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  1. KrisBlueNZ

    transistor Rbase value

    1. The fan control output of the MIC502 is not designed to provide the amount of current needed to saturate a BD135 or a TIP31 that is controlling a 600 mA fan. A simple fix is to insert an NPN emitter follower stage between the output and the BD135/TIP31. To do this, add a small-signal NPN...
  2. KrisBlueNZ

    confused about hookup of a gate.

    If you're using a genuine 7486 (TTL) or 74LS86 (LS-TTL) device, you would be better to use active low inputs and outputs. Connect your LED between VCC and the output, and put the input resistors from the inputs to VCC, not GND. Ground an input to test the circuit. The reason for this is the...
  3. KrisBlueNZ

    HP 1741A Oscilloscope

    I wouldn't worry about the capacitors. The solder does look new, but the joints look OK to me. Nice work on the plug pins. Personally I would resolder _all_ of them; I think of the other dry joints as a warning sign. Before you reassemble the unit, can you power up the power board with the...
  4. KrisBlueNZ

    cant play mp4 files saved from youtube

    Thanks for the pointer :-)
  5. KrisBlueNZ

    cant play mp4 files saved from youtube

    Great!
  6. KrisBlueNZ

    HP 1741A Oscilloscope

    I agree there's a problem with the joints on that connector. I've seen this before on the end pins of long headers when vibration, and usually, high currents, are present. I haven't seen it before on a double-sided board though. Is that wide connector where the secondaries from the transformer...
  7. KrisBlueNZ

    Samsung TV buzzing noise

    Hmm. I haven't heard of hot glue being used for that. I use spray-on lacquer. If you can remove the hot glue, you could try that. You may not have located all of the noisy inductors. Try holding a thin cardboard tube up to your ear, and move the other end around the board. Be very careful not...
  8. KrisBlueNZ

    cant play mp4 files saved from youtube

    Personally I would not touch RealPlayer with a barge pole. I also find that Windows Media Player is a waste of time. Personally I mainly use a program called SMPlayer, which internally uses the venerable mplayer and can be downloaded from sourceforge.net, and I keep VLC around for the occasional...
  9. KrisBlueNZ

    Help for switching operation

    If you're looking for an arrangement where any of several switches can change the output state, you can use cascaded exclusive-OR gates or a "parity detection" circuit. The general idea is that given a number of inputs, the circuit counts how many inputs are active, determines whether that...
  10. KrisBlueNZ

    Wireless trigger for LEDs and buzzers

    I wasn't suggesting that each slave keep a count of goals per se; just a counter that increments on each goal and wraps around in a defined way. It doesn't even need to be an 8-bit counter. The reason is so that if communication is lost for a time, when it is re-established, if multiple...
  11. KrisBlueNZ

    Wireless trigger for LEDs and buzzers

    What do you mean by "net"? Do you mean a physical net that's strung around the goal hoop? How many slaves will be present? Do the slaves all communicate with a single transceiver at the master? What happens if two slaves try to send messages at the same time? Will the master receive both...
  12. KrisBlueNZ

    Power supply help

    Yes you can drop 12V down to 3V for the fish feeder. If it doesn't draw much current, you can use a linear regulator such as an LM317. Calculate the power dissipation to see whether a heatsink is needed or not and how big it needs to be. If it draws significant current - say 100 mA or more - you...
  13. KrisBlueNZ

    Power supply help

    I don't understand why you don't want to power the Arduino from 12V. Yes, you could add a regulator to drop 12V to a lower voltage, but regulators need a certain minimum input-to-output voltage difference, called the "dropout voltage". Dropout voltage is usually a few volts for a switching...
  14. KrisBlueNZ

    Help me alter this device

    Can you clarify what you want to use this signal for. You said you want to emulate an injector signal; does that mean you want to control an injector with this signal? Or are you just using it to monitor engine RPM? Or something else?
  15. KrisBlueNZ

    [HELP] 10w and 50w LED on 220v schematic

    As well as being dangerous, a direct line-powered LED supply is not practical for currents above around 50 mA. I've simulated a circuit with 1A output and it's very impractical. The input capacitor would have to be extremely large, a large amount of smoothing capacitance would be required to...
  16. KrisBlueNZ

    Power supply help

    Here's a much better explanation of crowbar circuits: http://axotron.se/index_en.php?page=26
  17. KrisBlueNZ

    Power supply help

    No, don't use a resistor. The voltage dropped across a resistor depends on the current through it. At light loads it will drop less voltage, so the voltage going into the HRD regulator could exceed 40V. Sometimes, zener diodes are suggested as a way to drop voltage in this situation, but it's...
  18. KrisBlueNZ

    Wireless trigger for LEDs and buzzers

    If you have a situation where multiple slaves have information that needs to be communicated upstream, and you need that information to be received reliably, you should have some kind of poll-response system where the upstream device periodically polls downstream devices, or at least expects...
  19. KrisBlueNZ

    Car Battery Bounce Eliminator

    OK, here's my suggested circuit. If anyone suspects that it may be over-engineered, I can put that thought to rest right now: it IS almost certainly over-engineered. I've done that because I really don't know the variables involved in this application and I just want that MOSFET to turn ON as...
  20. KrisBlueNZ

    [HELP] Op-Amp used in resistance detection circuit.

    How are you going to regulate the voltage applied to the coil? You could apply a fixed voltage and pulse-width-modulate the MOSFET. Wouldn't it be simpler to sense the current flowing through the MOSFET when it's ON instead of disconnecting it and measuring the heater resistance? You would...
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