The entire CircuitMaker C logo can be constructed using equilateral triangle segments. Each segment is a triangle with 7 amber (or whatever color you want) LEDs, which are in series and powered by an LM317 linear regulator configured as a current source.
How the current source works
The 68Ω resistor from the output of the regulator goes straight to the adjust pin, no voltage divider. The way LM317 regulators work, is to adjust the output transistor's drive to fix the difference between the output and the adjust pin at 1.25V (the reference voltage). Therefore, the output current is set by taking 1.25V and using Ohm's law to find a resistor value for the set current. In this case I=V/R=1.25/68≈18.3mA. That's just about perfect for most LEDs out there.
Driving LEDs in series with a current source has the following advantages:
- All LEDs will have fairly uniform brightness (assuming they're all the same part number).
- The input voltage can vary fairly widely without concern for the LEDs wellbeing.
- The driving voltage can go fairly high if needed, because the LED forward drops add up to offset the maximum Input-to-Output voltage specification of the LM317 (which is already high at 40V).
- The series connection means lower current is needed for each segment, therefore the segments could be driven from open drain or open collector "power logic" registers, such as the (S)TPIC6C595D SPI shift register. Once I've made the sign I'll be using some '595 open drain devices to make the controller for the display.
Each triangle segment can be individually driven if needed. The power and ground pins are replicated in symmetrical positions around each edge of each triangle, so they can be effectively stitched together into any pattern that is made up of triangles. The CircuitMaker C logo uses 15 segments, and in the project is a second PCB document containing the mechanical 3D models (as components) for each of the 15 segments, arranged into the logo shape.