Pages: [1] 2   Go Down
Author Topic: Newbie guidance for dslr timelapse controller (use relay or transistor?)  (Read 748 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 7
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi all,

***Complete newbie warning***

I have chosen to make a time-lapse controller for my dslr camera as I think it should be a useful and relatively easy thing to achieve.

To make the camera take a picture remotely I plug a 2.5mm stereo jack into the camera and short the lower and upper sections of the opposite jack and it will snap away.

I want to do this with timing of snaps controlled from Arduino which i think will actually be the easy part...

The bit im stuck on is  whether to use a relay or a transistor as my switch?  It is vital that I don't ruin my camera lol!

 However the thing I seem to be struggling to get my head around with transistors (despite many youtube videos and googling) is regarding the voltage/current applied to the base...

Is the base voltage on a transistor isolated from the circuit running on the collector and emitter?  The reason I'm quizzing it is because I don't want any voltage coming from the arduino going into the camera... I only want it to effectively short the connection not put any unwanted voltage/current into my camera.

I'm quite a newbie so I may be missing some important things but will take as long as need to get my head around it before actually trying anything.  Hopefully someone can help or even point to something that might help explain what I'm getting at? 

Thanks for any help!
Logged

Offline Offline
Edison Member
*
Karma: 31
Posts: 1417
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You should use an optoisolator. That will completely isolate the camera from the Arduino.

Pete
Logged

Where are the Nick Gammons of yesteryear?

NSW Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 2292
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

A transistor will do just fine - or two transistors if there are two separate contacts for focus and "shutter".

A stereo jack has "tip", "ring" and "sleeve" contacts.  You are unclear about which two you are using here, I will presume tip and sleeve and that the "ring" corresponds to the focus contact.  Use a multimeter to check that the voltage on the sleeve is the negative and the tip or tip and ring are each positive in which case an NPN transistor (or N-FET) is appropriate, emitter to the ground (sleeve).  If the polarity is otherwise, then an opto-isolator may be more appropriate, but if your Arduino ground is the same as your camera ground, it should not be a problem.

A 2k2 base resistor from the Arduino control output should be fine.  If you use a FET (must be a "logic level" FET which operates with a low gate voltage), isolation from the gate is even more certain, not that it matters with the 2k2 resistor anyway.
Logged

Offline Offline
Sr. Member
****
Karma: 8
Posts: 271
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Here's a blog post about a similar project:
http://www.glacialwanderer.com/hobbyrobotics/?p=13

As @Paul__B said, though, use a resistor between the Arduino and the transistor.
Logged

NSW Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 2292
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Google shines again, eh?
Logged

Global Moderator
Offline Offline
Brattain Member
*****
Karma: 452
Posts: 18694
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I successfully fired my camera flash using an opto isolator. Relevant part of circuit here:



The resistor limits current through the LED in the opto isolator.

I found a similar circuit here:

http://als-project.blogspot.com.au/

Personally I would use the isolator, then there is no possibility of introducing unwanted current into the camera.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 7
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thanks for the help everyone.

Paul__B your exactly right the tip and sleeve are the contacts, initially I was not going to bother with the focus ring and just set the camera to manual focus, perhaps add it later once I know whats going on better.  And yes the tip and ring measure + 3.xvolts.

I am somewhat torn between getting an opto-isolator, or using a transistor with a resistor on the base.  I have three p2n2222a transistors that came with my starter kit.

But still think i need to get more understanding under my belt as a lot of the specs on the components baffle me to be honest.

I understand the basic idea that many of these how tos all over the net show... But blindly following them does not help me learn anything, for example I could go and do it all and may get it to work but would have no idea why a 2.2k resistor is the resistor of choice on the base why not a bigger one or smaller.... but I will try and research myself the answer to this.

I will often find what im looking for on google but its the answers to the questions about the little details that I sometimes can't find very easily.

But thanks again guys you've given me some things to work with!
Logged

NSW Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 2292
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I could go and do it all and may get it to work but would have no idea why a 2.2k resistor is the resistor of choice on the base why not a bigger one or smaller...

