A regulated LM317 constant-current driver designed in KiCad that holds output current constant independent of supply voltage. The set resistor fixes the current through \(I = 1.25\,\mathrm{V} / R_{\mathrm{set}}\), so a 62 Ω resistor gives roughly 20 mA, with the regulator dissipating about 0.12 W from a 9 V supply, low enough to run without a heatsink.

The planned test is a supply sweep from 7 V to 12 V confirming output current stays flat, which is a line-regulation measurement. That same test carries over directly to the laser-diode version.

From there the board branches toward a protected laser-diode driver with current limiting and modulation. Laser diodes fail fast under current transients, so the protection circuitry is the real engineering content.