This is the circuit I’m using for a Dave Lawton style dual 555-timer circuit Stanley Meyer water fuel cell pulse width modulator (PWM). I’m using an LM556, as there appears to be a run on 555s. This is the ‘D14′ circuit.  All the parts were acquired via Digi-Key.com , who continue to do an outstanding job… great web site, good prices, fast shipping.

27-JUL-2008 Something is wrong with the MOSFET bias.  I’m not getting any amperage.  I had this plugged into the test power supply I’ve been using, and while I’m seeing voltage, I can’t get any current flow.  It should have blown the fuse.  I’m thinking I’ll put a trimpot on the output of the second timer to the MOSFET.  Schematic shown here updated.  Quick fix for old circuit: cut resistor from MOSFET gate to Ground, it’s 1.1K, so brown-brown-red.  There are two of them, cut the one that connects to the busbar running under the IC.

28-JUL-2008 It works.  Schematic above updated.

01-AUG-2008 Here is a scope picture from my analog Tektronix 475, 5 volts per division vertical and 1 milliSecond / div horizontal.  This is with the 28V supply, scope hooked to the output across a 4.7K resistor… so this waveform is about 200 Hz gate and 2900Hz hum.

I put a self-resetting circuit breaker in the box, I was blowing too many fuses.  Also added was another LED with a 1.5K resistor across the breaker, this indicates when the breaker is tripped.   At 14 volts, 6 amps would be 84 watts, 7 amps would be 98 watts, and the MOSFET is 100 watts, so I thought a 6 amp breaker would work right.  Turns out it snaps (kinda makes a “ponk” sound) at a steady 2.4 amps, although it takes a while for it to heat up.  This isn’t really bothering me, as I don’t really plan on running it at more than that, but it is a little curious.  I suppose I should have expected it, but only experimentation really showed the result.  The breaker is in series with the fuse holder, which is now a 15 amp fuse, this will provide some safety, but likely still blow out the MOSFET if the electrodes get shorted.  With the zener diodes, maybe not.  I suppose I will find out one day on accident, not sure I actually want to cause that yet, I’m wanting some mileage out of this thing before I have to redesign or scrap it.  Then again, the incredibly awesomely named OSCILLATION OVERTHRUSTER circuit should run circles around this open-loop approach.

DOH! this isn’t a steady 2.4 amps, it’s an average 2.4 amps.  Maybe the breaker is more reactive than I thought it would be, and is doing what it can with a pulsed current.  Okay, I can’t blame it for that.  Another theory: I damaged the breaker soldering the wire to the spade lug and it’s overly sensitive.

One Response to “Dual LM555 Lawton-style pulse generator”
  1. Is there any chance you could dumb this down some? I currently have a working Lawton circuit. Is there any chance on controlling the Lawton PWM with a PLL.
    and is there any chance it can be I.D.I.O.T. approved? thanks again Don L Peoria, Il

Leave a Reply

XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

Copyright © 2010, Multi-Dimensional Visual Echo. All rights reserved.
concern-kittycornered