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  1. KrisBlueNZ

    Does this Circuit make sense?

    Mostly looks good, but your LEDs are connected backwards (reverse polarity) and they won't run at quite 20 mA. Each series LED chain has two LEDs, which drop 3.2V each for 6.4V total. That leaves 5.6V across each current limiting resistor (assuming your 12V power supply is actually 12V not...
  2. KrisBlueNZ

    A light-sensitive motor

    The problems with your circuit at the moment are: You need a clean switching behaviour in response to a gradual, poorly defined change in the resistance of the LDR. This can be done with a circuit that uses a threshold - a comparator such as the LM393 (dual comparator) or a circuit built from...
  3. KrisBlueNZ

    Problems substituting a relay

    Measure the AC voltage across it, and use P = V^2 / R. The voltage and current in that resistor is roughly a sinewave, so that method should be accurate to about 10% or so.
  4. KrisBlueNZ

    Problems substituting a relay

    The zener is going to get pretty warm, since it's dissipating up to 1.3 watts. The zener is rated for 5 watts but this doesn't mean that it won't get hot. Power is converted into heat which is radiated by the surface area of the component, so if 1.3W of power is being dissipated, a 5W zener will...
  5. KrisBlueNZ

    Wish Me Luck ~ Hard Drive Surgery Tonight

    I haven't tried it since it came back from the recovery place. Before I sent it, it was spinning up, but clicking constantly. I don't remember seeing it give up and spin down. It was in an external USB enclosure. Sometimes (but not on every power-up) it would be recognised, but then, only the...
  6. KrisBlueNZ

    Wish Me Luck ~ Hard Drive Surgery Tonight

    Thanks for the advice! Swapping the Flash ROM sounds do-able, but I understood that some of the drive firmware was on the drive itself. That didn't make much sense to me, but I heard this from the guy at the recovery company. Perhaps he was just making excuses, or trying to convince me that I...
  7. KrisBlueNZ

    How can I count analogue pulses over 10secs.

    I agree with using the ADC - I think you'll need to - and with timing the intervals between beats and using a running average for filtering. I think you should look at the waveshapes of some typical signals that your ADC will see, including some abnormal ones if your device needs to be able to...
  8. KrisBlueNZ

    Wish Me Luck ~ Hard Drive Surgery Tonight

    Cool thread CocaCola! I have a crashed drive. I sent it to a professional recovery company; they failed because the drive couldn't even load its firmware. I'm sure with enough knowledge and resourcefulness it would be possible though, so I'm holding onto it. Please keep us informed. Good luck!
  9. KrisBlueNZ

    How do I choose a power transitor to switch a PC fan on?

    Thanks :-) Likewise. It's helpful to do this when you're designing circuits for manufacture, since every extra reel of SMD resistors is an extra thing to be loaded into the placement machine. With the circuits I've designed since I've been posting here, I've been trying to stick with...
  10. KrisBlueNZ

    How do I choose a power transitor to switch a PC fan on?

    You're close. You need to LIMIT the current that the transistor's base-emitter junction draws from the Arduino, using a current limiting resistor between the Arduino output and the base. Beyond that, you need to use an NPN transistor with its emitter grounded - connected to the Arduino's ground...
  11. KrisBlueNZ

    Ohm's Law or not Ohm's Law... That is the question

    :-) Cute. And I WAS trying to be a smart-arse. But Ohm's law IS actually applicable to the DC resistance of inductors, and can be usefully applied - for example when you're calculating the average DC voltage dropped by a filter inductor in an SMPS at a particular load current. But this is only...
  12. KrisBlueNZ

    Need to fix a printed circuit board

    "I love it when a plan comes together!" - Hannibal, "The A Team"
  13. KrisBlueNZ

    Ohm's Law or not Ohm's Law... That is the question

    I think that's the important issue. It's certainly true that whenever you have a voltage across and a current through any component or circuit, you can calculate a "resistance" value, but this value is only really useful and meaningful for an ohmic component or circuit, where voltage and current...
  14. KrisBlueNZ

    Controlling amplitude of Sin and triangle waves...

    KJ6EAD's post reminded me. Analog Devices (www.analog.com) make a range of direct digital synthesis devices that might be applicable, depending on exactly what your needs are.
  15. KrisBlueNZ

    Ohm's Law or not Ohm's Law... That is the question

    Oh dear. I've been through this business before (not here though). In my case it was an argument about whether Ohm's law applies to the human body when it is being electrocuted. That's a much greyer area than inductors and capacitors. From what I learnt from that argument, Ohm's law is normally...
  16. KrisBlueNZ

    LDR circuit.. no luck :(

    The wire from A14 should go to the negative terminal of the battery pack. The wire from D14 should go to the middle pin of the transistor marked A2. The wire from K14 goes to the positive terminal of the battery pack, yes.
  17. KrisBlueNZ

    Controlling amplitude of Sin and triangle waves...

    That frequency range is probably going to be a problem. The LM13700 has a gain-bandwidth product of only 2 MHz. I doubt I'll be able to help, but if you want to describe your project in detail, I or someone else here may be able to suggest something.
  18. KrisBlueNZ

    Arcade 110v strobe flasher circuit help

    Thanks Chris :-) Yeah, I'm enjoying using LTSpice.
  19. KrisBlueNZ

    LED driver

    Yes, it's passed through the optocoupler as a "variable voltage". Optocouplers have a linear region. Actually it's not very linear, but it is at least analogue.
  20. KrisBlueNZ

    LED driver

    The optocoupler operates at DC. Increasing the current into the LED causes the controller chip to reduce the amount of energy it feeds into the transformer. In the application circuit, there are three sources of this "back off" signal, diode ORed together. I'm not happy with the way these...
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