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  1. KrisBlueNZ

    HP 1741A Oscilloscope

    I wouldn't worry about any of those. Let's assume they're innocent until proven guilty. The last one is OK because if it wasn't, you wouldn't be seeing the neons lighting up. If you want something to do, how about fixing the +48V rail from the LVPS? Have you tried replacing the four small...
  2. KrisBlueNZ

    What Is The Ohm Of This Resistor

    Yes that's a good idea, especially if the pictures are large. There are still people with dial-up Internet access!
  3. KrisBlueNZ

    What Is The Ohm Of This Resistor

    That sounds right. That's not enough to tell the value of the capacitor :-(
  4. KrisBlueNZ

    What Is The Ohm Of This Resistor

    With JPEG files, the file size is greatly dependent on the amount of compression that's used when the file is created or saved. Heavy compression affects the image quality. Sometimes, higher resolution with heavier compression can yield an image that looks better but is a smaller file. Too much...
  5. KrisBlueNZ

    Automated Sliding Door

    Re selection of limit switches, something like this would be suitable from an electrical point of view; you need to determine whether it's suitable mechanically. http://www.digikey.com/product-detail/en/V-10G3-1C24-K/SW1068-ND/369917 Microswitches are also available with rollers on the...
  6. KrisBlueNZ

    Simple power supply questions

    Most general purpose regulators have a fairly wide input voltage range. If the charger never outputs more than 11.2V you will be fine with a 12V supply. But 11.2V is only 1.4V per cell and I believe NiMH cells sometimes want more than 1.4V during charge... But if the charger says 11.2V I guess...
  7. KrisBlueNZ

    Relay query

    He might just be busy...
  8. KrisBlueNZ

    What Is The Ohm Of This Resistor

    I can't really tell what's happening with the yellow wires. It looks like it's a loop that goes through a hole in the core of the output transformer... is that right? Yes, the white rectangular components are resistors. the 1 omega J is a one ohm resistor and the 0.68 omega J is a 0.68 ohm...
  9. KrisBlueNZ

    Automated Sliding Door

    Yes you could use an inverter, but it would be simpler to find a timer that operates from 12V DC (or whatever DC voltage you have). It needs to have two changeover relay contacts for its output, like the DTU40. You're welcome :-)
  10. KrisBlueNZ

    Thermal vias in thermal pad of IC?

    I don't see any reason not to use thermal vias with that device; it seems like a good candidate. I did a quick web search and found this informative article on thermal vias: http://www.edn.com/electronics-blogs/the-workbench/4421218/PCB-layout-tips-for-thermal-vias
  11. KrisBlueNZ

    Automated Sliding Door

    OK, here's my suggested connection diagram. I hope you can read it! AC mains comes in on the left, and feeds the DTU40 timer and the 12VDC power supply, which provides 12VDC for the motor. The DTU40 accepts 115VAC and 230VAC. The timer must be programmed so that its output is ON during...
  12. KrisBlueNZ

    Automated Sliding Door

    Hi Bob and welcome to Electronics Point :-) If you use that timer, you can do everything you want with no extra relays. All you need is a 12V DC supply, a 12V DC motor, and two limit switches. The DTU40 has a "universal" input and operates from 120~277 VAC. Its product page is...
  13. KrisBlueNZ

    Dodgy Power Amp Design

    As BobK said, there's a problem with the virtual ground. You can't return the load to it because it's not a strong rail; it's just driven by a little op-amp. Connecting large capacitors to the op-amp's output will only help to a certain extent, and is bad practice anyway (it can cause IC1a to...
  14. KrisBlueNZ

    Simple power supply questions

    Yes, you've got it. The higher input voltage doesn't affect the regulator output - the regulator regulates its output voltage; you just need to provide an input voltage that's high enough to cover the dropout voltage (the minimum required input-to-output voltage differential) and low enough...
  15. KrisBlueNZ

    What Is The Ohm Of This Resistor

    OK, that's a start. Can you take a higher-resolution photo with the wires moved so they don't obscure things. Also if the large yellow cylindrical capacitor can be detached from the board, move it out of the way as well. Can you tell us what those wires connect to. There seem to be four thick...
  16. KrisBlueNZ

    Relay query

    I was thinking the same thing Chris. Good advice.
  17. KrisBlueNZ

    Which layout the best?

    I don't think it will be very effective unless it totally encloses the circuit to be shielded. I expect you would need a multi-layer board to do that. These are just gut feelings; I haven't worked with Faraday cages or heavy duty PCB shielding before. Try asking in a forum related to PCB layout...
  18. KrisBlueNZ

    Two way radio simplex repeater control circuit using ISD1820 voice record Chip?

    Hi Tom and welcome to Electronics Point :-) So, you want to monitor a receiver and detect when it is receiving. When it is receiving, you want to start recording the received audio with the ISD1820. Then when the reception stops, you want to enable the transmitter, replay the recorded audio...
  19. KrisBlueNZ

    Hot Glue Gun Power Indicator

    That's a reasonable way to make a simple, cheap, reliable, non-heating power indicator. The series capacitor (0.15 µF for 230VAC or 0.33 µF for 110VAC) should be an "X1" or "X2" safety rated part like these: 0.15 µF, 440VAC (to suit 230VAC mains supply)...
  20. KrisBlueNZ

    Simple power supply questions

    That's a start, and it's much easier to follow, but that circuit has a problem: the relay coil is powered from the outgoing 5V rail, so when that rail is energised from the 5V power supply OR from the battery, the relay will open! You need some way to isolate the 5V power supply from the...
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