Having finally gathered the correct bits and pieces, I’ve started putting circuits together. The basic circuit for an external time-lapse trigger is very simple and requires almost nothing more than the basic PICAXE 08M board with battery or DC power and a USB cable to connect to a CHDK-enabled camera.
If you wanted to make a very small external trigger box you could mount a coin-cell holder on the proto board and make a self-contained, battery-powered unit rather like the Gentles GentSTEREO box.
Interface circuitry to drive an infrared LED is no more than driving a normal LED but serial commands only operate on pin 0 of the PICAXE 08M, which is also used for programming the chip, so a switch needs to be included if re-programming is to be allowed.
My receiver set up doesn’t work yet and I need to check the rather clunky breadboard job I’ve constructed. I *think* I am very near to making and actual working pair of transmitter /receiver boxes. The circuitry is actually very simple and cheap to manufacture. Apart from the power supply, the Missing Link unit can be manufactured very small.
I am still having some problems with CHDK / PowerShot cameras. Using an external trigger allows autofocus lock (AFL) and autoexposure lock (AEL) to work but turning the screen off (in order to prolong the battery life) seems to exit both AFL and AEL. In which case I’m not much better off unless I use external batteries or mains power supplies.
After experimenting with an external battery box containing 3 x NIMH rechargeable batteries (3 x 1.2v = 3.6v) the camera complains and tells me to change the batteries. The stated power requirement is 3.15v. Does it really need to be that accurate? Well it appears so.
It turns out that when I test them, the NIMHs I have knock out over 1.3V each and I’m getting a little over 4.1V from 3 of them, not enough juice from 2 and too much from 3.
I built a simple voltage regulator circuit using the ubiquitous LM317 and information from National Semiconductor.
I’m getting 3.2V from my regulator but forgot the cannibalized connector cableso will have to let you know about that. I’d like to use large capacity external batteries so that I can get more life than from 2 high capacity AAs in situations where I don’t want or can’t use mains power. I’d like to make these as small as possible and hope to use a combination of pre-charged batteries and solar charging set-ups.
I bought a 2W “solar briefcase” from Maplin and they have some pre-built charge regulators which look good. It might be most efficient to assemble off-the-shelf parts rather than try to build such stuff. Maplin is great for convenience as it’s on the High Street, but sometime rather expensive. They also do a 13W version complete with a 3, 6 and 12 V charge regulator.
My favourite supplier by far is Bardwells on Abbeydale Road in Sheffield, and it’s an entertainment to go in there.