Here is what you'll need:

    1.  a Google Home, Mini, Max, Nest Hub or smart phone running Google Assistance

    2. a (free) account with IFTTT

    3. a (free or paid) account with Pushbullet

    4. an ESP32 DevKit board which you can get  in North America from Amazon or from China from AliExpress or Banggood

    5. a set of Max7219 display modules (I used 3 x 4-in-1 modules) from Banggood

    5. this open source Arduino code sketch

             which uses other libraries (with due credit given in the comments of the code itself)

    6. an enclosure of some sort - like this one / this remix which can be 3d printed 

    7. a red acrylic cover to go with the enclosure (which is hard to find, but I got one locally from a plastic's shop)

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Here is how you set it up (this is at the 100 foot level, I'm not going to go into great detail - you're smart and can figure it out):

    In IFTTT, you link your Google device to your IFTTT account

    In IFTTT, you link your IFTTT account to your PushBullet account

    In IFTTT, you set up an IFTTT applet to respond to a specific phrase

          for example:  

                the 'If This' option is 'Google Assistant' ,

                       'Say a phrase with a text ingredient', which you can set to:

                       "post Kay $"  (my wife's name is Kay), you can use 

                        Betty or Sam if you married a Betty or Sam.

                and 

                the 'Then That' option is to us PushBullet 

                      to send a note, where:

                         the title is "Leave a message", and 

                         the message is "Kay : {{TextField}} - {{CreatedAt}}"

   Update the Arduino code to include your PushBullet Access Token (found on your Pushbullet Settings window), 

       and your WiFi credentials

   Update the ESP32 board with the updated Arduino code

    Plug your assemble the case and plug in the ESP32

.

To make it work:

    You say (for example) "OK Google, post Kay I've gone to the store", or anything else you may like.

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Here are some things which I learned along the way:

i) using a phrase like "Leave a message for Kay to $" didn't work too well, "Post Kay $" worked better

ii) the enclosure listed above did not have a way to get the power cable in the back, so I remixed it to add one and to use a project box power coupler solution (also listed above) - but you could drill a hole too

iii) when first powered up for some reason all the Max7219 modules don't light up, but if I just unplugged it and plugged it in again it worked

iv) a free Pushbullet account expires after 30 days of inactivity; special code in the sketch above prevents that

v) the more Max7219 modules used the more power it takes, I used 3 x 4-in-1 modules (i.e. 12 individual modules) don't know how many, if any more, you can add and still power via a usb wall jack

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Bonuses:

Source code above also includes two Windows .bat files; one you can run to post a message via your keyboard (not needing your Google assistant), the other to clear the message board

Finally, for reading this far,...

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