Propagation Delay in ULN2003AN Decoder Chip

Discussion in 'The Projects Forum' started by Levitylab, Dec 13, 2013.

  1. Levitylab

    Thread Starter New Member

    Mar 16, 2013
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    First some background on the motivation for, and goals, of my project. Back in 1996 a Russian materials scientist, named Evgeny Podkletnov, reported a .05% drop in the force of gravity above a spinning, high-temperature Superconductor (HTSC), levitated in an oscillating magnetic field. He was going to publish his find in Physica D, when it was abruptly leaked to the press. It set off a firestorm, and Podkletnov became a pariah and laughingstock in physics circles, since his claim violated basic tenets of General Relativity.

    A few years later (1999-2001) Podkletnov, and a colleague, conducted further experiments along similar lines, and published their results in an online repository of physics papers. These experiments involved discharging several million volts between a HTSC and a target, in a partially evacuated chamber. They claimed that during these discharges a collimated force beam "gravitational impulse" was emitted that caused a pendulum with a rubber weight to be displaced.

    It is this latter experiment that I am trying to approximately duplicate, but on a very much smaller scale in terms of apparatus size, voltages, currents, etc. Also, I am using a commercial piezoelectric accelerometer instead of a pendulum as the detector. My setup includes a high voltage source, which charges a capacitor bank, a thyristor and associated circuitry to dump the charge directly through a small 1 inch superconductor, (or through a surrounding coil), a voltmeter (to monitor the capacitor bank charge), and a 433 MHZ RF receiver module to remotely activate the charging and discharge cycles. All of the above, except the cryostat containing the superconductor and accelerometer with associated circuitry (encased in an aluminum bud box), are contained on the "Main Project Board".

    One problem that plagued me from the start is that a loud 'pop' would emanate from the cryostat every time current was discharged through the superconductor, or surrounding coil, due, presumably, to the sudden expansion of the liquid nitrogen. The accelerometer positioned about 4 inches away, easily picks up this acoustic signal. Naturally, it spoils the experiment since it masks the sought for anomalous acceleration signal. But in Podkletnov's paper it's reported that the anomalous signal propagates at light speed, so I realized I could isolate the acoustic 'pop' just by the time-of-arrival at the detector.

    So I put together a circuit using a 556 dual timer which introduces a 350 microsecond delay on the capacitor bank discharge from the moment the button on the transmitter is pressed. This allows the trace on my Textronix 465B scope (set for single sweep, 100 microsec./div.) to reach 3 and 1/2 divisions on the screen where the anomalous signal should appear (if it really exists), while the acoustic impulse should show up approximately another 3 and 1/2 divisions further along.

    This concept worked fine when the trigger input to the scope came from the 1st channel output of the ULN2003AN decoding chip (pin 6), on the HD4RX 4 channel RF relay module on the Main Project Board. But when I attempted to sync the scope using the same pin 6 on a second HD4RX module mounted on a separate board (to physically isolate the scope from the Main Project Board), it wouldn't synchronize. The only thing I can figure is that the two ULN2003AN chips have some built-in signal processing delays that is sufficiently different from one chip to the other to foul up the sync timing. Any ideas to solve this would be appreciated.

    Here's my project's URL with photos: http://starflight1.freeyellow.com
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,282
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    The ULN2003 needs a pull up resistor that you may not have.
    I would expect to see a pulse on everything when the coil was zapped.:(
     
  3. Levitylab

    Thread Starter New Member

    Mar 16, 2013
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    Sorry, I made a major mistake. The pin 6 I was referring to is actually from the RXMOD, (also labeled A16-RX on the schematic), which decodes the RF signal (the antenna is attached to pin 12 on this chip). Here's the URL with the schematic: http://www.electronickits.com/kit/complete/elec/ck1616v3.pdf

    On both HD4RX boards I disabled the number one relays (driven by pin 6 on the A16-RX) so the relay coils aren't activated. To do that I just removed the jumper altogether that selects for either momentary or toggle mode. The result is that pin 6 on the A16-RX is now only connected to the clock input of the first of four flip-flops and to a 1K resistor that is connected to the base of a 2N2222 NPN transistor on my time-delay board. The collector of that transistor (with a 10K resistor to Vcc) goes into the trigger input of the first timer on the 556 chip. This was done to invert the pulse, since the 555/556 timer is active low.

