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  1. KrisBlueNZ

    Automated Sliding Door

    Hi Bob. Sorry for the slow reply - I just realised that I'm supposed to be doing something on this thread! Here's the diagram I suggest. It uses two timers. The left one opens the door in the morning; the right one closes it at night. I have assumed that: Fully extended actuator = door fully...
  2. KrisBlueNZ

    HP 1741A Oscilloscope

    9.1V across a 1.5k resistor works out to about 6 mA. That is not a huge load. And if there's 77V across C7, that means there's 68V between the collector of Q11 and the 120V rail, so Q11 should easily be able to provide the 36V needed for the +156V rail. I think VR3 must be faulty. Try replacing...
  3. KrisBlueNZ

    Malloc and it's use with MCUs

    It depends on how much free()ing you do, and the sizes of the blocks you are using. If you're malloc()ing and free()ing two or more different sizes of blocks, it's always possible to get into a situation where the whole heap is used up because of fragmentation. If you're very careful with how...
  4. KrisBlueNZ

    HP 1741A Oscilloscope

    OK, the NTE396 looks like a suitable replacement. If you've replaced it and nothing changed, VR3 may be faulty, but it could also be a heavy load on the +156V rail. If you can measure the voltage across R18 I should be able to tell you which case it is. I'm going to have to check out NTE's...
  5. KrisBlueNZ

    An interesting pipe dimmer project

    I can't really tell. There's less information than the previous one! It looks too big though. And the advert doesn't mention any safety certifications.
  6. KrisBlueNZ

    HP 1741A Oscilloscope

    After you've done step 5 in post #137 you can tell whether the fault is in Q11 or VR3. If the voltage across VR3 withi Q11 removed remains around 25V, VR3 is faulty. Replace it with a 1N5258B - 36V, 0.5W zener diode. http://www.digikey.com/product-detail/en/1N5258B-T/1N5258BDICT-ND/190874...
  7. KrisBlueNZ

    64 LEDs set out in a square?

    Good point. Lots of very good information in that post, Steve!
  8. KrisBlueNZ

    An interesting pipe dimmer project

    http://www.google.com/search?q=triac+dimmer Google is always a good place to start :-)
  9. KrisBlueNZ

    An interesting pipe dimmer project

    Electrically, it's probably OK. Mechanically... only you can say. I don't recommend buying cheap, unknown-origin products from eBay, especially for AC mains-powered applications. They can have problems with safety, reliability, interference... generally, standards-compliance. Edit: It looks...
  10. KrisBlueNZ

    Dodgy Power Amp Design

    Assuming that "With the power off ..." refers to the laptop power... If you need to use an ATX supply, you should add L-C filtering in both the negative and the positive rails. That is, break the positive rail and connect an inductor across the gap, ditto for the negative rail, then connect...
  11. KrisBlueNZ

    An interesting pipe dimmer project

    Find a design for an incandescent lamp dimmer using a triac - you'll find plenty with a Google search - and choose components that will fit inside the pipe. There aren't really any large components in a typical dimmer. There are some inductors for interference suppression, the triac itself, and...
  12. KrisBlueNZ

    Malloc and it's use with MCUs

    In embedded systems it's not a good idea to use malloc() and free() willy-nilly, the way you might in a Windows app for example. This is because of fragmentation, and the resource-constrained nature of the environment. It really depends on what kind of processing you're doing, but I would...
  13. KrisBlueNZ

    64 LEDs set out in a square?

    Good point KJ6EAD. He is talking about driving the LEDs continuously, using serial-to-parallel shift registers, or dedicated LED drivers that are configured using a serial data stream. A simple approach is to use shift registers, such as the 74HC595. A data sheet is at...
  14. KrisBlueNZ

    Dodgy Power Amp Design

    Is the noise coming in on the power supply or the signal? High-frequency noise on either one can be removed with filtering - simple R-C filtering for the signal, where some signal loss is acceptable, and L-C filtering on the power rail. Show us a diagram of how it's all connected. How is the...
  15. KrisBlueNZ

    Resistors and organization

    I just keep the bags in a modular large plastic drawer system. Each drawer is about 30 cm wide, 20 cm high, and 40 cm deep. They can hold a LOT of bags! You could also use cardboard boxes of suitable sizes, one for each category of component. Remember I said that I group the small bags into...
  16. KrisBlueNZ

    Another treadmill problem

    That sounds good. Yes, definitely use the GFI. Don't ground anything on the board! Use a battery-powered multimeter! Yes, the GFI will work without a ground connection.
  17. KrisBlueNZ

    Help with a circuit....

    Could you do it mechanically? Have the coin drop into a channel, e.g. a piece of wood with a groove in it, where its weight causes the channel to tip, operating a very sensitive microswitch. Get the channel to tip, but not so far that it's horizontal, so the coin will roll along it. When it...
  18. KrisBlueNZ

    64 LEDs set out in a square?

    Yes, you can do this with a technique called multiplexing. Your software drives the LEDs one column at a time. It outputs the eight control signals for the leftmost column on its eight row drivers, enables the leftmost column, and waits for a short time. Then it disables the leftmost column...
  19. KrisBlueNZ

    Understanding when a transistor swap is or is not appropriate

    tryppyr, I already told you what transistors to use for the transistors in the +48V regulator. You can use the same devices as the equivalent positions in the 120V regulator. See post #79 on the other thread.
  20. KrisBlueNZ

    Resistors and organization

    Personally I'm a big fan of resealable plastic bags. They don't waste space, they're easy to transport, and they don't spill their entire contents if you drop them. You can mark them clearly with an indelible marker or laundry marker. I put less commonly used values in individual bags by value...
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