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  1. KrisBlueNZ

    Samsung robovac

    It looks like the pulse transformer in a switching power supply. It is normal to measure a high DC voltage on the primary. This doesn't mean that the transformer is faulty. The transformer is driven by a switching transistor or MOSFET - a three-terminal device mounted on a heatsink nearby...
  2. KrisBlueNZ

    Chicken Coop Door Opener

    OK, here's some code. This compiles OK with an 8-pin M2 target but I can't guarantee it's free of bugs! You need to change the I/O allocation, including dirs_value, to suit your circuit. ; Code for PICAXE M2 to control a garage door opener for a chicken coop ; based on ambient light level with...
  3. KrisBlueNZ

    RF Energy Harvesting Project

    Correct, it's not viable. Transferring power through the air at distances measured in metres without enormous losses... well, I'd be foolish to say it's impossible, but it's never been done. Tesla couldn't do it. He wasted a lot of time and money trying though. Should have stuck with the big...
  4. KrisBlueNZ

    V-Reg Board for Breadboard use

    That's some bad advice there. If the output voltage is outside the stated tolerance, which is 4.75~5.25V or better, then the 7805 is faulty and should be thrown out. If not, then the PIC will work fine. Not true for fixed voltage regulators. In any case, using that "trick" can only increase...
  5. KrisBlueNZ

    V-Reg Board for Breadboard use

    That looks perfect. The diode on the input is a good idea. No, you won't need a 78(L)06. But check the power dissipation in the regulator. If you're drawing the maximum 100 mA from the output, the input voltage (after the drop in D1) could be say 15V, so the regulator will be dropping 10V. At...
  6. KrisBlueNZ

    Re-wiring a powered Subwoofer

    Have you plugged the powered subwoofer into the AC mains supply?
  7. KrisBlueNZ

    Re-wiring a powered Subwoofer

    The headphone output from an iPod or iPhone should be able to drive the amplifier to reasonable volume. If you don't hear anything from it, there is a problem. Either you connected it wrong, or something is broken. Post a diagram of what you did, if you like. Edit: Make sure the volume setting...
  8. KrisBlueNZ

    Designing a Time Delayed Relay

    Yes, that's right. The circuit is called an "active zener". The zener diode begins to conduct significant current when the voltage across it reaches its rated voltage. This current causes a voltage drop across the 220Ω base-emitter resistor. When this voltage drop reaches about 0.7V, the...
  9. KrisBlueNZ

    Re-wiring a powered Subwoofer

    It depends what kind of signals you have. The functions of a preamp are: Boost (amplify) the signal level, so a signal with low amplitude (low voltage) can drive the amplifier to maximum volume; Provide easy user adjustment of the volume; Provide multiple inputs with an input selector switch...
  10. KrisBlueNZ

    Splitting 12v output

    Yes, the MP2307 looks fine.
  11. KrisBlueNZ

    Splitting 12v output

    Just use a switching converter to convert the 12V down to 5V. As the voltage is reduced, the current is increased. Input power is equal to output power divided by efficiency, which is typically around 80%. So 1.5A at 5V = 7.5W, divide by efficiency gives 9.4W. If your LCD panel, which is...
  12. KrisBlueNZ

    Multimeter DT9205A problem

    Thanks Olivier for finding the schematic! Here's the power-down circuit. It's controlled by the DPDT swtich at the left. When it's in the position shown, the OFF position, C19 is charged up to the battery voltage. When the switch is turned ON, C19 is connected to R53, and via D14, it is...
  13. KrisBlueNZ

    SNES, 1/2 of CMC getting no power

    I found a schematic of an SNES at http://forums.nesdev.com/viewtopic.php?f=12&t=9890&start=60 and the power input section looks like this: That should help you figure out what's supposed to be connected to what. You should have the adapter voltage minus about 0.5V (the voltage dropped by D1)...
  14. KrisBlueNZ

    measuring signals above 1MHz

    The probes don't have to be the same brand as the scope. The compensation trimmer capacitor must be adjusted as you described. Your problem could be as Bob says, the trigger level is set too far from the centre of the wave, so when the amplitude drops, the scope no longer triggers from it, and...
  15. KrisBlueNZ

    Chicken Coop Door Opener

    Adam raised a good point. Using a lower smoothing capacitor is good because there's less of a surge when power is applied. I suggested 2200 µF but that gives a maximum ripple of only 0.23V p-p; you could easily halve that capacitance and double the ripple without causing any problem at all. You...
  16. KrisBlueNZ

    Chicken Coop Door Opener

    Over-rated in the current department, I guess. Components like transformers and regulators can get warm. But I think I was just being a bit paranoid. The only component that will dissipate any significant power is the regulator. Power dissipation in the regulator can be calculated using P = V ×...
  17. KrisBlueNZ

    power supply circuit

    Right. You know how to calculate the RMS voltage of a sine wave from the peak voltage?
  18. KrisBlueNZ

    Chicken Coop Door Opener

    Yes. If the whole thing has to go inside the chicken coop and get hot, go for good quality parts that are comfortably over-rated. Yes, and yes.
  19. KrisBlueNZ

    power supply circuit

    Do you mean primary voltage Vp = 220V AC RMS? Or does "peak voltage Vp" mean the peak voltage at the primary? If it means the peak primary voltage, you should convert it to an RMS voltage, then do the rest of the calculations using RMS voltages, because in circuits using sine waves, AC voltages...
  20. KrisBlueNZ

    Chicken Coop Door Opener

    Probably not. Your suggestion is probably better. Those look suitable to me. You just need to install it somewhere where it will be activated by some moving part as it goes past, and make sure the moving part moves along a well-defined path so it won't get too close to, or too far away from...
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