Take a peak at TI's ADC. They have several in the $2 range for 1 to 4 channels
with built in voltage ref. They are small TSSOP-16 or VSSOP-8 (or DIP for
easy prototyping ;-) Parts to look at: ADS7846, TSC2003, ADS7818. The
first two are touch screen controllers (TSCs).

For single or two channel use, the TSCs can be easily used. Using all four of
their channels requires a little more care.  The ADS7818 is a straight up 12
  bit ADC with internal vref.

Also look at the ADS7822 ($1.50). It needs an external vref. Packaged in 8 pin
DIP or SOIC or VSSOP.

Linear Tech has a couple of 12 bit ADCs in the $2.50 range. Look at
the LTC1860/1861.

cheers,
eric

>John, further to this thread, look at the Analog Devices web site at their
>low speed sigma-delta converters, such as the AD7705 - it's about $8 - it's
>a 16 bit device.
>
>Microchip has a line of cheap sigma-delta converters as well - look at the
>TC3400. Problem is they are hard to find.
>
>Also look at Maxim and Linear Technology and National Semiconductor - they
>all have 12 bit serial A/D.
>
>I like the Maxim ones with built in reference - I use the MAX 186 8 channel
>unit and the MAX188 (I think that's the number) single channel unit.
>
>Larry
>
>At 02:13 PM 2/12/2003 -0800, you wrote:
>>I am still working on this stupid project, but what I need is to either
>>connect a 12 bit adc  to my mpu, or amplify my signal  X 2 for the 10 bit
>>adc that my mpu has built in. Which would be easier to accomplish and/or
>>produce the best results.
>>
>>If amplify, what type of amplifier would I want to use.
>>
>>Thanks
>>
>>John
>>
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>
>Larry Bradley
>Orleans (Ottawa), Ontario, CANADA
>
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