Results & User guide

High Level Design
Results & User guide
Useful Links
A 2nd Try
Source Code

On this page are

Pictures of the final product

The video overlay device and the remote climate sensor.

Screen shots

Some of the later work was done using a B/W television hence the lack of color in the screen shots.

Device in operation, left without user comments, right, with user comments.
Help screen Reference voltage values

Device internals

Temperature and pressure sensor circuit.

Climate sensor box. Microcontroller and STV5730A video overlay IC. Underside of the board on left.

User guide

The device requires a 5V D.C. power source to be connected either via the power jack or the 5V and GND bannana posts.

Make sure that the keyboard is plugged in before powering the device.

The time must always be reentered when power is restored. Press t to enter the time and date.

To read the help screen, press F1 when the device is not prompting the user for input.

Keys Function
F1 Shows help screen. Press any key to return to main screen.
F2 Displays text in buffer on screen
F3 Hides the text on screen (Other than time, pressure, temp and ADC outputs)
e Enters edit text buffer mode
c Deletes the contents of the text buffer
v Overlay mode (Use when there is a NTSC video signal on the video input port)
f Self generated NTSC mode (Use when no NTSC video is input to the device)
r Set reference voltages( AREF and MPX Vsupply). For calibrating the ADC and Pressure sensor voltage conversions. The reference voltages are stored in non-volatile eeprom.

AREF: reference voltage on the Atmel ADC

MPX Vsupply: Power supply voltage of the pressure sensor, this should be measured at the remote sensor on the power supply pin of the INA121 differential amplifier.

d Show reference voltages.


Refresh rate of the device is NTSC standard at 60 Hz when running, the image is very stable and without any flicker. The text displayed is slightly translucent, with the background image showing through the white parts of the text. The degree of translucency can be varied by adjusting the potentiometer on the main board.

The ADC readings are updated at 60Hz, and have a range of 5.08 - 0V depending on the actual voltage of the 5V power supply.

The accuracy of the pressure sensor is about +- 3 mmHg. This could be improved using either a larger power supply for the sensor or a software lowpass filter on the ADC input for the sensor.

The temperature sensor is very accurate, measuring with up to .25 degree Celsius accuracy.

The system clock is accurate to 30 seconds per day.

A built in calendar updates the date according to the month of the year. Leap years are supported by the device.

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 Copyright 2002, Use the information on these pages at your own risk.
For problems or questions regarding this web contact Zhi-Hern Loh.
Last updated: 11/11/02.