You might have noticed the Slaveflash I built with an Attiny 24, the instructable can be found here: Slaveflash-trigger-for-digital-with-Attiny24

After building the first prototype I collected all my old flashes I got over the years and had four more slaveflash-triggers to built.
I already figured out an PCB-Layout for the SOIC-version of the attiny 24. But the biggest parts in the design are actually the hex-switch and the optocoupler, so it would make no sense to substitute only the microcontroller by a smaller one. Instead I replaced the hex-switch by a learning mode in software and also replaced the power source.

By replacing the 7805 voltage controller by a button cell with 3V, the power consumption was reduced from 2mA to below 0.5mA without the LED on.

So here it is: Let's got started!

Step 1: Changes in the Schematics

In comparison to the former model a lot of things are deleted and the schematics is much easier.

The complete voltage controller section is deleted.
The hex-switch is replaced by nothing.

And this is what is left:

The reset-button
the flash-detector
the status-Led
and the optocoupler.

Step 2: The Software

Also the software has changed a bit. The function to read out the hex-switch was omitted, instead two small if-statements were added in the timer overflow interrupt routine. And this is how it works:

After startup the variable "flashesneeded" is zero, that means unset. As long as this is the case the trigger waits to learn how many flashes there will be. The trigger will detect every flash and count it. After firing your real flash once you have to wait for the timer overflow (~1s). Then the if-function will recognize that there were flashes detected while the flashesneeded-variable is still zero. In this case the number of flashes detected will be written to flashesneeded and the learning mode is done. Now the variable differs from zero and no more learning occurs. To learn another number of preflashes only hit the reset button to restart the microcontroller.

It's so easy and simple!
And it saves you a lot of money!

Step 3: Making the Breadboard

I was up to print a dedicated PCB for this circuit, but when you look at how simple it is, this would be a waste of time!
I made the whole board in one hour in the evening. Just look at the two pictures to figure out what to connect. Or think on your own! ;-)

This is all set up with standard parts, no SMD and with a standard breadboard. The size of the whole circuit is about 3x4.5cm.

Step 4: Setup

Well the problem with these circuits is always: Where to store them! How to handle them and how to make it safe.

So far I chose to mount it on card-board.
I gave the cardboard a cut-out to fit the flash hot shoe in. Then I glued the cardboard to the sides of the hot shoe. Then I bend the straight part down a bit an glued the breadboard with one bigger drop of hot glue under the coin cell holder to the breadboard.
This way I can disassemble it again once I have a better solution.

Because the circuit is very light there is no problem with the weight. And also no cables are hanging around. The flash and the trigger have both different power sources which makes it very easy to change and replace the flash if you like.

Step 5: Test It!

The video shows how the slave-flash with the trigger works.

After pressing the reset button, the LED flashes two times to indicate boot-up. Then we learn the trigger three flashes and wait for the timer to overflow. The next time three flashes are detected the slave-flash fires too.

Step 6: Some Examples

Just a few pictures to show you what you could do with a slave flash trigger. I'm already looking forward to the next big family celebration to use these, but so far I only got to use them in the garden...
To understand the principles of flashlights look here: https://www.instructables.com/id/Tutorial-on-flashing-not-the-naked-thing/

Have fun and vote for me!