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DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC

6 DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC

The complete software is provided in an attached zip file (in assembly & C using ST7 software

library version 1.1) to this application note. It is only an example. It is up to the user to adapt it

to the application.

6.1 GENERAL DESCRIPTION

A 16-key keyboard is connected to the ST72F324 through the AIN0 pin on Port D.

A LED is connected to an output pin (PC0) to indicate to the user that a key is detected.

Figure 5. Application circuitry

The software uses a polling strategy. It makes conversions continuously (no wake-up

process).

First the software initializes the I/Os and the ADC.

When a conversion is done, the software decides if a key was pressed or not.

If not, it waits before analyzing the result of a new conversion.

If a key is pressed, it compares it with the former key to know if the key is stabilized. Then, a

LED is switched on.

ADC

LED

key 0

key 15

analog

input

output

ST7