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reading data from a serial port?

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Solidacid

Fri Dec 05 2008, 05:12PM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

hey everyone :D
i was hoping you could help me, im trying to built a temperature sensor for my serial port but i don't know how to send data to it.

i tried connecting 2 LEDs (in opposite directions) between pin 4 and 5 on the serial port, then i used This (from scitoys.com) program to send morse code to my serial port.
to my amazement BOTH LEDs started blinking?!

i serached around google for a while an found out that the serial port transmits data as both positive and negative pulses.

now, my question is: how do i send data TO my serial port? do i just plug some wires from a 5V source in some holes?
i would like to send binary numbers thru it.

it would be great if i could hook up 8 swithes (a DIP-switch?) and if i for example pressed switch 1,3 and 6 my PC would recieve 10100100

A DIP-switch:
DIP Switch

any ideas?

Sulaiman

Fri Dec 05 2008, 06:36PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

You could look at ic like MAX232
It would be a lot easier to use the parallel port though.

Solidacid

Fri Dec 05 2008, 07:03PM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

thanks for the reply!
i did i quick search for the MAX232 at my local(35 km away

) electronics stores website, the chip is pretty cheap

.

do you have any links or directions on how to connect it? or how to connect switches to the parralel port?

i played around with my parallel port a while back, i even made a small circuit to control a cellphone from it, so i could send text messages from my PC

.
it only used the outputs from the port though, i have no idea how to use the printer port inputs,
do i apply power to a pin or do i just connect a pin to ground?

as you said it would probably be easier to use the parallel port so ill try that first, but eventualy i would love to build a serial version for my laptop(using a USB to serial converter)

LithiumLord

Fri Dec 05 2008, 09:46PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Solidacid wrote ...
do you have any links or directions on how to connect it? or how to connect switches to the parralel port?

It's not a serial-to-parallel convertor, it's just used to convert logic levels. You need an MC or a clocked logic-based device (a bit of an overkill here) in order to transfer information through this port.

Solidacid

Sat Dec 06 2008, 12:17AM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

LithiumLord wrote ...

It's not a serial-to-parallel convertor,

i know

, i meant directions on how to use the chip OR directions on how to connect a DIP-switch to my parallel port or preferably both ofcourse

LithiumLord

Sat Dec 06 2008, 12:44AM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Heh, what exactly are you going to achieve? The parallel interface just needs 0/+5v signals supplied to each pin through resistors that prevent bus collisions. For the serial, the chip you are looking at is a level matching device, meaning you rig it to your serial port with one side and to the controller you'll use with the other, take a look at it's datasheet - it's pretty clear there. Then - just watch the RS232 interface specs to make the timing procedures. For the temperature sensor you'll only need an ADC, an MC (most likely serving as ADC as most of them can) - and the 232 matching chip to communicate with the computer. If you'll choose the parallel port, just rig a parallel ADC to your LPT port with the collision-proof resistors present.

Solidacid

Sat Dec 06 2008, 12:59AM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

LithiumLord wrote ...

The parallel interface just needs 0/+5v signals supplied to each pin

That's what i needed to know :D i was wondering if i should just connect a data pin to ground or feed it 5v

Bjørn

Sat Dec 06 2008, 02:50AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

You don't need to make it complicated, most rs-232 ports accepts 0-5 V instead of -12 - 12 V. The serial ports also have general input/output pins that you can use without thinking about rs-232 timing. The advantage with the serial port is that you don't need a driver in windows, since the driver is built in.

In the simples case you connect the sensor with a zener to limit the voltage to the general IO lines and make your program. Look at digital output sensors like DS1820 and SMT160 that can be interfaced without an A/D or rs-232 timing. One example (google has many):

There are many ways to do it, you just need to decide on how complicated you want it to be and the accuracy you need.

Conundrum

Sat Dec 06 2008, 06:34PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

modified surplus USB keyboard would work :)

also you can send a fair amount of data thia way, in fact i was looking into using it as a primitive A-D for laptops with no serial port.

regards, -A

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