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  1. L

    Summing difference amp outputs

    On further consideration it seems as though you are describing a simple level shifter, input goes from 0 to 5 volts, output goes from 3.5 to 2.3 volts, and that there should be a simpler way to design a level shifter than what you have. Refer to the attached diagram. The basic gain is given...
  2. L

    Summing difference amp outputs

    Not sure what the purpose of those 16 V zener diodes might be. With such high-value resistors, leakage current through the diode may have some affect on the signal level. If they are supposed to be overvoltage protection diodes, they should be placed on the other side of the 1 meg input resistors.
  3. L

    Summing difference amp outputs

    I think I would connect the wiper on that 100K pot to another op amp in voltage follower mode to reduce the output impedance into the PWM generator, unless you're sure the PWM input has a very high input impedance.
  4. L

    Voltage comparator debouncing

    So the inputs to the comparator are normally around 12 mV, but occasionally the probe to R4 will lose contact and the '-' input will jump to 12 V. Placing a capacitor across R4 will stabilize the '-' input but the capacitor will charge to 12 V through R3. Suppose that the probe loses contact...
  5. L

    Voltage comparator debouncing

    It is typical to provide only a few millivolts of hysteresis for comparator operation. Make R5 something larger than 10 ohms, perhaps 56K. As it is the output of the LM311 is trying to drive a 20 ohm resistance to ground, so the output voltage will be current-limited.
  6. L

    Voltage comparator debouncing

    Why do you have R5 & R6 connected in parallel?
  7. L

    BBC Documentary Error ?

    I don't understand the suggestion. If transistors work because they are made from semiconductor material, then how could they possibly work if you tried to make them from super conductor material?
  8. L

    sort of an odd situation

    You can do some very sophisticated electronic systems analysis using the Laplace transform. It is the Laplace transform and the inverse Laplace transform that let you switch back and forth between the complex frequency domain and the time domain representations of a signal. Already it sounds...
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    I/O Circuits

    For the 5V power supply you could use a voltage regulator such as the LM7805 mounted on a heat sink to dissipate at least 3 watts {(20-5)x(0.200)}. For the signal I/O it is not clear whether these are linear or logical interfaces. Also it makes a difference whether the motor draws 100 mA or 20...
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    Need some help please

    If the base current is negligible, then I1 is the current through R1 and R2. 1. I1 = Vbe1/R2 Current through R2 2. I1 = (Vbb-Vbe1)/R1 Current through R1 3. I1=I1, (Vbe1/R2)=(Vbb-Vbe1)/R1, Vbb=Vbe1(1+R1/R2) 4. Set Vbe1=0.7 to find Vbb. 5. Does...
  11. L

    please l need help.....

    OK. Your friend did a wye-delta transformation followed by a delta-wye transformation. http://en.wikipedia.org/wiki/Y-%CE%94_transform It works but I think it is simpler to take advantage of the symmetry.
  12. L

    please l need help.....

    When you think in terms of nodal instead of loop analysis the answer becomes obvious. First replace the vertical 2Ω resistor with 2 4Ω resistors in parallel. Now, split the center node in two with a 4Ω resistor going with each virtual node. Because of symmetry each virtual node is still at...
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    Bat Detector Prototype

    You have this bloated rail splitter to generate a virtual ground that has no load, just the "+" LM358 inputs which draw next to zero current. Your virtual ground could easily be generated by a simple RC voltage divider instead. But you say that the LED and 7805 also draw current from the...
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    How to calculate impedance of RC circuit

    If, in your RC circuit, the capacitors were replaced by resistors, then would you be able to calculate the resistance? For the circuit with capacitors you would calculate impedance the same way, only using complex algebra.
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    How does clock and data work?

    Since the clock and data signals are outputs you just need to be concerned with the clock phasing. On one clock edge the data is meant to be read from the data line, while on the opposite clock edge the data will change on the data line. Be sure to know which is which.
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    class C bias question

    It might improve your confidence to realize that the answer is so obvious it is almost a trick question.
  17. L

    Custom PWM

    Since these Chicago Electric Welders are available from Harbor Freight Tools for $139.99, are you expecting a custom design to cost considerably less than that? Does your "PWM" mean pulse width modulation? What I would do is get a heavy duty power supply such as the B&K Precision model 1791...
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    PCB equipment... :O

    I only ever did single-side boards but I drew the circuit in black ink on drafting vellum at five or ten times actual size. Then took it to a local lithographic print shop and got a reduced litho film negative. The shop owner would not take my money back then, was fascinated by the hi-tec...
  19. L

    Transistor as switch (newbie question)

    An opto-isolator seems made to order for this type of level shifting.
  20. L

    electronic cirucuit analysis

    This is a non-linear circuit that can be analyzed by the piecewise linear method. The linear regions are defined by points of discontinuity, in this case defined as the point where the base-emitter voltage reaches 0.7 volt and base current begins to flow. Each region has its operation defined...
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