The author of Instructables under the nickname Jocobs ordered for his homemade several printed circuit boards, and I thought, why not add additional circuit boards to the order, which will serve as postcards for relatives and friends. After all, there are business cards, why not card cards?
He decided to order boards at JLCPCB, where the most favorable tariff is obtained with sizes less than 100x100 mm. There are no square cards, it’s not Polaroid or Instagram, so the master chose the dimensions 100x70 mm and drew a vertical Christmas tree.
In Eagle, he created a new single-output component, the platform under which is just a circle. In fact, there will be no component there, this is a drawn ball on a painted Christmas tree. There will also be real LEDs on the board, as if the Christmas tree is decorated not only with balls, but also with a garland. Jocobs is used to using Eagle networks, so he connected all the LEDs in parallel to a subnet called VLED. Next to each of the LEDs, he placed a ball. He took one common resistor for all parallel LEDs, it is undesirable to do this, but if they are all the same, then it is possible. Through it, he connected them to a VCC power source. He connected the same balls that are not connected with LEDs in pairs. Under the tree, he placed an inscription in hexadecimal code, which when translated into ASCII reads as Happy X-mas.
This is the scheme:
And such is the board:
And it is on the reverse side, in order to parallelize all common conductors, it took one large polygon:
The master chose low-power red output LEDs with a diameter of 3 mm. The voltage drop on this LED is 1.8 V at a current of 2 mA. Unlike white ones, red LEDs, although less effective, continue to glow when the battery is depleted more deeply. The master also ordered the 2032 SMD battery holder, but then changed his mind in favor of the 2450 battery, which is rare but has a capacity of 620 mAh. With 13 LEDs, the current will be 26 mA, which means that such a capacity is enough for almost a day of continuous illumination. And it is unlikely that the recipient will leave the card turned on for a day.If you turn on for five minutes every day ... count yourself.
If the supply voltage is 3 V, and the voltage drop across the parallel LEDs is 1.8 V, then the resistor will have 1.2 V. To get a current of 26 mA, you need a 46 Ohm resistor, the closest from the standard range is 47.
Postcard is ready:
You want the same - here are the files boards and schemes. Only Jocobs asks not to repeat some of his mistakes. Do not screen printed conductors, let it be seen that they are metal. Instead, draw a silkscreen outline of the Christmas tree. You can also cut the board along this circuit. In order not to short circuit the power source, do not place the board on conductive surfaces, remove the battery only with dielectric objects, and store it in a dielectric package.