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  1. KrisBlueNZ

    24VAC power supply question about VA spec

    I think you can use the Reset input for that. It restarts the timer, beginning with the "A" output activation. So the next purge will be delayed until the "B" time after you reset it, if that's what you want. If you want an extra purge without affecting the timer, then you'll need an external...
  2. KrisBlueNZ

    24VAC power supply question about VA spec

    OK, here's the arrangement I'm suggesting. Mains voltage comes into the 24VAC transformer, which you already have. This provides the 24VAC that operates the zone valve, and it's also used for the purge valve. When the thermostat activates the system, it feeds 24VAC into the coil of relay K1...
  3. KrisBlueNZ

    24VAC power supply question about VA spec

    I understand. That's a good explanation, thanks. What a clever system - using the stable temperature of the earth way below the surface to provide the heating energy for your house! I am familiar with normal air-to-air heat pumps - many houses have them here in New Zealand - but I had not heard...
  4. KrisBlueNZ

    RC Transmitter Wont turn on

    The smoke would not have come from the crystal, nor probably from the electrolytic. The melted plastic looks like it's from a soldering iron. What have you been soldering on the board? No, capacitor problems are only common in high-energy circuits like TV sets and switching power supplies. I...
  5. KrisBlueNZ

    Protection from reverse polarity

    The OP seems to have seagulled this thread...
  6. KrisBlueNZ

    24VAC power supply question about VA spec

    This is a 12V DC adjustable time delay relay: http://www.ebay.com/itm/DC-12V-Delay-Timer-Switch-Adjustable-Module-0-to-20-Second-NE555-relay-/261263574868?pt=LH_DefaultDomain_0&hash=item3cd485c754 If you use 12V DC instead of AC with your dual timer, you can use this module. I think the way...
  7. KrisBlueNZ

    Need help to fix motion detector alarm

    Cool! Good work. Well, electrolytics have pretty wide tolerance, especially cheap ones. 4.6 µF could be within tolerance for a low-quality 2.2 µF capacitor, but it might have been leaky (not physically leaking chemicals, but leaking current) so that could have been the problem. It's always...
  8. KrisBlueNZ

    24VAC power supply question about VA spec

    I just re-read the thread. I think I get it. You have a controller that controls a heater, and when the heater is activated, you want to activate the purge valve for five seconds initially, then every X amount of time after that; when the heater is not powered, nothing happens on the purge...
  9. KrisBlueNZ

    24VAC power supply question about VA spec

    Well, how dumb is that. Pretty dumb! OK, I'm happy to try to help. But I need to understand the whole system. I simply will not design something for a system I don't fully understand; it's a characteristic of my personality I suppose. I always need to understand the big picture. Thanks for the...
  10. KrisBlueNZ

    24VAC power supply question about VA spec

    That's right. The outputs of the timer are (presumably) coming from the contacts of electromechanical relays - they're able to switch several amps of current. So you will not damage them by just testing them with a multimeter on resistance or continuity range.
  11. KrisBlueNZ

    24VAC power supply question about VA spec

    Neither is preferable, as far as the timer and power consumption are concerned. I would use AC because it leaves the DC power supply available for other things, and other things most often want DC.
  12. KrisBlueNZ

    Confused about transformer windings

    Yes, your colours are right.
  13. KrisBlueNZ

    Light Controlled Device (wireless)

    Yes, you need to explain your project in a LOT more detail than that. A diagram would help. Even just a scanned pencil sketch.
  14. KrisBlueNZ

    Design question on microcontroller and TIP122

    OK, this is what I'm suggesting. The pullup resistor is tied to VDD, not VMS. You could do it either way. The diode across the load isn't needed if the load is a modem, but should be present if you're powering a motor, as motors are inductive and generate back EMF which could damage the...
  15. KrisBlueNZ

    solar tracker

    Where did you get that design? It's not very good. Apart from the fact that the +12V output voltage from the comparators could damage the AVR, there's the problem with using four separate comparators instead of comparing the illumination levels on the pairs of LDRs with each other. I guess it's...
  16. KrisBlueNZ

    24VAC power supply question about VA spec

    I kind of get it. As I said, play around with the timer (when the replacement arrives) and see what it can do, and try to fit it into your scheme. I don't think it can automatically adjust its timing duration though. If you want more help, you need to explain it from the ground up. I have no...
  17. KrisBlueNZ

    Design question on microcontroller and TIP122

    What is "VSS"? Is that the voltage rail that you're feeding into the source of the switching MOSFET? If so, you should call it something else - VSS is the name of the negative supply rail of the 8051! Call it VMS for "modem supply" or something like that. Why does the switching MOSFET's source...
  18. KrisBlueNZ

    Design question on microcontroller and TIP122

    I can't suggest any likely reason for those observations. My recommendation should work fine, with a 4V supply to the MOSFET or with a 5V supply. So you were using a 5V supply for the 8051, and a separate 5V supply for the MOSFET source? How did you connect the two supplies together? By...
  19. KrisBlueNZ

    24VAC power supply question about VA spec

    Yes, definitely use a 12VAC transformer. Yes, you can test the contacts with a multimeter. I think you should spend a reasonable amount of time playing around with the timer to get a feeling for how it works. I think I get the general idea from the data sheet, although I think there's one...
  20. KrisBlueNZ

    Bush Tv (CRT) having horizontal lines on the top half of TV

    If tapping the set makes the problem come and go, that sounds like a bad connection of some kind, such as a dry joint. Have a close look at the solder joints all around the board and solder up anything that looks suspect. (Leave the set unplugged for at least ten minutes first.) I explained how...
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