robotpibot
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Detect hot shoe trigger from analogue camera

Tue Nov 07, 2017 7:30 pm

Hello,

Does any one know or tried to detach the short circuit from a analogue slr hotshoe using an raspberry pi? I’m planing on building a metadata logger which saves the time and date plus potentially gps when a photo is taken. Given I need a way to detect when the photo was taken I was thinking of using the hot shoe as such a method?

Any pointer would be most welcome?

Thanks

drgeoff
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Re: Detect hot shoe trigger from analogue camera

Tue Nov 07, 2017 9:27 pm

https://en.wikipedia.org/wiki/Hot_shoe

It seems to be nothing more than a normally open switch which is momentarily closed when the shutter is opened. The internet has many tutorials on attaching switches to RPi GPIOs.

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thagrol
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Re: Detect hot shoe trigger from analogue camera

Wed Nov 08, 2017 8:37 pm

drgeoff wrote:
Tue Nov 07, 2017 9:27 pm
https://en.wikipedia.org/wiki/Hot_shoe

It seems to be nothing more than a normally open switch which is momentarily closed when the shutter is opened. The internet has many tutorials on attaching switches to RPi GPIOs.
Yep, thats what it is, at least for non-dedicated hot-shoes. The PC flash connector is the same. The camera expects a positive voltage on the centre pin which it then connects to the outside of the shoe when the shutter fires.

Older cameras use a mechicanical switch, later ones may do it electronically.

The only real gotcha I can think of is doing this at the same time as connecting a flash gun. Not so much the wiring but the voltage output by the gun. Bulb flash guns generally used a 22v battery. Xenon flashgun have lower voltage battery packs (often around 6v) but it's common for them to put the voltage (several 1000) from their internal capacitor across the hotshoe. Either one will fry a pi.

Check the specs for your camera and any flash gun you might want to use.

robotpibot
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Joined: Sun Oct 19, 2014 6:31 pm

Re: Detect hot shoe trigger from analogue camera

Wed Nov 08, 2017 8:40 pm

Yep, managed to get a trigger detected through the rpi. I generally would not need to use flash at the same time. Now looking for a nice mount to connect the rpi to the hotshot, and someway to keep everything powered without it becoming oversized!

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thagrol
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Re: Detect hot shoe trigger from analogue camera

Thu Nov 09, 2017 2:31 pm

robotpibot wrote:
Wed Nov 08, 2017 8:40 pm
Now looking for a nice mount to connect the rpi to the hotshot, and someway to keep everything powered without it becoming oversized!
If you're using a pi zero(w), I'd go for an old electonic (xenon) flash gun. Strip out the electronics (carefull of the capacitor) but keep the battery box, power switch and hotshoe connector. Add your pi zero and an apropriate boost/buck converter.

robotpibot
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Re: Detect hot shoe trigger from analogue camera

Thu Nov 09, 2017 2:52 pm

That is a brilliant suggestion!! Thanks!! By boost/buck I assume you mean something to regulate the power supply like a piborg?

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thagrol
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Re: Detect hot shoe trigger from analogue camera

Thu Nov 09, 2017 3:04 pm

Yep. Though a piborg might be overkill for your needs.

PiGraham
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Location: Waterlooville

Re: Detect hot shoe trigger from analogue camera

Thu Nov 09, 2017 3:15 pm

You can get hotshow adaptors designed to connect off-cara flash units. They generally take a hotshoe flash in top as well to you can tap off the flash contact to the Pi and still have a way to use a flash is desired.

Be careful though, some flash guns can have high voltages on the shoe contacts. Us something to protect against voltage spikes (a zenner diode to protect the opto is probably enough) and connect to the Pi with an opto-isolator.

Using the old flash as a case is a great idea. It also gives you a mounting point that will fit common camera accessory brackets so you can keep it attached and use a flash when you want to.

robotpibot
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Re: Detect hot shoe trigger from analogue camera

Thu Nov 09, 2017 7:49 pm

thagrol wrote:
Thu Nov 09, 2017 3:04 pm
Yep. Though a piborg might be overkill for your needs.
Any suggestions with would save some $$ or ££ would be welcome :)

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thagrol
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Re: Detect hot shoe trigger from analogue camera

Fri Nov 10, 2017 7:11 pm

Google voltage regulator.

Other than that not realy, sorry. You'll need to know what input voltage you'll have and roughly how much current it will need to supply.

PiGraham
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Re: Detect hot shoe trigger from analogue camera

Sat Nov 11, 2017 9:33 am

just a thought about another way to tackle this.
You could use a car GPS GSM tracker. these can send an SMS of position, date, time when a button is pressed. You could wire the flash sync to the button contacts.
It could also be used to locate the camera if you lose it. Battery and gps stuff already sorted which is great if you are more interested in the function than the DIY aspects.

You could write a program for the Pi to fetch the SMS via a web gateway and log it all in a database and/or web page.

This one is a bargain http://www.lightinthebox.com/mini-vehic ... ngshopping

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