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How to powe up a device using serial communication?

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mosh11

New Member
i am connecting a barcode reader to a pic so how i can power up the device?

the pinout of the rs232 port doesn't contain a Vcc pin so does the serial devices take the Vcc from the TX Pin?

Thank you
 

Sceadwian

Banned
Could you provide a little more detail about your circuit? You're more than a little vague about how you have things setup.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
If the bar code reader has no independent power, then it must take the power off the PC serial port, possibly off the handshake lines?.

You need to find out what it needs and replicate it, I would have thought it's unlikely that it uses the TX pin.
 

mosh11

New Member
Could you provide a little more detail about your circuit? You're more than a little vague about how you have things setup.
i am connecting the output of the barcode reader to a max232 that will transform the 12v level to 5v level and then to a PIC microcontroller that will save the barcode to transmit it later

the idea of the project is to have a portable barcode reader in every shopping kart in the supermarket. the reader will read the barcode and then the pic will send it the server to add the product to the list and then the customer will pay his bill by using his mobile

So obviously i will need the barcode reader to be powered up independent of a PC that's the problem
 

mosh11

New Member
They have been around for years.

Palm SPT1800
PDA Scanner
thank you

but we need more common device and available everywhere in reasonable price

if the PC is supplying the Vcc for the serial device

which pin is responsible for the Supply?

if i knew the pin then i could connect it to the -12v level and the device is powered up
 
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Leftyretro

New Member
From the manual available on line:

http://www.electro-tech-online.com/custompdfs/2009/04/UniversalMenubook.pdf

The device expects +5vdc at 100ma available on pin 9 if using the DB9 connector or pin 25 if using a DB25 connector. This not standard on a standard PC serial comm port. You will not be able to derive that much current using any of the RS-232 signal pins. So you will either have to add a 5vdc power wire inside the PC's comm connector or 'break out' the power and ground connections on a serial cable and provide the 5vdc voltage. They have a USB version of this model, that would have been a better choice.

Lefty
 
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mosh11

New Member
i connected 5v supply to Pin 9 (i am using DB9 connector)

from the readings of multimeter the current drawn by Pin 9 is around 90mA So the barcode reader should be powered up but it doesn't !!

so what's wrong?
 

binzer

Member
i connected 5v supply to Pin 9 (i am using DB9 connector)

from the readings of multimeter the current drawn by Pin 9 is around 90mA So the barcode reader should be powered up but it doesn't !!

so what's wrong?
Does the device need initialization before it will operate?

I did not locate a data sheet so I can't give specifics.

Mike.
 

mosh11

New Member
Does the device need initialization before it will operate?

I did not locate a data sheet so I can't give specifics.

Mike.
i think not because when i connected it to the pc it turned on immediatly

the datasheet is available in Lefty post in the link.

it a datasheet for all opticon barcode scanners
 

binzer

Member
i think not because when i connected it to the pc it turned on immediatly

the datasheet is available in Lefty post in the link.

it a datasheet for all opticon barcode scanners
Do you know if it is programmed to use the handshake lines? If connected to the computer the computer may be asserting one of the handshake lines and allowing the scanner to run. Maybe you need to set the scanner to default conditions to start, or verify how the scanner is setup.
Do you have an rs232 breakout box??
mike.
 

mosh11

New Member
Do you know if it is programmed to use the handshake lines? If connected to the computer the computer may be asserting one of the handshake lines and allowing the scanner to run. Maybe you need to set the scanner to default conditions to start, or verify how the scanner is setup.
Do you have an rs232 breakout box??
mike.
i configured the barcode reader to the RS232 configuration and default settings(no handshaking).

but still didn't power up from the 5v supply

and i want to know what's the rs232 breakout box?
 
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binzer

Member
i configured the barcode reader to the RS232 configuration and default settings(no handshaking).

but still didn't power up from the 5v supply

and i want to know what's the rs232 breakout box?
Ok on the settings. How do you get power when plugged into the PC?

Are you using their power supply, if not are you sure you are connecting to the correct pin?

Rs232 breakout box has connectors to put it inline with your device and has led's for each pin to show you if it is a high or low level, it also can show lines changing / etc.

mike.
 
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mosh11

New Member
actually i am connecting the barcode scanner to the PC using an rs232 to ps/2 converter that comes with the device so the barcode reader is connected to the pc through the keyboard port.

but when i connect the barcode reader to my circuit i connect it through rs232 and remove the converter.

the device is taking power from the pc , iam not connecting any external power supply.

i am sure that i connect the vcc to pin#9 as in the manual
 
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