Hi,
I would like to know if the Low-Light HD USB Camera has a pin that can receive a trigger signal to capture an image. I see there are two unused pins marked as positive and negative. What they are for?
Thank you very much.
Hi Alberto,
This is an usb camera, there is no pin to take photos.
The + and - pins can be used to supply a 5V supply for the hardware if necessary.
If you want to take photos via an hardware event, you can use the raspberry pinout and probably a python script to do that for you.
Thank you very much Patrick. In the past I worked with other USB cameras, e.g., UI-3251LE from IDS GmbH, that had pins, including one for a trigger. Definitely we can do it with the Raspberry Pi, but we wanted to have as little delay as possible between the trigger event and the capturing of the image. We will probably for now go with the pin on the Raspberry Pi, and probably we will look at other cameras.
Patrick mentioned that there are two pins(+ and -) on the camera board. Is this an input to
power the camera or is it an output to power external hardware ?
Hi @heinz, welcome to the forum 
I would assume that a camera isn’t really intended for power passthrough, so it’s more likely intended as a power input for the camera to take strain off the USB bus power source. My reading of patrick’s comment is that ‘the hardware’ in question is the camera’s, since the camera is the topic of discussion.
For reference, USB 2.0 specification is expected to deliver up to 500mA, and our Low Light HD USB Camera technical details specify the camera draws a max of 220mA, so you may be able to draw up to 280mA from an external device connected to the camera’s +/- pins, but I wouldn’t suggest it. Note that over-drawing power beyond what the RPi can supply could cause undervoltage and cause the system to throttle and/or reboot/shutdown.
In general it’s a good idea to have the ‘path of least resistance’ between a device and its power supply, so if you’ve got something else that needs 5V I’d recommend just powering it directly from the 5V converter instead of via converter → RPi → USB cable → camera → device.
Hi Eliot,
thank you for the answer. Confirms my interpretation.
I’m using an USB-Ethernet pair with 50 m Kat6 cable
to connect to the camera mounted in a 2" BlueRobtics
acrylic tube. It will be used to inspect wells.
The camera consumes 200 mA when sending pictures and
additinal 20 mA will be needed for the lightning, but
the PoE only delivers a maxium of 150 mA.
The solution now is an additional power cabel delivering
12 V from the ground and a 5V regulator down to feed the
camera, without using PoE.
Kind Regards, Heinz.
Just some hints when using LogiLink USB/Ethernet pair to connect to the camera.
The converter down at the camera needs additional external power for cables longer than
about 15 m.
It’s working with a 50 m Cat6 cable if you supply well 200 mA @ 5 V to the converter down
at the camera.
Total consumption for camera and converter @ 5 V are 250 mA with no pictures sent and
400 mA when streaming. I’ve set the power supply limit to 1000 mA and there are only few glitches.
Kind Regards, Heinz.