[sdiy] mcu project with too few I/O lines :(

[Ingo Debus]

Rainer Buchty wrote:
 > As for the 16 LEDs, you probably want to have some LED drivers. One
 > 74245 per 8 LEDs should do the job as the data sheet claims Iol to be
 > 24mA, so attach them with the cathode facing the 74245 output which 
means
 > that pulling the corresponding data line low will lit the LED.

Easier: use low current LEDs. 2 or 4 milliamps isn't too much for most
uC port pins.

Here's another idea to save port pins: in my last project one pin
drives one LED and scans one momentary switch at the same time. LED
(in series with current limiting resistor) goes from pin to V+, switch
goes from pin to ground. When the switch is scanned, the LED is turned
off for this short time. The only downside is, the LED always lights
up when the switch button is pressed, but this doesn't matter in my
application.

Ingo