    One thing I haven't tried yet is to adjust the voltage supply of both HD4RX boards so they are the same. I just checked the HD4RX supply on the Main Project Board and it is below spec at 11.70 volts. The HD4RX supply on the scope trigger board is 12.51.

    Is there a way to change my thread headline, and text, to change it to the correct chip name?
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,995
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    Perhaps you could use one RF board and use an opto isolator for isolation of the signal to the scope. That would insure both signals are the same (except for the small signal delay of the isolator).
     
  5. Levitylab

    Thread Starter New Member

    Mar 16, 2013
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    Thanks for the suggestion. I'm going to try a few other things first. It occurred to me that the 1 K resistor into the base of the 2N2222 transistor is providing an effective path to ground of only about 1 K, and it may be overloading the output of the A16-RX chip. That, in turn, might be slowing the rise time of the pulse out of that output substantially delaying the triggering time of the first 556 timer. I'll try a 10 K resistor instead.

    Since the pulse output of the A16-RX on the other board only goes into the high impedance trigger input of the scope it's wouldn't be similarly distorted.
     
  6. Levitylab

    Thread Starter New Member

    Mar 16, 2013
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    I believe I may have my problem solved. But I need to clear up some confusion that I inadvertently introduced. My thread title indicates the delay problem comes from the ULN2003 chip. It actually involves the A16-RX module. On the schematic this module looks like an IC, but I looked at the board a few days ago and realized it refers to a separate PC board mounted at a right angle to the main PC board. It's connected to the main PC board via two right angle headers, one with 11 pins, the other with 2 pins. This module has the RF receiver and decoding circuitry on it. It is from pin 6, of this module, where the positive-going pulse originates, that ultimately drives the 1st of 4 relays.

    It turns out that this positive-going edge, from pin 6, on my second HD4RX unit precedes the positive going edge on my first HD4RX unit by 1460 microseconds, and it syncs just fine on the scope. This became clear when I set the time base on the scope at 500 micro-seconds/div. Now I could just leave it at that and examine the region where the anomalous signal should show up at that time resolution, which is now at the 1810 micro-second mark (1460 + 350).

    But I would like to look at the anomalous signal in better detail (assuming, of course, it actually exists). So I assume I could just use the delayed sweep function on my Textronix 465B scope to delay the single sweep by 1460 micro-seconds, so that the anomalous signal would show up at 350 microseconds and I could set the time base at a better resolution, say 50 or 100 micro-seconds/div. But, I'm embarrassed to say that in decades of work as a technician I've never used the delayed sweep function on any scope. I'll have to play with it and see how it works.

    Another option would be to cobble together a 555 timer ckt. that would delay the pulse from my second HD4RX unit by 1460 micro-seconds to accomplish the same thing as using the delayed sweep on the scope.

    Hopefully, all this doesn't sound too confusing. It's early in the morning and I'm barely thinking straight.
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,995
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    Using the delayed sweep option should do what you want. The delayed sweep simply generates a sweep from the main sweep, delayed by the setting on the knob. The delayed sweep normally is set to a faster sweep speed than the main sweep. Typically you can see the main sweep as well as the delayed sweep at the same time. On the 465B you simply pull out the sweep speed knob and then turn to adjust the delayed sweep speed.
     
  8. Levitylab

    Thread Starter New Member

    Mar 16, 2013
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    Thanks for the explanation, I'll give that a try.
     
  9. Levitylab

    Thread Starter New Member

    Mar 16, 2013
    20
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    Finally have gotten everything to work perfectly. I discharged about 0.4 megawatts through the contact point of two copper, 14 gauge wires, which created a bright flash and loud report. The arc was 14 inches distant from my accelerometer. Some 1500 microseconds after the arc was initiated, a raggedy, zigzag trace began. This worked out to a speed-of-sound measurement of 1100 feet per second; just right for sea level and ambient conditions.

    http://starflight1.freeyellow.com/
     
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