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  1. Merlin3189

    Help: Motor Question

    I've no idea what size your "spools" are, but I often attach things to small DC motors, which commonly have 2mm diameter shafts, by sliding a piece of rubber or plastic tube onto the shaft. This requires a bit of trial and error. I also wrap plastic tape around to increase the diameter until...
  2. Merlin3189

    Multiplexing project

    Since you have 64 elements, they can be selected individually with 6 bits. You will generally want some sort of clock/strobe so that makes 7 signals. 128x128=16334 or 14 bits, so with strobe you need 15 signals. This assumes you will only power one at a time. If you want to energise more...
  3. Merlin3189

    diode for collapsing magnetic field

    That's what I did. How did I miss Michigan ...? That's exactly what it looks like! And lo & behold, Wikipedia confirms mitten as a nickname for Michigan. Thanks. Yet again my knowledge increased and my interest stimulated. Since you have ongoing problems, I'll keep watching and see if I...
  4. Merlin3189

    diode for collapsing magnetic field

    What an interesting thread, though it's taken a long time to read all 18 pages and follow up the links. It's amazing how you can think you know quite a lot about a subject until you meet a topic like this. I have not only learnt things I did not know (thanks esp. to Electrician's lnks) but...
  5. Merlin3189

    dc motor resistor in parallel to slow motor down

    A bit late I know, but I just had a thought about this. Forget electronics. Use a worm gear. That gives a good stepdown gear ratio from motor to load and is almost impossible to run in reverse. So when the motor is not powered, the antenna is locked. I think it would theoretically be possible...
  6. Merlin3189

    dc motor resistor in parallel to slow motor down

    Dave's short cct is the way to go - the 'shorter' the better! If you think about it, the highest resistor you can put across the motor, is an open cct, which will do nothing. A smaller resistor will allow some current to flow and provide some breaking. The smallest resistor you can use is a...
  7. Merlin3189

    FM Stereo

    They thought about that when they designed it. So the two signals they transmit are the sum of the L & R channels and the difference of the L & R channels. A mono reciever ignores the latter and just hears the sum - the two channels added together. A stereo rcvr adds the two signals (L+R and...
  8. Merlin3189

    CRT anode voltages

    As well as accelerating the electrons with a high +ve Voltage, the multiple anodes also have to focus the beam, which would otherwise diverge from the electron gun. They do this with curved electric fields between consecutive electrodes, which requires them to be at different Voltages, typically...
  9. Merlin3189

    Question: Off Delay Timer

    So your 3 states are: 3:Off 1:Motor A on and Motor B on at 60rpm 2:Motor B on at 100rpm 3:Off with the 2 on states lasting 5 sec each and the off state being the quiescent state. So two timers with the first triggered by the start event and the second triggered by the end of the first...
  10. Merlin3189

    Stepper Motors. Any Experts?

    Which would imply an internal resistance of about 113 Ohm. As Dave says, the basic generator model is, an emf proportional to speed and an internal resistance in series. And the only realistic way to determine the emf/speed ratio is to measure it as you did here. What you also found is...
  11. Merlin3189

    Organizing Resistors

    I use transparent paper envelopes, which were sold for holding strips of 35mm film. These stand in order in boxes with dividers at 1, 10, 100, 1K, etc. The values are written on the visible end of the envelope and it's like flicking through a card index to find the value you want. But I only...
  12. Merlin3189

    Help with op-amp circuit

    Just like to add, don't forget to add a little bit of positive feedback if using an op-amp as a comparator. The standard school textbook circuit, with the signal to the + input and the reference Voltage (usually a potential divider) to the - input, tends to oscillate as the signal passes...
  13. Merlin3189

    Signal Processing

    To be honest, I would struggle to explain the detailed maths of Fourier transforms. I can only give you my qualitative understanding of window functions. If you have a single pure tone sampled from -∞ to +∞, the theoretical Fourier transform of this would be a single spike representing that...
  14. Merlin3189

    Find suitable capacitor for wind energy device

    I'm surprised by your 500MV/m so, what plastic are you thinking of? I'm no expert on this, but with air at 3MV/m (as a rule of thumb from TV days), I was sceptical and looked at Wikipaedia. The highest I could find was Mica 100MV/m or Teflon up to 200MV/m (which itself amazed me.) What also...
  15. Merlin3189

    Signal Processing

    I too am not sure what you are asking. But in a way, the question is its own answer! Harmonics are by definition multiples of the fundamental frequency. So for a note of any frequency, all the harmonics will be at exact multiples of that frequency. Eg. if you play a C at 260Hz, then the...
  16. Merlin3189

    More current and less voltage?

    Just in case you mean, what happens if you replace a 12V fan with a 6V fan, that's not a good idea, because the 6V fan will draw too much current from a 12V power supply. It will run faster, generate more noise and probably burn out quite quickly (if not immediately!) You can do the reverse...
  17. Merlin3189

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

    Well at least some good has come from this silly squabble! What do you think Mr Ohm would think of this? Did he claim his "law" applied to ALL components (most of which had not even been imagined at that time)? Did he claim that any relationship that looks like V=IR - like v=iZ, f=ma, s=ut...
  18. Merlin3189

    Isolation b/w DAC & Power amplifier

    Not a comment - I just wonder what " b/w " means in this context. I can't see how "bandwidth" or "black and white" would fit, so I wonder if there's another meaning I should know?
  19. Merlin3189

    Higgs Boson

    My thought about the finding of the Higgs boson is, does it make any difference? People have spent billions of dollars (or Euros or whatever) building the LHC to find it and a lot of physicists around the world already base their work on the assumption of it's existence. Would not the big...
  20. Merlin3189

    How to increase 555 timer output voltage

    Which with more than 20 LEDs might want more current than the 555 supplies, bringing us back to adding a transistor to drive them.
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