EasyCam – low cost, solar powered timelapse camera system
Update: Project photos here
In addition to the field and greenhouse versions of the Gigavision camera, we just started development on another camera system for Borevitz Lab. The goal is to create a low-cost, solar powered timelapse system using relatively cheap Canon powershot cameras running the CHDK firmware scripting tools. Justin will have a team of undergrads out in the Dunes this summer that can collect data, so we were thinking it would be great to be able to stick out a bunch of smaller cameras to collect timelapse data around the field site in the Dunes. Since the students will be going out there weekly, the cameras don’t have to be rock solid, they just have to mostly work.
Target System Specs
- Low power: 10w, 12v solar panel (or smaller)
- Frame rate: 12 images an hour, ~200 per day (One image every five minutes, +/-16hrs a day)
- Time-range: Sunrise to Sunset.
- Image Resolution: 12MP or greater
- Small and low profile
- The area where the cameras will be installed is public and so the cameras need to hide easily out of site. This means a small housing and as small a solar panel as possible.
The solar panel and batteries will need to generate and store enough power to run the camera for a full day plus a couple more days to make up for any rain days. My ballpark estimate for power generation is about 2Ah/day. This is based on a couple of guesses… 1st, the 1Ah battery packs are listed as being able to shoot about 300-700 images.
Estimates of images per charge seem to vary. Canon says 2-300 or so but some of the NB-4l batteries advertised on Amazon say 700. I’m guessing the high end estimates are for with the viewfinder off which is fine for our application. So lets assume 500 pics per 1AH battery. If we assume the battery is only half discharged before it is done then the camera uses about 500mA per 500 pics or 1mA per pic.
I haven’t had a chance to test how much resting power the camera uses, so lets round the power usage per pic by 1.5 to 2.5maH per pic.
Assume 200 pictures per day (1 picture every 5 minutes for 16 hrs a day in the summer). So we need at least 2.5mA * 200 = 500mA per day. I’d guess this was a low end estimate since I seem to remember running my Canon DSLR shooting timelapse all day and it only got about 4-5 hours on a battery, although it has higher power requirements.
A 10w,12v panel will produce 10/12 = 833mAH in full sun for each hour there is full sun. So 10w is probably a reasonable size for the panel if we only need 500mA – 1Ah of power per day.
Since the camera only needs around 3.5 – 4.2v input, I settled on this lead-acid battery for the first battery:
Unless I can find a nice low voltage charge controller that has a timer on it, I’ll probably eliminate the charge controller all together and so using a lead acid (LA) battery give us more leeway in designing the system. LA batteries can handle a lot of abuse and overcharging and should be fine for this application since we don’t have any weight requirements.
The Powershots cameras typically take an AC power adapter system that costs about $35 to $$50 and comes with an AC plug and a hollow battery coupler that fits in the camera to replace the battery. For DSLR cameras, you can buy just the battery coupler if you want to run the system on DC power or an external battery, but for the powershot cameras there doesn’t seem to be any way to buy just the hollow battery. This means you have to pay $40+ just to get a cheap piece of plastic and then throw out the AC adapter part since it isn’t any use for this system. In the interest of the DIY spirit, we tried building a fake battery adapter and it was pretty easy to do. It doesn’t look particularly high-tech but it is solid and works great.
Instructions and pics of prototype are here:
Ideally the system will wake up in the morning at first light and shut off at night when the sun goes down. For now it seems easier to just have the camera on all day rather than to wake it up and shut it down every 5 minutes. Also, based on my limited research I have yet to see an off-the-shelf 12v timer system that can be set to turn power off and on every 5 minutes for a whole day. Also, it seems like power cycling the camera 200 times a day would add a lot more wear and tear than just leaving it on, particularly since the power requirements are probably low enough that it won’t matter much if we leave it on.
I haven’t finished researching this part of the system yet. Currently I’m looking at the DC-DC-USB system that is a power switch that can be set using a USB connection. There are also any number of charge controller designed primarily for turning lights off an on that may be suitable. The DCDC-USB has a min voltage output of 5v so this may be an issue if we are using a 4v battery, although there is a comparable 6v battery we could easily upgrade to. The 6v battery is somewhat bigger though so it would be nice to go with the smaller battery.
There are a lot of options for cameras, but since CHDK development relies on someone deciding taking the time to hack the firmware for whatever new cameras comes out, there a bit of a timelag between Canon releasing a new camera and when (if ever) CHDK is available for it. Because I’m shooting for both low cost and a minimum resolution of 12MP, this limits the available cameras significantly because only the most recent set of the sub-$300 range Powershots have 12MP. For higher end ($300 – $400) cameras, the SX200 IS and the G11 both have CHDKs in beta, and the SD990 has an established CHDK. For sub-$300, the only camera available that does 12MP and has a CHDK is the SD950 which ranges in price from $220 – $350 depending on what’s available and whose selling it.
more to come…Follow @timescience