how should i get output from serial port of laptop...?

i want to get output from serial port or parallel port of laptop from matlab..

it should be in 0 or 5 V. means min or max voltage

Answer 1

[Walter Roberson]

0 to +5V is TTL levels, which you will not be able to get directly from a standard serial ports. Standard serial ports operate on both positive and negative voltages. It is possible to buy RS232 to TTL convertor modules.

Parallel ports operate on TTL levels. It is not recommended to create new projects that use parallel ports, as MS Windows is making it more and more difficult to access parallel ports.

Do you need these outputs as digital data, or as strobes, or as continuous high/low outputs? Or do you want variable output levels (e.g., 0.35V 0.91V at need) ? How quickly do you need to be able to vary the signals.

[kenil]

walter thanks but i need output in only two bit on and off i have to just switch on or off through relay just i need high voltage or law voltage.

[Walter Roberson]

Do you need the voltages held?

Do you have a true serial port on the laptop, or is it USB instead?

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/59311-hi-low-analog-output-to-usb

[kenil]

yap walter i need voltage held for constant voltage(minimum or maximum) i my laptop i had VGA port for projectors and USB VGA port is also serial port. Do you know how to get output from there??

[Walter Roberson]

Are you referring to a "KVM" type USB connector, the sort designed to allow you to switch your Keyboard Video and Mouse between multiple computers? You can sometimes find serial on those (but not usually.)

USB is a serial protocol but you have no control over the individual bits, unless maybe you managed to find a prototype from when USB was being designed. The driving of the serial lines in USB is done by hardware controllers.

USB to Serial convertors would at best allow you to break out the DTR being synthesized by the circuitry. DTR is logically carried over USB as a bit in the first byte of what would otherwise be the payload (real payload, if any, does not start until after that status byte) and the receiving hardware changes appropriately. From MATLAB, unless you want to go down the the MEX level, the fastest rate you can manipulate the DTR would be 20 ms.

Please consider using the devices that Image Analyst mentions in the Question I linked to, instead of trying to do this via serial.

[kenil]

is there any option to get output from laptop? except parallel port....

[Walter Roberson]

What connectors does it have? What switching rate do you need? Do you have a maximum latency defined?

[Muhammad Mohsin Khan]

i have usb to ttl converter can i use it to take 5v output signal please help

[Walter Roberson]

Muhammad Mohsin Khan: I would raise similar questions to what I asked those years ago: How long do you need to hold the voltage for?

If you need the voltage held instead of being pretty much a strobe, then I would recommend that you work with DTR; https://www.mathworks.com/help/matlab/matlab_external/dataterminalready.html