Electronic Valentine Heart: LEDs are red my dear（3）

Published:2011/7/31 22:20:00 Author:Li xiao na From:SeekIC

Design by F. Wolling

Printed circuit board and construction

The printed circuit board designed for the project is single-sided. The 3-mm holes in it enables the LED faces to be seen from the front side. For this to work the LEDs have to be inserted from the solder side of the board, their terminals being cut, bent and then soldered to the copper pads on the board. The other three parts in the circuit (battery holder. resistor and a 3-way SIL pinheader) are soldered in SMD fashion to the track side of the board. The battery holder is actually the only SMD component. Instead of the soldered battery holder you may, of course, use a separate holder (for example, containing two AA cells) and connect it to the board via wires.

When soldering the LEDs onto the board, make sure you get their polarity right. As indicated in the
circuit diagram, the cathode is the shorter of the two wires. This (negative) connection is marked by the bar in the diode symbol.

Our prototype is switched on by relocating a jumper on the 3-way SIL pinheader. For a more sophisticated approach to on/off switching, a miniature slide switch is recommended.

Finally

If you have been wondering all the time why the Electronic Valentine Heart does not blink just like most other LED ornaments, brooches and trinkets, well, it happens to be Unusual Aspect no. 5. There’s nothing to stop you making the LEDs blink, though, just consider borrowing the flip-flop element from our ’LED Christmas Decoration’ (December 2003).

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