» MAKE: NOISE — Discuss this article

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• Chemistry?
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  I'm curious about the chemistry of this rocket. The article hinted a little bit about the electrolysis and the need to add sodium bicarbonate as an electrolyte. But can anyone add some insight as to why the water molecule will decompose when there is a voltage potential between the two electrodes? And can anyone offer a little more detail on what the voltage and amperage needs to be at to induce electrolysis? Thanks!

  Posted by Compgeek on November 08, 2009 at 17:07:33 Pacific Time

• Chemistry?
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  Glad you are curious so let’s dive into some electrochemistry. Current is the flow of electrons (1 amp = 6.24 × 10^18 electrons per second). Current flows in a liquid through ions which are atoms that have a charge due to an unequal number of electrons and protons. Pure water has very few ions (about 2 pairs per billion molecules!).
  
  An electrolyte is a molecule that dissociates (breaks into ions) when dissolved in water. The baking soda (NaHCO3) creates lots of Na+ and HCO3- ions enabling chemical reactions that exchange electrons, resulting in a flow of current through the solution. Voltage creates a force that pushes electrons through the electrodes and provides energy to drive chemical reactions.
  
  The electrolyte ions also neutralize charges at the electrodes that would otherwise oppose the flow of current, i.e. H+ ions around the anode and OH- ions around the cathode. Finally the Na+ and HCO3- are not as electrochemically active (have less favorable electrical potential) than the H+ and OH- ions so H2 and O2 gas are formed. If you use NaCl (table salt) as an electrolyte, chlorine gas is formed instead of oxygen because chlorine is electrochemically more favored than oxygen.
  
  Further reading;
  http://www.science-projects.com/Electrolysis/eLysis.htm
  http://www.crscientific.com/electrolysis.html
  http://en.wikipedia.org/wiki/Electrolysis_of_water
  http://en.wikipedia.org/wiki/Standard_electrode_potential
  

  Posted by Tzim on November 10, 2009 at 16:38:00 Pacific Time

• Single Stage?
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  How would you create a single stage without the having to build the entire circuit so you can do several tests, and still add rest of the circuit to do the two-stage as a "finale"? Should I just build all the circuit and just no add the second stage?

  Posted by Callidus on January 08, 2010 at 18:34:16 Pacific Time

• Single Stage?
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  For a one-stage rocket just connect the ignitor to a battery through a switch with a LONG wire (e.g. 20 feet or more), no electronics or timer necessary. Throw the switch and the ignitor fires the explosive gas. Use the same switch circuit to fire the bottle attached to a wheel (as shown in the article) to test for the best mixture of air, HHO gas and water. Be safe and have fun!

  Posted by Teazer on January 08, 2010 at 19:24:40 Pacific Time

• Single Stage?
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  Having recently had an on-the-pad "catastrophic disassembly" event, yes, use a long wire. We had 30', and the debris was thrown more than 40' in the air (had it come sideways...).
  
  Long wires. And ear and eye protection.

  Posted by brdavis on February 08, 2010 at 16:31:58 Pacific Time

• Single Stage?
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  Good point. Longer is better and safety glasses are well advised.
  
  What caused the rocket to explode? Was it a rich mixture (lots of HHO little air), did the stopper not release, or were you using a water bottle that was not designed for pressure (non-carbonated drink)? It would be good to learn from your experience.

  Posted by Tzim on February 08, 2010 at 19:07:56 Pacific Time

• Single Stage?
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  Excellent question... the answer is "I don't know" :).
  
