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  1. KrisBlueNZ

    LED driver with current source bias supply?

    That's an interesting circuit! There are some ideas there that I haven't seen before. Not too surprising I guess, since this type of LED driver is outside my experience. I don't see anything wrong with the general idea, but that's no guarantee of anything. As I said, I'm not experienced with...
  2. KrisBlueNZ

    Stun gun charging mysteriously

    That trick can only be used when (a) the required current is fairly low, and (b) everything connected to the circuit is fully enclosed and insulated and there's no way for a person to make contact with it. IT IS NOT SAFE as a general way to power or charge devices. That technique is used in some...
  3. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Now you've put the 10k resistor in series with the current sink transistor! It needs to go in series with the connection into the comparator, and the 1N914 should be on the left side of it (i.e. also connected to the comparator input). Like on my schematic in post #14. So something's...
  4. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    I've got a few suggestions and questions. 1. Is the load circuit powered from a battery as designed? 2. Is there any other connection from the load circuit to mains earth, or to the power supply you are loading in the test? 3. Can you see any waveform in the noise? Try the scope at different...
  5. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    D2 doesn't need to be a 3A diode. A 1N914 or 1N4148 will be fine. Re the problem at high current. This may be caused by imperfect connections in the breadboard layout. Make the high-current path external to the breadboard, using all soldered connections. That means the connection from the power...
  6. KrisBlueNZ

    Stun gun charging mysteriously

    Yes, the series capacitor acts as a current limiter. With alternating current, a capacitor acts a bit like a resistor. It exhibits a behaviour called "capacitive reactance", which is like resistance in some respects, and is measured in ohms. The formula for capacitive reactance is: Xc = 1 / (2...
  7. KrisBlueNZ

    LED timer

    Yes, this can be done with a couple of low-Vgs MOSFETs and a few resistors, using an LDR (light dependent resistor) to detect ambient light level. I'll draw up a diagram for you, but I can't be sure how to "integrate it into your item" unless I know exactly what your "item" contains. Can you...
  8. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Re point 3, D1 is a good idea but it doesn't protect IC1D from having voltage on its input when there is no power to the circuit. This is the function of RP and DV in my design.
  9. KrisBlueNZ

    Multiplexing project

    Perhaps if we wait fifty years the file will be declassified... It's so exciting! :-/
  10. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Right. My design also requires a voltage source to remain ON. If the switch is held at the ON position, the circuit will stay ON, but if there's no voltage source connected, as soon as the switch is returned to the middle position, it will turn off. I don't see how this is a problem. What's the...
  11. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    Yes, you've used the right transistors. Q8 is a PNP. The parts list says it's an NPN; that's an error. D3 only has one anode pin. Looking at the photo in post #7 on this thread, the anode is the pin at the bottom left of the device. The pin at bottom right is not used. If that's the pin that...
  12. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    The +15V and -15V rails are supplied by Q6 and Q8, which are supplied from the main +V and -V rails via R78 and R76. There is another rail, "+15VSW", from the LM2574, which is actually +15V relative to the -V rail. It supplies U7 and U8 and associated buffer transistors, but I don't think it...
  13. KrisBlueNZ

    Want circuit to return to previous state when turned back on

    As gorgon suggested, a latching relay is the simplest option, if size is not a concern. These are available from around USD 3~6, in coil voltages of 3V, 5V and higher. Some types have a single coil, which is driven with a positive voltage to latch the relay ON, and a negative voltage to latch...
  14. KrisBlueNZ

    Switching possibilities

    How about a whole lot of changeover relays? DPDT (17 relays needed): http://www.digikey.com/product-detail/en/V23079A2003B301/PB1058-ND/1210004 - your cheapest option at USD 45 total 4PDT (9 relays needed): http://www.digikey.com/product-detail/en/HC4E-HP-DC24V/255-2211-ND/647869 - about USD...
  15. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    The diodes in series with the bases are to prevent possible damage to the transistors during the short negative pulses, where the base may be driven more than about 6~7V negative with respect to the emitter (because the power supply is 9V). The base-emitter junction of a bipolar transistor...
  16. KrisBlueNZ

    Newb needs help with a 2 second delay for milsim

    Neither of those igniter companies provides even the most basic specifications on the igniters! That's disappointing. I guess there's a standard voltage that all ignition systems use. Is that where you got your 6V figure from? Can you measure the resistance of one of your igniters? The...
  17. KrisBlueNZ

    Change DVD player from ac to 12v dc

    There are some devices that need sine wave supplies, so you probably did see an article about it, but it wasn't about DVD players. Sounds good. Good luck!
  18. KrisBlueNZ

    5U4 Rectifier tube

    Oh no! I think it is! My friends are suffering from it too! Or it might be that we're all just getting old... :-)
  19. KrisBlueNZ

    Newb needs help with a 2 second delay for milsim

    I don't think you'll find a simpler or smaller circuit that will do what you want. That thread on instructables.com is not relevant to your needs, and nor is the idea of using a large capacitor to draw current from the battery for a short time to delay the firing of the igniter. In any case, a...
  20. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    The caps are _supposed_ to turn the edges into pulses. There should be a detectable signal at the bases of the transistors, although the pulse will be short. I'm not sure what to suggest. I've run a simulation. Here's the result. I've attached a ZIP file containing the LTSpice source file in...
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