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5 ohm power resistor.  Display has to be bright!
Printed these out on 3D printer
close up of one segment.  4 LEDs wired in parallel
4 red LEDs make up one segment of a display
top part will say "your speed".
control board for display, run by Arduino Nano
Testing brightness and what resitor value to use
Had to add small transistor to isolate Arduino logic from 12Volts
First light!
Layout of the control board
schematic of the control board
Speed Sign
Sunday, April 04, 2021
The speed limit on the highway at end of our driveway is 40 kph. I've seen cars go 80 and motorcycles even faster.   So, I'm building this speed sign to let drivers know how fast they ARE going. 

It's built in two pieces: the display, and the detector.   The detector has to be about 100 feet from display to give enough time for detector to lock on, then display the value on the sign.   The two have to operate on solar (with batteries and charger) and will communicate with each other by 233MHz radio.  (I've tested the radio portion to check feasibility.)

Tuesday, April 06, 2021
This project is incomplete, only 50% done.  Left to do:
Breadboard Doppler sensor package  and test
👉 Test radio from Doppler package  to light display
👉 Make stand for light display
👉 Make solar charger for batteries in each piece

Optional: send speed info back to home base for data gathering, charts, etc