  The design that "disassembled" had two bottles coupled bottom-to-bottom with a Robinson coupling (hollow threaded rod bolting two bottles together) in an attempt to get a larger volume without worrying about splicing. In filling this, getting the gas into the upper bottle was a real pain, with fluid "locks" developing in the narrow connection repeatedly. As a result we're not sure how much HHO vs. gas we had in the rocket... it might have been too rich a mixture. During the actual detonation it was the (rather thick and hefty) bottle bottoms that failed, tearing apart, and blowing the metal coupling into the bottom bottle. That implies to me the it was overpressure in the top bottle that failed the bottom (otherwise the coupling would have been thrown upward), but the joined ends of both bottles was pretty well shredded. On the high-speed video, it's pretty obvious that the flame front started in lower bottle, and proceeded cleanly into the upper bottle, but there way no movement before it tore apart... so maybe it was due to pre-compression of the mixture in the upper bottle, or even due to the stopper in the bottom being wedged too tight that resulted in the pressure staying high just a *hair* too long.
  
  So, take your pick... too rich a mixture, flame front propagation in a longer volume, or a weak coupling. My money's on the last one, but with one data point, I really have little to go on.

  Posted by brdavis on March 04, 2010 at 16:08:14 Pacific Time

• Safer generator
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  My son and I have been working with a single-stage version for a science fair project. I didn't like the idea of working around water carrying those kinds of currents, so we modified it (of course ;) ). From the top of the funnel, we ran a clear vinyl hose hose out of the 5 gal bucket and into a neighboring one. Once filled with gas, this hose serves to isolate the water in the gas generator from the water in the rocket fill bucket... and putting a small hose clamp on the tube means you can even generate gas and "store" it in the tubing for a little bit (waste not, want not). This allow you to very precisely mix any ratio of HHO/Air/Water you want... ideal for a science fair project.
  
  We also modified the ignitor, using two very small alligator clips to hold the rocket ignitors. Much easier to replace, and more reliable.
  
  So far, 8.1 second flights are easy (without a parachute)... but the video of a dusk take-off is spectacular. This summer we'll try the multi-stage approach, but for now I think I need to make a ballistic pendulum to thrust test this puppy.

  Posted by brdavis on January 09, 2010 at 16:56:39 Pacific Time

• Safer generator
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  OK, and the modifications my 12 y.o. son added that I forgot. A simple nosecone cut out of the top of a second bottle (didn't even have the cap), taped into place on the top with a #9 rubber stopper trapped between the nosecone and the pressure chamber. Doesn't add much weight, but *drasticly* increases the stability by shifting the CoM forward. We actually used electrical tape for all construction (fins to body, etc.), and it's held up fine through 7 or 8 launches already. The ground impacts are hard, however.

  Posted by brdavis on January 10, 2010 at 05:43:47 Pacific Time

• What is probable PSI generation?
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  With 1/3, 1/3, 1/3 mixture, what is the likely psi generation per second?
  
  I want to restrict the nossle, but also want to keep the max psi under 80 psi.
  
  Assuming a positive delta per second to psi for the ignition and a negative delta per second to psi for the thrust output, what can be expected on a standard bottle.
  
  I don't mind doing research on this, but don't know the topics to start with to determine the psi/second generated from oxyhydrogen ignition in a contained volume.
  
  I don't think the energy generated is the key factor, I think that the volume expansion is the key factor.
  
  For the combusion PSI, is there a conversion model based upon the ideal gas law: PV = kNT?
  
  I have no idea what formulas are involved for expanding gas exiting a chamber...
  
  I picked up a Make mag while browsing magazines. It's the best thing that happened to me for years.
  
  
  

  Posted by rwagnon on January 13, 2010 at 22:43:44 Pacific Time

• What is probable PSI generation?
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  I'm now assuming that the combustion is effectively instantaneous ( < 1 second), but that the exit thrust continues for some time (2-3 seconds).
  
  Any knowledge that corrects this assumption is appreciated!
  
  The observed maximum height and the presumed pressure at a number below 120 psi (the average burst limit for a 2L bottle) seems to agree with assumption, based upon other water rocket (non-HHO) results.

  Posted by rwagnon on January 14, 2010 at 13:34:13 Pacific Time

• What is probable PSI generation?
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  rwagnon wrote:
  
  > With 1/3, 1/3, 1/3 mixture, what is the likely
  > psi generation per second?
  