Rule of thumb.  It sounds about right to me.  smiley-lol

It's a cross between providing sufficient current to turn the transistor on presuming it was switching something substantial like a relay (which it no doubt is not in a modern camera), and not "wasting" too much current from the Arduino output.

It could most probably be a much higher resistance.
Logged

Global Moderator
Offline Offline
Brattain Member
*****
Karma: 452
Posts: 18694
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Correct me if I'm wrong, but the basic calculation gives you the current out of the Arduino pin. Assuming a 0.7V drop over the base/emitter junction you have:

Code:
(5 - 0.7) / 2200 = 0.0019 A

So you are letting around 2 mA flow, which is well within spec for the output pin. One of the pages linked above suggested 1k, which would give:

Code:
(5 - 0.7) / 1000 = 0.0043 A

Still within spec for the pin.

Presumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).
Logged

NSW Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 2292
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

So you are letting around 2 mA flow, which is well within spec for the output pin.
OK, OK, I know it is well within spec.  And I doubt whether the current matters anyway for a relatively short period of time.  Just a matter of "no more than necessary".  If we assume a beta of 100 - which should be really conservative, it can easily switch 200 mA.  If it is switching logic levels in the camera as one would expect, that is immensely more than sufficient.


Presumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).

Eh?  Transistors ("transfer resistors") are current amplifiers.  FETs switch on voltage.
Logged

Global Moderator
Offline Offline
Brattain Member
*****
Karma: 452
Posts: 18694
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Oh, OK.
Logged

Offline Offline
Newbie
*
Karma: 1
Posts: 34
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Also have a look at http://www.martyncurrey.com/?p=34

This is a simple guide on using an optocoupler to activate the camera shutter but it can also be used to fire flashes.

EDIT:
Paul__B below has added a warning about flash trigger voltages so I wanted to add that the flash guns i have ( Yongnuo YN-560IIs) have a trigger voltage of 3.75V. So I believe it is safe to use an optocoupler.
I think it is mostly old film flashes that have higher voltages but it would be wide to check.

http://www.botzilla.com/photo/strobeVolts.html has a list of different flash units with trigger voltages.
http://dpanswers.com/content/genrc_flash_measuretv.php talks about checking the trigger voltage.

« Last Edit: October 20, 2013, 08:37:49 am by Sand_HK » Logged

Offline Offline
Edison Member
*
Karma: 20
Posts: 2101
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

So you are letting around 2 mA flow, which is well within spec for the output pin.
OK, OK, I know it is well within spec.  And I doubt whether the current matters anyway for a relatively short period of time.  Just a matter of "no more than necessary".  If we assume a beta of 100 - which should be really conservative, it can easily switch 200 mA.  If it is switching logic levels in the camera as one would expect, that is immensely more than sufficient.


Presumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).

Eh?  Transistors ("transfer resistors") are current amplifiers.  FETs switch on voltage.


Yes however you can switch voltage on with a transistor (from it's high side)
Logged

NSW Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 2292
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Also have a look at http://www.martyncurrey.com/?p=34
This is a simple guide on using an optocoupler to activate the camera shutter but it can also be used to fire flashes.

The fellow goes on about using isolation in case it "could kill your several hundred dollar camera", then proceeds to describe a circuit missing out on the resistor in series with the optocoupler LED.

Give me strength!

Granted that you are competent in assembling things, there is no reason a transistor - plus the resistor will not do the job in perfect safety.

And incidentally, since basic photoflash units use a trigger voltage upwards of 100V, a 4N28 is not rated (30V) for such service.  Presumably the "smart" ones may be different.
Logged

Offline Offline
Newbie
*
Karma: 1
Posts: 34
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The fellow goes on about using isolation in case it "could kill your several hundred dollar camera", then proceeds to describe a circuit missing out on the resistor in series with the optocoupler LED.

Give me strength!



I sent him a message and he says he will update the information.

Logged

Pages: [1] 2   Go Up
Jump to: