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Diamond necklace


Task

Controlling LED diamond necklace for theatrical spectacle. Control channels - 3, extendable to 6, "diamonds" should shine in darkness changing brightness randomly, but keep minimum brightness and does not fading out at all.

Technical solution

Arduino Duemilanove with Atmega168 microcontroller onboard is used for drive controlling device.

"Diamods" composed of blue, green and red 12 V LED strips. Each channel is controlled by Arduino PWM outputs through transistor keys.
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Schematic


Arduino microcontroller generates PWM signals on the outputs, and each transistor is switching one of LED strips.

The device is supplied from 2700 mAh 1.2 V NiCd rechargeable cells (8 pcs to gain 9.6 V, enough voltage for 7805 regulator on Arduino board). This voltage is low for 12 V LED strip, but LEDs are still working.

No external power supply is required for LED strips.

BC847 transistors are used as keys. These can be replaced with 2N7002 n-FET transistors. During exploitation, no heating were detected on transistors.

If more than 1 m of LED strip is connected to channel (power over 14 W per channel), TIP122 transistors required. More than 2 m of strips require heat sinks to be mounted on transistors.


Design

The battery cells are housed in rack base due to stationary position of necklace.

LEDs are connected with control block through 4-wire line 2 m of length. Top cover is removable for cells replacement or repair. This cover is mounted on screws.

Assembled without errors, the device should working without any tuning.

Algorithm and Arduino sketch

Main loop waits random time from 200 to 800 ms and then set random level of PWM from 10 to 48 on each channel.

Brightness to PWM level translation happens in logarithmic law, placed in array. This array was taken from Arduino - Physical Computing für Bustler, Designer & Geeks (Manuel Odendahl, Julian Finn, Alex Wengler).

The sketch have customizable parameters: change speed (tmax and tmin time) and brightness range (lmax and lmin levels).

Arduino sketch
Download Arduino sketch - diamond.ino

PostScriptum
Necklace would look more showily if 3-5 mm LEDs with 180 degrees field of light will be used. LEDs can be placed in symmetrical patterns, geometrical shapes, flowers, etc.

Number of channels are extendable to 6, or to 7 on Arduino Leonardo and to 17 on Arduino Mega. For advanced channel extension on Atmega168 or 328 processors see "16-channel DMX dimmer" project.

Also, by using some multiplication coefficient, fade effects can be added to this project.

Links

 

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