expand analog input in PIC16F887

[arras.badre]

Hello,
in my project i want to mesure about 70 resistor in a short time (Max 2 min ) and display there values in LCD, i have think to use PIC16F887 with analog inputs, now i want some circuit to interface that many resistor (expande my analog input) like D-flip flop 74HCT574
any idea about how the design will look like ?

 

[barry]

A D-flip-flop is a digital device, it's not going to help you measure analog signals. What you want is an analog multiplexer. Look at something like a 4051 (8:1 multiplexer).

 

[spudboy488]

You could also add more A/D converts (if you're going to add external circuitry anyway). The MCP3008 is a cheap, 8 channel, 10 bit A/D that I use all the time. If I have more than a few channels of analog, I usually use an external A/D since most of my designs are heavy digital I/O from the uP.

 

[crutschow]

Your choice is between adding analog multiplexers (such as the 8-channel CD4051 or 16-channel CD4067) as barry suggested, or adding A/D converters, such as spudboy488 stated. If you are concerned about power, then the multiplexers would take less power.

Of course either of those schemes will require some added decode circuitry to select a particular multiplexer/A/D and channel. For 70 channels this will require a minimum of 7-bits from the PIC.