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  1. hevans1944

    Wire temperature control

    Welcome to Electronics Point! Can you provide some details of what you are trying to do? There are many ways to sense temperature, some more practical than others. I would suggest you measure the resistance of the wire at several temperatures between 100 and 300 C using an oven and an accurate...
  2. hevans1944

    How to Test MOV varistor

    An ohmmeter will only tell you if a MOV is bad by indicating conductivity, typically a short. A good MOV will always measure "open" with an ohmmeter, but this is not a definitive test. It is not easy to tell if the MOV is good. It requires a special test setup to apply an energy-limited pulse of...
  3. hevans1944

    Cheap, Easy Way to Step Down 12-14VDC to 5VDC?

    Google buck switching regulators if your intent is to power the microcontroller. There are integrated circuits available that require minimal external components. And of course you can purchase them ready-made too. If you want to use the existing bulbs, and they are ground-switched, a simple...
  4. hevans1944

    Measuring digital coincidence

    It can be handy to verify setup timing constraints, for example to see if the inputs to a flip-flop are stable before the clock edge occurs. It can also tell you if there is clock skew if one signal is derived from the clock and the other signal is also derived from the clock but possibly...
  5. hevans1944

    Measuring digital coincidence

    You trigger the 'scope on one channel with one of your digital signals and apply the other digital signal to the other channel. When you select add mode, you will see a stable waveform (triggered sweep) from the first channel with the second channel superimposed on it. If the second channel is...
  6. hevans1944

    D-Type Flip-Flop (74HC74)

    Sounds okay to me, but why bother? It is trivial for software to invert a logic level. And, as @mofy said, remember to pull the collector of the Reset transistor high with a 10 kΩ resistor. Change your code and save the trouble of adding a transistor and two resistors to the 74HC74 flip-flop.
  7. hevans1944

    raydavis

    Well, if you give a minimally trained (or untrained) "technician" a VOM, an oscilloscope and access to the World Wide Web you can expecpt the kind of questions he asks. That doesn't mean you have to waste your time answering them. If this really is a re-incarnation of DannyDavis, expect your...
  8. hevans1944

    What is the diode going to?

    It probably connects to Vdd to rapidly discharge C when Vdd goes to zero. See Note 1 in your diagram.
  9. hevans1944

    power resistor vs resistor

    So-called "sandblock" resistors are simply wire-wound resistors encased in a cement or sand block shell. This is a less expensive alternative to encasing the wire-wound element in a (usually hollow) ceramic shell. A 10 Ω, 10 W, sandblock resistor will work as well as any other resistor of...
  10. hevans1944

    Why are halogen ovens more efficient than regular ovens?

    With regard to efficiency, I was considering only the efficiency of converting electrical energy to heat energy, not the efficiency of how that heat is used to cook food. For electrical efficiency it makes no difference whether you use a nichrome heating element or a halogen lamp. Both convert...
  11. hevans1944

    Why are halogen ovens more efficient than regular ovens?

    Air is most effectively heated by convection or conduction with a hot surface. Air is ineffectively heated by infrared radiation. Why? Because our atmosphere is transparent to infrared wavelengths. That is why the radiation from the Sun warms the skin on a cold winter day: the skin absorbs the...
  12. hevans1944

    Salt lamps - what effect would the salt have on the light from incandescent bulb

    Salt is also quite transparent to infrared to about 16 μm wavelength, so a secondary effect is you should be able to feel this as a warming effect on your hands through the salt from infrared radiation emitted from the incandescent bulb. We used to use precision-ground salt lenses for infrared...
  13. hevans1944

    Whack-a-mole

    You are going to have to be a lot more specific about what you want to do. All the whack-a-mole games I have seen involve a hammer and several electro-mechanical pop-up moles.
  14. hevans1944

    Help with a LED driver

    The typical forward voltage and forward current are specified on the data sheet. The reverse voltage is a cautionary maximum. You should avoid applying a reverse voltage to an LED. If a reverse voltage IS applied, and it is less than the maximum reverse voltage the LED will tolerate, a very...
  15. hevans1944

    Need advise for multimeter

    How much charge remains in any battery is a complex function of the chemistry of the battery, the ambient temperature, the unloaded terminal voltage, the loaded terminal voltage, and (for NiCd batteries) the charge/discharge history. The only reliable way to "measure" the remaining charge is to...
  16. hevans1944

    Best wall power supply for automotive 12v 1w ioniser module

    Theoretically. It depends on the density of ions in the air, the size and weight of the leafs. There are better (more modern) ways to do this. The leafs could also be charged first, like with an electrophorus, and then ions of the proper polarity will discharge the electroscope.
  17. hevans1944

    Best wall power supply for automotive 12v 1w ioniser module

    No. It has no way to distinguish positive ions from negative ions. The device you (almost) described is a (gold)-leaf electroscope. The two leaves are a single strip of thin foil folded in half and supported in the middle by a single "L" shaped wire exiting a glass jar (for visibility and to...
  18. hevans1944

    Need advise for multimeter

    This looks interesting, but I think a Wi-Fi version would be even better. Needs more digits and more accuracy to justify buying one. Voice response app is a great idea, especially if you can download different languages.
  19. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    The worst problem I found was the problematic timing with ICE versus the real deal. But as you said, stopping with a high-current load enabled does indeed release the "magic smoke" unless the hardware is specifically designed for 100% duty cycle under full load conditions. We didn't do any PWM...
  20. hevans1944

    Are deep red 660nm LEDS completely safe?

    Nothing in this world is completely safe, including "visible light deep red 660nm LEDs." You, and you alone, are responsible for your safety. Google is your friend here. For more information on eye safety, Intersil has some CYA documents you might want to read (see attached file). They also have...
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