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  1. KrisBlueNZ

    OMG can i use NPN substitute to FET?

    The 2N5458 is a depletion-mode JFET. You can't replace it with a bipolar transistor.
  2. KrisBlueNZ

    Help in identifying the schematic symbol

    The circuit is probably meant to be constructed in a metal (steel) box or rectangular tube. The metal is the circuit ground. You place a steel sheet with a hole in it between the two sections of the circuit, and solder it to the metal on three sides (the fourth side is formed by the clip-on...
  3. KrisBlueNZ

    2 pin flasher

    Oh right! I didn't know you could rely on that behaviour. It was just something I'd noticed.
  4. KrisBlueNZ

    2 pin flasher

    If an off-the-shelf flasher will do everything the OP wants, what's the reason for this thread?!
  5. KrisBlueNZ

    LED constant current driver 80 Watt?

    Not sure if this will help, but... http://www.edn.com/electronics-products/other/4399259/Buck-LED-driver-delivers-300W-of-power
  6. KrisBlueNZ

    Help in identifying the schematic symbol

    The one in the middle might indicate a feedthrough through a metal shield wall between the two parts of the circuit.
  7. KrisBlueNZ

    2 pin flasher

    That's an interesting idea duke37. Maybe I'm over-engineering here, but I have a bit of a list of requirements for the design. It's possible to satisfy them with a discrete solution, but it would be quite difficult. 1. The delay between activation of the indicator and the start of the first...
  8. KrisBlueNZ

    Flip-flop switch

    You have a conflict with your definition of behaviour. That's why you can't find a way to implement it! Look at your first two diagrams. Diagram 1 says that when both inputs are low, the output must be low. But diagram 2 shows a pulse on input 1, with input 2 low, and the output latching into a...
  9. KrisBlueNZ

    2 pin flasher

    OK. The normal way to detect the load current is by inserting a resistor in the current path and measuring the voltage across it. In this case I would insert this resistor between the source of the main switching MOSFET and the negative rail. At your nominal current of 3.8A I would aim for...
  10. KrisBlueNZ

    Voltage Protection from car battery

    That's not really workable with a 4.3A load current and a maximum input-output differential of 2V.
  11. KrisBlueNZ

    Voltage Protection from car battery

    Yeah, 0.4V dropout (typical) at 5A is quite an achievement for a PNP-based regulator!
  12. KrisBlueNZ

    6.5 minute speech timer, Please help

    As Steve says, 555s are not very accurate, and I guess some accuracy will be needed in this application. A microcontroller would be the obvious way to go here, because it's accurate, compact, and versatile. Of course the jump into microcontroller development is much bigger than the jump into...
  13. KrisBlueNZ

    Voltage Protection from car battery

    [re: automotive load dump] You're welcome :-) For more info see http://en.wikipedia.org/wiki/Load_dump and www.maxim-ic.com (Maxim make some regulators with automotive load dump protection).
  14. KrisBlueNZ

    Voltage Protection from car battery

    That and many other questions are answered by the data sheet for the Micrel MIC29xxx devices, which is just a click away from those pages I linked to. They are LDO (low-dropout) linear regulators. You would connect the regulator between the automotive supply rail and the device you're...
  15. KrisBlueNZ

    Voltage Protection from car battery

    You will need input overvoltage protection to suppress voltage surges during cranking and load dump in the automotive electrical system. These can exceed 80V. Varistor(s) and/or TVS diode(s). Do some googling. Here are two 5-pin 5A low dropout regulators that should be suitable. Micrel...
  16. KrisBlueNZ

    Help with time delay relay circuit

    #2. The relay is not normally energised. When the fuel runs low and stays low for long enough, the output relay is energised and stays energised until the fuel rises above the low float or the power is disconnected.
  17. KrisBlueNZ

    Help with time delay relay circuit

    Just as a matter of principle I would normally have the relay energised to allow the engine to run. You seemed to be pretty clear that you wanted it the other way, which shouldn't be a problem either, and does save a bit of power while it's running I guess. Do you want to change the circuit...
  18. KrisBlueNZ

    Help with time delay relay circuit

    You mean the main relay at the output of the circuit? You want it to be energised to enable the engine to run, and de-energised when the fuel runs low, so it will kill the engine? Or are you talking about the signals from the floats themselves?
  19. KrisBlueNZ

    diode for collapsing magnetic field

    I think the OP said it wouldn't be often. Less than once every few minutes or maybe longer.
  20. KrisBlueNZ

    diode for collapsing magnetic field

    That sounds good. You don't think there will be much electrical energy generated at turn-off by the pump as it runs down? I guess the run-down would be pretty short and not able to generate much power? Are you suggesting this across the pump? How can you estimate the amount of energy that the...
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