aredhel_vlsi
Member level 4
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?
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?