In these cases, the problem is not the ability of such systems to
communicate with many cameras simultaneously and to solve massive data
flows, but problems arise with the power of connected devices. The
digital camera does not have a constant power consumption. At rest,
its consumption is minimal, while at the moment of digitizing the
image it increases significantly. With fast CMOS cameras, the supply
current can increase by nearly 500mA during digitization. Thanks to
high-quality converters in the sources inside the cameras, the current
increase is not steep, it is relatively slow. Although the power
consumption does not exceed the allowable load, the simultaneous
digitization of the images of four cameras connected to one USB
adapter is often beyond the power system of some cheap adapters. The
mean DataCam power consumption does not exceed 300 to 350mA even at
maximum frame rates.
Řešení systému pro mnoho kamer není obtížné, musíme však použít
externě napájené adaptéry s dostatečně dimenzovanými zdroji. Hlavní
zdroj počítače má obvykle pro 12V externí napájení adaptérů dostatečné
rezervy.
Our experience is based on cases where 16 USB cameras were
connected to one computer. Even these solutions are relatively easy,
but we have also noticed the failure of the adapters after several
years of operation due to the drying of the electrolytic
capacitors.
Also, USB cables are not all the same. Some have such thin cores
that even a 2 meter length leads to a critical drop in supply voltage.
For cables, the resistance of the conductor must be taken from tenths
to Ohms per meter of length. Thanks to their high-quality power
converters, DataCam cameras are very tolerant of voltage drops and
fluctuations. With longer cables, however, a drop in the supply
voltage below the critical value is quite a common problem. The
solution could be eg externally powered hub near the camera.
What about the USB ports on the computer motherboard? In most
cases, the power supply system is sufficiently dimensioned, but there
are exceptions. For some motherboards, however, there is another
problem where communication with massive data flows puts a heavy
burden on the core of the operating system. External communication
adapters can provide greater data throughput in these cases and can
save a significant amount of CPU usage on the computer.
With a larger number of cameras, it is good to ensure that software
works sequentially and alternately when capturing images. This is
obviously only possible for some applications. The system must then
usually be designed for synchronous operation of all connected
cameras.
RC
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