Simple, No Code Lightning Trigger/Flash Slave Trigger From Cheap Sensor

In the downtime between storm seasons here in Australia I've been building an Arduino based lightning/flash trigger.  Its been a fun time experimenting with code and different tech. I ordered some light sensors from eBay to have a play with and work out a nice system to add delays and various other sensors.

The sensors I ordered are a fairly simple circuit based on an LM393 comparator IC.  The trimpot adjusts the sensitivity and when it detects light, it drops the output voltage to the Arduino to signal a triggered event.  I liked it for the Arduino because it helps simplify coding and allows a more modular approach to expand on.  While experimenting on it, I relised that a basic trigger could be made out of it, and an Arduino isn't necessary for basic operation.

This Instructable doesn't need an Arduino, its a relatively quick and cheap hack to make the sensor trigger an Opto Coupler and therefor, trigger a camera or a flash.  The opto coupler isolates either the camera or the flash from the board, meaning you can use some older flashes without fear of blowing up the trigger.

I'm using the SMD LED on the board to trigger the Opto Coupler.  While I was hacking it, I thought I'd prefer a bigger LED to replace the SMD one, so I wired it in between the pot and the opto.

You can watch the build video, including early tests here:

All the images used in in the instructable are screen caps of the video.

Cost for the project without a case or batteries is approximately  $10.  Thats pretty cheap for a lightning trigger.

Parts List:
* Light Sensor - eBay http://www.ebay.com.au/itm/181091463800 ($10 for 5 or you can find it for $4 each)
* NEC 2501 Opto Coupler - eBay or any well stocked electronics supplier ($2)
* 3 - 5 volt battery
* Hook-Up Wire
* LED ($0.20)
* 10k Potentiometer ($1.50)
* 2.5mm male stereo jack (Canon) ($1.50)

Tools:
Soldering Iron
Solder
Wire Snips

You should have some basic soldering skills and some sense of problem solving simple electronics.  I'm no electrical engineer, far from it, I'm just a tinkerer having fun and sharing along the way.

Step 1: Remove SMD LED and Trimpot

The trimpot will come off by simply pushing and pulling at it.  Eventually the pins give way and snap.  The neat way would be to de-solder it but my soldering iron won't get hot enough to do lead free solder in any quantity and I'm still waiting for my new digital soldering station to arrive in the post.

Next, remove the SMD LED next to the label "D1".  Heat it on both sides and push with soldering iron.

Step 2: Trim the Down on the Opto Coupler

Trimming the legs down on the 2501 will help make sure it doesn't short out on nearby parts when soldered on to the board.

Step 3: Solder the Opto Coupler to the Board

Add some solder to all the pins of the opto coupler.

Pin 1 is the pin next to the dot on top of the chip.  Some chips have it printed and others have a little circular imprint.

Pin 1 is soldered closest to the D1 label on the board.

If you want to be doubly cautious, you could wrap it in heat shrink or lay some electrical tape under it.  I'll be encasing it in epoxy or plastic at some point, so I left it as is.

Step 4: Prep for the New Potentiometer

Add some solder to the broken pins from the trimpot.  I've soldered pots straight onto those pins, this time I wired it on.  We'll wire in the pot a bit later on.

Step 5: Add LED

Solder the positve terminal of the LED to the positive pin for the potentiometer.  The negative is soldered to pin 2 of the opto coupler.

Step 6: Add Potentiometer

Now its time to add the potentiometer.

Most single gang pots can be wired up with thier pins facing away from D1, in order.  Some pots may be wired differently.

Step 7: Test Wiring of Your Jack

I have 3 canon cameras.  A 400D, 50D and 5D2.  I use the 400D as my test camera, the 400D uses a 2.5mm stereo headphone jack for its remote trigger.  The other 2 use canons proprietary jack (N3?).  I have an adapter cable I bought off eBay that has a female 2.5mm jack and an N3 plug on the other end.

I test the the jack wiring by plugging it in and use a single wire to test the pins.  One end of the wire on ground and the other tests the left and right signals of the jack.  One will be focus and the other is shutter.  From memory, the right side (generally a red wire) is shutter.

For lightning, there is no need for focus as it acts too slow and you must use manual focus, so there is no need to wire it up.

Step 8: Wire Up the Jack

Solder the jack with two wires and the other ends of those to the opto coupler.  There's no need to worry about which way to wire them as it acts like a simple button or short.

Step 9: Battery

Solder your battery terminals/wiring to the board.

The top of the board has "-" and "+" labels on them to guide you.  You could also use a plug on the pins that are available on the top of the board, I chose to solder wires directly to the bottom.

I've tested CR2025 coin batteries and they last a good 12 hours+ running non stop with 500 Shots over that time.  I've also tested mini rechargeable lithiums from a toy quadcopter with success as well.  Anything that pushes out 3.3 - 5 volts is fine.

Step 10: You're Done - Go and Test

And thats it, once you put batteries in, it should be up and running.  Turn the Pot until the LED lights up, then turn it back slowly till it turns off.  The LED signals that the LM393 is triggering the opto coupler.

Some other mods I've done with this board are changing the Light Dependent Resistor (LDR) and replacing it with a Photodiode.  It should also work with IR based diode receiver as well.

I'm also considering adding in a pre-amplified Mic so it can be a sound trigger.

Now, go and put it in a nice case or box and take some lightning photos. :)