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Building a mult-camera rig

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Offline bismo

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Hey really sorry this reply took so long, because I have school kinda far from home and I can't bring this equipment there.

Anyway thank you again for both of you for the suggestion, since last time this is what I did:

1. Try passing the 5v power (on a regular cable, 1 camera, connected to pc) through a switch.
result: I successfully triggered the usb remote without losing the connection to pc.

2. On that note, rather than connecting the relay to each switch on the usb hub, I tried just solder a switch to the 5v power that connect the usb hub to the pc (like I did on the #1 attempt).
result: while I successfully triggered the USB remote, the camera and the pc lose connection and have to connect again (like waterwingz said).

conclusion is that means that my previous failure was due to electric problem (like reyalp said).

Next step I'll do is source another usb hub (that have different wiring) and just re-do what I did.
Do you guys have any suggestion?

Next step I'll do is source another usb hub (that have different wiring) and just re-do what I did.
Do you guys have any suggestion?
I would not recommend trying different hubs.   Maybe you will get lucky and find a good one but it seems unlikely.

When you disconnect power from the hubs, the data lines D+ and D- lose power and that kills the connection.  I'm not sure a different hub could get around that. Also, if you use more than one hub, the power off time will be a little different for each, throwing off your sync.

So either you insert a multipole relay or electronic equivalent into each +5v line going to each of your cameras or you avoid all hardware mods and start using the software calibrated sync'd shooting of reyalp's  chdkptp scripts.  The software script solution may be precise enough for your application?

Ported :   A1200    SD940   G10    Powershot N    G16

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Offline bismo

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Hey,

turns out the other kind of different usb hub I ordered a couple days ago already arrived, and after testing it, you're right.

Although this one is more expensive, it is wired the same way the only difference is this one got a diode.

After further google search I think you're right and I should try wire relay each power line between the usb hub and the camera, because all my previous attempt is wiring relay before usb hub logic board and what you're referring to is after the usb hub logic board.

anyway I'll do that next and also try reading up threads about reyalp's multicam.lua

I'll update however it goes (this weekend probably)
Thanks again!

After further google search I think you're right and I should try wire relay each power line between the usb hub and the camera, because all my previous attempt is wiring relay before usb hub logic board and what you're referring to is after the usb hub logic board.
You have not mentioned how many cameras you want to control but if it was me doing the project, here's what I would probably try to do.

  • Buy a USB hub with enough ports to connect all the cameras. Or if you have many cameras, buy 2 or 3 or however many hubs you need with at least 8 ports per hub.
  • Carefully open each hub and examine how the connection to the +5V pin of each USB connector is made
  • If all the +5V pins are connected in parallel, determine if you can isolate them by cutting a single trace to the +5V source
  • I you can't cut a single trace, determine how to individually isolate each +5V pin on the circuit board.
  • I you can't cut a traces, consider cutting the +5V pin above the PCB at each connector
  • Once you have the +5V pins isolated, connect them in parallel with some jumper wire.
  • Connect the parrallel jumper wire through a relay contact or manual switch to the +5V power inside the hub
  • If you are using more than one hub, repeat the process for each hub. Use a multipole relay to switch all hubs +5V jumper at the same time.
  • Alternatively,  wire all +5V jumpers between the hubs to a single power source in one of the hubs.  Make very sure you have a good solid ground connection between each hub (the 0V line). Cameras draw very little power from the +5V pin so this should not create any loading issues
  • Toggle the +5V relay (or switch) when you want to shoot.

How hard the above process will be depends on the hub.  It will likely be easier if the hub only uses a 2 layer PCB board, suggesting that the most inexpensive hubs might be the best choice.
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline bismo

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Hey sorry this reply took so long

Anyway, I'm trying to run just 9 cameras (2 usb hub)

Thanks so much for the advice, so to do that I invested in a multimeter (I know its bad that I just bought this now)

anyway I tried finding the PCB trace that connect the 5v to each camera but I can't. It looks like coming out of the logic board is an individual +5v connected to each usb and its even harder to cut because its so small, so I just go with the original plan and cut the +5v and then jump the relay to below the usb connector.

Thankfully after so many mistakes(I made) I'm happy to say it is working now, the pre-shoot, the shoot, the download. I haven't tested how close the timing is between each camera, probably next weekend when I got all of them.

Thank you for the replies and assistance again
hopefully this is my last mistake regarding this matter so I wont bother again in the future :D

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Offline reyalp

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anyway I tried finding the PCB trace that connect the 5v to each camera but I can't. It looks like coming out of the logic board is an individual +5v connected to each usb and its even harder to cut because its so small, so I just go with the original plan and cut the +5v and then jump the relay to below the usb connector.
Just FWIW, since this thread was originally started, CHDK has added support for alternate remote inputs. This gives you some alternatives if controlling the +5 in the USB is problematic, though each has pros and cons:

