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Check this link, you will have the 5V at the RX/TX of the micocontroller. I mean, replace the microcontroller with whatsoever you want to operate with 5V.
5V is already available at the USB connector. I would suggest disassembly of the USB converter and tapping the +5V line as at enters the device. Either that or splicing into the cable ahead of the converter.
5V is already available at the USB connector. I would suggest disassembly of the USB converter and tapping the +5V line as at enters the device. Either that or splicing into the cable ahead of the converter.
An USB-to-RS232 adapter isn't designed to get 5V out of it, although the voltage is present at the USB connector. You could also ask: How how to get 5v from my USB mouse or my USB memory stick?
Actually, the 5V USB bus voltage is converted to +/-10V inside the adapter and used to drive the RS232 lines. Typically, you are able to sink a few mA from the RS232 interface, if this is enough for your purposes, you can connect a low power voltage regulator and get 5V. The technique has been used e.g. for some microcontroller Dev. Kits with low current consumption.
Otherwise, cut the cable, disassemble the adapter (I fear, it's molded) or design an USB T-connector to connect VBUS.
While it is possible to pull some power from the RS232 lines, there are a couple of serious limitations.
First, remember that the efficiency will be lower than tapping the source voltage directly. (There is no free lunch, you always get out less than you put in.)
Second, some software is required. This tapping a control line as a power source, assumes that you have a driver that sets the control lines to the required state. If the control lines are not at the proper state , or other code using this serial port changes the state, you will lose your power source.
Lets say you are using this device with a serial port terminal program that gives you lots of control. It won't be a big deal, as you can set the required control lines high with the terminal program. However, if you want to use this power source with a third party application that you have no control over, it may not work. That third party app, may reset the port on startup and turn off your power source.
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