  A lot :). Seriously, the rocket goes from ambient pressure to maximum in a fraction of a second (less than 0.06 seconds based on video). From that point on, it behaves very much like a "standard" water rocket - the pressurized gas drives out the water, providing thrust.
  
  Note that Dean Wheeler seems to have done this first back in 2000:
  
  http://www.et.byu.edu/~wheeler/benchtop/hydropyro.php
  
  He estimates that a pure fuel ignition would hit about 187 psi - above what the bottle is likely to survive, but... My son & I have managed a couple of launches at HHO/air ratios of 2 or 3... a predicted pressure of 170 psi and 7000° F (and yes, it does flash rather brightly!). The bottle is still slightly warm to the touch upon landing, with a ballistic flight time of about 7 seconds. That's for a single stage BTW (with a weighted nosecone).
  
  > want to keep the max psi under 80 psi.
  
  That's not going to work well, as it means your initial pressure would end up being 80 psi, and falling from there; the pressure generation is effectively instantaneous.
  
  > I don't think the energy generated is the
  > key factor, I think that the volume expansion
  > is the key factor.
  
  As you note, those are tied together. The combustion increases the temperature due to heating the gas (energy 'generation'), while hot gas exerts a higher pressure (gas law physics). So you can treat the combustion as just energy generation, and then do some simple thermo to get the pressure/temperature (OK, not perfectly simple, as at those temperatures your disassociating some of the products, but it's close).
  
  > I have no idea what formulas are involved
  > for expanding gas exiting a chamber...
  
  Conservation of energy, mass, momentum, etc. You can use a 'normal' water rocket simulator for this, you just have to estimate the pressure.
  
  > the exit thrust continues for some time
  > (2-3 seconds).
  
  Much much MUCH less. All the water leaves the bottle in the couple meters of flight without a restricted nozzle (under a fifth of a second). Even with a mildly restricted nozzle I'm not sure you'll get up into the range of 2+ seconds.

  Posted by brdavis on January 19, 2010 at 05:55:32 Pacific Time

• 10 Question
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  1) Using steel wool as an ignitor won't affect the flight will it.
  2) Could anything be change in the HHO to positively affect the flight (like using H2O2 to create the gas or adding CO2)?
  3) How many times can you reuse the water for the gas. Or can it be used infinite number of times?
  4) Why does the water turn brown? Is it iron oxide, if so whered the iron come from.
  5) Will the bottle weaken at a rapid rate as you test over and over, or can it withstand several consecutive tests?
  6) If you only use air and HHO shouldn't it still fly as long as it has something to push against? The only problem would be the possible breaking of the bottle.
  7) Is there a possibility of the bottle melting because of the explosion?
  8) When adding baking soda, the more the better?
  9) What is the best way to test the rockets thrust without using a ballistic pendulum
  10) If you want test the efficiency of a mixture would it be better to test distance/height/time or thrust itself.

  Posted by Callidus on February 15, 2010 at 12:03:47 Pacific Time

• 10 Question
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  > Using steel wool as an ignitor...
  
  I'm not sure how well that would work (haven't tried it), but it might work OK, if a little less reliable. I can't think of any reason it would alter the actual flight.
  
  > Could anything be change in the HHO to
  > positively affect the flight (like using H2O2
  > to create the gas or adding CO2)?
  
  Probably not. Burning HHO gas produces pressure, plain and simple... and pure burning HHO produces enough pressure to rupture the bottle. So even if there was a way to make it "better" (and with H & O, there's pretty much not), the rocket wouldn't handle it.
  
  > How many times can you reuse the water for
  > the gas.
  
  Probably an infinite (or at least very very large) number of times. We've done a dozen or so launches at a time, the only reason we've not reused the water is it's easier to make it again then to store 5 gallons of the stuff.
  
  >Why does the water turn brown?
  
