Stupid mini-christmas tree idea. Choosing the right components. Or trashing it

[Moriambar]

Hi.

I was just wondering about creating a small circuit as a gift for some friends of mine: a triangle made of 0805 LEDs (I was thinking about 15 of them) arranged alternating rows of green ones and red/yellow ones. I was thinking about powering them with about 10mA each.

The first problem arises, though, because I have no frame of reference for the mcd of a single LED, so I really cannot say whether those are bright or not (eg. a jellybean 5mm green LED is how many mcd usually?).

This was not the worst part, though, because I was thinking about making the red/yellow rows light intermittently via a 555 timer (which is not a problem), but which will increase my battery consumption.

Originally I was thinking about powering everything through a Cr2450 battery, via a smd holder: all of the non-led components would go one side of the board, and the led are mounted on the opposite side. I was thinking about coin cell because they're quite compact and thus my tree would be really small, but I don't know whether the battery can hold all of the power consumption (I mean it's around 150mA + the 555 consumption, way above the 0.3mA for which these are rated).

So I guess my question is: is my project feasible? Should I just make it bigger in order to accommodate 2 standard aa batteries, instead? (I think I would need more LEDs then, though)

Thanks for reading this.
Cheers

[Gyro]

10mA sounds quite high for modern smd LEDs, you ought to be able to get reasonable light out at around 1mA. Being point sources makes them look brighter. The other thing is to use the CMOS variant of the 555, not the bipolar one - supply current is much lower.

Regarding supply, you need it to be higher than 3V for the 555 to operate (I can't remember the minimum supply of the CMOS ones off hand*) - an alternative might be to make something with 74HC logic.

Current consumption of the LEDs is much lower if you can arrange them in short series chains - if in parallel then you may need to allow individual current limiting resistors, which wastes power. You may want to look at a 9V battery for your application (physically smaller than two AAs anyway).


EDIT: * My mistake, the LMC555 will operate down to 1.5V

[Moriambar]

Thanks

[girts]

5 volts from MicroUSB.
This allows to use any phone charger or powerbank.