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• basic and simple question
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  Hello-
  
  Apologies in advance for this basic and simple question. I live in Alaska where all my friends own guns, but nobody owns a soldering iron. So this is my only resource for this simple issue.
  
  I'm trying to build the simple BEAM pummer circuit from this Make Magizine article. The circuit schematic can be found here, on page 3:
  http://downloads.oreilly.com/make/08/pummer.pdf
  
  I have two questions: First, the schematic seems to only point to a ground connection for the place to attach the LED. Where to I attach the positive end of the LED?
  
  Second, when looking at the inverting buffer on the schematic, is the view looking down on it, with the connectors bent outwards (i.e., like looking down on the back of a bug, with its legs squished out)? Is that right? Or is the view looking up at it (i.e., at the belly of a bug).
  
  Thanks for any help.
  
  Tom
  Fairbanks, AK

  Posted by jamgochian on September 25, 2008 at 11:03:29 Pacific Time

• Try This Better Pumming
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  The circuit design in the Make article has a flaw in the pumming portion, or at least the pumming behavior can be improved greatly with a simple change.
  
  I built the circuit as shown, except I omitted the solar cell, and tied the enable inputs of the '240 (pins 1 and 19) to ground instead. It worked, but when the light pummed, it didn't fade all the way down to dark. It was more like an LED blinking on and off at a 50 percent duty cycle, where the beginning of each "on" period was brighter, but then it stayed at a constant semi-dimness until switching abrupty off in a very un-pummy way. Some other guy's video shows the same behavior: http://www.youtube.com/watch?v=mO_YMSpNIaU
  
  My fix is to remove the 1K resistor, and add a second LED connected to the same points as the first LED, but oriented in the opposite direction. This works way better, and now you get two lights pumming at opposite phases. If you only want one light, then use a regular diode instead of a second LED. Works for me!

  Posted by Steve Chamberlin on June 11, 2008 at 22:20:55 Pacific Time

• Cap Direction and True Breathing
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  Hi all. I built this circuit up last night, and it seems to work. However, the LED doesnt have that true "breathing feel". The LED comes on instantly (like a flash) and then dies down slowly. I would like it if it could come on slowly, and then die down slowly. I was wondering if anyone else was able to get their LEDs to pulse this way, and if anyone had a video of their pummer pumming away!
  
  Also, for the two smaller caps, I am using electrolytic instead of ceramic. Is there a particular direction they should point? IE, which side should pins on the IC should the positive LEDs be?
  
  ~Shane

  Posted by LoopUniverse on March 15, 2007 at 08:18:45 Pacific Time

• Resitor location
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  After breadboarding the circuit, I found that the LED would not pulse unless R2 was changed to a different location on either of the 224 caps.

  Posted by mfryer100@hotmail.com on January 28, 2007 at 23:32:20 Pacific Time

• Resitor location
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  Confirmed, I had the same behavior and it was driving me nuts.
  
  Moving the leg of the 4.7M resistor to pin 3 of the 74AC240 fixed the circuit.

  Posted by eltoozero on December 21, 2008 at 12:31:59 Pacific Time

• Resitor location
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  Can anyone explain WHY this 'fix' works?
  It worked for me too, and I am surprised, since if there is an error in the original circuit diagram, I would have expected to find a reference to this somewhere. I mean, this circuit diagram is everywhere, and if there were a problem, you'd think there'd be mention of it.
  Any ideas?
  tnx,
  Vic

  Posted by avlewis on June 22, 2009 at 09:14:52 Pacific Time

• Resitor location
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  I can't answer your question, but I found that once my pummer starts pumming, it works fine, but often when the lights go out, it doesn't start pumming, it just glows the LED very, very dimly. However, if I switch the lights on and off, it will usually start up at some point.
  
  Moving the resistor as mentioned makes the pummer work more consistently, but changes the pumming rate and also makes the light fade less smoothly. I'm thinking that a different resistance value rather than different resistor placement may be the key. I'll experiment and post results here if I have anything useful to report.

  Posted by trebonius on August 16, 2009 at 14:36:52 Pacific Time

• Ready-made pummer kit
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  I bought a solar powered outdoor light at the local hardware store. It has a sturdy solar cell, two nicad batteries and an LED in it. This is a great starting point for a pummer. The light was only $12 USD.

  Posted by RSBohn on December 08, 2006 at 09:10:14 Pacific Time

• R3 in Pummer Schematic
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  The article or supplies list doesn't mention a third resistor, but the schematic shows a 100k resistor right below the solar cell. What is the story here?

  Posted by matt.grieser on November 21, 2006 at 03:57:37 Pacific Time

• R3 in Pummer Schematic
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  The 100K resistor is required as shown in the schematic. This appears to be the exact same schematic and parts list that is available on the solarbotics site, which also does not list the 100K resistor.

  Posted by bomb19 on November 30, 2006 at 12:08:14 Pacific Time

• R3 in Pummer Schematic -- also, on diodes and love.
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  There is one key difference between the pummer schematic published in MAKE and the one availible on the Solarbotics site (under the name "BEP Pummer"): the BEP Pummer schemo has the big capacitor (the one that sets the decay rate for the LED) mounted *backward*. Ooops.
  
  Also, for the curious, I'm pretty sure ANY diode will work for this. I breadboarded the circuit, then tried a 1434a (i.e. Germanium diode), a big-fat 1n400x zener, and a little 1n4148 (the kind you use when building a crystal radio set), and all three worked just fine.
  
  I built a pummer for my wife for V-Day (she's always agitating for a solar panel on the house) using the MAKE schemo and she LOVED it. Very cool project.
  

  Posted by McWee on February 14, 2007 at 14:04:57 Pacific Time