I Finally Captured a Clean Coil Sine Wave Across the Middle Coil

Hook

I swapped the rotor magnets for a big bottom drive coil and finally locked in a clean coil sine wave across the middle pickup while the top coil ran from the signal generator.

Watch this experiment

We ran three 12 V supplies into the solid-state board, used a trigger coil to pulse the bottom driver, and watched the scope while spinning the wheel by hand. The iron core bounced at low frequency, then settled into a 220 Hz bass wave. Flipping on the top coil gave us a steady 1.2 kHz sine that mixed with the lower wave on the middle coil.

What you'll learn

How two separate coil frequencies interact on a center pickup coil, what the waveform looks like when the bottom coil is turned off, and that magnetic induction alone can still send a small pulse variation through the trigger coil with zero power applied to the bottom circuit.

From the bench

Three power supplies at 12 V, dual-drive board with only one side active, trigger coil doing the pulsing, big drive coil on the bottom, signal-generator-driven top coil, and the middle coil feeding the scope. Wheel was hand-spun to get things moving.

How it works / what we changed

Replaced the spinning magnets with a stationary bottom coil so the iron core sits inside it. The trigger coil fires the solid-state circuit. Top coil runs independently from the signal generator. We read everything off the middle coil. At low frequency the iron core physically bounces; once speed comes up the noise stops and the electrical waves take over.

coil off yes sir

I said "coil off yes sir" and killed the bottom coil. Instantly the scope showed a clean straight sine wave coming only from the little middle coil at about 950–1000 Hz. No more mixed junk, just a nice steady wave.

coil okay

Everything stayed okay once the bottom coil was off. The middle coil kept delivering its own clean output and the top coil continued at its set frequency without any obvious loading or heating problems on the bench.

coil sine

We got a steady coil sine from the top coil via the signal generator. On the middle pickup it sat around 1.2 kHz across the board. After the bottom coil was switched off we saw an even cleaner coil sine at roughly 950 Hz.

coil off

With the wheel power off and then the bottom coil off we still picked up a usable wave from residual spin and from the top coil alone. The middle coil gave us a clean reading once everything below it was disconnected.

coil even

Even with the wheel power off and the bottom coil off we still saw a slight variation riding through the trigger coil. The scope showed the wave was not perfectly flat; a little pulse made it through from magnetic induction only.

coil which

The middle coil is the one which gave us the cleanest reading. Both the top and bottom coils affect it, but when we turn the bottom coil off the middle coil which we are measuring shows a straight sine wave at 950–1000 Hz.

Builder checklist

• Trigger coil wired to pulse the solid-state board
• Bottom drive coil large enough to hold the iron core
• Signal generator feeding the top coil at 400–1200 Hz range
• Middle coil connected to scope probe
• Three 12 V supplies ready (two for solid state, one for wheel if needed)
• Hand-spin or low-speed start to avoid initial bounce

Troubleshooting

If the wave looks noisy, turn the bottom coil off and see if it cleans up. If the iron core bounces too much at startup, increase frequency slowly. When you lose the trigger pulse, check that the wheel is still spinning enough to keep magnetic coupling alive.

Safety

Keep fingers clear of the spinning wheel. 12 V supplies are low voltage but the currents can get warm on the coils. Don't leave the bottom coil powered at high amplitude for long periods while the core is bouncing inside it.

FAQ

Why does the iron core bounce? At low frequency the magnetic field is strong enough to physically push the core up and down inside the coil.

Can you run without the wheel spinning? Yes, but you lose the extra induction effect that gives the slight pulse variation through the trigger coil.

What frequency gave the cleanest sine? Around 950–1000 Hz on the middle coil once the bottom driver was off.

Related on this site

• How to Build a Pulse Motor: Parts, Coil Gap, First Spin
• Pulse Motor vs Bedini Motor: What's the Difference?
• Reading Oscilloscope Output on a Pulse Motor
• DIY Magnetic Induction Motor: Hobbyists in 2026
• Understanding Back EMF in Pulse Motors

Watch this experiment on YouTube

• ▶ Watch full on YouTube