NE555 Light Jockey | Natalie Lin

I built a light controller that uses a handmade, three-position selector to change how quickly two LEDs blink. The circuit combines an NE555 timer with copper-foil traces on cardboard; the switch is made from laser-cut cardstock.

I simulated the circuit in Falstad, laid it out in KiCad, cut the adhesive copper foil with a Cricut, and designed the mechanical parts in Fusion. The main challenge was making the cardstock mechanism both movable and electrically connected.

Completed Light Jockey board with copper-foil traces, two LEDs, and a curved cardboard selector — The finished board. The selector connects the timer circuit to one of three resistors to change the blink rate.

The NE555 repeatedly switches its output, making the LEDs blink alternately. Choosing a larger timing resistance slows the blinking; choosing a smaller one speeds it up. The selector makes this choice through physical contact with one of three copper-covered pads.

Switching between the three blink rates.

A closer look at the rail and slider.

Designing the selector

First iteration: a spring latch

My first design borrowed the spring mechanism from my 3D-printed Fidget Toy. Pressing the spring was intended to retract a locking tip so the circular selector could rotate. Releasing it would let the tip return into a slot in the outer frame.

The thin cardstock did not behave like the printed PLA spring. It did not reliably return to its original position, and the narrow spring broke after repeated presses. The arrow-shaped pointer was even more fragile: it broke while I was removing the part from the laser cutter.

Fusion sketch of a circular selector with an integrated spring latch and arrow-shaped pointer — The first design used a spring latch to release and hold the selector.

Laser-cut cardstock prototype of the first circular selector — The cardstock prototype exposed the spring's poor recovery and fragile features.

Final iteration: a pivoting rail and slider

For the second version, I separated the mechanism into three parts: a curved guide, a pivoting rail, and a slider that moves along the rail. Living-hinge cuts let the outer guide bend into an arc, with openings aligned to the three contact pads.

The rail sets the direction of the slider, while the slider moves toward the selected pad. Its copper-covered underside acts as a sliding contact, connecting the rail to that pad. This design lets me position the contact manually without relying on a cardstock spring to return.

Fusion sketch of the outer guide, with living-hinge cuts and three openings — Curved guide: living-hinge cuts allow a flat sheet to bend into an arc.

Fusion sketches of the interlocking pieces that form the pivoting rail — Rail: supports and guides the slider.

Fusion sketches of the slider base and upright finger tab — Slider: a moving base with an upright tab for the user's finger.

Connecting the moving parts

I made the pivot pin by rolling the copper foil’s release liner into a cylinder and wrapping it with a narrow strip of copper foil. I inserted it into the rail and soldered it to the board. Foil lining the rail and covering the slider’s underside forms the electrical path through the moving assembly.

View the rail and slider assembly

Top view of the rail showing its copper lining and foil-wrapped pivot pin — Copper foil lines the rail and wraps around the pivot pin.

Side view of the assembled cardstock rail and pivot pin — The assembled rail supports the slider above the board.

Side view of the slider with its upright finger tab — The slider's upright tab provides a place to grip.

Copper foil covering the underside of the slider — Copper foil on the underside forms the sliding contact.

The rail and the solder joint at the pivot raised the slider above the board, leaving a gap at the resistor contacts. To bring the contacts up to the slider, I wrapped small cardstock spacers in copper foil and soldered them onto the three resistor pads.

Side view of the selector, with a red arrow marking the pivot's solder joint above the board — The pivot's solder joint (red arrow) added height that the contact pads had to accommodate.

View the raised contact pads

Three small cardstock spacers wrapped in copper foil — Cardstock spacers wrapped in copper foil.

Raised copper contact pads soldered to the board beside the attached curved guide — The raised pads and curved guide installed on the board.

Building the circuit

From simulation to copper foil

The circuit uses an NE555 timer, two LEDs, one capacitor, and six resistors, including two that limit current through the LEDs. I first tested the switching behavior in Falstad, then transferred the schematic and trace layout to KiCad.

Falstad simulation of the NE555 circuit with three selectable timing resistors and two LEDs — The initial simulation established the circuit's behavior; I adjusted the resistor values during fabrication.

View the KiCad schematic and trace layout

Initial KiCad schematic showing the NE555 timer, selectable resistor branches, capacitor, and LEDs — The initial schematic, before the resistor substitutions described below. Select the image to view it at full size.

KiCad trace layout with three separate resistor contact pads for the handmade selector — The KiCad layout used to cut the copper-foil traces.

Correcting the fabrication scale

My first copper pattern was enlarged from an intended dimension of 71.5 mm to 95 mm, about 1.33 times its original size. I had used the board outline on KiCad’s Edge.Cuts layer as the sizing reference in Cricut, even though the imported copper pattern had different bounds. This increased the pad spacing and made it difficult for the components to bridge the gaps, requiring excess solder.

I rechecked the copper pattern’s coordinate span (142 − 70.5 = 71.5 mm), corrected the import scale, and cut a new pattern for the final board.

Choosing resistor values I could build with

The original design called for three 1 kΩ resistors and one each of 22 kΩ, 47 kΩ, and 100 kΩ. Some of these values were unavailable in the footprints I had chosen. My first substitutions reduced the timing resistance too far, making the LEDs blink too quickly to distinguish clearly.

After testing, I desoldered the resistors and changed the set to two 22 kΩ, two 10 kΩ, one 3.3 kΩ, and one 1 kΩ resistor. This made the changes in blink rate easier to see.

Oversized copper-foil pattern on cardboard before components were soldered — The first copper pattern was scaled up by about 33%, increasing the gaps between component pads.

Early assembled circuit before the timing resistor values were corrected — Early circuit testing showed that the substituted timing resistances were too low.

What I learned

Prototype mechanisms in the intended material. The spring concept from my PLA fidget toy did not transfer directly to thin cardstock. Testing its recovery and strength earlier would have helped me choose a suitable mechanism sooner.
Design the motion and electrical contact together. The slider needed both room to move and contact with the resistor pads. The rail, pivot joint, and raised pads all contributed to that alignment.
Check scale and available components before fabrication. Verifying pad spacing at the cutting stage and testing with the actual resistor values would have reduced rework and repeated soldering.