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  1. KrisBlueNZ

    button on/off

    It would be helpful if you told us where you're located. There's an option for this in your profile settings and it's there for a reason. As donkey says, you need to describe what you want. You can get push-on/push-off and momentary (ON while button is held in); both types are readily available...
  2. KrisBlueNZ

    nimh charger

    Temperature rise is the best way to detect end of charge. The voltage drop method doesn't work reliably below 0.5C charge rate. And you need to monitor the battery temperature anyway so you don't charge them outside the recommended range. It doesn't take much to overcharge them, and they must...
  3. KrisBlueNZ

    JFET Voltage Controlled Switch

    I've used JFETs for audio switching and had no problems. Can you post some schematics? There may be an error we can spot.
  4. KrisBlueNZ

    JFET Voltage Controlled Switch

    One thing to beware of, when using MOSFETs like this, is the body diode. It's in parallel with the MOSFET between drain and source, and obviously, it's still present when the MOSFET is turned OFF. So when the MOSFET is OFF, it is open-circuit in one direction, but in the other direction, it's...
  5. KrisBlueNZ

    ad 620 instrumentation amplifier

    You haven't changed the schematic at all. It still has the problems I mentioned. Please read the article that Laplace referred you to. You need a DC bias on the non-inverting input of the op-amp. With only a capacitor connected to it, you will not get this. You still haven't answered several...
  6. KrisBlueNZ

    LED VU meter with transistors, dotted...

    I've had a good look around and the best example of an envelope follower for your application is actually in the LM3916 data sheet! It's in Figure 10 on page 14. Unfortunately that circuit needs a negative supply voltage for the negative supply pins of the op-amps. It would be possible to...
  7. KrisBlueNZ

    LED VU meter with transistors, dotted...

    Right. That's because you're feeding your audio signal directly into the LM3916. The LM3916 responds constantly to the instantaneous voltage at its input. An audio signal consists of a complex series of "ups and downs", with the signal going above and below the 0V reference line hundreds or...
  8. KrisBlueNZ

    Home karaoke recorder

    Perhaps he's suggesting that his machine would be a suitable replacement for an existing karaoke machine that fails? Anyone with a dead karaoke machine would be best advised to buy a dedicated laptop, some external sound hardware, and a lot of software, as I suggested the OP should do. It's the...
  9. KrisBlueNZ

    ad 620 instrumentation amplifier

    And the answers to the other questions?
  10. KrisBlueNZ

    ad 620 instrumentation amplifier

    The diagram is hard to read. Use a better light source and take the photograph looking directly at the diagram. What's the value of RG? What is the reason for the 0.1 uF capacitor between the input source and the non-inverting input? Why are you using an instrumentation amplifier for a simple...
  11. KrisBlueNZ

    multiple displays

    It's probably a reasonable way to go. The alternative would be to convert the current into a digital representation and transmit that to the indicators, but I've never heard of an off-the-shelf panel meter that accepts data in digital form. You would have to design one, as well as the method of...
  12. KrisBlueNZ

    ad 620 instrumentation amplifier

    I can't help with a description like that. What circuit did you build? What input did you connect to it? What output did you get? What's wrong with the output? Can you upload a photo of your breadboard? Measure the voltages on all pins of the AD620 Give a lot more information.
  13. KrisBlueNZ

    Home karaoke recorder

    It's totally impractical unless you use a PC but hide the fact that that's what it is. Do you have any idea how many man-hours have gone into the programming of even just a small part of the system such as an MP3 decoder? Or a file system handler for a USB Flash drive or memory card? Then you...
  14. KrisBlueNZ

    Home karaoke recorder

    Sounds like a nice wish list. If you drop the requirement for it to run from eight D-cells or two lantern batteries, there's a solution available. It's called a PC (a laptop, even) with an external audio interface and lots of software installed on it.
  15. KrisBlueNZ

    ad 620 instrumentation amplifier

    Have you even LOOKED at the AD620's data sheet? It's full of detailed information on how to use the device, and includes lots of circuit diagrams. Analog Devices also have an application note on instrumentation amplifiers that might help.
  16. KrisBlueNZ

    multiple displays

    Wiring a lot of current inputs in series and using a high voltage source will cause a problem if the meter inputs are simple current shunts. Assume each meter has an input current shunt of 250 ohms, a typical value. At 20 mA the total series voltage drop will be 110V, so a 120V power source...
  17. KrisBlueNZ

    Sign with 175 LEDs

    It means the switch is designed for automotive use with a 12V battery. Technically you're running it outside its ratings at 19.4V but your current is much lower than the 16A specified, and your load is non-inductive, so they will be fine. No need to worry.
  18. KrisBlueNZ

    HELP: CCFL (LCD Backlight) Driving Circuit

    Excellent Ashley. All of those comments show that you have a really good attitude. Good luck!
  19. KrisBlueNZ

    Readily Available Energy

    Where did you get this idea from? Can you give a link to a source?
  20. KrisBlueNZ

    Amplifier antenna question

    To the OP. Are you imagining that the sound from your guitar amp would be transmitted? No it wouldn't; for that, you need a device called a modulator, which generates a radio-frequency signal that is modulated by the sound from the guitar amp. Modulated means varied in some way - either by...
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