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  1. crutschow

    Why does zener voltage decrease as series resistor increases?

    A Zener is not a perfect regulator. Its voltage will change some with a change in current through it. Look at the value for the Zener impedance to determine what the change with current will be. A much better regulator is an IC that mimics a Zener, such as the TL431 shunt reference. It can be...
  2. crutschow

    automatic forward reverse motor with limit switch and relay

    Okay, I missed the "pause" request. How long is the pause?
  3. crutschow

    automatic forward reverse motor with limit switch and relay

    I assumed that would be a standard plug-in timer operating from the mains to power the supply. I see no reason to do anything custom.
  4. crutschow

    automatic forward reverse motor with limit switch and relay

    No error. Yes, the "little down arrows" are standard schematic common/ground symbols, which is the negative connection for the 12V supply. Virtually all mechanical relays are break-before-make due to the way the contact mechanism works. There is a movable contact (the wiper) which moves between...
  5. crutschow

    automatic forward reverse motor with limit switch and relay

    I forgot to add a diode across each relay coil to prevent arcing from the coil inductance across the limit switch's contacts when they open. See below:
  6. crutschow

    automatic forward reverse motor with limit switch and relay

    Seem a bit overkill for this application. ;)
  7. crutschow

    automatic forward reverse motor with limit switch and relay

    Here's my take on doing that: It uses two SPDT relays in a bridge configuration and connected as a FF latch. In operation, one relay will always be ON and the other OFF, with alternating action. To understand its operation, assume U2 is ON, U1 is OFF (12V on both sides of the U1 relay coil)...
  8. crutschow

    How change the Frequency of a 555 timer with another circuit ?

    Depends upon whether you are driving will emit noise from the pulses. Below is the circuit operating at 20kHz.
  9. crutschow

    How change the Frequency of a 555 timer with another circuit ?

    Yes and yes. At frequencies low enough so the comparator transition time is not a significant factor, the approximate frequency is F ≈ 0.345 / (R1*C1).
  10. crutschow

    How is current passing through the capacitor in the following schematic?

    Below is the LTspice simulation the circuit, to perhaps help clarify what has been said: The Q1 collector voltage (yellow trace) shows the waveform driving C1. The red trace shows the capacitor C1 current, which has a small, longer current pulse when Q1 goes high, and a higher, shorter current...
  11. crutschow

    How change the Frequency of a 555 timer with another circuit ?

    Not too involved. LTspice simulation below of an analog-control PWM circuit using one chip comparator (LM339/393), that goes from 0% (fully off) to 100% (fully on) duty cycle.
  12. crutschow

    Can't find the transformer I need so need to build my own

    Since roughly equal power goes through the primary and secondary windings, the primary wiring size also must be properly selected.
  13. crutschow

    How change the Frequency of a 555 timer with another circuit ?

    So you are changing the requirement from controlling the frequency to changing the duty-cycle of a fixed frequency. That's a big difference. Do you want to control the duty-cycle in steps by changing the values digitally, or do you want an analog continuous voltage control. If you want steps...
  14. crutschow

    Determine Sampling

    What is the maximum frequency rating of the accelerometer? I would sample at more that twice that frequency.
  15. crutschow

    How change the Frequency of a 555 timer with another circuit ?

    Is the 555 running as an astable oscillator? Do you care if the duty-cycle of the 555 output changes with frequency? How accurately does the frequency need to follow the control voltage? Or do you just want step changes in frequency?
  16. crutschow

    convert 110v dc to 110v Ac

    The difficulty is creating an AC sinewave, which the pumps may require to avoid overheating. You need to know the battery capacity and the motor power required to determine how long the batteries can power the pumps. Might be simpler to just buy a small AC generator. They aren't that...
  17. crutschow

    Solenoid Current Flow

    Did you also read that the time depends upon the value of the capacitance and inductance? 1µH is a very low inductance.
  18. crutschow

    Solenoid Current Flow

    Edit: That will allow the inductor current to reach the maximum current (red trace) where the capacitor voltage reaches zero and, at which point, the diode starts to carry the current, The current then decays to zero as determined by the resistive and diode losses from the current.
  19. crutschow

    Solenoid Current Flow

    Below is my LTspice simulation: The current (yellow trace) starts at zero since current can't instantly start in a inductor (you have to use the uic option in the transient simulation). It then rises to the resonant peak (here about 7.3A simulated) where the capacitance voltage (green trace) is...
  20. crutschow

    Need circuit for sine-to-square/sawtooth generator

    Are you referring to the 60Hz from a main's outlet? You will need to run that through a transformer for isolation. And I don't know of any "simple" circuit to convert that to a ±12V, 1A square to sawtooth signal.
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