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  1. (*steve*)

    Dc - dc Charging question

    A lot of these are designed to jump start cars. Does yours have any instructions describing how to do that? Do you have a make and model so we can look it up?
  2. (*steve*)

    Testing capacitors

    Here's one way to test leakage. In place of an electrometer you can probably use a multimeter, but you'll be limited to testing capacitors having fairly significant leakage.
  3. (*steve*)

    HP 16500b no video

    Can you explain? The new card doesn't have the connectors, but you reconnected the cables? I'm somewhat interested because I think I have one of these in my pile of test equipment.
  4. (*steve*)

    Testing capacitors

    If the capacitor has a specified leakage and it's in a circuit where this is important, then if you suspect a problem with leakage, yes it's worth checking it. Did you say you check for the actual capacitance?
  5. (*steve*)

    power station question

    That's a great story told by our energy regulators. In reality, I believe absolutely nothing has been done to change the voltage. Western Australia used to have 250V, and now it has a nominal 230V. But check the standard for 230V. It allows up to 254V,. If one were cynical, one might think...
  6. (*steve*)

    Need Help Choosing NPN Transistor

    It should significantly improve the speed at which the transistor turns off. This is where most power is likely dissipated in the transistor (so it should run cooler) and a faster turn-off should also give you a higher output voltage. Because this is not run from a fixed frequency but operated...
  7. (*steve*)

    74HC oscillator, how fast?

    I thought I might be able to get a slightly higher frequency using a loop of 3 inverters. And I can! But it's pretty nasty. Actually, you wouldn't believe how nasty it is. The spectrum analyser shows a really nasty smear up to 1GHz or so whereas the 74HC14 has the sort of spectrum you'd...
  8. (*steve*)

    Howdy. Can someone please advise me how to disable microchips

    A high altitude nuclear detonation should do the job.
  9. (*steve*)

    Howdy. Can someone please advise me how to disable microchips

    A stick of gelignite would probably do it.
  10. (*steve*)

    Need Help Choosing NPN Transistor

    Connect the diode as shown in the datasheet for the MJ10021 It provides a path to discharge the base emitter junction capacitance.
  11. (*steve*)

    Need Help Choosing NPN Transistor

    The main magic with the MJ 10021 is the diode connected between the base of the second transistor and the base of the first transistor. There is no reason why you can't do that with your discrete design. I would recommend a Schottky diode. You put transistors in parallel in order to switch...
  12. (*steve*)

    basic electronics question: types of oscillators

    Often these can be varied independently. The one where there is a relationship is where you can set the clock multiplier. That sets the ratio between the internal clock and whatever it is a multiple of. With memory, wait states can have more impact than actual clock speed. It's been a while...
  13. (*steve*)

    Need Help Choosing NPN Transistor

    Can you get an MJ10021?
  14. (*steve*)

    74HC oscillator, how fast?

    Here's one for you AK: Sorry for the poor focus. A simple RC oscillator using a single Schmitt trigger inverter. R is the output impedance of a gate and C is the input capacitance of 2 gates. I shorted pins 1, 2, and 3 of a 74HC14 and measured the output on pin 4. As my probe has a...
  15. (*steve*)

    74HC oscillator, how fast?

    Using bog standard 74HC series logic, what is the fastest oscillator you can make?
  16. (*steve*)

    Need recommendation for rheostat or potentiometer

    The rules have an interesting wrinkle in the scoring. They reward heavier craft. In a sense it rewards over-engineering and waste (i.e. inefficiency) Why don't they award points for lighter vehicles, or the "cargo" they can carry, or even better the ratio of the cargo weight to the weight of...
  17. (*steve*)

    Need Help Choosing NPN Transistor

    In my head. (i.e. not in reality)
  18. (*steve*)

    Need Help Choosing NPN Transistor

    The things you need are: High current capability High breakdown voltage Fast switching (specifically switching off) You might investigate using an IGBT but you'll need for gate drive to get the fast switching speed you require. At the low voltage you're looking at (9V) the voltage drop across...
  19. (*steve*)

    Cheap Motion sensors , chinese I think

    I've done my best based on the datasheet and the not-too-good photographs. The possibilities that still exist: The datasheet is wrong The chip is not the one described by the datasheet. I made a mistake reading the board. I made a mistake reading the datasheet. There is something odd that...
  20. (*steve*)

    Need recommendation for rheostat or potentiometer

    Having read the rules and the FAQ,it seems that more weight is a good thing, so a rheostat may be reasonably acceptable. However the limitation on max voltage means you really need to find a fan which will operate at 9V (or lower). The rules clearly allow discrete electronics. I would assume...
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