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  1. L

    CTR of opto-coupler at low diode current (IF)?

    The stated 63% to 125% CTR applies only to a single point on the graph in Figure 5. The graph shows that at If=10mA the CTR is 95%, but it could be as low as 63% or as high as 125%. The graph also shows that the CTR is significantly less at reduced diode current.
  2. L

    some elementary questions

    In the physical world, current will always consist of negatively charged electrons. However, in electronics you will not usually be working with the physical world but rather with abstractions of the physical world where the rules can often be whatever you want them to be. For instance, in...
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    Calculating Gain for a datasheet?

    If the sensor is already calibrated to provide a certain voltage for a specified velocity, 4mv/mm/sec, then what more needs to be done? Whereas gain in dB would be defined as the power ratio of an output voltage to an input voltage or reference voltage. What signals would you be using to...
  4. L

    Operational Amplifier + Diode

    So you have translated the problem and also given the answer from the solutions manual. Now you want to know how to get the answer the hard way. C'mon, 'fess up! Did you cut class on the day they taught all the other newbies how to do node and mesh analysis in the complex frequency domain...
  5. L

    Help pleeeaaassseeeee?? :)

    The PCB switch most likely has 4 lugs for mechanical stability, with 2 lugs connected to each contact. Look on the foil side of the PCB to determine if just 2 foil patches are used to connect the switch, with 2 lugs connected to each foil patch.
  6. L

    passive filters

    Well then I would ask, can you get 12 dB/octave attenuation from the formula that you have provided? To derive a transfer function in the steady-state frequency domain, do a circuit analysis where the passive elements are replaced by their reactive impedance, R=R, L=jwL, C=1/(jwC). Then use...
  7. L

    passive filters

    Normal roll off for a simple first-order filter is 6 dB/octave or 20 dB/decade. It would seem the problem is to design a second-order filter. You should derive the transfer function of your second-order network, and from that calculate the attenuation in dB at any frequency. Use that result...
  8. L

    Explanation needed please

    At SK1 in the upper-left corner there is a signal output terminal and a high impedance voltage sensing input which is AC coupled to a low pass filter, then to a non-linear amplifier with voltage-limiting and then to a comparator whose output is fed back to the PIC. So what is supposed to...
  9. L

    Digital Logic Circuits Project help

    A few questions about the problem statement: "If motor A is started and runs..." Does this mean that a motor could be started but not run? Does the motor provide a signal to indicate it is running? What is the control interface? Push-button switches? What should happen if 2 or all 3...
  10. L

    Circuit help needed

    Is one side of the speaker grounded? You could use a low power Schottky diode to rectify the speaker signal then feed it to a low pass RC filter and use a comparator to sense the voltage level. Use the output of the comparator to drive the controller.
  11. L

    555 or is there an easier way?

    Optocouplers? Is there enough current available to drive both the LED's and the optocouplers? Instead of current sensing, using high resistance voltage sensing with the LM324 (100K sensing resistors) will provide plenty of electrical separation. You have to run cabling between the two systems...
  12. L

    555 or is there an easier way?

    "Complement of the transit signal" means use the transit signal to inhibit activation of the open or closed display indicators. So when transit is HIGH the complement going into the AND gates will be LOW. Hold RESET low? Possibly. How often is the device powered on? Is it important to...
  13. L

    555 or is there an easier way?

    It appears that either LED goes through the same cycle. First it is off, then it begins to flash, and finally it is steady on. Can we assume that an LED turns off when the other one begins to flash? So the only problem is to detect when an LED begins to flash (easy) and when it stops flashing...
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    Discrete FET driver turns off slowly

    I can't see the need for a gate driver circuit, especially if the microcontroller interface has a CMOS driver where the two states will be Vgs=0V and Vgs=5V. Why not a direct connection to the gate? Addendum: Apologies. When I first looked at the picture of the PWM signal, I saw no signal...
  15. L

    flip flop projects

    @(*steve*) While there are a variety of flip-flop types available, I would recommend the JK type as most flexible and useful for the design of complex finite state machines.
  16. L

    Please Help with a (supposedly) simple RL Circuit Problem

    The same problem you describe is solved in section "9-4 First-Order System Excited by a Sinusoidal Wave" in the book Linear Circuits by Ronald E. Scott, pp 298-301, published by Addison-Wesley, 1960. However, it is not clear whether your answer should be just the steady state solution. If so...
  17. L

    flip flop projects

    Perhaps you are familiar with a BCD counter where the binary count value is decoded to drive a seven segment display. Now imagine a different concept where seven JK flip flops each drive one of the display segments directly. Your project is to design the gate circuitry for the JK inputs. For...
  18. L

    No one in my class can figure this out!

    I don't know of any way to simplify an assymetric bridge but the equivalent resistance can be calculated using generic circuit analysis. Once you have the equivalent resistance of the 5-resistor bridge, it's easy enough to get the resistance of the whole circuit. I wrote the node equations for...
  19. L

    Defusable Practice Time Bomb

    If your password can be hardcoded, then a matrix of NO & NC pushbutton switches could be wired in series. When the NO switches are pressed simultaneously, the closure of the circuit can be used to defuse the timer. But if one or more of the NC switches are pressed, no circuit closure will be...
  20. L

    Defusable Practice Time Bomb

    Not sure what you mean by 'defusable' but those LCD kitchen timers will have a pushbutton switch for turning it off. A passworded switch would be difficult to accomplish with aything but a micro-controller. However, a micro-controller could also handle the timer function as well - no need for...
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