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  1. Alec_t

    First electronics repair question

    @roughshawd Do you realise you are posting in a 6-year-old thread?
  2. Alec_t

    why 74hc inputs are high by default?

    Ditto. I don't know how accurate the 74HC Spice models are, but simulation with LTspice suggests the simple gate inputs are actually internally pulled somewhat below mid-rail voltage.
  3. Alec_t

    CONVERT from 15-0-15v to 9v

    Which op-amp? (Either should give at least 5V peak-to-peak output if all component values are as shown in the circuit I posted.) Do you have both non-inverting inputs (pins 3 and 5) connected to the virtual earth? Are you sure the battery is putting out 9V under load (~9mA or more)? What load do...
  4. Alec_t

    why 74hc inputs are high by default?

    AFAIK, for compatability with old 74xx series bipolar logic circuits.
  5. Alec_t

    CONVERT from 15-0-15v to 9v

    The pot can be grounded at either, since the output is capacitor-coupled. What will the pot output be feeding?
  6. Alec_t

    CONVERT from 15-0-15v to 9v

    This should do what you want :- Note the new split supply with a virtual ground (4.5V), the addition of a 10k pot to give you an adjustable output amplitude, and that the non-inverting inputs of the op-amps connect to the virtual ground. The other component values are unchanged.
  7. Alec_t

    I need help with a project !!

    Which terminals of the MQ7 connect where in J6 in your schematic? Welcome to maker.pro.
  8. Alec_t

    Shortage in 3 terminals of mosfet

    I've replied over at the AAC site.
  9. Alec_t

    Shortage in 3 terminals of mosfet

    Use three pieces of wire (G to S, G to D, D to S), and don't remove them. If you want to simulate the fault actually occurring, a timed switch across the relevant terminals could be used. Again, that won't add much to your knowledge. You need to identify which of the many causes of FET failure...
  10. Alec_t

    Shortage in 3 terminals of mosfet

    A piece of wire will simulate a short circuit, but I don't see how that will add to your knowledge?
  11. Alec_t

    SD card reader cleaner

    This might help. I've not used the stuff, but I understand isopropyl alcohol is used for cleaning contacts of the cards themselves, so hopefully would be suitable for the card slot contacts too.
  12. Alec_t

    Powering laptop via DC source

    Welcome to maker.pro. It sounds as though the current drawn by the laptop via the step-up device is greater than the rated output current of the source. The source is going into self-protect mode and shutting down. Your laptop needs 20V x 2.25A = 45W. Assuming 100% efficiency (85% is more...
  13. Alec_t

    Tricking Solar inverter

    I doubt it's as easy as that. Interfacing between your solar system and the grid would have to be via a DNO-approved unit, which ensures that your system doesn't drive the grid when the grid is suppoedly unpowered for maintenance. The DNO doesn't want its workers electrocuted! Also, the inverter...
  14. Alec_t

    PWM hall effect throttle problem

    If you presently have 0.8V to 4.2V but want 0V to 5V then you need a rail-to-rail op-amp as Bluejets mentioned. Just using a diode won't do what you want.
  15. Alec_t

    Truly embarrassed - help what have I done wrong

    A distinct possibility. I've known a reed-switch to become permanently magnetised and hence closed continuously.
  16. Alec_t

    Truly embarrassed - help what have I done wrong

    To help us to help you, please post the full schematic. Are there any voltage spike suppression components? Do you have a pull-down resistor between gate and MT1 of the triac, to help prevent false triggering?
  17. Alec_t

    EMP attack!

    Are you inferring that you suffer from normal age-related hearing loss of high frequencies?
  18. Alec_t

    EMP attack!

    IMO any EMP attack is likely to be directed at the national grid and other infrastructue, so even if your gizmos are protected they are not going to be functional.
  19. Alec_t

    Crop circles. Easy reading

    Maybe. Perhaps. Possibly. Who knows? But are you seeking advice/approval/constructive criticism/whatever from electonics enthusiasts for non-electronic projects?
  20. Alec_t

    Some of good gyration air mouse?

    What is a "gyration air mouse"?
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