Remember this? Cigarette lighters were universal accessories in cars until the mid-1990s. We put one in a CT scanner to see how it works and discovered a marvel of efficient, low-cost analog design.

Check out the video below to see the cigarette lighter in action and walk through the CT scans with us:

An analog system

A cigarette lighter in a car connects to a 12V DC power supply. To heat it up, you press the handle in. It starts to draw current, and after a few moments, the handle pops up, revealing a glowing coil hot enough to ignite a cigarette. 

You might think such a system would involve a thermostat, a microcontroller, and an actuator, but this design, developed in the 1950s, is entirely analog and optimized for simplicity and cost-efficiency.

Examining the CT scans

We used a Neptune industrial CT scanner to capture detailed scans of the lighter. This scanner works on the same principle as a medical CT scanner, capturing X-ray images from different angles and reconstructing them into a 3D model.

Lighter in the popped-out position

In this scan, the lighter assembly is in its popped-out position, as it would be after heating. By stripping away the less dense plastics, we isolated the metal components for a clearer view.

Give the lighter a spin for yourself in the Voyager window below:

Cutting into the model, we see the removable lighter with a large bolt fixing the plastic handle. Surrounding the handle is a single coil spring. The heating element is visible in the center, with another bolt below it attached to the arms of a spring clip. The coloring indicates relative material density, showing stamped steel and a ceramic insulator around the lower bolt.

Lighter in the pushed-in position

Next, we examined the lighter after the handle has been pushed in, simulating its heating configuration. The heating element is held in place by the spring clip, creating a circuit.

In a car, the bottom bolt connects to a positive lead, and the housing tab connects to a negative lead. Current flows through the isolated bolt, the spring arms, the outer rim of the heating element, the heating coil, the center bolt, and finally back to the negative terminal. 

The current is forced through the high-resistance coil due to a tiny gap insulated by a strip of paper, preventing it from taking a shorter path.

Detail: Heating element

A closer look at the heating element reveals its design. The coil, made of nickel-chromium alloy, is bonded to the surrounding shield on one end and the center bolt on the other. Each loop is oxidized, insulating it from adjacent loops and forcing the current to traverse the entire resistive filament.

Pop-out mechanism

The spring clip, which holds the lighter in its depressed position and conveys current, has bimetallic arms with steel on the outer surface and copper on the inner surface. As the filament heats up, the arms warm up, causing the copper to expand faster than the steel. This expansion pushes the arms open, releasing the lighter. The coil spring then causes the handle to pop out, signaling that the lighter is ready.

Conclusion

This entirely analog device, developed in the 1950s, showcases the ingenuity of efficient, low-cost design, capable of being manufactured by the millions without any digital control.

You can explore these scans yourself in the Voyager. If you’d like to learn more about industrial X-ray CT technology and how engineers use it to improve everything from running shoes to medical devices, check out our introductory video or reach out to our team.