Time to actually build it !

For a first board, I put 100Ω in series with each LED and 39K for the pulldowns.

The PCB is too small to make the typical cross but the 5 switches fit anyway.

Now, let's code !

for o in 22 23 24 25 26
do
  echo $o > /sys/class/gpio/export 2>&1 > /dev/null
  echo out > /sys/class/gpio/gpio$o/direction
done

while true
do
  for o in 22 23 24 25 26
  do
    echo -n " "$o
    echo 1 > /sys/class/gpio/gpio$o/value
    sleep .3
  done

  for o in 22 23 24 25 26
  do
    echo -n " "$o
    echo 0 > /sys/class/gpio/gpio$o/value
    sleep .3
  done
done

The green LED is quite dim, as noted in a comment of the project's main page.

...

Aaaand... the buttons don't work ! I totally forgot about the internal pull-ups...

In particular, GPIO2 & 3 are wired for I²C and have a 1K8 pull-up, the 39K pull-down lowers the voltage to 3.15V. Others are measured at 1.6V, meaning that about 30K of pull-up is already present. Damnit !

So there is no need of pull-downs and the common rail can be tied to GND instead of Vcc.

for o in 2 3 4 5 6 22 23 24 25 26 ; do
  echo $o > /sys/class/gpio/export
  sleep 0.1
done
sleep 1
for o in 2 3 4 5 6 ; do
  echo in > /sys/class/gpio/gpio$o/direction
  sleep 0.1
done
for o in 22 23 24 25 26; do
  echo out > /sys/class/gpio/gpio$o/direction
  sleep 0.1
done
echo "loop:"
while true
do
  for o in 2 3 4 5 6
  do
    if [ "$(cat /sys/class/gpio/gpio$o/value)" = "0" ]
    then
      echo 1 > /sys/class/gpio/gpio2$o/value
    else
      echo 0 > /sys/class/gpio/gpio2$o/value
    fi
    sleep .01
  done
done

Now the buttons return 0 when pressed...

The init code has taken quite a while to finally work, some setup time seems to be required...

.