Search results

Search Forums New Posts
  1. hevans1944

    Circuit that sends 1 pulse when input goes high, 2 pulses when input goes low

    This project could be a great way to get some microcontroller experience! The circuit is simple because you have just one input signal and one output signal. Here is an example schematic from a project @KrisBlueNZ was working on when he passed: The details are not important, but notice there...
  2. hevans1944

    How do constant current loads work and how to make one

    Huh? Aren't we friends again with Cuba? Surely Miguel can order and receive parts from DigiKey now!? And American's can now visit the island without fear of getting arrested upon re-entry to the United States.
  3. hevans1944

    Capacitor Protection Boards- How do they work?

    I sure am glad you posted that link, Steve. It led me to your adventures in laser ablation of circuit board "resist" using paint sprayed onto bare copper-clad boards. And it sure does look like your constant voltage load circuit, re-purposed to "protect" supercaps from excessive terminal voltage...
  4. hevans1944

    Need to know if this freq Gen will give me a 2100Hz signal over a 25MHz carrier

    I just linked to the "most likely" result from a Google search using the string "25MHz Dual-channel DDS Arbitrary Waveform Function Signal Generator". It isn't confirmed that this is what the OP was considering. This thing has the capability to store, using a USB connection to a PC and external...
  5. hevans1944

    Circuit that sends 1 pulse when input goes high, 2 pulses when input goes low

    We all miss him. But I disagree that Kris would automatically offer a discrete approach. His last projects were heavily involved with Microchip PICs. This would be ideal for PIC10F200 series operated from a coin cell. Depending on output pulse requirements (not specified completely by the OP) an...
  6. hevans1944

    Need to know if this freq Gen will give me a 2100Hz signal over a 25MHz carrier

    If you are thinking of purchasing this cheap import arbitrary function generator, it will not do what you want it to do. It has no amplitude modulation capability.
  7. hevans1944

    EEG Question on Getting Data to Computer

    This should be the FIRST consideration BEFORE making electrical connections to the human body. It should be tested and verified that there is ZERO leakage current between the "patient" and a good earth ground. Do this BEFORE powering up ANYTHING. There should also be ZERO leakage current between...
  8. hevans1944

    EEG Question on Getting Data to Computer

    Are you planing to build an EEG (Electroencephalogram) or an ECG aka EKG (Electrocardiogram) instrument? The EEG uses electrodes applied only to the scalp, because EEG signals are microvolts compared to the heart's millivolt electrical signals. It is difficult enough to record EEG from the brain...
  9. hevans1944

    Mobile phone metal detector

    Not to mention the multi-billion dollar cell phone industry! Imagine it, everyone with a metal detector able to discriminate gold from lead, or copper from silver, or whatever and paint a 3D image precisely pointing where to find the valuable stuff. And all this from an audio signal piped into a...
  10. hevans1944

    Mobile phone metal detector

    So what is the benefit of using a mobile phone as an interface to your metal detector? Why not just wear a set of earphones like everyone else does? Have you ever actually tried to use a metal detector? Finicky beasts they are. Huge range of prices and performance too. I like @davenn's...
  11. hevans1944

    radio waves

    That is just one way to produce AC. The purpose of an oscillator circuit is to convert DC into AC of appropriate amplitude, wave shape, frequency, and power. There are many circuits available to do this. But all electronic oscillators have two things in common: an amplifier circuit with...
  12. hevans1944

    Axial power inductors x2 needed

    You might want to try DigiKey to purchase small quantities, i.e., less than a lot of 5000. This particular model should measure about 29.9 ohms (not a dead short!), have an inductance of about 12 mH (12000 μH), and carry a maximum current of 0.11 A. See this pdf file for specifications of this...
  13. hevans1944

    The collapse of a magnetic field

    There is no such thing as simultaneity. Read about it in the Special Theory of Relativity by Albert Einstein. There is no such thing as instantly either. For a beginner's introduction, written pretty much in layman's terms, read this paper. OTOH, if all you want to do is create a magnetic...
  14. hevans1944

    Need a 15Wh battery that can charge in 20 minutes

    Believe-it-or-not, there is actually a useful and informative Instructable that you can use to answer your questions! And here is another link with a lot of useful information.
  15. hevans1944

    Sticky black plastic cleaned & removed with 70% alcohol - no damage! GREAT!

    I like to save the brown plastic bottles that my prescription medications come in, but removing the labels applied by the pharmacy usually leaves a tacky residue. I discovered by accident that WD40 will remove the residue but leave behind a film of its own. That WD40 residue can then be easily...
  16. hevans1944

    Multiple interrupt functions but one interrupt vector

    I am glad you and Adam found the solution. I ran across this last year with a smaller PIC, and the solution is essentially the same: poll the devices that can generate a shared interrupt vector and act accordingly. That does look inefficient, but from a hardware point of view the processor can...
  17. hevans1944

    Radio and boosting signal

    The Baofeng UV-5R +Plus is a cheap amateur radio handy-talky (HT) that is NOT type-approved by the FCC to operate on unlicensed FRS (Family Radio Service) frequencies, nor is it type-approved by the FCC to operate on licensed GMRS (General Mobile Radio Service) frequencies. Both of these...
  18. hevans1944

    SCR latching trouble

    Three things will prevent an SCR, once triggered, from latching on: insufficient holding current, insufficient voltage across the SCR, and a defective SCR. Since you have already tried increasing the holding current with a 2.2 kΩ resistor without success, I would decrease this resistance further...
  19. hevans1944

    SCR latching trouble

    Try replacing the buzzer with an LED and a current-limiting resistor to make sure the thyristor is (still) working. Shorting the SCR with a NO push-button switch is not as good, IMO, as inserting a NC push-button switch in series with the load.
  20. hevans1944

    VPOKE VPEEK

    Generically, PEEK and POKE are constructs of the BASIC computer programming language that allow reading (PEEK) and writing (POKE) of specific memory and/or register locations. Their implementation on specific hardware depends on the hardware and the BASIC interpreter or compiler used with that...
View older results
Top