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  1. KrisBlueNZ

    Why need crystal for microcontroller?

    A quartz crystal is an accurate way to generate a clock frequency. If accuracy is not required, you can also use a ceramic resonator, or an RC (resistor-capacitor) oscillator. Many microcontrollers have a built-in RC oscillator that can be used f high accuracy is not needed; this reduces the...
  2. KrisBlueNZ

    PIC code oscillations at set frequencies?

    If you only want one tone at a time, you only need one 555. You can enable and disable the oscillator via the 555's reset input (pin 4) and you can set the oscillation frequency using four different resistors that are selected according to your four control signals.
  3. KrisBlueNZ

    Sizing a mosfet

    Digikey have the NTD4906N for USD 0.57 http://www.digikey.com/product-detail/en/NTD4906N-35G/NTD4906N-35GOS-ND/2194521 Rds(on) is 0.008 ohms at Vgs=4.5V
  4. KrisBlueNZ

    Multiplexing project

    Bit-banging through a parallel port can be very time-consuming. Assuming you're driving an LED matrix, you may be better off with a serially interfaced driver IC that handles the multiplexing itself, if you only need to update LED control data at a slower rate. Bit-banging will be very much...
  5. KrisBlueNZ

    Controlling the voltage into heating element

    I agree with Electrobrains's comments, apart from his suggestion that the PWM cycle time would be one minute; I think it would need to be a lot shorter. Phase angle control is a Bad Idea for a 1500 watt load. I would use a triac or similar non-mechanical switch, switching on zero-crossings...
  6. KrisBlueNZ

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

    Personally I would leave the track and just add a wire on top of it, running down the middle. And LOL (slightly :-) Yes I noticed you said that the working amp has the same overheating issue. I would fix that as well. Perhaps move the resistors off-board - mount them against the heatsink, or...
  7. KrisBlueNZ

    Newbie Needs Help With Transistors

    If the crackling starts when it's warmed up, get some rapid freeze spray and spray the semiconductors one at a time, and then the capacitors.
  8. KrisBlueNZ

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

    That's an extremely thorough problem description, and thanks for the link to the service manual! You are very methodical and thorough, and this is a very good thing. I've had a look at the schematic and it seems pretty straightforward, so I should be able to help you diagnose it. It's a...
  9. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    The trigger pulse needs to have nice clean edges. If it doesn't, add a common emitter stage to buffer it. It will also invert, it, but that doesn't matter. Use an NPN with its emitter grounded, base connected to 100k to the oscillator's output and 22k to ground, and collector through 4k7 to VCC...
  10. KrisBlueNZ

    PIC code oscillations at set frequencies?

    Do you want to generate four frequencies simultaneously? Or just one at a time? Read up on Microchip application notes that relate to square wave generation using timers and the output compare feature. Consider what frequency accuracy you need, and consider the accuracy of the clock source - do...
  11. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    I've never actually used the bistable multivibrator with steering diodes myself, so I can only be of limited help here. There are many good explanations of the circuit available using http://www.google.com/search?q=bistable+multivibrator+steering+diodes Some of those designs use PNPs; that's...
  12. KrisBlueNZ

    Class D "trouble" shooting

    Five hours is not long. Keep waiting; I think you will get more replies. What does "the line array tops above it" mean? You didn't describe the problem. You mentioned an extra noise... audible in the speaker? Have you looked at the waveform? It might be interesting to know what shape it is...
  13. KrisBlueNZ

    Need help with 24V and switch

    Latching relays don't need any current to keep them in either state.
  14. KrisBlueNZ

    Trying to identify this IC

    I doubt it's a dual op-amp. The power supply pins match, but the rest of the pin connections don't make sense. There's no point in connecting just a switch to ground to an op-amp input (pin 2). There's no signal feeding pin 3. The output of an op-amp doesn't normally have enough drive capability...
  15. KrisBlueNZ

    Resiliance of ceramic caps to overvoltage?

    Here's a very interesting article on the general limitations of MLCCs: http://www.edn.com/design/components-and-packaging/4394871/Power-Tip--49--Avoid-these-common-MLCC-pitfalls
  16. KrisBlueNZ

    Trying to repair an amplifier

    It doesn't look as if the transformer has lost very much wax, and it looks to be in good condition - from the outside, at least. It might still be alright. As Duke suggested, disconnect all the secondaries and apply mains. If the transformer is OK, the problem is probably downstream from it...
  17. KrisBlueNZ

    Programming of MUC

    I don't know. You haven't even told us the part number of the LCD display! My crystal ball is having its 10,000 km lube and oil change this week! You have the data sheet for it, right? You should be able to figure out what command to use, if there is one.
  18. KrisBlueNZ

    Magnetic Pickup Ignition Control Module for Mercedes

    Sorry to rain on your parade, but... We're talking about an automobile here. There are safety and insurance considerations. If an accident occurs, and you have used anything other than manufacturer's genuine or manufacturer's recommended replacement parts, this may nullify your insurance and...
  19. KrisBlueNZ

    Programming of MUC

    Bear in mind that you should not update the LCD from within an interrupt handler, for several reasons: it probably takes a significant amount of time to update the LCD, and interrupt handlers should take as little time as possible, and other parts of your program may need to update the LCD now...
  20. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Sure, of course! Post the design on a new thread and PM me with the URL of the thread.
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