/ / Programmable LED

This is a tiny blinking device. The blinking sequence can be reprogrammed with the use of a flash light. It detects changes in lighting and records these changes and finally plays them back.


The LDR (Light Dependent Resistor) is used as input sensor to detect the light changes. It is attached to an ADC (Analog Digital Converter) port of the microcontroller. If the controller detects short light changes (dark, bright, dark or the other way round) it switches into recording mode. It records up to 10 seconds with 40 samples per second. Then it switches back to playback mode and plays the recorded sequence.

Parts and Tools

parts


• ATtiny13v, microcontroller, 1024 bytes flash memory, 64 bytes RAM, preprogrammed
• Resistor, 1k (brown, black, black, brown, brown)
• Resistor, 10k (brown, black, black, red, brown)
• Low power LED, 2mA, red or green
• LDR, photocell
• Coin cell, 3V, 220mAh, CR2032
• Paperclip

The follwing tools are needed:

• Soldering iron and solder
• Pliers
• Third hand

This circuit is built in, so called, free form. That means there is no PCB (Printed Circuit Board) involved. Components are soldered directly to each other. That can get a bit tricky but it will increase your patience. Also, note that you can not reprogram the controller, once you have soldered it.

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First bend the legs of the microcontroller gently up.

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Bent them in a way, that the controller lays flat on the surface.

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Then cut off unwanted pins. These are pin 1, 5 and 6. Or bend them a couple of times until they come off.

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Bend the LDR.

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Bend the resistors

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Cut the legs of the LDR to adjust the spacing between LDR and controller. Try to get the legs well aligned before you solder. Then solder the LDR to pin 2 and 3. The orientation of the LDR does not matter. Note that you should take care to not heat up the controller for too long as that will destroy it.

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Solder the 10k resistor to pin 3 and 4. Cut to desired length.

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Solder the 1k resistor to pin 7. Cut to length as well.

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Bend the LED

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Bend one leg of the resistor up.

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Solder the longer leg of the LED to the resistor. Cut off the extra part of the leg. Solder the shorter leg of the LED to pin 4 or the other resistor.

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Bend up the inner part of the paperclip.

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Next, after measuring with the coin cell, take the head of the paperclip and bend it up. The coin cell should fit tightly. You may have to bend it a while until it forms a good stand for the Programmable LED.

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Now solder the paperclip to pin 8 of the controller. That is the pin for power supply.

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Take a piece of wire or one of the cut off legs and solder it to pin 4 of the controller. That is the pin for ground. Adjust the length and form it to have a steady contact with the top of the coin cell.

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Insert the coin cell with positive side on the bottom. And … that’s it. Now you are ready to program it.

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Program it

When you insert the battery, the LED should flash 5 times. That’s a kind of hello. Next, it switches to programming mode, because it has no recorded sequence. Switching to programming mode is signalled with 5 fast flashes. Now you can record a 10 second sequence of light and dark before it switches to playback mode, signalled with 5 fast flashes as well.

You can re-enter the programming mode by giving it a short flash of half of a second. A flashlight works well or cover it with your hand to cast a shadow for half a second.

To program the chip before soldering navigate to liz_arum_classes:assignments:physical_programming:2009:leds:progled. Simply type make
make fuse
make flash.