Not long ago, I posted an article about how to modify a cheap eBay wireless flash trigger to make poor man’s RadioPopper PX. At that time, I tested the modified transmitter and receiver and found that they worked reasonably well. However the entire system was not practical because all I had were the exposed circuit boards with exposed parts and dangling wires. In order to evaluate them for real world applications, I managed to re-solder the parts and put them in the original enclosures. There is enough space inside the original enclosure to hold the parts.

For the receivers, I took out the original PC sync port and fitted the IR LED there as shown in the following photo (left: unmodified, right: modified). I used Velcro with sticky back to attach the receiver to flashes so the IR LED is facing the IR sensor window on the side of the Nikon SpeedLight flash.

DIY RadioPopper

This is how it looks when mounted on a Nikon SB-800.

DIY RadioPopper

For the transmitter, I removed the 2-bit DIP switches that was for channel selection and placed the photodiode there (the small black square in the photo below). Instead of the original BPW34 photodiode, I switched to a BPW34FA (DigiKey Part #: 475-1072). This one has the same size as BPW34 but comes with an IR filter so it is only sensitive to infrared light. I also added a piece of wire for a better antenna but it is not essential part of this DIY.

DIY RadioPopper

The transmitter had to be placed about two feet or more away from the wireless master unit if the photodiode faces the wireless master directly. The reason is that the photodiode can be saturated due to strong signal then the pulses are distorted. The easiest way to mount the transmitter is to use Velcro to attach it to the top of the lens hood. I needed to adjust the angle of the transmitter relative to the popup flash so the photodiode receives proper amount of light. The cell phone photo below shows you the idea.

Another important note is to prevent the pulses from master from entering the flash directly. This causes ghost signals that can confuse the flash. For SB-800, the light can somehow gets to the sensor through the red front panel when I test the setup indoors.

Basically it worked but the maximum range I could get was about 30 feet. Once this range is exceeded, I started to see some reliability problems. So it is not very attractive if you can get the Nikon CLS AWL working directly (max 33 feet or 10 meters in the front position, 16-23 ft or 5-7 meters at both sides ). This can still be helpful if the light path is blocked or the flash is placed out of the typical 60 degree angles in front of the master unit (required by Nikon CLS AWL). Another approach is to modify the antenna on the receiver to extend the range. I have not had a chance to try it but based on what I saw the range could be greatly increased.

Noise was a big concern since the receiver has no way of validating the data. I have seen the flash with the DIY receiver attached fire occasionally without trigger, most likely due to random noise. However it is not very often. The CSL AWL system does expect the pulses come at precise timing. The random noise will have very little chance to line up perfectly with the expectations of the AWL protocol. At the Polish Nikon user forum where the whole idea was started, the guys are hacking a set of commercially available RF transmitter/receiver modules in order to create a DIY RadioPopper that runs on the less crowded 868MHz band.

Posted in: DIY Photography on May 28th, 2010. Trackback URI
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