20/01: Perfect weather for Solar Powered Digital Signage
A really interesting project has come our way - can't say too much about it at the moment, but it involves solar power. It sounds odd, but the middle of January is actually the perfect time to be testing solar systems. If it all works now, then it'll definitely work in the middle of summer!
The solar power side is actually the easiest part, we've got a small 18W panel with a big battery and a big 60W panel with a small battery just to see which combination works best in pseudo-real world tests. We're sticking with lead acid batteries purely from the ease of use point of view - they're much easier to charge and look after than lithium batteries and weight isn't really an issue for this project.
On the signage side, we're doing initial tests using Point Four DecisionVision screens (which run MediaCAT software) . Although designed for shelf edge and point-of-sale advertising in convenience stores, petrol stations and other retail outlets, they're also very low-power embedded machines - perfect for solar powered digital signage.
The project doesn't need the screens running all the time, PIR sensors will be used to detect when people are present, so that the screens can sleep the rest of the time. We'll be testing out several different ways of putting the hardware to sleep - ranging from full shutdown, to powering down as much of the system as possible and idling the CPU. A slightly higher quiescent power consumption may be acceptable if it means the screen can wake up a bit quicker.
Another thing we'll be looking at is using OLED screens instead of LCD screens. LCD screens always have a back light lit across the entire back surface of the screen, even if you're only showing content on one part of it, so their power consumption is pretty constant. OLED screens on the other hand, only emit light where it is required by the content, so a black screen should draw very little power.
This should allow us to only display content on a small part of the screen when in sleep mode to keep power usage down, but then instantly light up the rest of the screen with extra content when we detect someone walking past. An OLED screen should be a lot brighter than an LCD screen too, which is a must for outdoor usage!
OLED screens have been troubled by costs, poor lifetimes (especially the blue LEDs) and available sizes in the past. However, the latest models have apparently overcome these issues, so you can expect to see them becoming very common in Digital Signage over the next few years. We have a prototype 10 inch screen on its way to us right now - providing Apple hasn't used them all - once we've got it, we'll put it through its paces and compare it with traditional LCD screens both indoors and outdoors.
