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  1. KrisBlueNZ

    Power to 555 pulse gen

    Cool :-)
  2. KrisBlueNZ

    Help needed for 12V lead-acid switched mode battery charger.

    I think you're probably wasting your time using ferrites out of TV sets. You want an output of 14.4V at 30A which is 432W. No transformer in a standard TV will carry that kind of power. There are many factors that will need to be correct just for the circuit to deliver a few watts. And if...
  3. KrisBlueNZ

    Need help determining components for a circuit.

    Yes, you need two PNPs and a diode. Radio Shack have a few: http://www.radioshack.com/product/index.jsp?productId=12651122 If you put your location in your profile, I can search for suppliers near you. Adding the 1 µF capacitor will not enable you to drive anything less sensitive than...
  4. KrisBlueNZ

    Power to 555 pulse gen

    That's the right idea, but that capacitor is not what I meant. You need to remove the capacitor from the path from the 555 output to the NPN's base. The decoupling capacitor(s) I'm talking about are across the power and GND pins (8 to 1) of the 555. They're needed to ensure it works properly...
  5. KrisBlueNZ

    Optocouplers - What data to they transmit.....

    The optocoupler provides feedback that is necessary for voltage regulation. When the power supply starts up, the output voltage starts to rise. As it approaches the set output voltage, a voltage monitor (often a TL431) in the output circuit starts to pass current through the LED in the...
  6. KrisBlueNZ

    Broken Cans (headphones)

    Hello and welcome to Electronics Point :-) Unless these headphones are expensive, you're probably better to buy a new pair. It may be possible to fix them, but often, once something breaks in a cheap pair of headphones, keeping them going becomes an uphill battle. There is obviously a break in...
  7. KrisBlueNZ

    Help needed for 12V lead-acid switched mode battery charger.

    You say you have an "unknown type" of ferrite core? The chances of it being suitable are not that high. I agree with Steve. You would be best to start with a PC power supply. If you don't have one, you should be able to find one at a dump or from a friend... You can control the output voltage...
  8. KrisBlueNZ

    How does diode dissipate energy?

    The lost energy definitely is converted to heat... But I would also like to know how this happens, if anyone can explain it in a simple and understandable way.
  9. KrisBlueNZ

    Debugging an avr atmega 8 microcontroller code

    What compiler are you using? What does the message "Exit code 2" mean? Look up the compiler documentation. When you post code, surround it with (CODE) and (/CODE) tags (use square brackets instead of parentheses). This makes it appear in a monospaced font with whitespace preserved, so things...
  10. KrisBlueNZ

    Samsung TV Repetitively Turns On and Off

    One other small point. The discolouration around the slots in the board, around the MOSFETs, is not caused by heating; it's caused by tiny currents flowing across the gap and tracking around it due to dust and contaminants. If you keep that power supply, you should clean up those slots, remove...
  11. KrisBlueNZ

    Help with portable speaker system | Fried circuit board

    I'm surprised that you say it sounds OK when powered from a single 12V battery. If you want to power it properly, you need two separate batteries - one for the negative supply rail and one for the positive. But each one should be more than 12V if you want maximum power output. The TDA2030A is...
  12. KrisBlueNZ

    Need help determining components for a circuit.

    As duke37 says, the 2SA1015 is silicon, not germanium. None of the 2SA devices on that page is germanium. You can use any small-signal 2SA or 2SB transistor that's germanium. Other suitable germanium transistors are AC126 and AC128. The 1N34A should be fine.
  13. KrisBlueNZ

    Designing a Time Delayed Relay

    Voltage doesn't follow a path. Current follows a path. Voltage is measured between two points, always. Sometimes voltages are quoted at a single point; in this case it is measured relative to the "0V" ("zero volt") rail of the circuit, which is the default reference point for voltage...
  14. KrisBlueNZ

    M2732A can not erase or program

    Can you post the complete markings from the package, or a photo? EPROMs do not last forever, especially old ones.
  15. KrisBlueNZ

    Adjustable Hz flashing lights

    If that's the right component, you may also have a hard time seeing them... according to the Radio Shack web page you captured, they're infra-red LEDs!
  16. KrisBlueNZ

    Power to 555 pulse gen

    It's a kind of latching action so I would describe it as positive feedback. But there is a problem with using an bipolar junction transistor as an emitter follower when you're driving the base from a circuit that is powered from the emitter. The base needs to be around 0.7V more positive than...
  17. KrisBlueNZ

    Which voltage transformer for a laser printer

    OK. It's a shame you have to throw away a good laser printer. Maybe you could give it to a makerspace where they might be able to use it.
  18. KrisBlueNZ

    Need help determining components for a circuit.

    That's an old AM radio. It's actually just a crystal set with a two-stage audio amplifier. The two transistors are old Germanium PNPs. Yes, Toshiba did make these, but so did other companies. You're right, there are many "2SA" and "2SB" transistors. 2SB transistors are designed for use at low...
  19. KrisBlueNZ

    Help with portable speaker system | Fried circuit board

    Hi and welcome to Electronics Point :-) So you let the positive supply from a 12V battery touch some components on the board? Most likely you will have fried (that's the technical term for it) at least one of the semiconductor components on the board, possibly all four. These semiconductors...
  20. KrisBlueNZ

    Next/previous switching a multiplexer

    Right. You mustn't tie any OUTPUT to any defined level - or even to other outputs (unless they're "open collector" or "open drain" outputs, or "tri-state" outputs and won't ever be enabled simultaneously) - because the IC will try to drive them to a certain level, according to its own internal...
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