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  1. AnalogKid

    24Vac, 24Vdc or 12Vdc universal input interface to 3.3V microcontroller

    In post #1, the optocoupler outputs are saturated transistors, and the output signals always are below about 1.3 V (3.3 V rail minus the LED Vf). In post #4 the transistors are emitter followers, and the emitters (and output signals) can be pulled up to 32 V with a 24 Vac input. The LEDs might...
  2. AnalogKid

    Electric curtain project: single Push button design

    Very possible. For a DC motor, current sensing is a small-value resistor called a shunt, a comparator to determine if the current has exceeded the trip level, a latch to hold things off until reset somehow, and a relay or power transistor to control the motor. Perf board, a couple of...
  3. AnalogKid

    what is the difference/s if i use a thyristor instead of the transistor in this circuit?

    It doesn't prevent it. When current is removed rapidly from an inductor, the magnetic field collapses. This causes *induces* a current into the wiring of the inductor (hence the name). That current produces a potential difference (voltage) between the two ends of the inductor. Depending on...
  4. AnalogKid

    what is the difference/s if i use a thyristor instead of the transistor in this circuit?

    No. If you look at the internal schematic on the 4017 datasheet, you will see that the Reset input is not gated by either the Clock or Enable inputs; it goes directly to the flipflop reset inputs. This is called an asynchronous reset, and happens no matter what the state of the clock input is...
  5. AnalogKid

    Help with powering a circuit board

    Depends on the age and (really) the weight of the wall wart. Old warts have a big lump of iron in them, the linear power transformer. New chargers have a small switching power supply with a much smaller transformer. So if it feels almost like it's empty, that is a regulated switcher. If it's...
  6. AnalogKid

    Advice for temp controlled fan

    200 mA is too much for either chip directly, and too much for a 2N7000 small MOSFET transistor driver. But an LM358 can make enough output current to drive a small power transistor like a TIP29 or TIP31. I'd stay away from a Darlington unless you don't need full speed from the fan. Plus, I...
  7. AnalogKid

    Envelope detector design

    Good more. A power rectifier has a fat junction area which means high capacitance which means low speed. ak
  8. AnalogKid

    what is the difference/s if i use a thyristor instead of the transistor in this circuit?

    Internally, a 4017 isn't a counter in the traditional sense. It is a 5 stage shift register with a bunch of decoding gates around it. When the Reset input goes high, the shift register is set to all 0's by resetting each of the five flipflops. Forcing the 4017 to the 0 state means the 0...
  9. AnalogKid

    Advice for temp controlled fan

    I vote for 1/2 of an LM393 for an open-collector output or LM358 for a true totem-pole output. Both are designed specifically for single 5 V operation, unlike the LM741 opamp, and are ultra-rugged. What is the fan current at 5 V? That determines what you need to drive it. ak
  10. AnalogKid

    what is the difference/s if i use a thyristor instead of the transistor in this circuit?

    A thyristor will change the operation of the circuit in a significant way. Once the buzzer is activated, it will not turn off when SW2 is pressed again. It will stay on until power is removed by SW1. Are you sure you want the circuit to behave that way? A thyristor will dissipate slightly...
  11. AnalogKid

    Clap switch confusion!

    A 4017 can make 4 mA, granted at a sagging Vout. That should be enough to see something if the diode Vf isn't too high. I'd change to a standard little green LED and reduce the base resistors. ak
  12. AnalogKid

    Clap switch confusion!

    In a quiet room, look at the collector of T1 and report its voltage. Hopefully it is sitting near 5 V. ak
  13. AnalogKid

    Clap switch confusion!

    1. There is no decoupling of anything anywhere. Add a 100 uF electrolytic and 0.1 uF ceramic in parallel across the two power rails where the red and black wires enter. Add a 0.1 uF ceramic cap across IC1 pins 1 and 8 and IC2 pins 8 and 16. 2. Disconnect IC1 pin 3 from IC2. Add an LED and...
  14. AnalogKid

    Decoupling capacitors

    Correct. Also, decoupling capacitors are really necessary for ALL ICs regardless of the signal frequencies. Some tolerate no decoupling better than others, but do not be fooled. For example, the bipolar 555 has a design quirk, where both output transistors are on briefly every time the output...
  15. AnalogKid

    Envelope detector design

    Changed them from what to what?
  16. AnalogKid

    Decoupling capacitors

    You are correct that the capacitor is acting as the shunt leg of a series-shunt voltage divider. The series leg is the resistance and (inductive) impedance of the wiring or traces leading up to the capacitor from the voltage source. This is why it is critical that a decoupling capacitor be...
  17. AnalogKid

    Detecting a 12v stepped current - automotive DLR

    It works like this: The carpet in the trunk has a warranty. If you touch the headlight wiring, the warranty on the trunk carpet is void. Car manufacturers have lots of lawyers, and those guys have zero sense of humor - or proportion. ak
  18. AnalogKid

    Envelope detector design

    The gain of the first stage is only 13 (22.3 dB). That's not much. Any reason why it is so low? From the scope shot it looks like there is a clear amplitude difference between the quiet gap during propagation and the start of the reflected pulse. Why not use a simple level detector? It will...
  19. AnalogKid

    Restoring a FOXX FUZZ-WAH

    Photos or schematic? ak
  20. AnalogKid

    Variable Frequency Op-Amp Astable

    Note - for this analysis we assume that the LM324 output voltage range is 0 V to 9 V. It makes the arithmetic much less cluttered. This is a Schmitt Trigger astable. R1 and R2 set the basic trip point at 4.5 V (Vcc/2). Hysteresis added by R3. This creates two distinct trip points, one with...
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