  My guess is rust, (iron oxide), from the screens rusting. Let's face it, you're exposing them to a lot of destructive oxidizing agents :).
  
  > Will the bottle weaken at a rapid rate as you
  > test over and over, or can it withstand several
  > consecutive tests?
  
  So far, we've used one bottle for about 24 launches, with no noticeable weakening (and the strongest or highest pressure tests have been near the end, with a roughly 3:1 fuel:air ratio).
  
  > If you only use air and HHO shouldn't it still fly?
  
  Yes... and it will. But while the air will come out very fast, there's not a lot of mass being ejected, so the actual thrust is much less. In fact there's a balance between the amount of water, the amount of HHO gas, and the amount of (largely inert) air... different mixtures produce different results, but no water at all flies rather poorly. The bottle certainly won't explode under these condtions, as it would only have to hold the pressure for a couple thousandths of a second (with no large water mass to push, the pressure drops very rapidly).
  
  > Is there a possibility of the bottle melting
  > because of the explosion?
  
  Read the temperature discussion below. The temperatures are *much* too high for plastics... but the plastic is only in contact with that hot gas for a few thousandths of a second. That's not enough time to melt any substantial amount of plastic, so the bottle holds up fine (at least so far... like I said, two-dozen launches and counting).
  
  > adding baking soda, the more the better?
  
  Not really. I'd stick with the amounts in the article (although I don't know how well tested they were).
  
  > What is the best way to test the rockets thrust
  > without using a ballistic pendulum
  
  Invent a method :). Seriously, a force gauge that records the push every thousandths of a second or better is one way... a ballistic pendulum is another (much cheaper)... analysis of the flight video is a third (to get the actual launch velocity)... etc. There are lots of ways. But here, "best" might be "which can I do easily", and that depends on what you have, and what you understand.
  
  > If you want test the efficiency of a mixture
  > would it be better to test distance/height/time
  > or thrust itself.
  
  It sounds a lot like you're repeating my son's science fair experiment :). Thrust is ultimately "best" in a sense, because it doesn't depend on the aerodynamics of the rocket, winds aloft, air density variation, atmospheric drag, etc. But let's face it, timing the flight is probably the *easiest* solution... and it allows you to think about other aspects as well (for instance, we've found that in terms of "time aloft", above a certain fuel:air ratio there's no increase in time... can you guess why?).
  
  --
  Brian Davis

  Posted by brdavis on February 25, 2010 at 06:43:44 Pacific Time

• 10 Question
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  Okay thanks very much.

  Posted by Callidus on February 26, 2010 at 16:49:40 Pacific Time

• 10 Question
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  Oh, and also would it be alright to quote you and use you as a source for my science fair project. I need to have an interview in part of it. Thanks much.

  Posted by Callidus on March 08, 2010 at 18:29:57 Pacific Time

• 10 Question
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  Brian did an excellent job answering you questions. Here's my additions;
  
  > Using steel wool as an ignitor
  Probably not since the ignitor gets wet when you install it. I tesed the Estes ignitors by soaking them in water for an hour, letting them dry, and they still worked. You really want a reliable ignition, especially for the second stage, so even though they cost almost $1, it's worth it.
  
  >Baking soda
  Baking Soda reduces the resistance of the water, creating more current and gas. So use as much as baking soda as your power supply can handle, using the table I provided in the article.
  
  BTW has anyone tried using a computer switching power supply to make HHO? They are inexpensive and deliver lots of amps at 12 volts. The 5 volt supply has even more amps.

  Posted by Teazer on April 29, 2010 at 08:38:39 Pacific Time

• Hydrogen-oxygen bottle rocket?
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  Help, (please) I think that this HHO rocket,may be beyond my abillities. Too late to turn back now, this is the approved science fair project my son has started. All I need to do is build and launch this puppy.(note no small dogs will be hurt, in the making or launching of this rocket) Question #1, Make:Volume 20, page 93 set up,says use clear silicone sealer, page 94, 1d.1e. and 1f. say glue with silicone sealer. should I use silicone glue or sealer, product name, thank you.
  

