Date: Tue, 7 Jan 2003 11:03:42 +0000 From: Axel Simon <A.Simon@ukc.ac.uk> To: hymette@wanadoo.fr Cc: phk@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: I/O question Message-ID: <20030107110341.GA24812@myrtle.ukc.ac.uk> In-Reply-To: <BF6AA4F2-21C4-11D7-97CA-000A27AFC7DE@wanadoo.fr> References: <24529.1041889348@critter.freebsd.dk> <BF6AA4F2-21C4-11D7-97CA-000A27AFC7DE@wanadoo.fr>
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On Mon, Jan 06, 2003 at 11:18:13PM +0100, hymette@wanadoo.fr wrote: > Ok, pretty complicated huh! Let's be more realistic : suppose I get a > digital thermometer and would like to connect it to a port to treat data > afterwards with my code: where could I get the information that would > help me read (and write) data to the selected port ? On which basis will > I choose this port? (I assume that I'd like to leave room for data > coming from other sensors to be transmitted - selectively - through the > same port in the following steps.) These questions are more depending > upon the FreeBSD part of the stuff, aren't they? Interfacing to FreeBSD is probably easiest through the serial port and most microcontrollers have one. USB requires a complicated protocol and dedicated chips which are hard to get. Designing your own ISA card is possible and not too complicated (if you're able to make double sided PCBs). The reserved I/O space is at $300-$330 or so. I would not recommend for measuring analog values, though. You can't use the PC's power supply because it's too noisy and you need to shield all your circuits from the electrical noise in the PC. Any other interface (reading in through the "paper out" pin of the parallel port, etc.) is most likely causing problems since Windows 98 and let you access I/O directly, but FreeBSD doesn't and you would have to replace the parallel port driver. There is some sort of driver for a I2C ISA card in the FreeBSD collection of drivers. You could use that and ready-to-use I2C temperature sensors (LM34?). I did an 8 channel 10 bit temperature measuring module once. It uses one opamp (LM324 - very cheap) and a Philips KTY-81 sensor per channel. An 80C552 Philips processer transmits the values via the serial port. If you're interested, I can send you the design. Hope this helps, Axel. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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