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  1. KrisBlueNZ

    Rewiring 7-band EQ

    Yes, that looks good. You could duplicate the two capacitors at the other end too. This makes it similar to a "pi" filter (see https://en.wikipedia.org/wiki/Pi_filter). Then if you need to add another stage, add two more inductors and a pair of capacitors on either end. Edit: in reply to your...
  2. KrisBlueNZ

    Any Ideas to get the image without noise

    I guess the obvious way to eliminate shadows is to include one or more sources of illumination - for example, some white LEDs. They would only need to be enabled while the camera is actually taking a picture. To capture a smaller area, you could bring the camera closer to the display or use a...
  3. KrisBlueNZ

    ATX Power Supply

    Perhaps the hard drive needs to receive a spin up command? In my experience, IDE drives spin up as soon as power is applied, but your drive could be different I guess. Many power supplies require a certain amount of load before they will operate. Typically people will connect a resistor across...
  4. KrisBlueNZ

    I am having trouble with an intercom system can some one help

    If the output from the intercom system is a normally open contact that closes to activate the latch on the pedestrian gate, you need to measure resistance across the terminals on the intercom, not voltage. You should measure open circuit (often indicated as OL on the multimeter), the same as...
  5. KrisBlueNZ

    HP 1741A Oscilloscope

    That's a pretty thorough circuit description. This used to be typical for really responsible, professional companies who respect their customers. Nowadays, providing technical information on products is often considered a legal risk (because it could be seen to encourage people to poke around in...
  6. KrisBlueNZ

    I need to fix a sub amp

    Sounds like the hum may be an earth loop. If both of your signal sources are earthed independently to the mains earth, when you plug them both in to the amp, a loop is formed, with a low resistance. For the rest see https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29 I couldn't hear...
  7. KrisBlueNZ

    Yet another What Is This thread

    I found your other thread at http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=235796 Several people there have said that these components are notoriously unreliable. That could easily explain the fact that you don't measure any continuity across any combination of the wires. A second...
  8. KrisBlueNZ

    LED Flasher help.

    You're welcome :-)
  9. KrisBlueNZ

    auto dialer output to trip relay

    Yes you can do it that way. But the line circuitry is already isolated; that's why they use the relay and the transformer. There's a chance that you can just connect the telephone line connections from the autodialler to the dry contact input on the cellular alarm and it will work, but it's...
  10. KrisBlueNZ

    Simple power supply questions

    You're welcome :-) If you want to do the charging yourself, have a look at charge controller ICs. There are lots of types available, from several manufacturers, and the data sheets usually have lots of applications information. You may also find detailed application notes on the manufacturers'...
  11. KrisBlueNZ

    delay circuit

    MOSFETs are very cool. They're not new-fangled nowadays, but there does seem to be a lack of accessible tutorials covering the basic practicalities of how to use them. I'm not obsessed with them, but for many applications they are an excellent choice. The best thing about MOSFETs is that they...
  12. KrisBlueNZ

    2.0 to 3.0 desk speaker EQ mod

    What value was the electrolytic? Unless it was a very small electrolytic (under 0.1 µF) it would have been much too high to give a corner frequency in the audio band. The corner frequency (in Hertz) for a single pole RC filter is f = 1 / (2 pi R C) where R is in ohms and C is in farads. This...
  13. KrisBlueNZ

    Timer help

    Hi James and welcome to Electronics Point :-) Yes, as Harald says, a simple solution is a 555 timer used as a monostable ("monoflop" seems to be the German word for monostable). A Google search for 555 monostable will find literally thousands of diagrams and pages; here's a good one...
  14. KrisBlueNZ

    Desoldering

    Probably, but a lot of them will be damaged. Large surface-mount packages absorb moisture from the atmosphere (this is why they are packaged in airtight bags) and if heated (apart from during initial assembly when they are fresh out of the bag) they can crack! Even if they don't crack, their...
  15. KrisBlueNZ

    Yet another What Is This thread

    You measured resistance across all combinations of pins and they were all open circuit, right? In that case it could not be an R-C integrator... But this guy sounds like he knows what he's talking about...
  16. KrisBlueNZ

    Simple power supply questions

    Yes, a low dropout regulator will give you a stable voltage from a higher-voltage battery, but it wastes power. You would be better to use a buck switching regulator. These generally have higher dropout voltages than linear LDO regulators, but you don't actually need low dropout voltage -...
  17. KrisBlueNZ

    Interference into amp from LEDs

    I'd suggest that you bring the power supply leads in at one point, connect a low ESR electrolytic (around 1000 µF) across those points, and from there, use separate two-wire connections to the amp and the LED circuit. This is a good starting point but will not necessarily eliminate the...
  18. KrisBlueNZ

    broke my chair again

    Yeah, I broke an office chair by leaning back on it. The point of failure was the steel plate that sits under the seat cushion. A cylindrical section is welded onto it, and the upright from the wheel base goes up inside the cylinder. Well, the steel plate, which was about 3 mm thick, just broke...
  19. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    Sure Chris. Here's iimagine's first design from post #1 on this thread. I've redrawn it so it makes more sense to me. iimagine posted a revised version, which I'll call version 2, in post #10. I didn't do anything with this one. Here's iimagine's third design, based on an emitter coupled...
  20. KrisBlueNZ

    Desoldering

    PC motherboards have at least eight layers, including two internal power plane layers, so the board itself absorbs heat very rapidly. That's why it's almost impossible to salvage components from them. I used to try; now I normally only try to salvage crystals and crystal oscillators, which are...
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