ADC0831/2/4/8 quirks?

Paul

Im building a circuit with the ADC0834 and finding some really odd things about it.
1. The Vref (usually tied high) has quite a low input impedience. If you want to give it 2.5 Volts and connect it to a voltage divider of two 10K ohm resistors (one to +5, the other grounded) you will only get about 1.5V at Vref. Strange.
2. The Data Output D0, D1 are TRI-STATE according to the spec sheet and required a Pull-up resistor to get any signal out of them. I've looked at lots of ADC circuit and never saw a pull up resistor. Strange again.

That my rant ..I hope someone finds this interesting.
--Paul

Jon Williams

I've always used a pot to set Vref and never a pull-up on the DO/DI pins; note that that when you tie those pins together you must do it with a 1K so that the output of DO doesn't swamp the input of DI. Make your connection to the Stamp on the DI side of the resistor.

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Jon Williams
Applications Engineer, Parallax