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Battery third (temp) terminal as multipurpose analogue input

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Offline Karmaschinken

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #120 on: 26 / January / 2014, 13:53:29 »
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Ah, the power supplies have no ground as you can see (attachment). Maybe this is also a reason why I got these small electrical shocks without grounding the complete rig?

Is this what you meant by "isolated"?
« Last Edit: 26 / January / 2014, 14:00:37 by Karmaschinken »
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Offline waterwingz

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #121 on: 26 / January / 2014, 14:19:56 »
Quote from: Karmaschinken on 26 / January / 2014, 13:44:35
2.: Until now I have powered the Arduino directly from the USB-Port of my notebook. But I also have a  Voltcraft PS1152A I could use. What would you suggest?
Stay with powering the Arduino from the USB port.  One less thing to go wrong, one less thing to wire up, and as I'm going to state below, that fits with the way this is grounded.

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3.: What do you mean by "isolated" power supplies? At the moment 5 blocks of each 10 power supplies are wired together into a single 240V cable that goes into the normal 240V socket. I attached a picture.
"Isolate" means there is no DC path between the 240V mains input and the DC output ( i.e. there is a transformer in between).  Now that I see your power supply units and their mains plug,  I believe that is what you have.  Good.

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1.: I did not intend to put the grounds all together yet, now your question already implies I should, right?  ::)
With the circuit diagram the way you have drawn it,  it looks like the common ground point will be the USB 0V power line.  This should work okay - there are no built-in ground loops with the 240 VAC supplies - they float off the 0V rail.

Quote from: Karmaschinken on 26 / January / 2014, 13:53:29
Ah, the power supplies have no ground as you can see (attachment). Maybe this is also a reason why I got these small electrical shocks without grounding the complete rig?
This is concerning - I guess everything is "floating" relative to earth ground.  Somewhere you probably need an the DC 0V reference tied to building ground - I''d suggest maybe the 0V DC input connection on the Arduino?
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Offline Karmaschinken

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #122 on: 26 / January / 2014, 16:56:00 »
Okay so I'll glue the things together as shown. Great thing.

You wrote: "Somewhere you probably need the DC 0V reference tied to building ground". What does that mean? When I head the problem with the electrical shocks I was putting a cable from the steel carrier system of the whole rig to the ground an the problem was gone.

I don't understand why I should connect the Arduino input connection to building ground? Isn't this already done, I mean it already HAS a ground? No? Sorry, I have been around with my girl friend when I was supposed to learn this at school. Sometimes I regret that, but not really.

Thanks a lot.
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Offline waterwingz

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #123 on: 26 / January / 2014, 17:18:25 »
Quote from: Karmaschinken on 26 / January / 2014, 16:56:00
You wrote: "Somewhere you probably need the DC 0V reference tied to building ground". What does that mean? When I head the problem with the electrical shocks I was putting a cable from the steel carrier system of the whole rig to the ground an the problem was gone.

I don't understand why I should connect the Arduino input connection to building ground? Isn't this already done, I mean it already HAS a ground? No? Sorry, I have been around with my girl friend when I was supposed to learn this at school. Sometimes I regret that, but not really.
Simply put,  between the 240 to 4.5V power supplies,  your laptop power supply, and whatever powers you USB hubs,  you have a whole lot of voltage sources all hooked together. 

But none of them are actually connected to "ground" and so they just "float" to some voltage level relative to ground.  This actual voltage is determined by the various device leakage currents and high impedance paths to ground. 

When you touch any point on such a system,  you get a shock as your body becomes a lower impedance path to ground.  The size of the shock depends on the amount of leakage current and the resistance of the existing high impedance paths to ground.

The steel carrier of your system probably gets charged via the tripod socket on the camera to the camera ground to the power supply ground.  It's all floating until you ground it somewhere.   That's exactly what you did when you ran a cable from the carrier system to ground - you  pulled the floating system back to ground.  However,  a better way to have grounded the system would be to have grounded the 0v level of any of the power supplies, or USB hub, or Arduino,  rather than an accidental path though the carrier frame.


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Offline waterwingz

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Re: Battery third (temp) terminal - use the Canon remote instead ?
« Reply #124 on: 29 / January / 2014, 19:28:27 »
I had an additional idea that I thought I'd just drop here for safe keeping.

