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  1. KrisBlueNZ

    Discrete FET gate driver for LED driver

    Q2 is seeing that negative base-emitter voltage because its emitter doesn't get pulled down towards 0V when its base is. This is because of the interaction of R6 and the MOSFET's gate capacitance. Why is R6 needed? You might be better to remove R6 and if necessary add a very small...
  2. KrisBlueNZ

    How to not hear Mylie Cyrus when I am playing guitar?

    I'd suggest using the 100 pF capacitors. Electric guitars have relatively high output impedances. With 100 pF, assuming a source impedance of 100 kilohms the cutoff frequency is only 16 kHz. In fact you might even have problems with resonance with the pickup inductance! Also, you can add it...
  3. KrisBlueNZ

    Electric/Battery Metronome

    Hi Jen, and welcome to the forums. That sounds kind of interesting. I guess you want to use a real mechanical metronome? Any vintage type would be clockwork, I think. The charm of the clockwork ones is the sound. The ones that are made of wood or have wooden parts inside have a distinctive...
  4. KrisBlueNZ

    4 quadrant speed control of brushed DC motor

    Can you describe your project? What are you trying to achieve? Have you chosen the motor? Give us a complete description of your project.
  5. KrisBlueNZ

    Yamaha HS -80m Powered Speaker

    Google Yamaha HS80M service manual. You can download the service manual with a full schematic diagram. It looks like it's biamped with two LM3886 amplifiers, one for each driver, running from unregulated supplies of about +/- 30V (the actual voltage isn't indicated anywhere!) with regulated +/-...
  6. KrisBlueNZ

    High-voltage failsafe?

    12) Do not assume that this is a complete list or that Steve is implying that nothing can go wrong even if you follow every instruction exactly. Regard this as a partial list of suggestions and take ultimate responsibility for your own safety and the safety of anyone working with you. Gain a...
  7. KrisBlueNZ

    DC motor polarity reversal?

    I don't know of any single component that does that; if I did, I would have suggested it. You can create that behaviour using a latching relay with some external components as I showed. There's also a logic function that implements it, called a T-flip-flop (T stands for "toggle") which can be...
  8. KrisBlueNZ

    programming help!!!!

    Assuming you want either 0 or 1 in each ALM[] variable, here's some replacement code: u16 value; // unsigned 16-bit value int r, bitn; int p = 0; for (r = 0; r < 9; ++r) { restart_wdt(); value = hold_regs[r]; for (bitn = 0; bitn < 16; ++bitn) { ALM[p++] = value & 0x0001...
  9. KrisBlueNZ

    Is this a diode?

    That diode looks like it has has a J-shaped connection at each end, like an SMT Tantalum. When you melt the solder on one end, the whole component can be tilted without affecting the other end because the thin metal at the other end just flexes. Even if that was relevant, it's not the same as
  10. KrisBlueNZ

    Battery Powered Power Supply

    Yes, Steve, I was thinking that as well. I would prefer a design where voltage and current were both controlled by linearly varying the control voltage.
  11. KrisBlueNZ

    Help with simple project

    Steve, that's an excellent explanation. I'm concerned by the quoted specifications: "Voltage 9~12V" and "Forward voltage 10V" do not compute. I was going to suggest two linear current sources with very low voltage drops, one for each LED, both controlled together to give low or high...
  12. KrisBlueNZ

    Opamp current measurements

    Yes. It's the non-inverting input that's connected to the negative rail. That's the "+" input. There is normal negative feedback around the op-amp.
  13. KrisBlueNZ

    Help with simple project

    Whether you can avoid the diodes or not depends on the details of the circuit and components. For example if the other lights in the circuit are incandescent, they won't be affected noticeably by 12V through two LED current limiting resistors in series. But their presence will affect the values...
  14. KrisBlueNZ

    Opamp current measurements

    Yes. Change it to match schematic #3 :-) The addition of the filtering is the only difference. The capacitor in the negative feedback path will provide a lot of filtering as well - more than the extra capacitor. So there will be very little difference between the two. Run a simulation using...
  15. KrisBlueNZ

    High-voltage failsafe?

    You do not understand the relationship between voltage, resistance, and current.
  16. KrisBlueNZ

    Is this a diode?

    No it isn't. If the diode only has two pins (some SMT ones have three), lifting one end is enough. Obviously you don't measure it while the PCB is powered... Having one end connected to the PCB makes no difference, as long as your multimeter is isolated.
  17. KrisBlueNZ

    Two 12v inputs switching

    What is the problem if both inputs are on at the same time? Show us a diagram of how the LED is driven from the two inputs. If you're just using two different current limiting resistors, you can modify the circuit slightly (addition of two diodes) to get the behaviour you want, and throw away...
  18. KrisBlueNZ

    Opamp current measurements

    #1 and #3 are the same apart from the smoothing network (R5 and C2) in #3 which will help with filtering if the current being measured is noisy. Diagram #3 has a gain of exactly 100 mV per amp measured. Diagram #1 has a gain of 101 mV per amp measured; this could be changed to 100 mV per amp by...
  19. KrisBlueNZ

    Quartz crystal help

    And no they're not polarised. You can tell this from the fact that the schematic symbol is not polarised, i.e. it looks the same either way round.
  20. KrisBlueNZ

    Battery Powered Power Supply

    That schematic is OK. You could make it more readable by reducing the number of right-angles - instead of zig-zagging, try to keep everything direct. Do you have the schematic of Dave Jones's design for comparison? Is there a circuit description in text form? I looked on eevblog.com but it just...
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