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  1. L

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

    The real problem here seems to be determining just what is Ohm's Law. Georg Ohm published his work in the 1820's whereas alternating current was not invented until the 1830's. So Ohm's Law as originally understood only applied to DC and the proportionality constant between voltage and current...
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    Ohm's Law or not Ohm's Law... That is the question

    That is not a true statement. Ohm's Law applies to reactive components in both the steady-state AC domain and the complex frequency domain. Complex frequency is normally represented by the 's' variable and the Laplace Transform is used to shift the analysis between the frequency domain and the...
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    Ohm's Law or not Ohm's Law... That is the question

    Suppose that R is a non-linear function of the voltage or current. Does that invalidate Ohm's Law? The usual method for analyzing non-linear circuits is to treat them as piecemeal linear and use the dynamic resistance as constant over each linear segment. Ohm's law applies to that...
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    Multi Resonant Circuit

    Here is a MathCAD analysis of one such multi-resonant circuit, including a magnitude plot for a sample set of component values.
  5. L

    Sweat monitor using electrodes.

    If the object is to light an LED then nix the picaxe. Use low-power opamps to conserve battery power. I would not try to put more than a few tens of microamps through the horse. Corrosion of the electrodes will depend upon the material used. Gold would be good. Doesn't a horse have hair...
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    Voltage Divider help

    Maybe it would be instructive to consider why meter XMM3 is reading 1.539 volts in the third circuit. The 'In' terminal has an AC voltage source applied but for purposes of DC biasing the 'In' terminal is at DC ground. So R2 and R5 together form a 20K resistance in parallel with R8. (10K ||...
  7. L

    detect pulse of 140ns and 50mv.

    One approach would be to use a high speed comparator such as the LMV7239. It has low input offset, low cost, and 5V single supply operation. For 50mV detection I would pre-bias the input with 15mV offset and use capacitive coupling for the pulse signal. Since the input signal is fast...
  8. L

    create a 110 volt ac to 5 volt dc.

    Just draw the following components from left to right- AC source : switch : fuse : transformer : diode : capacitor : regulator Now connect them in a way that makes sense. Voilà.
  9. L

    Bike trainer concept I've been messing with in my head

    If you only just spin the shaft of an alternator, you will generate a potential but no power. In order to create power one needs to dissipate power in a load such as a filament bulb. That is the usual setup for an introductory science demonstration: an alternator driven by bicycle pedals and...
  10. L

    Pulse Problem...

    Please explain what you mean by "High State is not different from Low State". Show graphs of what the pulse waveform from the controller looks like and what you want the waveform to look like after it has been conditioned by the interface circuit.
  11. L

    Effective current and effective voltage

    When you bring calculus into the picture it becomes possible to calculate the RMS value for any arbitrary waveform (the hard part is to integrate the square of the voltage over one cycle). But is it possible to measure the RMS value of any waveform? It should be possible for a digital...
  12. L

    Problem understanding how a Bias Limiter works.

    In this circuit the diode acts as a switch. The diode switches ON to ensure that Va can never be less than Vbias-0.7 volts. Because the diode has two states (ON & OFF) the circuit operates in two different states, i.e., there are two different circuits. I would suggest that you draw the two...
  13. L

    How to generate AC frequency from DC waveform

    A transformer with a 1000:8 impedance ratio has sqrt(1000/8)=11.2 turns ratio, so a 12V input could produce as much as 134V out. However, since this is a small signal transformer, it may not have been constructed with the wire insulation for this voltage. Just something to watch for. Also...
  14. L

    FM question

    Suppose that the modulator/demodulator was perfect and no noise was added, then the signal (including noise) at the demod output would be a perfect reproduction of the signal at the modulator input; Si/Ni=So/No. Is there any modulation technology that can recognize the noise component of an...
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    Transformer noise - what can be done about it?

    I would try two things. First, use rubber stand-offs to mount the transformer so that it does not contact any hard surface that could amplify the sound. If that does not work then try potting the transformer in slow-curing epoxy. Use a vacuum pump to exhaust the air from the crevices of the...
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    Voltage to decibel conversion

    True, to this point we are still not doing voltage to dB conversions. However, we have illustrated the math necessary to understand dBu and dBV, which are direct conversions from voltage to dB. In this case V1 is understood to be a defined reference voltage, 0.775V for dBu, and 1.0V for dBV.
  17. L

    How to generate AC frequency from DC waveform

    A simple way to increase the output voltage might be to wind an output transformer on a toroid ferrite core.
  18. L

    Voltage to decibel conversion

    A decibel is a measurement of a ratio of power, not a measurement of voltage. dB = 10*log(P2/P1) However, power can be calculated from voltage, P=(V^2)/R. So the decibel calculation for voltage is (for the same resistance): dB = 10*log((V2^2)/(V1^2)) = 20*log(V2/V1)...
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    Power Increase In Rheostat Problem

    Are you using the terms 'power' and 'current' interchangeably? They are not the same thing. If a value changes for example from 0.0002 to 0.002 then that is not a change of 10% but rather a factor of ten, i.e., 1000%
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    Question about resistor networks in the Electronics Demystified book

    So question #2 asks for the total resistance of the resistor network. Have a look at a similar example with different values. Due to the structure of the circuit, one must first combine the series resistors into an equivalent valued resistor. Then combine the parallel resistors into an...
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