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  1. KrisBlueNZ

    Dark activated light

    Yes, I have lots of useful observations. First, it's far more complicated than you need, and second, it doesn't have any hysteresis, which means it will not switch cleanly. But it's very hard to follow that circuit. It's just a jumble of wires. Start by redrawing it with the negative rail along...
  2. KrisBlueNZ

    MOSFET Gate Driving Problems

    No. The optocoupler can only pull down to 0V. R1 is there so the output will pull up. So look at the circuit with the optocoupler completely removed. You have R1 from +V, R2 from QA's base, and R3 from QB's base. QA's base is never going to be more than 0.7V less than +V. QB's base is never...
  3. KrisBlueNZ

    Omega special character

    Character codes 128~255 are sometimes called "high ASCII" codes. They can be entered (on PCs at least) by holding the Alt key and typing the number on the numeric keypad, then releasing the Alt key - "Alt-keypad" entry. The "extended ASCII" characters listed at www.asciitable.com are the...
  4. KrisBlueNZ

    why does my rotel 855 not respond to any rotel cd remote

    Have you tried THIS?
  5. KrisBlueNZ

    Measuring high current with PIC

    Have you looked at the Allegro isolated current sensing ICs? http://allegromicro.com/en/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-Sensor-ICs/ACS710.aspx You feed your current through the IC, where it generates a magnetic field that is detected across an isolation barrier.
  6. KrisBlueNZ

    MOSFET Gate Driving Problems

    As Harald says, the main problem is that when the optocoupler transistor is OFF, its collector will not rise all the way to +V_DRIVE because of the voltage divider effect caused by R1, R2 and R3, and QA will not turn OFF. You can test this out using a simulator such as the free LTSpice...
  7. KrisBlueNZ

    Op-amp, changing LED colour!

    It's possible to generate 13V from 8.4V using a boost converter, but running the LEDs from a 13V supply when lower voltages are available would waste power and I doubt they would do that. Does the backlight only work when the unit is powered from an external supply? That might explain a few...
  8. KrisBlueNZ

    help! would this still work

    It's hard to say for sure. I'm not really sure what we're looking at. A wider view of the board could help. It looks like some kind of circuit board with a conductive track, but nothing soldered to it. Are you concerned about the extra hole in the top pad? It doesn't look like it breaks the...
  9. KrisBlueNZ

    Op-amp, changing LED colour!

    According to the diagram on page 45 of the PDF, the positive rail should be around 13V. That's plenty of voltage; there should be no problem using blue LEDs. In your first post you said that the "Voltage at the LEDs currently is 1.95v". Do you mean the voltage across the LEDs? Have you turned...
  10. KrisBlueNZ

    which capacitor is best

    That's a nice little circuit. A VCO for a synth, right? If the designer recommends a C0G/NP0 that's what you should use. This one from Digikey looks good: http://www.digikey.com/product-detail/en/C412C222J5G5TA7200/399-4487-1-ND/818344 The initial tolerance is only ±5% but that can be...
  11. KrisBlueNZ

    Z80 Computer

    I think that code should work. Re cross-assemblers, I have no recommendations but I found the following: http://sourceforge.net/projects/z80toolsforwind/ (I downloaded this but couldn't get it to run because of some problem with the required DLL comdlg32.ocx) There's also this one if you're...
  12. KrisBlueNZ

    Designing a Time Delayed Relay

    Maybe. The reason I chose 24V (initially I wanted to use 48V) is that the relay coil needs a certain amount of power, and power is voltage multiplied by current. The higher the voltage, the lower the current. And with a capacitor-fed power supply, you want to keep the current low, because that...
  13. KrisBlueNZ

    LED parallel array wizard

    OK, so the calculator has used two chains, with three LEDs in each chain. You should use three chains, with two LEDs in each. This is like repacking the books into more boxes. Instead of having two boxes, each containing three books and a very thin piece of foam, you have three boxes, each...
  14. KrisBlueNZ

    Z80 Computer

    Yes, HCT is designed to work with LS. It's probably better not to mix them though. What's this TASM? It's not Borland's TASM! Your code is inefficient but it should work. But the baud rate control variable is not initialised anywhere. You could save code - at least to start with - by just...
  15. KrisBlueNZ

    LED parallel array wizard

    Thanks Harald :-)
  16. KrisBlueNZ

    LED parallel array wizard

    Yes that's a big difference and it could be a problem. It shows that there's not enough voltage across the resistor. Imagine it like this. Your LEDs are books that you need to pack side by side into a wooden box. Each book is a slightly different thickness (different forward voltages) because...
  17. KrisBlueNZ

    Diodes, low voltages and gaming systems

    I don't think diodes will be appropriate - not for video, anyway. To get any kind of decent frequency response you would have to use a pretty low load resistor. If you can multiplex your signals at the digital level, before they're turned into composite (for the video) and before the channels...
  18. KrisBlueNZ

    Designing a Time Delayed Relay

    The amount of power dissipated by a component is equal to the voltage ACROSS it multiplied by the current through it. The regulator will be dropping about 22V (27V - 5V) so every milliamp it passes causes 22 mW of power dissipation. 30 mA x 22V is 660 mW. The regulator itself consumes some...
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