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Main pageTechnical supportTips for creating applications

Tips for creating applications - connecting multiple USB cameras
 If you need to connect multiple cameras via USB to one computer, we usually must to add additional communication adapters to the computer. That shouldn't be a problem - you might be wondering what could go wrong with such simple things.

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.

With this adapter we can see immediately that it will not be enough for more cameras

With this adapter we can see immediately that it will not be enough for more cameras

An external power connector, a reasonably powerful voltage converter and electrolytic capacitors for each port are a good sign of this adapter

An external power connector, a reasonably powerful voltage converter and electrolytic capacitors for each port are a good sign of this adapter

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.

The external power supply of the adapters is important here, the power distribution on the PCI-X bus may not be enough for this

The external power supply of the adapters is important here, the power distribution on the PCI-X bus may not be enough for this

There are 28 USB 3.0 ports added to the computer

There are 28 USB 3.0 ports added to the computer

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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Moravian Instruments, Masarykova 1148, Zlin 4, CZ-76302, Czech Republic