com port power supply

[xlogan]

hi there

I am developing an application that comunicates with a PIC microcontroller (pic16f88) and my aplication is recieving data from the PIC, everything works fine, i can recive the data from the PIC and viceversa, but... when i whant to power my circuit with the lines of the com port it doesnt work.

i try to power up the circuit by using the 7 -> RTS y 4 -> DTR pins and usin a pair of diodes (1N4148) i conect them to a voltage regulator (LM7805), i use the diodes because this lines dives voltage from -10 to +10, the thing is that this configuration diodes works, because i test the circuit with the HYPERTERMINAL program and works all right, but when i use my VB application y does not work, it is becaus one of the pins do not give me the +10 voltage instead it gives -10, but with HYPERTERMINAL both gives +10

any idea how to solve this problem?

[namrekka]

Enable RTS/CTS handshaking and enable DTR/DSR.

MSComm1.Handshaking = comRTS
MSComm1.DTREnable = True
MSComm1.RTSEnable = True

Remember it only works with desktop PC's and no more then ca 5mA per pin.

[gtilles]

I don't know how much current the Com Port can source but I know it is very small, I would not rely on the com port to supply power to your circuit unless you know the requirement draw is less than the source can safely supply.

[Al42]

Most COM ports can supply enough current for most PIC microcontrollers. In fact, it's common practice to design microcontroller programmers using the COM port as a power supply.

[xlogan]

Thanks a lot, i will try this out today

[xlogan]

hi, it doesnt work

MSComm1.Handshaking = comRTS  
MSComm1.DTREnable = True  
MSComm1.RTSEnable = True

but i try a diferent handshaking and try with comNone and the code was like this

MSComm1.Handshaking = comNone  
MSComm1.DTREnable = True  
MSComm1.RTSEnable = True

and with this works allright.

[namrekka]

OK. Success.