On camera with a built-in external remote input ( G series,  SX50, etc ) for a Canon remote switch,  I would expect the input bits from that device to pass through the same input  physw_status[] words as the other digital inputs.   So it should be possible to intercept that input,  and reroute to the USB remote code,  allowing a tidy way to get precision sync & ptp communications without having to hack the battery input terminal.
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Offline reyalp

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Re: Battery third (temp) terminal - use the Canon remote instead ?
« Reply #125 on: 30 / January / 2014, 00:09:23 »
Quote from: waterwingz on 29 / January / 2014, 19:28:27
I had an additional idea that I thought I'd just drop here for safe keeping.

On camera with a built-in external remote input ( G series,  SX50, etc ) for a Canon remote switch,  I would expect the input bits from that device to pass through the same input  physw_status[] words as the other digital inputs.   So it should be possible to intercept that input,  and reroute to the USB remote code,  allowing a tidy way to get precision sync & ptp communications without having to hack the battery input terminal.
Good idea.

Another thought: In the cameras where video out is combined with USB, the video cable detected electronically, rather than a mechanical switch like the old dedicated A/V plug. So you could make a splitter like http://www.achillies.com/CHDK_Files/USB_Splitter.htm with a switch on it.
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Offline ahull

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #126 on: 30 / January / 2014, 07:41:32 »
Quote from: waterwingz on 26 / January / 2014, 17:18:25
Quote from: Karmaschinken on 26 / January / 2014, 16:56:00
You wrote: "Somewhere you probably need the DC 0V reference tied to building ground". What does that mean? When I head the problem with the electrical shocks I was putting a cable from the steel carrier system of the whole rig to the ground an the problem was gone.

I don't understand why I should connect the Arduino input connection to building ground? Isn't this already done, I mean it already HAS a ground? No? Sorry, I have been around with my girl friend when I was supposed to learn this at school. Sometimes I regret that, but not really.
Simply put,  between the 240 to 4.5V power supplies,  your laptop power supply, and whatever powers you USB hubs,  you have a whole lot of voltage sources all hooked together. 

But none of them are actually connected to "ground" and so they just "float" to some voltage level relative to ground.  This actual voltage is determined by the various device leakage currents and high impedance paths to ground. 

When you touch any point on such a system,  you get a shock as your body becomes a lower impedance path to ground.  The size of the shock depends on the amount of leakage current and the resistance of the existing high impedance paths to ground.

The steel carrier of your system probably gets charged via the tripod socket on the camera to the camera ground to the power supply ground.  It's all floating until you ground it somewhere.   That's exactly what you did when you ran a cable from the carrier system to ground - you  pulled the floating system back to ground.  However,  a better way to have grounded the system would be to have grounded the 0v level of any of the power supplies, or USB hub, or Arduino,  rather than an accidental path though the carrier frame.

I would operate the entire rig through an RCD protected plug/socket (which unlike a fuse or other protection, will actually save your life when things go wrong). I would also suggest that grounding the metalwork of the chassis is probably a good idea, more especially when used in conjunction with an RCD device. Operating mains voltage equipment in any environment where there is even the slightest risk of moisture penetration is asking for trouble without any form of protection.

The shocks you are getting may well be as high as the line voltage (i.e. 220V or so), at relatively low current, but of one of those cheap PSUs decides to short, the current could be lethal.

I know from experience that RCDs will save you from grief, having cut through my hedge trimmer cable, not once, but twice in the same day. Without the inline RCD plug I would most likely have been toast  :o .
« Last Edit: 30 / January / 2014, 08:02:49 by ahull »
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Offline Karmaschinken

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #127 on: 01 / February / 2014, 17:44:53 »


Hmmmm, reading this it seems well paid equipment then. I'll see where to get one of those here. Thanks for this advice!

Meanwhile I have been soldering some dummies, 14 are the work of a whole day, with the help of some friends.

Now I'll gonna test them soon.
« Last Edit: 01 / February / 2014, 17:51:38 by Karmaschinken »
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Offline waterwingz

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #128 on: 01 / February / 2014, 17:50:53 »
Quote from: Karmaschinken on 01 / February / 2014, 17:44:53
Meanwhile I have been soldering some dummies, 14 are the work of a whole day, with the help of some friends.
Power User Tip :  it goes faster if you don't give them free beer until after everything is soldered.

It also looks like you are definitely going to need the battery door switch hack - or a dab of epoxy to stick the door switches permanently closed.
« Last Edit: 01 / February / 2014, 18:00:31 by waterwingz »
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Offline Karmaschinken

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Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #129 on: 01 / February / 2014, 17:58:58 »
Hehe!  :D

Seems you've got some experiences with the working class!?!
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