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  1. hevans1944

    SPTT reed relays

    There is no such thing as a "Single Pole Triple Throw SPTT" reed relay. Google reed relay construction and you will see why. If you need a three-position switch (ON-ON-ON) you will need at least two reed relays with two coils, or three reed relays with three coils, depending on how you want to...
  2. hevans1944

    How to control 700 solenoids?

    I wouldn't know about that, not having worked on cars since carburetors went away. I suppose it is possible, since modern cars use an ECU to control everything. Conceptually, all you need is a capacitor from the MOSFET drain to common to store charge, and a resistor in series with the power...
  3. hevans1944

    How to control 700 solenoids?

    True in principle, but probably not so much for this application. The solenoid valves have short duty cycles, on to make a raindrop then off to allow space between drops. Speed is on the order of ten milliseconds between valve cycles. Variable coil current would probably needlessly complicate...
  4. hevans1944

    Final Electronics Project...Am I on the right track?

    Remember, when forming your working group, to select people with a variety of interests and skills. Four to six people is about the right size for this project. You never know where the next good idea will come from, so encourage discussion. Set some project goals and follow the KISS principle...
  5. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    The final product will be a round disk, so there is plenty of time to find a work-around to the license problem... maybe even <gasp!> purchase the software. Adam is building a prototype board for test and evaluation. @TenderTendon can create a CAD file to mill one of his own, but that isn't at...
  6. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Looks like there is room to run a trace from R2-1 to U1-3. But that's pr'ly the trace Dip Trace removed for you.
  7. hevans1944

    How to control 700 solenoids?

    Well, it's certainly a more expensive approach at £480 for sixteen valves. In the quantities you need, a better target price would be closer to £48 for 64 valves per board. This is a rectal extraction for the price, but I think it is near the actual cost to manufacture a few hundred boards with...
  8. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Hello, Adam I did know that CMOS logic isn't appreciative of open inputs. And so it seems that analog inputs need some finite impedance too. I learned years ago that there is always some bias current (could be very small) associated with analog inputs, so some sort of resistive path must be...
  9. hevans1944

    Final Electronics Project...Am I on the right track?

    That's pretty dumb, IMHO! Does your instructor specify what solder you can use? The Raspberry Pi is a power hog, and way more than you need to light up and synchronize a few dozen graduation caps, but I suppose you could fit each student with a backpack concealed under their clothing to operate...
  10. hevans1944

    How to control 700 solenoids?

    Well, I knew there was more than one way to skin this cat. This is an even better solution! It has the dual-latches I mentioned in paragraph four of post #6, so updated data can be shifted in without changing the current state of the outputs. Then, after all the new data is present, a single...
  11. hevans1944

    voltage drop help

    Do the three AAA cells power anything else other than the red LED? Like, a circuit of some sort that might be sensitive to the voltage supply? If it is just the LED you want to power from 12 VDC, then @Laplace suggestion is the best way to do this.
  12. hevans1944

    Final Electronics Project...Am I on the right track?

    An Arduino Uno with an XBee shield and Xbee module would probably do it for you. Writing the sketch (program) might take a bit of effort, but there are examples galore on the Internet. The Uno can be powered with a 9 V "transistor radio" battery.
  13. hevans1944

    Temperature Control Help

    The days when mechanical engineers could remain clueless about electrical engineering are over. Today's engineers, no matter their specialization, must be able to understand systems. This requires a broad understanding of physics, chemistry, optics, computers and software, hydraulics...
  14. hevans1944

    Flash tube

    From your image, it looks like a short-arc linear flash tube with an external trigger electrode attached to the cathode (left electrode with pointed tip). There is probably a high-voltage pulse transformer inserted in series with the cathode lead to fire the tube. This tube is somewhat unusual...
  15. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Update on my progress with learning to use the MPLAB X IDE... turns out there is a disassembler built into it. I just need to learn how to use it if it turns out that I need it. My original objective was to read the oscillator calibration bits from the PIC10F206 I bought, so I could write those...
  16. hevans1944

    Flash tube

    Can you tell us how you are using this flash tube? Any idea of how many watt-seconds it will dissipate? Flash rate? Size of energy storage capacitor in microfarads? Voltage?
  17. hevans1944

    How to control 700 solenoids?

    Don't be so sure about that. Virtual pinball machines use high-resolution flat-screen displays and computers to simulate the "pinball experience" but rely on relatively "slow" electro-mechanical devices (knockers and what-have-you) to enhance that experience. I would not expect accessories sold...
  18. hevans1944

    How to control 700 solenoids?

    So we would need only 234 of these chips to control 700 valves. Each chip forwards serial bit information at 800,000 bits per second, and each valve uses 8 bits, so the bit-rate per valve is 100,000 bits per second for a cycle time for all 702 valves of about 7 ms per valve... well within the 10...
  19. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Ouch! I completely forgot about the push button switch load! Especially when the LED is on and available current is at a premium. I love your PicoScope screen captures! I guess I will have to bite the bullet and somehow squeeze the cost of one into my budget. A few weeks ago someone brought a...
  20. hevans1944

    How to control 700 solenoids?

    It will require a latch and a coil driver for each valve. To create the falling rain type display it is essential that all 700+ solenoid latches be updated at the same time. That means the data for each latch must be present when the latch is "clocked" to update the solenoid state. The solenoid...
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