Last week I got frustrated and annoyed that I’d bought a whole bunch of older style dumb strobes and had used few of them because they lack the remote control niftiness of Nikon’s Creative Lighting System (CLS). Regular slave strobes pop attached flashes when they see the first of the many sent out by the Nikon CLS master. So, I pulled the trigger and ordered parts to make up to three “smart” slave triggers…
I considered using two good old 555 timers to create a delayed trigger to pop the dumb strobes but all the resistors and capacitors it would take to wire those up point to point was a major turn off. I wanted something simple and programmable, so I ordered the 8-pin PICAXE 08M2 microcontroller. It’s a Microchip part that has a BASIC interpreter burned into it. I chose it because the programming cable was simple and cheap, as was the device itself.
I already had a bunch of Infrared phototransistors I’d ordered a while back, so the only thing I really lacked was some NPN transistors, which I picked up at lunch today.
Here is the schematic:
I have not assigned any component values because I’ve only bench tested it, and only at close range that. I suspect R1 may need to be resized to make it more sensitive at greater distances.
Q1 is the phototransistor which forms a voltage divider with R1. C1 and R2 comprise a high pass filter that only lets the CLS master’s flashes through. (This portion of the circuit came from combing the many slave trigger schematics on the web over a long period of time, so I apologize for not having any specific attribution for this.)
Transistors Q2 and Q3 make up a wired AND that pops the dumb flash when Q1 sees a flash from the CLS master and when pin C.2 is high. For the older high voltage strobes, Q2 and Q3 will be connected to an opto-isolating triac.
The current code has flashes LED D1 as an indication that power is applied and that it is alive. Pin C.3 is set up as an interrupt input; when a flash is detected, it jumps to an interrupt service routine that waits a certain amount of time based on the setting of R4. When the delay period is up, pin C.2 is driven high, turning on Q2 for a short period of time. If a flash is detected when pin C.2 is high, both transistors turn on and the connected slave pops. (I can’t post the code at the moment because I don’t have access to it at the moment. I will blog on this more in the future and include the code then. Hit me up if you’d like it sooner.)
The current code turns on pin C.1 during the delay period. On the prototype, there is no LED connected – I had a scope connected so I could see the signal. In practice, R4 can be adjusted until LED D2 is no longer seen in an image, meaning the photo is being taken after the waiting period has expired. This allows for adjusting the delay since the pulse train in CLS is not fixed – it changes depending on what all is configured.
The proof that it works is in the pudding, though. It’s nice to see the signals on the scope but nothing is more satisfying as seeing the dumb slave pop when a real CLS remote would. Here is the photographic proof which includes the prototype itself:
I’d like to make a PCB, but unless I build a bunch of these, it’s probably not worth it. Nor is it worth it to draw up and etch boards myself – I don’t like using the ferric chloride etchant anymore and it’s hard to step back to funky homemade boards after having had real ones made… (Maybe there is a market for kitted up/assembled versions, in which case making a board would make sense.)
I still need to box it up so it’s not so fragile and figure out how I want to power these. I have a bunch of button cells but I’m not sure how long they’ll last even if I turn off or disconnect the LEDs.