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  1. L

    Phototransistor latch circuit?

    Have a look at the CD74HC109 J-K flip-flop with Schmitt trigger clock input. The Schmitt clock input would be a suitable interface for a phototransistor, and a J-K flip-flop can be configured into any kind of latch you might want.
  2. L

    Is RF transmitting electrons over the air?

    The movement of electrons in the antenna generates corresponding vibrating electric and magnetic fields which manifest themselves as transmitted photons which then create vibrating electric and magnetic fields at the receiving antenna that generates the movement of electrons. Yes, as you...
  3. L

    Find Amplifier Output

    At first I did not understand why you calculated Re since it is not relevant to the solution. But now I can see you don't use Re anywhere in your solution. Then I did not understand the marked paths labeled with circled '1' and '2' going from Vin1 to GND and from Vout to GND. That is still a...
  4. L

    Find Amplifier Output

    My solution for Vout is the same as yours. However, I do not understand your method. My method is to realize that the voltage difference between the op-amp inputs must be zero.
  5. L

    Why diode switching speed varies (p-n junction)?

    There are actually two effects involved in switching off a forward biased p-n junction: storage and transition. On sudden application of a reverse bias voltage a reverse current flows as excess minority carriers in the immediate vicinity of the junction are swept back across the barrier. The...
  6. L

    Problem with phase calculation

    What you are doing wrong is NOT using what you already know to be true in order to construct the phasor diagram. Recall that for a capacitor with sinusoidal excitation the current leads the voltage by 90 degrees. So the current in this circuit is the same in both the resistor and capacitor...
  7. L

    Half-wave Rectifier with Smoothing Capacitor

    Instead of the task being to create a numerical simulation and graph in MATLAB, how would one just sketch the relevant features of the output voltage? For what it's worth, my approach is attached.
  8. L

    Band-Pass Filter Help

    Rather than design a bandpass filter with a pass band of almost 6 octaves, a better approach might be a low-pass with a corner frequency of 1000 Hz followed by a high-pass having a corner frequency of 20 Hz.
  9. L

    Pulse Train Detection

    I don't know where it came from. Latent dyslexia? With a 150 microsecond pulse length it would be so much easier to charge a capacitor through a diode as the sample & hold mechanism!
  10. L

    Pulse Train Detection

    So the problem is an analog pulse stream of 1/3 Hz with 150 ns 5 V pulses where the 5 V pulses will degrade over time and must be alarmed when the pulse voltage is only 2.5 V. Possibilities for a solution are sample-hold-compare and gated-compare. A gated-compare would generate a digital pulse...
  11. L

    Op Amp and capacitors

    So what is the DC gain of the amplifier? What component provides the feedback loop at DC? What is the high-frequency gain of the amplifier? What component provides the high frequency feedback loop? What components provide the feedback loop in the mid-band? So it seems that there is a...
  12. L

    Mind boggling question

    That is a valuable lesson. Of course, I knew it was true at one time in the distant past. But more recently it seemed counter-intuitive and I just did not want to believe. So while adding a reactive load will substantially change the circuit behavior, connecting a point of zero voltage to...
  13. L

    Mind boggling question

    As before, isolate the numerator of the transfer function, split the load impedance into its real and imaginary parts, set both the real and imaginary parts of the transfer function to zero, and solve for the frequency at which the output voltage is zero. However, in this case the result does...
  14. L

    Mind boggling question

    There is no reason to suppose that this would be true, and in fact it is demonstrably not true when the load impedance has a reactive component. But now the OP will be robbed of the experience of discovering this for him/herself.
  15. L

    Mind boggling question

    Yet on the positive side there is still a lot of work necessary to account for the effects of non-ideal source and load impedances.
  16. L

    Help with simple project

    One other thing you might check is whether the LED modules run in series for the half-power operation from 14V. Is the brightness correct for running lights?
  17. L

    Help with simple project

    Some things that need to be investigated and considered: Do the running lights need their own on/off switch? Will you tap into a fused circuit for LED current? Is the fuse adequate for the additional current? How are the brake lights activated -- brake switch controls '+" power or '-' power...
  18. L

    Mind boggling question

    Begin by writing the node equations for the circuit. To keep it simple assume that the source impedance is zero and the load impedance is infinite. (Additional credit may be available accounting for these complicating factors.) From the node equations derive the transfer function then shift...
  19. L

    Summing Amplifier Problem

    Check out the attached application note from http://www.edn.com/design/analog/4340300/A-single-formula-approach-for-designing-positive-summing-amplifiers- What I was able to make of it is in the attached pdf. Note the node equations for the voltage at the '+' input of the op amp, Vi, and at...
  20. L

    DC motor polarity reversal?

    Sounds like you would need to start with an H-Bridge motor driver. Google has much info available for H-Bridge.
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