  Posted by MiCkEy/tD on April 07, 2010 at 16:14:19 Pacific Time

• Hydrogen-oxygen bottle rocket?
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  Silicone sealant and glue are the same thing. I usuall get mine at Home Depot; GE Silicone II Kitchen and Bath 2.8 oz. Clear Model # GE284 3TG SKU # 469301 $3.89. Remember to let it dry overnight.

  Posted by Teazer on April 29, 2010 at 08:30:28 Pacific Time

• Question about the schematic?
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  I have built the circuit and it appears to sequence correctly. The question that I have is where do the arrows lead back to coming off the top side of the igniters. Is it just back to ground?

  Posted by Bubbajoe on April 28, 2010 at 22:41:24 Pacific Time

• Question about the schematic?
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  Referring to the schematic, each MOS power transistor is pulling one side of the ignitor to ground, so the other side of the ignitor must be connected to +9 volts.

  Posted by Teazer on April 29, 2010 at 08:25:43 Pacific Time

• Question about the schematic?
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  Awesome thanks!
  

  Posted by Bubbajoe on April 29, 2010 at 18:35:12 Pacific Time

• Question about the schematic...
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  Hi guys! I'm midway through the construction of the circuit, and was wondering how important it is that the 0.01 uF capacitor be an electrolytic one? I'm trying to use a ceramic button style cap, and I can't get my circuit to work (which may be entirely due to my crap breadboarding skills). And if I do need an electrolytic 0.01 uF cap, wgere do I find it? I can't find any at Digikey or Mouser or Newark (at least none whee I don't have to order like 500 and pay $$$ and wait six weeks).
  
  Thanks!
  
  Corey Richter

  Posted by kebo26 on May 07, 2010 at 11:53:01 Pacific Time

• Question about the schematic...
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  Any 0.01 uF (or 0.1 uf) will do. Pin 5 is the control voltage of the 555 timer and we are NOT using this function of the timer. Putting a cap on this line prevents noise from messing up the timer.

  Posted by Teazer on September 13, 2010 at 12:50:30 Pacific Time

• HHO vs HHCl
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  It just occurred to me that if you use salt instead of baking soda as your electrolyte you will get a mix of Hydrogen and Chlorine gas instead of H2 and Oxygen. Since Igniting a mix of H2 and Cl produces much more energy than igniting HHO you can increase the amount of water in each bottle (stage) which should result in longer flights. Caveat: Chlorine gas is toxic so don't inhale much and it takes less energy (less heat) from a spark to ignite an HHCl mixture. Furthermore, the product of burned H2 and Chlorine is hydrochloric acid (muriatic acid). But I'm sure if you've taken the proper precautions for handling pure H2/O2 mixtures then you should be safe enough even with chlorine replacing the O2. Keep baking soda handy anyhow since thats a good first aid treatment for contact with acids...So, GO, set a record or something! That's what I'm gonna try to do tomorrow ;)
  

  Posted by lotusdiver on June 20, 2010 at 07:20:10 Pacific Time

• Sequencer timing failure
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  I've finished my igniter sequencer but I'm having a problem. If I omit the transistors and use resistors and leds, everything works fine. When I use the transistors and lamps or the transistors and igniters, once the first one goes, the second one lights almost imediately after. When using lamps, the first bulb shines bright while the second glows dim. The second is ignoring the clock pulse. Any ideas what could be wrong?

  Posted by brushyfork on September 10, 2010 at 17:05:25 Pacific Time

• Sequencer timing failure
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  Seriously, this is almost literally killing me. I want nothing more in life than to launch this rocket. Please help me figure out what is wrong. I swear the circuit matches your schematic exactly. But every single time, it fails. It's like when the transistor lets the voltage flow, it floods the positive side of the battery and that feeds into the other lamp/igniter. I thought maybe the transistors were oriented, the wrong way, but I've tried every combination I can think of.
  
