Search results

Search Forums New Posts
  1. hevans1944

    8-Pin Development Board

    It's really hard to argue against a neat layout that flows with the schematic, voltage rails on opposite sides, silk-screened component identification, tin-plated copper traces, plated-through holes and all the other nice amenities a factory-made board provides. But I wouldn't characterize...
  2. hevans1944

    Greetings to all members electonicspoint

    The biggest problem I ran into was attempting to remove a faulty power jack from a multi-layer motherboard using just a soldering iron. Can't be done without ruining the outside layer circuit traces. You need some way to heat both sides of the board and the vias to get through-hole parts removed...
  3. hevans1944

    Capacitors

    @BobK: The point is the capacitor may be receiving its initial charge from a potential much less than the charged (or partially charged) battery potential, say from a weak power source in the environment (energy harvester application). Remote sensors can be configured to operate in this fashion...
  4. hevans1944

    LPF and HPF

    I think the OP (if they are still around) should rephrase their question in light of the entertaining discussion between @Ratch and @Laplace. And here is a helpful Venn Diagram:
  5. hevans1944

    Newbie Needs Help In a Dark Sensor

    Looks okay in principle, but the 150 kΩ resistor may not provide enough bias to turn the transistor on enough to reliably operate the buzzer. You might consider a Darlington connection using two of the BC547 transistors.
  6. hevans1944

    Best cheap material for diy low power heating element

    I don't think your posts are inappropriate here... just a tad bit on the naive side perhaps, but that is to be expected from a rank beginner still learning the basic concepts of the art. We don't exactly cater to beginners and newbies, but we do cut them a lot of slack if it looks like they...
  7. hevans1944

    Frankenstein's Components.

    A really good source of "interesting" parts is the typical "hamfest" that includes parking lot flea market activity. Hamfests are really popular here in the States, but I imagine similar activities occur elsewhere. Hamfests are held all year long at various locations around the U.S.A., but most...
  8. hevans1944

    Is there is some kind of physical phenomenon that occur between 4 terminals of 4T resistor?

    No magic here. The current flows through two terminals and the other two sense the voltage drop between the first pair. You need to minimize the load on the voltage sense terminals for an accurate measurement. This arrangement is commonly called a Kelvin resistance measurement, after the English...
  9. hevans1944

    Homemade Capacitor

    Nanoparticles of charcoal offer your best hope of constructing an ultracapacitor with more than one farad of capacitance. Good luck with that. I have a attached a file explaining how one company manufactures ultracapacitors using activated carbon particles. You would need to place about fifteen...
  10. hevans1944

    mosfet diode

  11. hevans1944

    mosfet diode

    I have never had an opportunity to play with IGBTs either, but may do so if I can find some for less than a dollar with a few tens of amperes current capability at 200 to 300 V or so. It's a toss-up for me whether an IGBT is better or worse than a comparably rated MOSFET. I think the IGBT might...
  12. hevans1944

    how do I make pulse oximeter

    You are kidding me, right? This is homework, so go find your own circuit schematic(s). All I did in the previous post was outline an analog approach. If I were to build an analog pulse oximeter, I would start from scratch and use the latest analog devices available. Well, actually, I wouldn't...
  13. hevans1944

    Address bus

    Tristate operation means an input/output pin can be in one of three states: sourcing current, sinking current, or open-circuit. When in open-circuit mode, other devices that source or sink current can (one device at a time) drive the I/O line. The STM32F407 is a very complicated...
  14. hevans1944

    Simplest Way 13 KV To Charge A 9 KV

    It is fairly easy to build a high voltage probe for a multimeter, at least for measuring DC and low-frequency AC. You just solder together a series string of high-value resistors and place them inside a small PVC tube of appropriate length. I happen to have a bunch of surplus 100+ megohm...
  15. hevans1944

    Address bus

    The first time I encountered this was with the Intel 8085 microprocessor, which multiplexes address and data on the same lines. Auxiliary control signals are necessary to determine when the lines have address information and when the lines have data. The lines must be capable of tri-state...
  16. hevans1944

    How is transformer impedance selected here:

    They probably were not trying to match impedance so much (you only need to do this for maximum power transfer) as they were trying to provide a usable level of audio for amplification by the 6AV6. In other words, the transformer is being used to step up the voltage from the speaker used as a...
  17. hevans1944

    how do I make pulse oximeter

    The simple answer, if you want it to actually work and provide accurate blood oxygen percent readings, is... you can't. Oh, you could rig a pair of red and infrared LEDs on a spring clamp you place on a finger or an ear lobe, and then alternately pulse the LEDs on and off, reading the light...
  18. hevans1944

    mosfet diode

    @BGB Well, maybe a little bit tangent, but I can see where you are coming from. I plan to use either BJTs or MOSFETs to drive small stepper motors with PWM and current feedback to control the PWM duty cycle. There are H-Bridge ICs that make this a no-brainer, at least for currents less than a...
  19. hevans1944

    CircuitStudio by Altium

    @chopnhack I haven't sold anything in years. Too busy playing with other people's toys, right up to the day I retired. I now have a couple of weeks to decide if I want to renew my "maintenance" on a 3D design software. I could purchase a really good antenna for what that costs. <sigh> 73 de...
  20. hevans1944

    mosfet diode

    There is a huge difference in effective on-resistance between a BJT and a MOSFET of comparable power rating. The saturation voltage of a power BJT can be a few tenths of a volt, but the on-resistance of the MOSFET channel can be milliohms. This translates, generally, into lower power dissipation...
Top