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  1. KrisBlueNZ

    impedance of a constant current source

    I think (I'm not an expert) that using a constant current collector load would not reduce the distortion due to the Early effect, because the collector-emitter voltage would still be varying over a wide range. Using a current mirror as the load would work, because the collector-emitter voltage...
  2. KrisBlueNZ

    Simple parallel EEPROM programmer

    Yeah, I think the whole idea is too fragile for practical use. As I expected, 74HCT590 is not listed on Digikey. So you would have to use 74HC and put pullup resistors on the outputs of any 74LS devices that were driving the circuit, or use a 74HCT device as a level translator (74HCT outputs...
  3. KrisBlueNZ

    Simple parallel EEPROM programmer

    Sort of. No device will have a problem with leaving -CE active while the data and address are being set up, as long as -WE is high. Whether you need to control -CE at all may depend on how (or if) you want to detect completion of the write cycle using data polling. (Not sure if that device...
  4. KrisBlueNZ

    Current Direction

    Are you sure about that gorgon? Current flow from positive to negative is called "conventional current" and it goes "in the direction of the arrow" on circuit symbols. I prefer to use that model myself as well in schematics and descriptions, and those diagrams certainly do show "electron flow"...
  5. KrisBlueNZ

    impedance of a constant current source

    I would be less concerned about the use of the LED as a voltage reference than the fact that a current source won't work if the base bias circuit is connected in parallel with the transistor. To be specific, if you want to use that circuit to source current from the positive rail, you have to...
  6. KrisBlueNZ

    No voltage drop

    OK, I guessed wrong. I'll throw out some other suggestions. Have you connected the "-Vin" pins of the DC-DC converter module to the ground rail? That connection is not shown on the schematic. You need to do that, otherwise it won't do anything. When you plug your power adapter (wall wart) into...
  7. KrisBlueNZ

    impedance of a constant current source

    Click Go Advanced, then click on the paper clip icon at the top of the edit window. From there it's pretty obvious.
  8. KrisBlueNZ

    impedance of a constant current source

    You need to clarify your question. Are you asking "How do I calculate what the correct impedance of the current source should be in a particular amplifier stage", or "How do I calculate the actual impedance of an existing current source that I have a schematic for?" In either case, you need to...
  9. KrisBlueNZ

    Current Direction

    Your three circuits don't really make sense because no voltage appears across a piece of wire (well, a perfect piece of wire with zero resistance, anyway), so (neglecting the very small resistances of the wire), putting two pieces of wire in parallel, or putting a resistor in parallel with a...
  10. KrisBlueNZ

    No voltage drop

    You're probably using the switched contact of the socket instead of the power contact. Have a look at the data sheet for the socket at http://www.cui.com/product/resource/pj-102a.pdf In the bottom left corner, there's a "schematic" showing the three pin numbers. You need to use pins 1 and 2...
  11. KrisBlueNZ

    Simple parallel EEPROM programmer

    That's an interesting design. Thanks for the circuit description! A small point relating to your description of programming parallel EEPROMs: it's not necessary to drive -CS low before presenting the address and data; you just need to have it low in conjunction with -WE being low, to program a...
  12. KrisBlueNZ

    74HC595 shenanigans..

    LOL :-) That would certainly make the analogy memorable! Very fair comment. I shouldn't expect anything less from you Steve. Thanks for your honesty :-)
  13. KrisBlueNZ

    Strange sound

    The signal could also be coupling into your cable inductively. Try moving the cable away from any other cables, and away from the TV if it's a CRT-type TV. The lead from the wall socket to the TV, or to the laptop charger, will emit a magnetic field. Also, wall wiring. Edit: Oops! Forgot to...
  14. KrisBlueNZ

    Ringing Transformer from overloading or overdriving

    In addition to what Steve said (which I totally agree with). You can detect core saturation by monitoring the primary current - either insert a low-value non-inductive resistor in the return line to 0V and scope the voltage across it, or use a current probe on the scope. If you see the current...
  15. KrisBlueNZ

    Anyone know what this is? Bullet shaped resistor?

    Try Googling those numbers along with "thermal fuse". They could be part numbers and/or temperature numbers; the 72 could mean 72 degrees Celsius. Also I think the colour of the plastic bit is different for different temperatures. I wouldn't bother with Radio Shack; their range will be pretty...
  16. KrisBlueNZ

    74HC595 shenanigans..

    Interesting, Steve. An analogy where distance == voltage, and tension/force == current. If you replace the weights of the objects with tension springs to ground, you also have stretchiness == resistance. That will also make the model more accurate, because a frictionless see-saw with a...
  17. KrisBlueNZ

    OP AMP comparison,

    You're right to be concerned. Older op-amps don't generally perform well at lower voltages, and both the useful input voltage range and the output voltage swing can become too small to be useful. You would be best to use an op-amp that's designed to operate at low voltage. Microchip, Analog...
  18. KrisBlueNZ

    74HC595 shenanigans..

    CMOS inputs will float if they're not connected to anything, and pick up noise. If you connect a pushbutton from VDD to an input, while the pushbutton is not being pressed there is NOTHING connected to the CMOS input, so it will float. Only when you press the button will the input have a...
  19. KrisBlueNZ

    No voltage drop

    Hi Stephen and welcome to Electronics Point :-) It's kind of hard to know what you're talking about. Can you post a schematic, a PCB layout, and a photo of the assembled board? Use Go Advanced and click the paper clip tab to get the Upload dialog box.
  20. KrisBlueNZ

    VOLTAGE ISSUE?

    Yes that sounds workable. Silicon diodes drop between 0.6V and 2V, sometimes more, depending on the amount of current flowing. Schottky diodes have lower voltage drops but are more susceptible to damage. Connect the diode with its anode to the battery and its cathode to the battery input to the...
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