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  1. KrisBlueNZ

    Treadmill, strange problem on Motor control board

    I don't understand the question.
  2. KrisBlueNZ

    KLH R3000 Stereo Receiver wont turn on.

    Not if you want the unit to remember its settings during a brief loss of power, for example if you move it to a new power socket. But otherwise, yes.
  3. KrisBlueNZ

    Variable voltage dropper for speed control of tattoo machine

    Sorry for the delay. Here's a design with all the features we've discussed.
  4. KrisBlueNZ

    Simple Alarm Circuit help

    Hi Alan and welcome to Electronics Point :-) I think I understand your question. You have a single signal that you want to use in two different ways, with two different inputs to the alarm controller. When you connect it to one input, this prevents it from working properly with the other input...
  5. KrisBlueNZ

    Simple amplifier needs simple bipolar PSU

    Yes this can all be done pretty easily. Your simplest option would be a transformer with a centre-tapped secondary. The centre tap connects to the 0V rail and the two ends connect to the AC input pins of a bridge rectifier. The positive and negative outputs from the bridge become the positive...
  6. KrisBlueNZ

    LED TV - power circuit damaged after lightning strike

    Yes, it's possible that replacing the fuse and powering it up with the MOSFET still short circuit could have forced enough current through the bridge rectifier diodes to take them out as well. Have you identified a suitable replacement for the MOSFET? If you want suggestions, add your location...
  7. KrisBlueNZ

    It is designed to run off of 12VDC, I would like it to run off 24VDC

    Right. You can just use a 24V relay with no series resistor. Yes, R3 limits the base current. You can leave it at 15k (1.5 mA isn't going to harm the transistor) or increase it to 33k if you like. It does also form a voltage divider with R4 when the optocoupler is OFF (and C3, if connected, is...
  8. KrisBlueNZ

    Hardware to play loud MP3 in traffic?

    I agree with Gryd3 here. An audio amplifier and speaker are not the answer. Speakers are designed to reproduce a (reasonably) wide range of frequencies fairly accurately, and are not very efficient (modern speakers are 5% or less, usually). A horn will be a lot more efficient in terms of power...
  9. KrisBlueNZ

    Variable voltage dropper for speed control of tattoo machine

    Gryd3's diagram in post #31 is what I'm suggesting. The battery needs to connect with positive at the top. Yes Adam, the output voltage will vary if the battery voltage varies due to changes in load. That's definitely not ideal but I'd say it's unlikely to be a problem in practice. No, there's...
  10. KrisBlueNZ

    Variable voltage dropper for speed control of tattoo machine

    A good solution would be an emitter follower. This will act as a buffer for the potentiometer and supply the required current. This will enable you to use a standard low-power potentiometer without worrying about power dissipation in the potentiometer. And as long as the input voltage is...
  11. KrisBlueNZ

    understanding circuit operation

    Pins 3 and 7 of a 555 are not the same. Pin 3 is designated as the "output" and pin 7 is designated as the "discharge" pin. They are both driven from the same internal signal. Pin 7 is an open collector output and pin 3 is a totem pole output. You can avoid the "R1" resistor in the standard...
  12. KrisBlueNZ

    Toob to transistor conversion

    Hello Neurotic Norman and welcome to Electronics Point :-) I suspect this project is really mostly a huge time sink. But I'll try to answer your direct questions. 1. Generally, solid state circuitry works at lower voltages and higher currents than toob circuitry. This generally means that...
  13. KrisBlueNZ

    Nand Gate oscillator help

    OK, here's the schematic: The oscillator formed by the two NAND gates in the middle is the standard two-inverter CMOS gate oscillator and should work fine, if you've built it as shown. All I can suggest is to check the connections to the components and pins in the oscillator circuit (pins...
  14. KrisBlueNZ

    Timing Circuit? Counter?

    Yeah. It's not unusual for components to have an inconvenient connection to the tab. Usually it's the collector or drain of the largest transistor or MOSFET in the device. If you have a double sided board, and you just want a copper area on the underside that's connected through to the top side...
  15. KrisBlueNZ

    Power supply

    Looks like you have the high current version of the power supply but your schematic is for the low current version. Let's see what happens when you replace the zener diode.
  16. KrisBlueNZ

    Timing Circuit? Counter?

    Oops sorry for the confusion! "VCCplane" is what I would call a groundplane that's connected to VCC instead of ground! I just meant that you could add a copper fill, connected to VCC, for the purpose of heatsinking the regulator. I would make it larger than the regulator's body outline, but I...
  17. KrisBlueNZ

    It is designed to run off of 12VDC, I would like it to run off 24VDC

    Wow! What a lot of discussion over a simple question! Yes! You don't even need to change R3 and R4. They're just there to limit the current to the base of the PNP and ensure it turns OFF cleanly when the optocoupler stops conducting. Just add a resistor in series with the relay coil of the...
  18. KrisBlueNZ

    ID diode help

    Or, just throw them away! Then if you need a diode in future, spend ten cents and get a diode whose characteristics you know about!
  19. KrisBlueNZ

    Timing Circuit? Counter?

    You're right, on the AP1117, the tab is connected to VOUT. You can't spread the heat onto a groundplane. And you can't bolt it to an aluminium heatsink. You'll have to use a smaller "VCCplane". You can still put it on both sides and use thermal vias, though it might work out better to put it on...
  20. KrisBlueNZ

    Need help with fixing pc subwoofer+speakers please

    I wouldn't use Ethernet cable; it should be shielded. I'd go with Roberto's suggestion in post #18 - add another wire, either spiralled around the existing cable or held to it with rubber bands or cable ties, to replace the broken one.
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