1) The battery temperature terminal
Requires you to be able to change the resistance on the the pin that would normally connect to the middle battery terminal. Only valid for non-AA battery cameras. If you are using AC adapters with dummy batteries ( ACK-DC90 for a2500), you'd need to add the terminal to the adapters, and arrange for it to be switched between open circuit and a resistor to ground, or two resistance levels. Adding a terminal to the dummy batteries or masking the existing terminal on real batteries isn't terribly hard (example: https://chdk.setepontos.com/index.php?topic=10385.msg137582#msg137582)

2) The Analog AV detect pin
Only valid for cameras which combine the AV plug and USB plug into a single, 11 pin connector (cameras using AV Cable AVC-DC400/AVC-DC400ST style cables for AV). Requires a custom plug for the USB socket. AFAIK no off-the-shelf cables break out the AV detect pin, but some USB+AV splitters are available: https://chdk.setepontos.com/index.php?topic=13448.0

3) HDMI hot plug detect:
Only valid for cameras with HDMI (not A2500). Requires the ability to connect the HDMI +5 and HPD pins, which can easily be done with off the shelf components (examples https://chdk.setepontos.com/index.php?topic=13451.30).

These are currently only enabled for a few cameras, but in general are trivial to enable on cameras with the appropriate hardware.
Don't forget what the H stands for.

@reyalp - if I want to use the BTT method (1) in your post to do multicam sync on some D10s using dummy batteries with a common power source, could I just run a wire from the middle terminal of each of the (3-terminal) batteries and join all of them to a single resistor with a push-button switch that connects to the common ground? This sounds much easier than the wiring and hubs for the USB setup, and leaves USB/AV available for download/view (goal is an underwater multicam rig).
A720 1.00c | D10 1.00b |SX220 1.01a | SX230 ? | SX30 1.00p CHDK ver. 1.1.0-r1727

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Offline reyalp

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@reyalp - if I want to use the BTT method (1) in your post to do multicam sync on some D10s using dummy batteries with a common power source, could I just run a wire from the middle terminal of each of the (3-terminal) batteries and join all of them to a single resistor with a push-button switch that connects to the common ground?
I'm not sure what the implication would be of having the different cameras A/D inputs all tied together. If I had a couple cameras I didn't care much about I'd probably just try it, but it seems dubious. Maybe someone with less rudimentary electronics knowledge (cough @waterwingz) can comment on the right way.

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This sounds much easier than the wiring and hubs for the USB setup, and leaves USB/AV available for download/view (goal is an underwater multicam rig).
Presumably stating the obvious, but some modding would be required do this while remaining waterproof.

For the remote part, it should be possible to do everything in the battery compartment with a reed switch or hall sensor triggered by a solenoid (see these threads https://chdk.setepontos.com/index.php?topic=11058.0 https://chdk.setepontos.com/index.php?topic=13451.msg137306#msg137306 for somewhat related discussion). This would also keep the A/Ds isolated. You'd still have to deal with the USB / power plug area of course.
Don't forget what the H stands for.


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I'm not sure what the implication would be of having the different cameras A/D inputs all tied together.

i'm sure it means that the effective resistance that each individual camera sees will change, depending on how many cameras are connected and how many are turned on, eg a 1k resistor with 5 cameras connected is equivalent to each camera seeing 5k, when you have 10 cameras connected, that is now equivalent to each camera seeing 10k, which may be outside the working range.

@reyalp - if I want to use the BTT method (1) in your post to do multicam sync on some D10s using dummy batteries with a common power source, could I just run a wire from the middle terminal of each of the (3-terminal) batteries and join all of them to a single resistor with a push-button switch that connects to the common ground?
I'm not sure what the implication would be of having the different cameras A/D inputs all tied together. If I had a couple cameras I didn't care much about I'd probably just try it, but it seems dubious. Maybe someone with less rudimentary electronics knowledge (cough @waterwingz) can comment on the right way.
Had to spend some time rereading the Battery third (temp) terminal as multipurpose analogue input thread to figure out what we actually did.  Hard to believe that was five years ago  :blink:

Assuming you have the cameras all on a shared ground (which you should get via USB pin 4 if they are all plugged into connected USB hubs), then I'd suggest an individual 1K resistor connected to each "3rd terminal" with the other side of the resistors all connected together and switched to ground via a relay contact / toggle switch / transistor.

To be really rugged and noise immune,  connecting a ground wire between the "- " or ground terminal of each dummy battery is also a good idea, albeit more work.  That's the "ground" point for the common side of all the resistors too.

(Technically it's the 2nd terminal as you count across the battery contacts - how did we mix that up?)


i'm sure it means that the effective resistance that each individual camera sees will change, depending on how many cameras are connected and how many are turned on, eg a 1k resistor with 5 cameras connected is equivalent to each camera seeing 5k, when you have 10 cameras connected, that is now equivalent to each camera seeing 10k, which may be outside the working range.
Correct. That's why you should interconnect each camera with its own 1K resistor.  That means they each see 1K when you pull all the other sides to ground.  And there will be effectively 2K between any two cameras when the ground contact is not closed, limiting any meaningful current flow between the cameras if their internal power supply voltages differ slightly.

« Last Edit: 04 / April / 2019, 18:44:33 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

 

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