cheap USB A/D converters?

I'm wondering how to hook up common analog sensors to my Mac. I've done some searching for USB A/D converter boxes, and found them for $150 (or
$85 at Phidgets but you have to use their special cables). This seems steep when I can by a USB game pad or joystick for $50 that sends multiple analog signals in just fine.
In fact, I'm half-tempted to hack a game input device, but I'm not really a hardware whiz -- is that likely to be harder than it sounds? Has anyone already done this, by any chance, and posted their findings somewhere?
Another alternative I'm considering is to buy a Baby Orangutan ($25) and program it to report values from its analog inputs over the serial bus upon request.
Any other suggestions for getting analog signals into my Mac cheaply would be much appreciated.
Thanks, - Joe
,------------------------------------------------------------------. | Joseph J. Strout Check out the Mac Web Directory: | | snipped-for-privacy@strout.net http://www.macwebdir.com | `------------------------------------------------------------------'
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wrote:

Search ebay for "USB game port adapter" and you will see some with 4 ports, with each port possibly supporting 4 joystick analog inputs (two joysticks per port, with two analog inputs per stick). Most of these go for ~$17 including postage. You would have to convert your analog signal into a resistance to put across the analog input pins. USB gamepads have a lot of buttons that could be used in conjunction with an ADC chip. You would have to figure out the Mac programming to read the USB inputs. If the Macs support the USB to serial adapters, then there are a lot of serial boards around.
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shb*NO*SPAM*@comporium.net (Si Ballenger) wrote:

That sounds like a really good option.

Can you give me a few pointers on how to go about that?

If they appear to the computer as a game input device, then I've got that covered -- these are easy to read.

They do and I already have one. But I haven't found any serial analog I/O boards that are much cheaper than the USB ones. Are there any in particular you recommend?
Thanks, - Joe
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wrote:

You would have to work this up. I've only looked at this for use with thermisters temperture monitoring.

I got several cheap joypads from www.geeks.com on sale for $2.99 (regularly $4.99) the other week (they are currently out). These have an 8-way X-Y button (but not analog), and 10 other on/off buttons. You may want to keep watch to see if they get some more in.

You may want to check the RS232 board below. It apparently has provisions for ADC using an extra ADC chip. If you send a request, they will send you a pdf manual for the operation of the board so you can see how to interface with it.
http://www.futurlec.com/RS232DevBoard.shtml http://www.futurlec.com/ICADC.shtml
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Joe Strout wrote:

The old game ports used the pot in a joystick/steering wheel in series with a capacitor to adjust the charging time of the cap according to the position of the stick/wheel. It's cheaper than a conventional A/D but not easily useful for reading things other than resistive sensors in the correct resistance range. I have not looked at the new USB peripheral controller chips, but I expect that they use the same approach for cheapness. You could replace the pot with a voltage to current converter (an op amp, a transistor and a couple of resistors), but the range and linearity probably wouldn't be great.
Look at Cypress Semiconductor's USB peripheral stuff (www.cypress.com). A cheap eval board with a CY7C63101A or similar part could talk to a conventional A/D converter with a few lines of code in it's little processor. Cypress also had an app note listed for starting out on USB and the MAC.
Another idea would be to use a USB to parallel port adapter and then bit bang the parallel lines to drive an SPI interfaced A/D chip. A similar thing could be done with a USB to serial adapter with the status and control bits. Note that it would be necesary to bypass the logic to RS323 level shifters if you used the serial version.
Good Luck, Bob
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snipped-for-privacy@DUMPSPAM.yahoo.com says...

A variety of SPI A/D devices can be hooked up to the U401 or U421 from www.usbmicro.com. The devices work with Win/Linux/OSX.
-Rob
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