I built a second "prototype" of the Interactive Frequency Reader on a 12x5 cm perfboard slice. I hope that showing it to interested builders will give a glimpse of the build (non?)complexity.
The display this time is white on blue, very charming. It does require backlight 100% of the time, increasing the current consumption to 32mA.
Noteworthy is that the backlight diode Anode-Cathode is reversed as compared to my other black/green LCD: always, always check your display pinout before soldering it in!
Display and keypad are connected to the board with 2.54mm pin header rows, so that it is easier to remove them for maintenance or re-programming the ATmega168.
Here you can see the actual position of these connectors on the topmost and lowest rows.
CAT cable enters on the mid-left 4-way connector, which is equipped with an old-fashioned jumper if the future owner wants to insert an on/off switch.
Many connections can be kept short if some building tricks are adopted, like keeping close display and ATmega or using resistor leads to join PCF8574 to the keypad connector.
One useful mod would be to add a backlight intensity control (100R fixed + 100R variable would do).
I am trying to take a decent photograph of the lit LCD. but I need to work on ambient light a bit more. Stay visually tuned!