by Many times, I had given a thought about the societal usefulness of my projects and seriously pondered upon an opportunity to implement one. The opportunity came in the form of “Texas Instruments’ Analog Design Contest ” in 2011. The contest required us to design a project of our wish which employs atleast three of Texas Instruments ICs. Another mouthwatering offer was, we were allowed to order any Evaluation kit/module from TI which costs below $200.
Unable to resist the urge, I applied for the contest and cleared PHASE 1, which required us to design an Instrumentation amplifier and analyze their parameters. It was then the proposed project as mentioned in the title began.
GOAL:
The goal was to design a module which can be worn on the head similar to a tiara that helps the
differently abled person to control a computer just by tilting their heads and emulating a mouse
with voice commands. The inputs to the module were as follows.
- Head Gestures, which are angles of tilt with respect to x and y axis in space parallel to ground
- Voice commands “CLICK” and “RIGHT CLICK”
The computer has to be wirelessly controlled based on the above inputs; the module acts as a voice
and gesture controlled wireless mouse attached to the user’s head.
Components Required:
- MSP430G2452 -16 bit microcontroller
- LM741
- REG710-5 Boost Converter
- TLC555 timer
- MMA6361 -Freescale 2-axis accelerometer
- TSOP1738 – Infrared Sensor
- Microphone
- Single sided Copper circuit board*, FeCl3 solution, masks and gloves
- Miscellaneous – Surface mounted Resistors, Capacitors, headers, battery
PCB was etched at my room so didn’t cost much except for the fact that I spoiled my roommate’s cot with ferric chloride. 😀
HARDWARE:
The important modules of this project are:
- 2-axis accelerometer MMA6361
- Wireless IR transmitter
- The Main circuitry with MSP430G2452 and other chips
- Wireless IR receiver connected to virtual com port of PC
SCHEMATIC:
BOOST CONVERTER:
The boost converter chip REG710-5 is used to boost up the input 3.6v to 5V and is used to supply the microphone amplifier.
The boost converter chip REG710-5 is used to boost up the input 3.6v to 5V and is used to supply the microphone amplifier.
TILT SENSOR:
The accelerometer used is MMA6361, which is a 2-axis accelerometer from freescale. The accelerometer is used to decode the orientation of the head in x-axis and y-axis with reference to ground level.
MICROPHONE AMPLIFYING UNIT:
It has a simple electric microphone whose output electric signals are fed to the operational amplifier LM741 whose output is fed to the microcontroller.
MSP430G2452:
This is the low power 16 bit microcontroller which acts as the brain of the head gear that processes the data from the accelerometer and from the microphone amplifier and controls the Infra-Red transmitter.
TLC555 TIMER:
It is a low power timer chip used in astable mode to provide a square wave of approximately 41Khz frequency. This timer controls the Infrared LED which transmits the data to the PC.
The transmitter designed using timer IC and IR LEDS:
RECEIVER:
The receiver is a creative and yet simple design. Most IR receivers are powered externally while this is powered by serial port itself. Referring the specifications, it was found that thevirtual comport can supply around 30mA at 5V. That was sufficient for us to power the circuitry. And I have used a cheap transistor BC547 for shifting the level instead of pricey level shifter chips like max232. This transistor acts as inverter and shifts the voltage level received. This is possible since we have used a external USB-Serial port cable which doesn’t emulate true serial port voltage levels which are +12V to -12V. The voltages were very low and were below the safer limits that the transistor can withstand. This not only saved the pcb space but also the cost.
The tiny cheap wireless receiver which I made:
MAIN CIRCUIT BOARD:
The circuit was hand drawn using a permanent marker pen and etched in room at the hands of an amateur (that’s me ! ). So please disregard the non-uniformity in the traces. The circuit was tested and it works like a charm.
FINAL PROJECT :
This is how it looked after assembling the individual modules together:
The microphone amplifier circuitry is not shown here in the picture.
RESULTS:
The various stages where the functionality of the project is tested.
This project was an excellent learning experience for me since I had to implement about low-pass filters to avoid noisy data and also to learn control systems to keep the mouse pointer stable with significant accuracy.
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