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AT89S52 powered digital clock/thermometer with alarm

All > Tech > Hacks/Mods > Gadgets > AT89S52 powered digital clock/thermometer with alarm by seemanta

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This is a simple digital clock/thermometer which I made using an AT89S52 sometime back for my sister for her Birthday. I have also used a Dallas DS12C887 along with the AT89S52 micro.

Features include:
1. Fully realtime - Time is maintained even when turned off(within the accuracy specified by Dallas Semiconductors)
2. Daily/Hourly Alarm
3. Ambient temperature display.
4. Customizable display(User can control whether he wants both time and temperature, only temperature,only time display or neither time nor temperature to be displayed).This is achieved via a very simple DIP interface.
5. Integrated backlight and contrast control for the LCD.
6. Daily/Hourly alarms can be turned ON/OFF independently of each other using the DIP interface.
7. Good user friendly 'Text Interface' to set the time and alarm ;-)

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I had made a working prototype before plunging neck deep into making the actual thing.
This working prototype has been made with a simple 8052 development board and my own board which
has all the components necessary for the clock.

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With the prototype done, I gathered every component before I started out with building the actual thing. Looks intimidating, eh ?

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This is the original circuit schematic diagram which I had done on paper before getting on with it.
Since I had used a general purpose pre-drilled PCB for the final thing, I did not go into trouble of making a 'proper' PCB with eagle or something.

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I had just put on the ZIF socket here. I preferred to use a ZIF socket because I still had to use the development board to program the AT89S52 IC. Using a ZIF socket meant longer lifetime for my AT89S52.
(I remember damaging a few ICs by trying to pull them from an IC socket)

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With some more progress in making the circuits. The biggest challenge was to effectively pack the whole system onto the board in a way that it was convenient for me to bring out wires to the outside 'cover' where all the switches/display were located.

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Here you can see the outer cover with its switches outfitted. I wanted the design to be very clean and did not want my sister to call me each time she needed to replace the batteries. They way I made it was to envision the whole thing into 3 layers:

Layer 0 (bottom) : Batteries and power switch
Layer 1 (middle) : The main board with all the circuitry and interconnections between individual components
Layer 3 (top) : The user interface with all the controls like contrast control, back light, DIP interface etc.

Each layer had to be connected to the next layer only at predefined points and these had to be snap-on contact points. So that if desired, each layer could be disassembled separately and taken out of the box. This also facilitated replacing batteries and repairing the clock in case of any problems.

This feat took a lot of patience and clever soldering to achieve. Basically, I brought out every external connection to layers above and below to the edges of the main board. And used snap on connectors there. That needed numerous drawings and re-drawings, not to mention extra care so that I do not mess up the connections. That's where color coding my connecting wires came in handy.

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Finally!! After completion, this is how it looked like. Making this clock was a very profound experience for me. Firstly, I wanted to build something with my own hands and gift it to my sister.

Secondly, I learned a lot of things when doing it :-)

Overall, I was very happy that I undertook this project and finished it on time to be able to gift it to her exactly on her Birthday! It took about 2 months (I know...I am a lazy bum) right from the conception of the idea to finally realize it(taking into account my day time job as a software engineer ;-) )

Here is a video of this clock on YouTube at: http://www.youtube.com/watch?v=PYa9IwQrN_o

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