UPDATE: Work has indeed started on the (near) IR version of this tool. Details on the AF Assistant IR 1.0 (in early development stages) can be found here.
Right from the get go, i wasn’t the happiest with the v3.0 design (see v3.0 link for details of why I built this, and previous version history) of the AF assistant. The main concern i had with it was the sloppiness of the case, and the extra cables that were required (which some of you commented about on the hack-a-day post).
So I did some searching around at local electronics shops and came across a small case that has a battery compartment for one AA battery. Digikey also sells a version of the case in black, which I will grab for the next upgrade. Much sleeker then cream colored on a black camera, though more expensive then the $0.25 I paid for the cream colored cases.
About the same time, i received an order from DealExtreme for some line lasers i had ordered some time ago. So I put together a circuit based on the v3.0 design (plugs in the side of the camera in the remote trigger port) and i have added a dc-dc boost voltage regulator that takes any voltage (0.7volts and higher) and turns it into a constant 3.3volts (based on suggestions from the hack-a-day post comments). This is perfect since that means that regardless of what battery i use, (1.5v alkaline or 1.2v NiMH rechargeable battery) i can get a constant voltage to drive the line laser.
I whipped together a circuit and mounted it inside the small case. But this alone still meant a mess of extra cables. So i added a pass-through ETTL hot shoe connectors, so that I can slide my PW Flex TT1 on top of the AF assistant, and be good to go.
The line laser was aligned vertically, and lined up with the lens, which means that the center focus point (and in landscape mode, the top and bottom AF points get to use the laser line to focus) always has a contrasting line to use to focus on regardless of the subject to camera distance.
The grey ribbon cable is the E-TTL passthgouth connection. For the hotshoe, I took apart a Yongnuo ETTL Extension Cord and cannibalized the end that sits on the camera. That end has a pass-through. Took that case apart, and used on half of the case on top of my project box, and the other half on the bottom of the box.
There is no electrical connection between the camera hotshoe and my circuit. My circuit is purely driven by the remote shutter release side port on the camera.
The battery voltage first gets boosted to 3.3V then an op-amp senses the camera voltage and switches a transistor on or off to enable the laser module.
The DC-DC booster circuit is built around the MAX756 IC, which will boost any voltage above 0.7Volts up to either 3.3V or 5V. I choose 3.3V since my laser modules were made for 3V. The battery
The switching of the LED on and off is handled by the same op-amp as in the v3.0 design (the low voltage op-amp NJU7016D), though, a low voltage op-amp is not required (I only used it since it was available); I could have used any other general purpose op-amp that runs on 3V (most do) like a LM358, since the voltage it will see is a regulated 3.3V. The op-amp switches a regular PNP transistor (I used a generic 2N3906) which will conduct when the op-amp input drops to a low state. When the op-amp input goes high, the transistor does not conduct.
The laser is switched off during image capture (full shutter press). This is accomplished by using the ‘shutdown’ pin of the MAX756 IC. When that pin (pin 1) goes to ground, the IC does not boost the voltage, and since the laser does not run at 1.2V or 1.5V, it essentially turns off. The shutter release port’s 3rd pin (the full shutter press) normally has 3.3V on it, which when applied to pin1 of the MAX756, enables it’s operation. When the shutter is fully pressed, that same pin goes to ground, turning off the laser.
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