fab Lab Inventory	100mm x 100mm	30
6	3mm Acrylic (Clear)	Fab Lab Inventory	100mm x 100mm	30
7	FR1 PCB Blank	Fab Lab Inventory	70mm x 70mm	20
8	AtMega 328P	Fab Lab Inventory	1	149
9	20 MHz Resonator	Fab Lab Inventory	1	50
10	Hall effect sensor A3144	Online purchase	1	35
11	Liquid Crystal Display	Local purchase	1	140
12	I2C Module for LCD	Local purchase	1	160
13	4.9 KOhm Resistor	Fab Lab Inventory	2	20
14	10 KOhm Resistor	Fab Lab Inventory	2	20
15	0 Ohm Resistor	Fab Lab Inventory	4	40
16	10 uF Capacitor	Fab Lab Inventory	2	20
17	5V Regulator	Fab Lab Inventory	1	20
18	Diode	Fab Lab Inventory	1	10
19	ISP Header Pin	Fab Lab Inventory	1	10
20	Pin Head(1 x 4)	Fab Lab Inventory	1	10
21	Jumper Wire	Fab Lab Inventory	4 Nos	10
22	Wire	Fab Lab Inventory	2 Nos - 10 cm long each	10
23	Screws	Fab Lab Inventory	4 Nos	10
#24	Magnetometer Sensor	Online purchase	1	465
#25	Red LED	Fab Lab Inventory	4	40
#26	499 Ohm Resistor	Fab Lab Inventory	4	40
#27	Pin Head(1 x 4)	Fab Lab Inventory	1	10

# - Optional - for Digital Compass

Total Amount for the Speedometer : INR 1596/- (Approx 20$)

Total Amount for the Speedometer with compass : INR 2151/- (Approx 30$)

Design & Development

Speed of rotation is computed by making use of a digital hall effect sensor, which produce a pulse, each time a magnet mounted on a rotating disc passes by. The pulses are counted by an ATmega328P microcontroller, which computes the speed of rotation and display the information onto an LCD.

The final board was designed during the Networking & Communications week, the working of a hall effect sensor was experienced during the Input Devices week and the Interface & Application programming week. The working of an LCD was experienced during the Output Devices week.

The original design files (and also the STL files) of the 4 mechanical parts ("housing", "rotating disc", "Top Cover", "Acrylic cut") which were designed in SOLIDWORKS are available below.

The "rotating disc" is press-fitted on a part reused from an old analog speedometer which transferes the rotation from the wheel onto the rotating disc. The "rotating disc" has a hole to mount the magnet. The magnet is mounted at the outer periphery for getting a distinct pulse at the sensor. It is for this reason, the diameter of the disc cannot be reduced much.

The "housing" was originally designed to accomodate the "rotating disc", the reused platform for the rotating disc, a hall effect sensor PCB, a main PCB, a magnetometer sensor and a 128x64 OLED display. It was later adapted to fit an LCD display. The design can be made more compact by reducing the overall diameter after redesigning the internal support structures made for the PCB's and by using an OLED display.

"Top Cover" is primarily for holding the LCD in place and also supports the acrylic covers on the top. This is designed to be press fitted onto the "housing". Provisions for tightening with screws are also provided.

The files "Acrylic Cut" are the drawings designed for laser cutting and engraving the black and clear acrylic's, which forms the top surface of the speedometer.

The electronic design was made in EAGLE and the files of the schematic drawing and the board are available at the below link. The output of the digital hall effect sensor is connected to the interrupt pin of the ATmega 328P to detect and count the pulses made by the magnet. Provisions are given for connecting two devices (LCD & Magnetometer Sensor) over I2C communication. 4 LED's are provided to mark the four directions when used as a digital compass.

The arduino sketch uploaded to the MCU using the FabISP can be found here.

The entire process of design, development, integration and testing can be found on the Project Development Page.

Download the Design Files