Vol. 20: Hydrogen-Oxygen Bottle Rocket

Use electricity to split tap water into hydrogen and oxygen gases, then use this explosive gas mixture to power a two-stage, electronically timed rocket.

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Schematic diagram (PDF)

Schematic Notes

Tom Zimmerman
December 12, 2008


The circuit consists of a 555 timer that outputs pulses at about one per second to a 4017 counter/decoder. The pulse rate is determined by the 1 M variable resistor, indicated by the flashing green LED connected to pin 3 of the 555 output. When the FIRE switch is closed the 4017 counter/decoder raises the output of one pin at a time, turning on in sequence the green, yellow and red LEDs, to provide a visual count down, then turns on transistor Q1 to fire stage one, followed by Q2 to fire stage two. If the rocket starts curving back to earth before stage two fires, decrease the variable resistance to speed up the sequence rate.


To launch open both the ARM and FIRE switch and make sure no LED is on. Connect the igniters to the circuit with alligator clips. When the rocket is on the launch pad and you are ready to launch, close the ARM switch and make sure the green sequence rate LED is flashing about once per second. Make sure the launch area is secure, yell "FIRE IN THE HOLE" (my favorite part), watch the yellow sequence LED go on, then run to safety. If after a minute the rocket doesn’t take off, walk back cautiously and turn off both switches.

Part Label Part Number Description Vendor Number
Q1, Q2 BUZ72L MOS Power Transistor Jameco #209058
U1 LM555 Timer Jameco #27423
U2 CD4017 Decade Counter/Decoder Jameco #12749

The record for a multistage water rocket is 1,000 feet. Mine went under 100 feet because the fins were too small, not low enough on the bottle and didn't have a nose cone, so it tumbled. I also didn't optimize the mix of water, HHO gas, and air. I focused on making fuel (HHO gas) and reliably igniting multiple stages. I leave it to the readers to optimize the water rocket part, since many people have been working on those aspects.

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