My latest time-lapse camera rig, was failing to run due to the constant ground connection on the camera power input.

This is an off-grid, solar-powered rig, combining a Raspberry Pi and an Arduino, to share tasks using a minimum of energy.

As a novice in electronics I felt I was making progress, having used GPIO controlled relays to break the positive wire connection on several of my rigs.

However, in this rig, I use two different methods to take the pictures:

1/ An in-camera script (C.H.D.K. Canon Hackers Development Kit) which takes a picture automatically, on power up of the camera by the Arduino,

2/ A PTP connection to the camera's USB port when the Raspberry Pi is active and supplying the power to the camera as well.

Due to the ground wire of the Raspberry Pi remaining connected to the Camera power input, I found that my on-board script failed, due to it falsely detecting a USB connection. On disconnection of the ground wire, the script works as intended.

I imagined this need for 'double disconnection' ie. of both the positive AND negative wires, would be a common issue in electronics and that there would be a relay component ready made for the job but Google doesn't turn one up.

I suspect I simply just don't know the right name for the task, among the many versions of relays out there.

Please advise, or, if there's another approach in circumstances like mine, I'd love to hear it. it seems wasteful to be using a two channel relay to operate a single power switch. ie. one channel for the positive wire and one for the ground. I hope I explained myself well enough. If not, I apologize and will correct as best I can Thanks in advance

  • \$\begingroup\$ Double-pole double-throw relays \$\endgroup\$ – analogsystemsrf Nov 20 '18 at 4:40
  • \$\begingroup\$ That looks promising.. In [this example] electroschematics.com/9601/dpdt-switch-relay) the first application isn't right.. it reverses polarity of the inputs but, in the second example, it switches between two loads, which, in my case, if the second load lead nowhere at all, would achieve my goal, of disconnecting both poles of the input power. Thanks for that @analogsystemsrf \$\endgroup\$ – Hazy Nov 20 '18 at 5:02
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    \$\begingroup\$ Really you want a double-pole single-throw (DPST) relay, but if you happen to have DPDT available it will work just as well. \$\endgroup\$ – The Photon Nov 20 '18 at 5:30
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    \$\begingroup\$ I wonder if the ground is the best thing to disconnect. If there is current draw due to idle USB data lines I would seriously consider disconnecting the power and data lines and leaving the ground connected. This will prevent a possible floating potential difference between the data lines of the two USB ends, \$\endgroup\$ – KalleMP Nov 20 '18 at 14:08

Hi you really need a DPST ( double pole single throw) relay.

but DPDT (double pole double throw) will be mostly available with the hobby stores.

You can use any of the above

Pls follow the link


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    \$\begingroup\$ It's worth mentioning that these are also called 2-Form-A or 2-Form-B relays, depending if they're open or closed with the coil de-energized. (Actually those would be DPST, which is what OP really wants) \$\endgroup\$ – The Photon Nov 20 '18 at 5:28
  • \$\begingroup\$ Yes he wants dpst but dpdt is most avaible in the market.. so that he can move ahead. For prototyping there will be no problem whether it is dpst or dpdt – \$\endgroup\$ – Satish Singupuram Nov 20 '18 at 6:50
  • \$\begingroup\$ Thanks Satish, Your answer is exactly what I need. Not only a detailed and informative reply but you offer an easily available and functional alternative. You're a legend, as we say here in Australia. \$\endgroup\$ – Hazy Nov 21 '18 at 21:08

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