Why is a longer cable not able to stream from a camera

why longer cable not able to stream form camera

Hello,

This is my problem: I have two connectors on a pcb to which I connect two cameras. One of them is 5 times longer than the other (long is aproximately 1.5 meters). Unfortunately I can't reduce the length of the cable, it is vital. The cables have vcc= 5V, data-, data+ and gnd. In some pcbs, where iI m looking for the fault, the longer cable has trouble to stream. please note that it's not always the case. Sometimes, by swapping the connectors, it might work. Unless there is a fault on the pcb, which I examine in another thread https://www.edaboard.com/threads/363858/, I would like to clarify this:

I guess that it is tricky to have long cables. They might behave as inductances. According to this formula,

R= r*l/A, where r is the resisivity, l is the length and A is the siemens/m, I would expect bigger ohmic resistance for the ohmic cable.

When I measured:

short cable: R = 8.3Ohms, long cable: R= 0.3Ohms. How's that possible? Wrong measurement? The truth is that the value is not fixed in the digital multimeter but it's hard to capture it.

What is that is causing the connector not able to provide enough current to the bigger load (long cable)?

Please help to clear things up!

- - - Updated - - -

Ok, remeasured please see the update: I have three states

1. Turned off
2. On and not streaming
3. On and streaming

1. short cable Data+ : R= 0.1 Ohms, Vdd : R = 0.1 ohms
2. short cable Data+ : R = 0.1 Ohms, Vdd: R=6.6 Ohms
3. short cable Data+ : R = 0.2 Ohms, Vdd = 36 Ohms

1. long cable Data+ : R= 0.2 Ohms, Vdd : R = 0.2 ohms
2. long cable Data+ : R = 0.3 Ohms, Vdd: R= 15.2 Ohms
3. long cable Data+ : R = 0.8 Ohms, Vdd = 80 Ohms

Now these values make more sense to me.

I have a bigger load for the long cable but unfortunately I can't make it shorter in my system. What can I do to be more robust and not loose the streaming?

Re: why longer cable not able to stream form camera

There will be no meaningful answer without some information about the camera interface and used cable type.

If it's e.g. an usual USB interface, it should work well with standard USB cables up to 5m, but probably not with an unsuitable cable of different kind. Other high speed differential data standards have also special cable requirements.

Re: why longer cable not able to stream form camera

FvM said:

There will be no meaningful answer without some information about the camera interface and used cable type.

If it's e.g. an usual USB interface, it should work well with standard USB cables up to 5m, but probably not with an unsuitable cable of different kind. Other high speed differential data standards have also special cable requirements.

Click to expand...

Thank you very much. The cable is usb 2.0 standard: has 4 channels, as the common usb 2.0 (Vcc =5V, data +, data -, gnd). The cable of each camera connects to a 4 pin connector. The channels of the connector get the usb channels through a usb hub. the usb hub chooses which camera will stream (one at a time). So to sum up:

USB port -> pcb (usb hub) -> : 1. connector 1-> camera 1 and connector 2-> camera 2

I hope it's clear now.

I select the camera I want to stream from with the camera app of windows, no special interface. When I have trouble finding the camera, it does't appear on Devices and Printers at all. Or, sometimes it finds it, it streams in the beginning but then is not recognized anymore, disappearing from the Devices and printers. My connectors are stable and well connected. that's why I am afraid of the cable.

What can I do to increase the robustness of the cable? The load is to high and I loose the camera streaming.