  I've tried removing the transistors one at a time and I still have a problem. When just one transistor is hooked up (with a lamp connected between the drain and positive bus), the lamp will not stay lit for the entirety of the clock pulse. It's as though the voltage is being quickly drained out of it. Is that supposed to happen?
  
  The drain from the transistor goes to the igniter and then to the positive bus, right?
  
  Please god help me. I could email you pictures of the breadboard if that would help. I have no one to turn to for assistance, and I've already sunk $150 into this project.

  Posted by brushyfork on September 11, 2010 at 14:21:54 Pacific Time

• Sequencer timing failure
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  I don't even have to flip the fire switch for it to break. Just by arming it, the clock pulses slower and slower until evenutally it stays solid. Is there even such a thing as a .01uf electrolytic capacitor? I'm using disc capacitors, because the schematic calls for electrolytic but I couldn't find one that small.

  Posted by brushyfork on September 12, 2010 at 11:25:15 Pacific Time

• Sequencer timing failure
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  A disk for the 0.01 uf is fine. You state "Just by arming it, the clock pulses slower and slower until eventually it stays solid." Measure the voltage on the battery when you turn it on. You might have a short somewhere that is loading the battery. You could also put a large capacitor (e.g. 100 uF) across the battery (positive side of the capacitor to the positive of battery, negative of the capacitor to the negative of the battery), to help the battery maintain voltage when the ignitor (or bulb) is turned on. I used a fresh alkaline battery and had no problem.

  Posted by Teazer on September 13, 2010 at 12:47:05 Pacific Time

• Success!
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  I've gotten it working! I was able to stop the timer from flatlining by using an electrolytic cap for the 1uf. The igniters were firing way too quickly, so I added an extra 1500 ohms in series with the potentiometer and was able to get it down to a useful delay.
  
  I'd also been having trouble earlier because I was using an AC/DC converter that supplied too much current.

  Posted by brushyfork on September 16, 2010 at 17:20:15 Pacific Time

• Boo, double post
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  all the way across the sky.

  Posted by brushyfork on September 16, 2010 at 17:21:33 Pacific Time

• Success!
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  Great. I'm glad you got it working. If you shot a video, post it!
  
  >> The igniters were firing way too quickly, so I added an extra 1500 ohms in series with the potentiometer.
  
  Adding 1500 ohms to 1 Meg shouldn't make that much difference. Are you sure you have a 1 Meg potentiometer?
  
  >> I was using an AC/DC converter that supplied too much current.
  
  Do you mean too much voltage? Having a power supply that can source as much current as needed to keep the voltage constant (e.g. 9 volts) is a good thing. That's why I was suggesting using a fresh alkaline battery or a power supply.
  
  

  Posted by Teazer on September 16, 2010 at 17:45:54 Pacific Time

• Success!
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  Oops, I meant 1500k ohms more. I used 3 470ks in series with the 1M.
  
  As for the current thing: that was really more of a guess. I just re-ran the light bulb test using my 800mA max adaptor and it failed, then swaped the adaptor for a 9V battery and it worked. With the battery, the bulbs both take equal turns shining brightly. With the adapter, one shines bright for a little bit, then the other weakly flashes and the decoder is suddenly lighting a random sequence LED.

  Posted by brushyfork on September 16, 2010 at 19:47:15 Pacific Time

• Sequencer Firing Debugging
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  The good news is electronics always obeys the laws of physics so there is a reason why things don't work. My first guess is you have a power dipping problem. Are you using a fresh alkaline (good) or an old or carbon (bad, bad) 9 volt battery? Put a volt meter on the battery and see if the voltage drops. Test your circuit with a regulated power supply. Do you still see the same problem?

  Posted by Teazer on September 13, 2010 at 12:39:50 Pacific Time