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  1. KrisBlueNZ

    Help with voltage follower

    In post #1 he mentioned an accuracy of 2~3%. That may just have been a guessimate. A 0.7V base-emitter drop is a 7% error (offset), or a 14% offset if it's a Darlington. Yes. I pointed that out in post #6 where I suggested a power supply voltage of 15V. That will still have the 0.7V offset...
  2. KrisBlueNZ

    Help with voltage follower

    The reason for using the op-amp is that the output voltage will then follow the input voltage accurately. If you use just an emitter follower, the output voltage will be about 0.6~0.8V lower than the emitter due to the base-emitter voltage drop (twice that, if you use a Darlington transistor)...
  3. KrisBlueNZ

    Fluke 199B Scopemeter Repair

    I don't have any suggestions, sorry :-(
  4. KrisBlueNZ

    Pioneer H-R100 8 track player

    Bummer :-(
  5. KrisBlueNZ

    Detecting spike from DC relay

    You need to tell us a LOT more about your project.
  6. KrisBlueNZ

    Need Some Help Figuring Out How to Use the PDSP2112

    That schematic looks great! Nice work there. Only four pins used for the display interface. I don't think you'll get much less than that! Re isolating bit 0 of the data word. The "if (w2 & 1) = 1" is not allowed in PICAXE language because it's too complicated! There might be ways around it, but...
  7. KrisBlueNZ

    Stage Line 500W amp repair project

    When you say "no reading", do you mean that the meter shows 0L, just like it does when nothing is connected to the probes? If so, then those transistors are probably OK. The second transistor, MJ15003, that reads 0000 to the emitter and to the base, is definitely dead. When you tested the...
  8. KrisBlueNZ

    My Project motor driver Smoked what driver i really need ?

    NO NO NO! That was just an example of a high power MOSFET, in response to Colin's comment. It's not related to your problem!
  9. KrisBlueNZ

    Help with voltage follower

    I recommend Adam's circuit in post #4. But you will need a higher voltage power supply, especially if you use a Darlington (which I recommend). I think your power source should be around 15V DC because most op-amps can't drive their outputs closer than about 1.5~2.0V below the positive rail, and...
  10. KrisBlueNZ

    Power supply circuitry not working

    OK, those pictures make it pretty clear that the positive pin of the adapter socket IS supposed to be connected to the anode of the diode. If you're not getting continuity, my guess is that the adapter socket's copper pad has detached from the circuit board. This can happen if the socket is not...
  11. KrisBlueNZ

    My Project motor driver Smoked what driver i really need ?

    Not nowadays! Technology has been moving forward, as usual. Check out the specs for the Vishay Si4448DY-T1-E3 N-channel MOSFET in SO-8 package: At 1.7 mΩ RDS(on), even at 10A continuous, it will only dissipate 0.17 watts. No heatsink needed! This one is the best SO-8 device I could find at...
  12. KrisBlueNZ

    Power supply circuitry not working

    F-G is the diode, so I wouldn't expect continuity, just a voltage drop, as you measured. The diode's voltage drop would normally be around 0.6~0.7V but it's a lot lower for a Schottky diode, a special kind of diode. The "819" marking is probably the last three digits of the full part number...
  13. KrisBlueNZ

    Help! Question about a pressure sensitive switch

    If the item is always going to be lifted in a lit room, you could detect light falling on a light-dependent resistor (see http://www.digikey.com/product-detail/en/PDV-P8103/PDV-P8103-ND/480610). But I think Adam's suggestion is the best. You just need a microswitch recessed into a sheet of...
  14. KrisBlueNZ

    FM modulator light only and no transmitting

    You can test zener diodes using the circuit above. You will need a 9V battery, a resistor of about 330Ω, and your multimeter. Connect them together as shown. The multimeter will read about 9V. Then connect your diode as shown, with the cathode (the end with the stripe) to the positive side of...
  15. KrisBlueNZ

    Arghhh! I Hate RS232 :)

    OK, that's enough time wasted on this argument.
  16. KrisBlueNZ

    Stage Line 500W amp repair project

    That's right. The MJ15003s are NPNs and the MJ15004s are PNPs. There should be two of each. Each channel has one NPN and one PNP.
  17. KrisBlueNZ

    FM modulator light only and no transmitting

    I don't know what you mean. You need a 1N5232B diode, not a 1N4007. Hold the transistor like in the first photo in post #24, so you can see the number and the leads are pointing downwards. Put the red probe on the left pin, and the black probe on each of the other pins. If the meter shows 630...
  18. KrisBlueNZ

    Arghhh! I Hate RS232 :)

    And this relates to RS-485 somehow?
  19. KrisBlueNZ

    ATX PSU Power Toggle Circuit

    Yes.
  20. KrisBlueNZ

    FM modulator light only and no transmitting

    Yes, try to remove the capacitor from the old board. I don't know why you bought a 1N4007. The diode on the board is a 1N5232B 5.6V zener diode. Have you measured the transistor to confirm the pinout?
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