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  1. AnalogKid

    Capacitor between collector and emitter help

    That circuit is a simple AM radio receiver. The transistor is acting as a rectifier with gain, and the capacitor is a lowpass filter to recover the audio signal. It works with the impedance of the earphone to form a single-pole R-C filter. ak
  2. AnalogKid

    Calculating frequencies

    Not to be picky or anything, but - "Calculating frequencies" of what? I calculate the frequency of my lawn mower engine by observing the dominant component of the acoustic noise and dividing that by 2. ak
  3. AnalogKid

    Building a two digit counter

    If you want to start with a kit and then modify it, this kit on ebay is a better place to start: https://www.ebay.com/itm/Digital-2-Digit-Counter-up-Unassembled-electronic-kit-for-student-Education/141001633090?hash=item20d45a2d42:g:EbwAAOSwofxUcXWL Because it is a discrete design, all of the...
  4. AnalogKid

    25V vs 35V capacitor?

    Generally speaking with aluminum electrolytic capacitors (all other things being equal for each parameter): The smaller the case diameter, the higher the ESR The higher the voltage, the higher the ESR The higher the temperature rating, the higher the ESR The higher the life rating, the higher...
  5. AnalogKid

    Building a two digit counter

    I think you have the wrong part for the job. Because the counter is based on a microcontroller, there is no way to alter its function (like stopping at 21) without replacing the firmware. This would not be a difficult circuit to build from scratch if you have that skill set. ak
  6. AnalogKid

    Robust delay circuit?

    When the circuit first turns on the MOSFET is saturated and dissipates very little power. As the voltage ramp on its gate decreases, after a while it pulls out of saturation, moving through its linear active region. After the timeout period it is off and dissipates zero power. The length of...
  7. AnalogKid

    Robust delay circuit?

    1 capacitor 1 resistor 1 MOSFET What is the current (at 12 V) you want to sink through the ballast resistor? ak
  8. AnalogKid

    What do I need?

    Eventually you will have to have a scope, but there are many layers of scopes. To start out, especially if you have an old laptop you can dedicate to the workbench, consider a USB scope peripheral. They have enough voltage range and frequency bandwidth for the kind of troubleshooting you are...
  9. AnalogKid

    I need help determinig correct voltage.

    What was the battery voltage for the camera? ak
  10. AnalogKid

    Which other transistors can I use

    Tsk tsk TSK - kids these days ... https://en.wikipedia.org/wiki/VU_meter ak
  11. AnalogKid

    The shape of schematic components

    The primary role of a schematic is to show the electrical relationships among the signals. It is not to show the physical relationships among the pins. The two are generally related, and sometimes a schematic is very close to the physical layout. But never assume that the pins on a schematic...
  12. AnalogKid

    Oscillator

    ak
  13. AnalogKid

    3 switched earth's to a decoder to produce 6 earth outputs

    What is the open circuit voltage? What is the closed circuit current? ak
  14. AnalogKid

    3 switched earth's to a decoder to produce 6 earth outputs

    Yup.
  15. AnalogKid

    3 switched earth's to a decoder to produce 6 earth outputs

    The question is whether that is a low current signal ground or a power ground with all of the display current. Also (this may be a British/American thing), since no part of the bike's systems are tied to a copper stake driven into the dirt underneath it, a better term for the circuit reference...
  16. AnalogKid

    3 switched earth's to a decoder to produce 6 earth outputs

    Note that most logic families (TTL, CMOS, whatever) have output stages that can source or sink only a few mA. You've given us almost zero information about your circuit's inputs, outputs, and the "display", but the odds that a logic chip output can drive the display directly, without some kind...
  17. AnalogKid

    Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

    (H and AG - this long form explanation is intended for the OP) Not to be picky or anything, but ... 1. A comparator, or an opamp acting as a comparator, does not oscillate when the two inputs are very close to the same voltage. A comparator is at its heart a linear amplifier. It spends most...
  18. AnalogKid

    Why the crazy price for a decade resistor/resistance box?

    Start with your salary or hourly rate at your day job. For salary, divide by 1920 for an approximate hourly rate. If you get benefits at work such as health insurance, increase the hourly rate by 10-20%. This is the total hourly rate for the project. Keep track of every *minute* you spend...
  19. AnalogKid

    Why the crazy price for a decade resistor/resistance box?

    There is a big difference between 1 piece of what a hobbyist needs to putter around at home, and hundreds of units that 100 different professionals doing 100 different things need at work. The test equipment needed to document the accuracy of a resistance box costs way more than the resistors...
  20. AnalogKid

    Getting full power output from 120VAC to 5V40A DC supply?

    Please post the datasheet for the supply. We don't know if it is linear or switching, a huge difference in your application. In general, no, you cannot just combine multiple outputs together for more output current unless the supply is designed specifically for that. 8 x 8 x 8 = 512 512 x...
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