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i have a trouble with connection between device and computer. what is D+ and D- in USB? I have no background in electronics i don`t know what it mean. so, i cant connect device for experiment. i want to connect rs232 and 4 pin usb(for connect computer). how can i connect rs232 and usb? enter image description here

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    \$\begingroup\$ That's not RS-232. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 12 '16 at 6:47
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    \$\begingroup\$ The DE-9 connector commonly used for RS-232 serial ports can also be used for many other applications. The connector you show is clearly NOT an RS-232 connector, and MUST NOT be connected to a normal serial port. \$\endgroup\$ – Peter Bennett Aug 12 '16 at 16:14
  • \$\begingroup\$ For any readers who are interested, I found the image supplied above in this user guide for the Omega FMA-2700, 2800, 3700, 3800 mass flow meters - which explains more about the interface and confirms it is not RS-232. \$\endgroup\$ – SamGibson Aug 12 '16 at 17:02
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In summary: you can't.

You won't be able to wire that connector directly to any sort of PC port without some form of interface device.

The blue wire and orange wire look like the output from some form of sensor. "4-20mA" indicates a typical current loop which is commonly used among industrial sensors and lab equipment. Neither of these can be directly connected to a computer without translation to a digital interface (serial/RS232 or USB).

Neither serial or USB can provide 24V directly either. It's possible to get 24V from USB with a boost converter if you only need low current but it would be better to power your device externally.

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Firstly, it's not RS-232 cable. It's called D-SUB connector with 9 pins. From what I can try to assume it looks like it's a connector to control some device, maybe laser system or something similar. As you can quite clearly see, it has no data pins, so it would be silly to try and connect it to computer as it could result in some exciting smoke. You should make additional PCB board which would control it. Firstly, I would read datasheets thoroughly and make sense of what I'm trying to achieve and how

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