Week 19

Applications and Implications

This week's lecture gave a wonderful insight into the present state of digital fabrication (or rather personal fabrication) and also about several successfull and intersting projects that developed from Fab Lab's across the globe. It was a good experience to learn about the impression's made by the Fab Lab's in areas of electronic devices, machines, robots, satelites, energy, food, etc which developed from Fab Lab's.

This week's assignment was to propose a final project that integrates the range of units covered, and to describe its function, the present state of affairs in the subject area, the design plan, the materials and components to be used, the source and cost of materials, the parts and systems to be made, the processes to be used, the questions to be answered, and about it's evaluation.

Digital Speedometer cum Compass

During the input week, it was learned that measuring the speed of rotation is done using a hall effect sensor. It developed an interest in me to make a make a digital speedometer for my motorcycle so as to replace the existing one. The existing one is left broken for its mechanical wear and tear developed over decades. It was preferable to mount the entire electronic components away from the wheels to avoid the harsh effects of weather, shocks and vibrations, dust and dirt. Also, if the sensors are kept near the wheels, it will difficult and messy to power up the sensors by routing wires near the wheels. I wanted to make the adaptation simple by replacing just the existing speedometer housing and to make use of the existing speedometer cable to transfer the revolution of wheel. Below is the intial sketch of my final project.

The rotation of the wheel is transferred to to the speedometer casing through a cable which is free to rotate. The spinning disc assembly from the old analog speedometer which spins along with the cable will be reused. On top of the rotating part of the assembly, a 3D printed disc carrying a magnet will be mounted. The magnet will be rotated along with the wheel and a hall effect sensor will detect the magnet each time it completes a revolution. The microcontroller will take the input from the sensor and compute the speed and will then display it onto an LCD. Im also planning to add magnetometer sensor and temperature sensor to display the direction of movement and temperature onto another LCD.

Who's done what beforehand

A Google search gave several instructional websites for building a digital speedometer. This website describes the construction of a digital speedometer, with its MCU calculating and displaying the speed and distance on an LCD, with the help of a reed switch mounted directly on the wheels.

This website is about making a digital speedometer working with the GPS. This website is about making a digital speedometer working with an IR LED and phototransistor. The mechanical arrangement for mounting the input devices are similar to the mechanism in my final sketch.

This website is about displaying the speed in an android app by using bluetooth input from an arduino. The Arduino detects the speed using a hall effect sensor mounted directly on the wheels. The following code obtained from the website uses the interrupt function to measure speed.

This website is a continuation of the earlier one which uses a microcontroller to display the speed onto an LCD. This website is also about using a Reed switch mounted on the wheels and an Arduino for displaying speed on an LCD.

The Design

The speedometer housing has to accomodate the entire electronics and also have the mechanism to rotate the magnet along with the speedometer cable which comes in. The housing has to accomodate the hall effect sensor, PCB, LCD, signal and power cables. The housing has to be covered from the top using a 3mm plywood, atop which an acrylic will be placed for making it weather proof. The initial design idea requires below listed components to be designed.

1. Speedometer Housing to be made from 3D printing

2. Rotating disc to be made from 3D Printing

3. Hall effect sensor module to be made by milling the copper blank and soldering of the components.

3. The main PCB with the microcontroller and all the required i/o pins.

4. 3mm plywood top cover to be made from laser cutting

5. 3mm acrylic top cover to be made from Laser Cutting

Bill of Materials

Machines required

1. 3D Printer

2. PCB Milling Machine

3. Laser Cutter

4. Soldering station

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$)

Parts and Systems to be made

The main housing is to be designed and 3D in tune with the physical measurment on the motorcycle. In addition to the measurments, the design should have arrangements to hold the sensor module, the main PCB, the OLED display. It should be made weather proof by making a press fit cover from the top.

The magnet mount is to be designed and 3D printed in tune with the measurement of the rotating aseembly of the old speedometer. It should be press fit so as to rotate along with the assembly.

The main PCB is to be designed to fit into the main housing. The components should be arranged in such manner to aid functionality and reduce the amount of signal wires.

The top covers of plywood and acrylic are to be precisely cut for a press fit which will be weather proof.

Processes to be Used

1. 3D Printing - The housing has to be compatable with the measurements of the motorcycle and is to be 3D printed. The housing ought to have supports for the PCB.

2. Laser Cutting - The cover for the housing and the top cover has to be made in acrylic.

3. Electronics Design & Production - A PCB with an ATmega 328 as the MCU is to be designed. A hall effect sensor (connected to the interrupt pin) is to be used as the input device and an L.C.D as the output device. The design should take account of the size and shape of the housing for proper incorporation.

4. Embedded Programming - Each interrupt pulse of from the hall effect sensor is to be counted and processed into speed and distance by the MCU. The computed instantaneous speed and distance has to be displayed onto an L.C.D

Questions to be answered

1. The battery on the motorcycle is of 12V. The voltage has to be regulated down to 5V without much loss of energy and also without the risk of the regulator getting heated up.

2. While the motorcycle is idle, a possibility exists where the magnet and the sensor are in the same line with the sensor sending continous pulses tricking the MCU to output erroneous calculations.

3. Making it weather and dust proof and taking care of possible short circuits.

Evaluation

It will be tested at lab by turning the disc by manually turning the speedometer cable. Further, it will be installed and tested on the motorcycle.