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  1. Old Steve

    Pull Down Resistors

    I just did a quick LTSpice simulation of the wiper in the centre of the pot. (Attached, and screenshots below.) The circuit:- The trace, green is Vb1, (T1), and blue is Vb2, (T2):-
  2. Old Steve

    Pull Down Resistors

    A pulldown resistor holds an input low, until a high is applied to the input. And see my last post.
  3. Old Steve

    Pull Down Resistors

    My problem now, though, is when the pot is in the centre, I get 0.4V at the base of both transistors, so they should be off and LED1 still not lit! ???
  4. Old Steve

    Pull Down Resistors

    It's OK, I made a silly mistake. In reality, (with the pot wiper to the left), the base of T2 will be at about 0.35V and it will be off, not on, so the LED could not be lit. And the right-hand side of the pot will be at about 0.7V, so LED3 will be fully off. R3 / R5 act as a voltage divider...
  5. Old Steve

    Pull Down Resistors

    If it could turn 360 degrees, yes. (At least I got that right.)
  6. Old Steve

    Pull Down Resistors

    Interesting. Maybe I'm missing something, but the way I see it LED1 will always be on, if your circuit is identical to the drawing. Even with the pot wiper all the way to the left, there will still be a little under 1V available at the base of T2, (which will clamp at 0.6V), turning it on, and...
  7. Old Steve

    Pull Down Resistors

    It means it's 10 kilo ohms, 10,000 ohms, (in any context). That's a fairly standard value. If you measured correctly, it will be 5K from one end pin to the centre pin, 5K from the other end to the centre pin, and 10K from end to end. It's actually handy to number the components, to make them...
  8. Old Steve

    Pull Down Resistors

    Oh, pity. It would have been easier to calculate the exact values for you knowing that. Do you have a multimeter to measure it's resistance? (Measure across the outer terminals, with the pot out-of-circuit.)
  9. Old Steve

    Pull Down Resistors

    What value is the pot?
  10. Old Steve

    Drill bits for homemade PCBs?

    Sex??? What's that. :D Yep, I've been surprised how many of us are also into woodworking. (chopnhack for one - the name gives him away.) For me, mostly woodturning, but I do a bit of everything. Wooden scale model cars are one of my passions. I made a scale 1928 model A a little while ago, for...
  11. Old Steve

    Drill bits for homemade PCBs?

    I promise not to snap. :) I think that it's 'horses for courses' Chris, with relation to hand drilling. I've done it that way for 20 years+ without problems. When printing the PCB transparency, I set the output to "Show holes", and it leaves a nice little spot to centre the drill bit on, making...
  12. Old Steve

    Wiring pot as voltage divider across polarities

    Normal aluminium electrolytic caps are fine. (Technically, tantalum caps are also electrolytic.)
  13. Old Steve

    Help with using shift register to expand uC output

    Aaaaargh, you're kidding! max_torch, first a point I must raise - you have to use code tags when posting code. The above looks terrible. The length doesn't help - it's virtually unreadable. You'll find the code tags on the toolbar above the edit window. Hover your mouse over the fourth item...
  14. Old Steve

    Drill bits for homemade PCBs?

    Of course you're right, Chris. Sometimes I should just hold my tongue. :(
  15. Old Steve

    Wiring pot as voltage divider across polarities

    Here's the promised diagram. Take careful note of the 7905 pinouts. They're different to the 7805. With these values, no protection diodes are really necessary, but if larger caps are used, it's a good idea to add reverse diodes across the input/output of both regulators. With larger caps...
  16. Old Steve

    Wiring pot as voltage divider across polarities

    Yep, 7805 & 7905. They need to be set up on both rails, the 7805 on the positive and the 7905 on the negative, with all of the usual caps and a protection diode on each. It's 12:42am here right now and I'm exhausted and on the way to bed, but if nobody else has helped by tomorrow morning I'll...
  17. Old Steve

    capacitor replacement in non-psu circuit.

    I'd better explain further - the voltage rating is simply the maximum voltage that the capacitor can safely handle without damage. Nothing more. It has nothing to do with limiting voltage.
  18. Old Steve

    capacitor replacement in non-psu circuit.

    No truth whatsoever.
  19. Old Steve

    Hacking a Mattel Mindflex Headset for Brainwave Control

    I couldn't leave it alone without a quick test, so I set up a receiver and serial monitor on the PC and gave the headset a burst. This data is unparsed, so means little, except for the 0xAA 0xAA sync bytes at the beginning of each packet, and they're being received without a problem, so it's...
  20. Old Steve

    Hacking a Mattel Mindflex Headset for Brainwave Control

    I tested the regulator and get 3.48V - it's good-to-go, so I mounted the assembly on the headset. I did away with the SMA 'Rubber Ducky' antenna. It's too heavy, so instead I wound a 173mm 1/4 wave coil. It'll be more than enough for the range I need. Incidentally, I haven't mentioned it...
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