Twincam: camera-to-camera communication - Hotwire! Hardware Mods, Accessories and Insights - CHDK Forum
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Twincam: camera-to-camera communication

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Offline fbonomi

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Twincam: camera-to-camera communication
« on: 30 / October / 2009, 07:41:02 »
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I have been playing with a very simple camera-to-camera connection, pulsing the focus assist LED on one camera and reading it in the USB on the other camera.

I know this has been done already several times, but I wanted a VERY simple solution... actually the circuit is so simple it's embarassing:



The phototransistor is a BPW77 (but almost any NPN will do) and the resistostor is a 22K trimmer. R goes to the USB red wire, B goes to the black wire (of the slave camera)

The LED I am using is the focus assist LED, for three reasons:

- the Print led (which is often used too) is cumbersome because it's a button (you need to pres it!) and therefore placing the photo-transistor in front of it is a bit tricky
- the Print led sometimes turns on by itself when shooting by night (during noise reduction)
- on cameras like my A570, you can build a nice support for the phototransistor attaching it to a lens adaptor: connecting and removing the phototransistor is extremely simple, thanks to the bayonnet of the adaptor.

This is a photo of the setup. The container is waaay oversized (the only electronics contained in it is a trimmer  :D ) , but I started thinking about using a microcontroller with a lot of options, then I decided to KISS.



Power currently comes from 3 AA batteries,. but consumption is so  little that the whole thing could be powered by button batteries and re-built as a tiny thing...

Proof-of-concept video:

http://www.youtube.com/watch?v=hys6EdIo7w8#normal

The camera on the right has a LUA script sending pulses to the LED, the camera on the left has an uBasic script receiving them. There's no need to have different languages on the two sides, of course :-)

If I have time during the weekend, I would like to develop a Lua script to send/receive serial information.

What I am aiming to is a night-time panoramic time-lapse with a modified verions of the sunset script. In this case a master camera will calculate exposure and inform the slave camera of the settings to use...

There were at least two threads speaking about this, but I can't find them.... Doe anybody else feel the search function in the forum is buggy???
« Last Edit: 30 / October / 2009, 07:44:34 by fbonomi »
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Offline Microfunguy

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Re: Twincam: camera-to-camera communication
« Reply #1 on: 30 / October / 2009, 09:29:08 »
Quote from: fbonomi on 30 / October / 2009, 07:41:02
There were at least two threads speaking about this, but I can't find them

Well, one of them mentions a system where the two cameras communicate via an ATtiny microcontroller.
The developer has sent me a programmed chip but due to work commitments cannot do further work until February.

SDM of course can already generate pulse sequences (representing any parameter you like) using uBasic commands and SDM 1.82 has the option of using the autofocus led.

A commercial application is being developed by someone to drive RC servos using this system.

The Canon firmware will randomly interrupt any pulse-generation code and that sets a limit on speed of communication.

For some applications, that is not important.

The ATTiny system communicates at very high speed but has extensive error checking.

So far, I do not understand the code  :-)

The developer says that the code will be made available on completion.



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Offline spinorkit

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Re: Twincam: camera-to-camera communication
« Reply #2 on: 03 / November / 2009, 06:18:40 »
Quote from: Microfunguy on 30 / October / 2009, 09:29:08
Quote from: fbonomi on 30 / October / 2009, 07:41:02
There were at least two threads speaking about this, but I can't find them

Well, one of them mentions a system where the two cameras communicate via an ATtiny microcontroller.
The developer has sent me a programmed chip but due to work commitments cannot do further work until February.

The Canon firmware will randomly interrupt any pulse-generation code and that sets a limit on speed of communication.

For some applications, that is not important.

The ATTiny system communicates at very high speed but has extensive error checking.

So far, I do not understand the code  :-)

The developer says that the code will be made available on completion.


My original post is here:
http://chdk.setepontos.com/index.php/topic,3697.msg34622.html#msg34622

Just a quick update on ATTiny system using the blue led and the USB power line.
The initial version used one level of error correction to overcome the problems caused by interrupts in the camera firmware causing timing variations. This resulted in communication of approx. 100 characters per second with an overall error rate of about 1 error per minute "in the field". This is high enough to be annoying, so I have started writing a more sophisticated 2nd layer of error correction based on variable size packets.

I am very busy at work at present and have only been able to find an hour or 2 per week to work on this. Currently I am debugging a PC simulation of this packet error correction system. This is going quite well but I have yet to try out the code in the ATTiny. If I can squeeze it into the ATTiny (it has been written with this in mind), I should have something ready by Xmas.

Regards,
Kit
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Offline fbonomi

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Re: Twincam: camera-to-camera communication
« Reply #3 on: 05 / November / 2009, 05:01:24 »
I missed you post at that time.
Pretty impressive.
We are working at the two oppsite extremes of the spectrum, I would say :-)
Your solution is high speed, high technology etc.
Mine is kow technology, VERY low speed etc.
I couldn't work on it (I left one of the cameras at someone else's house!) but I will be happy if I can get to 1 byte per second :-)

TMTOWTDI indeed :-)

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Offline Microfunguy

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Re: Twincam: camera-to-camera communication
« Reply #4 on: 05 / November / 2009, 05:55:04 »
Quote from: fbonomi on 05 / November / 2009, 05:01:24

TMTOWTDI

On this International Group, and including native English speakers like myself,  what does that mean ?   :)
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Offline fbonomi

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Re: Twincam: camera-to-camera communication
« Reply #5 on: 05 / November / 2009, 06:09:47 »
There Is More Than One Way To Do It.

Perl's Motto

I swear I didn't make that up :-) en.wiktionary.org/wiki/TMTOWTDI
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