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  1. hevans1944

    Crowbar Circuit - Help !

    Looks like a PASS to me. The datasheet does say temperature-induced drift is minimized by making R2 less than or equal to 10 kΩ, so it looks like you are good to go with the values you selected. If all your DC-to-DC power supplies share the same common, have you thought about crowbaring the...
  2. hevans1944

    How to design analog circuit

    It is the starting point for building a logarithmic amplifier. Isn't this a little off the original topic of how to design an analog circuit, which I tried to answer in post #4? We are not here to guide you through all the analog circuits posted in your text book(s). The text book should...
  3. hevans1944

    Can u solve this op amp ?

    Also really sorry about @Zeeshan Sajid's attitude. Perhaps we have a language/cultural problem and not an electronic problem? If I were a moderator, I would have closed this thread after post #8.
  4. hevans1944

    Can u solve this op amp ?

    The problem states it is an ideal op-amp. You won't find one of those anywhere, so using a simulator is not going to solve your problem unless you create a sim model with ideal op-amp characteristics. An ideal op-amp has zero bias current, zero differential offset voltage between the inverting...
  5. hevans1944

    Reducing amps in a circuit without change in the voltage

    The wide AC input voltage range almost guarantees this is a switching regulator.
  6. hevans1944

    Question about operational amplifier circuit Dorf exercise 2.5?

    GIGO principle in effect here: Garbage In, Garbage Out. You should find another text book with accurate pictures and text. If you have an instructor, ask him or her to discard this one to the rubbish heap. How many more errors have you found in this text book? Is it your job to correct the...
  7. hevans1944

    How to design analog circuit

    You can start by learning physics and math. Learn about the passive components used in electronics: resistors, capacitors, and inductors. Learn how resistors behave in circuits by learning to use Ohm's Law and Kirchoff's Laws to analyze the currents in, and the voltage drops across, resistors in...
  8. hevans1944

    Input to a microcontroller

    It should be pretty simple to wire up a 555 and use it to clock a single 74HC4040, but I would not recommend that. With a single 12-bit counter, the maximum frequency division ratio is two to the twelfth power or 4096, but you don't get the full benefit of that. If you use the zero-to-one...
  9. hevans1944

    Feedback loop for constant voltage amplifier. Simulated Aircraft Power.

    Maybe that 200 watt wall-banger amp was designed to drive the 4 to 16 ohms load impedance of a loudspeaker. If you hook up a 400 Hz step-up transformer to it, the amp may not like an open circuit on the transformer secondary. Try adding a permanent resistive load to dissipate a few watts, say...
  10. hevans1944

    Need help with circuit design

    You can visit this page to see what your options are. Buy or build, but I would avoid any of those five dollar imports you can find on the web. You are switching some serious current here and proper heat sinks and back emf protection are required, especially to dissipate the energy when the...
  11. hevans1944

    Timer with NE555

    What is wrong with the mechanical switch timer? Hard to beat for simplicity: synchronous gear motor driving one or more cams that operates micro-switches. Any possibility of replacement or repair of the original equipment manufacturer's timer? And what is "an analog washer"?
  12. hevans1944

    Need help with circuit design

    A PWM controller with a slow ramp up to 100% duty cycle when turned on, and a slow ramp down to 0% duty cycle when turned off should do it.
  13. hevans1944

    Confused what voltage would be depending on its location?

    Ha! You are asking this of someone who doesn't have a clue yet. Maybe we should direct him to the Hyperphysics web site for fundamental reasons. Lots of links there to internal references that will take weeks, maybe years, to explore and understand.
  14. hevans1944

    Input to a microcontroller

    Digital timers built from TTL components are ancient! I remember doing what you did, although I think I might have used BCD counters, seven-segment decoder/drivers, and seven-segment LED blocks. I used my favorite 120 Hz zero-crossing pulse circuit and scaled that down to 1 Hz pulses to...
  15. hevans1944

    Input to a microcontroller

    The simple push-button that charges up a capacitor which then turns on a field-effect insulated-gate transistor (very low leakage there!) that drives the coil of a relay is indeed a possible solution, one that you mentioned in post #3. Problem is, the leakage properties of a capacitor will...
  16. hevans1944

    Confused what voltage would be depending on its location?

    Voltage is always measured (if it exists) between two points in a "circuit" of any kind, "closed" or "open". Both of your circuit diagrams show "open" circuits because switch SW1 is open in the top diagram and switch SW2 is open in the bottom diagram. Or does your top drawing attempt to show SW1...
  17. hevans1944

    Input to a microcontroller

    Very good explanation. In my own words: If one of the four buttons is momentarily pressed, a time interval begins, determined by which button was pressed. During this time interval, a relay is energized with SPDT contacts capable of switching a 240 V AC load. The contact switching load may be...
  18. hevans1944

    Input to a microcontroller

    This sounds like an ideal PIC project. What do ya want your timer thingy to DO after you push its button? Do you want to program the time interval? How accurate must the timer be? Does it sound an alarm or control an electrical circuit? If it controls a circuit, how much voltage and how much...
  19. hevans1944

    Explain this circuit: Digital linear PSU

    The problem is the parallel resistance of R10 = 22 kΩ and R11 = 3.3 kΩ is only about 2.9 kΩ. This is larger than the R19 = 1 kΩ so there is no way to choose a value for R9 that would make the parallel value of R9 and R19 equal to 2.9 kΩ. It isn't a problem with this circuit because the bias...
  20. hevans1944

    Feedback loop for constant voltage amplifier. Simulated Aircraft Power.

    For your application, controlling the output amplitude of a 400 Hz power amplifier, driven by a 400 Hz function generator, by means of a negative feedback control system, you would have to control either (1) the gain of the power amplifier or (2) the amplitude of the function generator signal...
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