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  1. KrisBlueNZ

    delay circuit

    Yes, I would be concerned about electrical noise on the supply rails. If you don't want to add proper surge suppression, at the very least, use an IC socket for the 555! Noise on the ignition input might cause the relay to chatter but the 555 is not used as a monostable here, so noise won't...
  2. KrisBlueNZ

    Yet another What Is This thread

    Hmm. That doesn't make much sense. If it was two 1.8 nF capacitors with a common terminal, you would measure 0.9 nF between pins 1 and 3. But I guess this does imply that it contains capacitance. You could try asking on a vintage electronics forum - perhaps vintage radio. There's probably...
  3. KrisBlueNZ

    2.0 to 3.0 desk speaker EQ mod

    Google biamp triamp "active crossover". There should be plenty of documentation and project designs out there. Wikipedia also has some good information. Passive RC filters aren't really suitable; the slope is pretty gradual - 6 dB per octave for each pole (each capacitor) and they only ever...
  4. KrisBlueNZ

    auto dialer output to trip relay

    The alarm autodialler will probably have a line grab relay that activates to connect the coupling transformer to the phone line. This will be a small electromechanical relay or a reed relay. Probably an electromechanical relay, since the autodialler has a cascade output for other phones. When...
  5. KrisBlueNZ

    Need help with 555 circuit

    Your definition is not clear. You say when the door is opened, and the microswitch's NO contact opens, you want the relay to close for ten seconds, but then you don't want the relay to activate again "regardless of the door remaining open or being closed or opened again later". This implies...
  6. KrisBlueNZ

    Sense turning

    Why don't you describe your whole project from start to finish. There may be a way to make it work, but that way may not be the way you imagine. Give us a thorough descripiton of what you want to achieve, including, but definitely not limited to, telling us about the rotating device that you...
  7. KrisBlueNZ

    Stepper motor raw / with driver / programmable driver

    Re your second question, about stand-alone stepper control signal generation ICs. I haven't heard of any. That's not to say there aren't any, but all the stepper motor drivers I've seen require at least two inputs which are driven by a microcontroller. This is the way to get the best flexibility...
  8. KrisBlueNZ

    I need to fix a sub amp

    Can you give more information? 1. So the sound like sizzling bacon comes out of the subwoofer? Not from the plate amplifier itself? 2. Does it do this all the time while the amp is powered? 3. Does it sound like a clean hiss, or does it have crackles and pops? Can you describe it in more...
  9. KrisBlueNZ

    ME TOO!! (A "what is it?" thread...)

    Yes I would go for an external monostable, to provide a pulse stream that the tachometer will always be able to use. You say the tachometer needs a Toff of 1.48 ms or longer, and works with a Ton of around 1 ms. What is the minimum total cycle time at the maximum RPM displayed on the...
  10. KrisBlueNZ

    Yet another What Is This thread

    I've never seen anything like it, but I guess it could be a dual capacitor in a single package. If the markings mean that the capacitors are 87 pF and 10 pF (not likely, but just for illustration) it could be something like: 1 -------| |--------2--------| |------3 . . . . 87 pF . . . . . 10 pF...
  11. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    This one is pretty straightforward. I've redrawn it so its operation is clear. You can see that the charge current is not constant, and that will cause distortion in your class D amplifier. Also the symmetry depends on the gain of the charge transistor which will vary with temperature, but...
  12. KrisBlueNZ

    clap based volume control

    Congratulations :-)
  13. KrisBlueNZ

    Help identifying item, finding datasheet or replacement

    I'm not sure I agree. I doubt that R701 connects to either the collector/drain of Q701 or to 0V. We can't tell what else connects to the gate/base apart from the two 2k2 resistors, because that signal also disappears into a via. It doesn't make sense for R701 to go to ground; the driver, Q702...
  14. KrisBlueNZ

    Phillips PM 3262 unable to switch on

    Sounds like a high voltage is arcing over. Often due to dust or moisture. Can you see any other sparking or corona if you look inside in a dark room? Can you scan and post the schematic? Or at least the schematic of the high-voltage circuitry and the power supply? It will probably be too large...
  15. KrisBlueNZ

    Rewiring 7-band EQ

    Thanks Phil :-) No, the harmony vocals weren't hard to do. If I had done them properly - that is, all starting and ending at the same time - they would have been more difficult :-)
  16. KrisBlueNZ

    Phillips PM 3262 unable to switch on

    It's an oscilloscope BTW. Can you find a schematic or service manual for it?
  17. KrisBlueNZ

    LCD 3.5" display out of order

    A Chinese product, sold through eBay, that didn't work properly? Surely not! LOL Do you have a question?
  18. KrisBlueNZ

    Help identifying item, finding datasheet or replacement

    I agree Steve, it's either a P-channel MOSFET or a PNP transistor (non-Darlington). Digikey don't have any suitable MOSFETs in that package (the lowest Rds(on) is 9 ohms), and the best Mouser have is the Zetex / Diodes Inc ZXMN3A01ZTA with Rds(on) of 0.12 ohms...
  19. KrisBlueNZ

    reverse engineering help

    Yes, that schematic shows what I'm suggesting. As I understand it, the relay shown on the schematic is the one that's on the isolated relay board, and it's driven by the Arduino, right? I call that the "first" relay. It takes the place of the triac in the original circuit. And the connector on...
  20. KrisBlueNZ

    reverse engineering help

    You don't connect the snubber across the 5V coil of the first relay. There should already be a diode across the 5V coil of the first relay, which suppresses the back EMF from that relay coil. The resistor-capacitor snubber is needed when the energising voltage is AC instead of DC. The snubber...
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