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craig_b
19-03-2003, 11:01 PM
I am trying to gather data from an analogue system into a microcontroller of the 8051 variety. (Specifically an AT89C51)

It has no integrated A/D input capability, so I need an external chip to do this. However, the only ones I can find are too powerful and expensive for the task.

I need approx 10 - 50 analogue samples per second at the most, more likely to be 1-10 most of the time, but I can oly find chips capable of several thousand...

Also, I don't need huge accuracy, 8bit is fine, and I am looking at spending $10 at the most on the chip.

Can anyone point me in the right direction?? I have tried the farnell catalogue and website (my primary supplier), plus just general web searches...

Cheers,
Craig.

Dolby Digital
20-03-2003, 02:03 PM
Have you tried Dick Smith... (I think I am joking). What about emailing Silicon Chip magazine in Aus.

Graham L
20-03-2003, 04:47 PM
What you want are the serial A-D converters. Texas TLC548 and 549 are nice. There is a National Semiconductor ADC0831 (and ADC0832). They are 8bit, and do "upto" about 40000 samples/sec. Actually, the transfer time to the CPU is the limiting factor. I have built a couple which fit in DB25 covers, on a piece of Verobard soldered straight to the DB25S which fits on the parallel port (and gets its power from the unused data lines). Draws less than 2 mA.

One or two of the EA and SC kits (DSE have (or have had them) use these chips. One of the TI chips has 11 channels of input in a 20 pin chip; the others have one channel (2 for 0832) and are in 8 pin DIL. (The single channel TI and NS ones are not pin-compatible --- but it's non destructive, just don't work --- I've done it. :D )

craig_b
20-03-2003, 08:52 PM
Thanks Graham, but I have found the chip I need, I found that phillips market a low speed a/d converter that meets my needs and is available from RS.

E.ric
20-03-2003, 10:38 PM
What about using a 8 bit port to a Digital to Analog converter (resistor ladder), to a input of Op Amp, with the Digital of the op amp back to the interrupt line, and the other input of the op amp going to the source to be measured, just program the 8 bit port as a counter,