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  1. KrisBlueNZ

    Boiling capacitor!

    Adding an electrolytic capacitor isn't going to help you charge a worn-out SLA battery at all. If you connect the capacitor BETWEEN the charger and the battery, the capacitor will charge up to the charger voltage in a very short time and current will stop flowing (unless you connect the...
  2. KrisBlueNZ

    Project Help!!

    It depends on the characteristics of your "sensor/switch" and the solenoid. If you already have the sensor/switch, can you describe it, or give a part number, or ideally a link to a data sheet? Can you explain what you want to do, in more detail? So far, it sounds to me like you want to remotely...
  3. KrisBlueNZ

    Piezo buzzer at 20 hz

    I think piezo transducers typically have a pretty low capacitance. It will be hard to transfer a lot of power to them at a low frequency because their reactance will be so high. You might need a very high voltage signal in order to transfer any real power to a piezo transducer at 20 Hz sinusoidal.
  4. KrisBlueNZ

    Newbie questions

    Cool! Don't get the wrong idea because my analogy uses little men to roughly model semiconductors. After all, semiconductors ARE called "active" devices! But even if you don't like that part of it, it's still useful as a model to help you understand voltage, current, resistance and capacitance.
  5. KrisBlueNZ

    Newbie questions

    Re WeaselNo7's two more things. Reverse current, for a diode, is the maximum current that the diode will pass when reverse biased by a specified voltage. An ideal diode does not allow ANY current to flow when it's reverse biased. Any current that DOES flow is called LEAKAGE current. This does...
  6. KrisBlueNZ

    Blown capacitors in PC

    It's common to see "uF" for microfarads. It's from the days before the Mu symbol was widely available. You'll also occasionally see "mfd".
  7. KrisBlueNZ

    Newbie questions

    I don't find either of those ideas helpful when understanding the relationship between voltage, current and resistance in circuits. Here is an analogy that I like. I came up with it myself, though I'm probably not the first to think of it. It is not a traditional analogy, but I find it works...
  8. KrisBlueNZ

    plz help

    LOL :-) While you're at it, please send me Scarlett Johansson. Seriously, if you want anyone to help you, you need to do a lot more. 1. Specify what you want in much more detail, and use the right unit (Ah is amp-hours which is only used with batteries). 2. Make some effort to find what you're...
  9. KrisBlueNZ

    Can a transistor do this?

    You've got the right idea. Yes, many transistors have no problem switching 1A at 12V. You will need something in a decent sized package though, like the very common TO-220 package, which has a metal tab at the top so you can attach it to a heatsink. There are two types of transistor that you...
  10. KrisBlueNZ

    Interval Time Delay Relay

    I've designed a simple circuit that might do what you want, if you're still interested. It accepts two dry contact inputs and provides two dry contact outputs. It needs a supply voltage of 12VDC. The two relays are SPST (Form A) relays with 12VDC coils. The run timeouts are set by the two...
  11. KrisBlueNZ

    Quick Op-amp Questions

    I'm not too keen on that op-amp/discrete supply splitter circuit... I think the four capacitors on the output will make the design very sensitive to supply noise. It's not normal, and I think a very bad idea, to have capacitance to ground (and/or positive supply) connected straight to the...
  12. KrisBlueNZ

    Blown capacitors in PC

    EXCELLENT advice Steve. But advice that's rarely followed - I've NEVER seen any notes on previous repairs inside any electronic equipment I've looked at. I'm not a professional repairman though, so I haven't see that many. But even when I was an apprentice at an electronic repair outfit, I never...
  13. KrisBlueNZ

    Quick Op-amp Questions

    Another option is a negative rail generator, that generates a negative supply rail for your op-amps from the positive supply. You can do this with an inductor-based switching regulator (see National Semiconductor, Maxim, Linear Technology etc), or a switched-capacitor charge pump device like the...
  14. KrisBlueNZ

    Blown capacitors in PC

    The CapXon data sheet you pointed to DOES state the ESR, in the "Impedance" column in the table. Every capacitance / voltage combination has a different ESR, so ESR is listed independently for each combination in the table. In fact, "impedance" is a more appropriate name than ESR for this...
  15. KrisBlueNZ

    Quick Op-amp Questions

    When you're using an op-amp that requires split supplies, you generally have a "half-way ground" rail that is half way between the two supply voltages, and you can usually generate this using a resistor voltage divider, often with a decoupler from the half-way ground to the negative rail if...
  16. KrisBlueNZ

    Blown capacitors in PC

    In this application, ESR (effective series resistance) is a very important parameter (as well as capacitance and voltage, and to a lesser extent, temperature). These capacitors are providing smoothing on voltage rails that may be generated by a switching regulator (which produces ripple) and the...
  17. KrisBlueNZ

    Parallel Circuit - Fireworks Firing System

    Yes, your supply has to be able to provide its specified output voltage when driving the maximum load (current) that you will be drawing from it. If each e-match draws 1A at 12V and you want to be able to power ten at once, it must be able to supply 10A. If you have mains available, one or more...
  18. KrisBlueNZ

    Parallel Circuit - Fireworks Firing System

    CocaCola, he isn't using a battery and his figures are mA not mAh. The simple answer is that you need more current. With two (or more) matches in parallel, the combined resistance is too low and the power supply voltage drops. If you need to be able to fire all ten matches at once, you need a...
  19. KrisBlueNZ

    Need help from all the pros out there...

    PID control: http://en.wikipedia.org/wiki/PID_controller I think the main issues that relate to choosing a controller are (a) the need for DAC(s) - many microcontrollers don't have them, or have only one channel, and (b) the need for floating point speed, if there is a need. Smaller...
  20. KrisBlueNZ

    blowing up capacitors

    Small 9V batteries can't produce very much current, because they have a relatively high internal effective series resistance. Measure the voltage across the series string while the electrolytic is connected; you'll probably find it drops quite low. You need bigger batteries, or a power supply. A...
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