The Lamp is a portable object which communicates with the satellites in order to find important (or not) places in the world, and then shine a light.
Pretty simple. But the details are important.
The important part of the above sentence is the concept of portability. I can’t tether the lamp to mains power, or require a giant car battery.
Of all the limitations this project has, is the battery. Right now I’m specifying a 3.7v 2000mAh Lithium Ion Battery with an alternate being the 3.7V 6600mAh Lithium Ion Battery Pack, and connecting it to the system through an Adafruit PowerBoost 500 rechargeable 5V power shield. I guess I could design my own charging system, but lithium-ion batteries scare me. They pack a lot of power per cubic centimeter, but don’t play well with others, tending to melt or blow up if they are shorted, bent, crushed or punctured. So, I will have to create a cage for it so it doesn’t hurt me.
Let’s look at what the system draws without lighting the lamp at all:
So I have 2,000 mAh at worst case battery to play with, but let’s assume a 10% reduction due to recharging, storage loss, etc. This gives me 1,800 mAh to work with. I also am assuming worst-case scenario where the lamp is fully lit (for example at a center of population). In reality, most of the time all the LED’s will be lit. I’m sure there I can use calculus to find the slope and areas of illumination to derive the typical power consumption.
|Item||1 hr ops||2hr ops||3hr ops||4hr ops|
|Lamp power remaining||1689.89||1579.78||1469.67||1359.56|
|WS2812 LED @ 60mA|
|28 lamps||26 lamps||24 lamps||22 lamps|
|Luminous Intensity @ 233 (mcd)3||6524 mcd||6058 mcd||5592 mcd||5126 mcd|
|84 lamps||78 lamps||73 lamps||67 lamps|
|Luminous Intensity @ 600 (mcd)3||50400 mcd||46800 mcd||43800 mcd||40200 mcd|
Besides the total power available, the real limiting factor of the battery is the standard discharge of 500mA which can peak at 1000mA. I don’t want to go toward peaking, because see exploding, above.
I have some options: I could source alternative batteries, use multiple batteries to run different systems or parts of systems, or find a better illumination system so I can get the maximum luminance per mA.