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  1. AnalogKid

    Why drop in voltage in this circuit ?

    What is the voltage on the base of T1 when the buzzer is on? ak
  2. AnalogKid

    12 volt DC lamp flasher.

    The very first solid state circuit I messed with was a code practice oscillator based on this two-transistor classic, a looooong time ago. Great link, love the Marx generator. ak
  3. AnalogKid

    Programmable negative constant current source

    Your verbal description of the circuit is very incomplete. For example, where does the other end of the load go? If GND, the circuit will not work. ak
  4. AnalogKid

    Linear amplification for kids robo project

    OK circuit, wrong opamp. Hunt around for one with rail-to-rail inputs *and* outputs, and that can run on a single 12V supply. Also, to go from 500 mV to 9 V you need a gain of 18, not 11. ak
  5. AnalogKid

    Got a new project and need some help

    The issue here is not one of quality or cost, but size. Larger fans turn more slowly. Also, fans with a lower CFM rating have blades with a less aggressive pitch and a frame with fewer struts supporting the motor. Both of these contribute to the acoustic signature of the fan. But for really...
  6. AnalogKid

    Triangular signal shift phase

    What you are describing is a variation of a phase-locked loop. There are two basically different ways to do this. One is to recreate the input signal at a different phase; that is what is discussed in posts #2 and #3. A potential problem is that a circuit based on a square wave and integrator...
  7. AnalogKid

    Conditioning signal circuits damaged

    What is the input signal voltage range? What is the input signal output impedance? What is the input signal current capability? What is the required output signal voltage range? What is the output current from each opamp? How much DC offset error is acceptable? Is there a reason why the 548...
  8. AnalogKid

    120 AC to 120 DC

    3.8 horsepower is over 2500 watts. Between the current level and the thermal management issues, there is nothing simple about it. ak
  9. AnalogKid

    Got a new project and need some help

    That fan will make a significant (as in audible at a distance) amount of high pitched noise. No sneaking up on anyone. ak
  10. AnalogKid

    special oscillator

    The parts you will list can not be combined to produce an audio frequency oscillator. What is this for? What kind of oscillator do you want (sine wave, square wave, etc.)? What output voltage range? What power sources do you have available to run it? ak
  11. AnalogKid

    Simple inverter circuit

    I think he's stating the current rating of the battery, not what his circuit will draw from it. His first test is to produce 12 W at 220 Vac. Correct? ak
  12. AnalogKid

    Problem: Schmitt Trigger not giving ON/OFF output

    To answer some of your questions... Post #3, the circuit is architecturally OK, but the 741 will not function as indicated under those circuit conditions The output voltage range is not close to 5 V overall with a single 5 V power supply. Post #5, yes it says a 741 will operate with Vcc+ = +5...
  13. AnalogKid

    Simple current circuit regulator issues

    There are a few issues with your circuit, and all of them are covered in the datasheet. A 317 will not regulate down to zero anything, zero volts or zero milliamps. This is because the little bit of current that the 317 needs to function flows through the load. Also, somewhere on the...
  14. AnalogKid

    Radio Reciever Circuit

    Fortunately, not every circuit that isn't oh-my-god-wowzer is junk. Something well known in the 70's but mostly lost today is that first generation CMOS gates, called unbuffered, were the original CMOS amplifiers. An unbuffered CMOS inverter is a high gain, not-all-that-great-bandwidth, above...
  15. AnalogKid

    Automatic Triggering of a Water Pump with 12 volts followed by 7 volts operating voltage

    Without getting into PWM and all of that borscht, the simple approach is to put a resistor in series with the pump to set the low speed, and then short out the resistor during startup. This can be done with a small power MOSFET or bipolar transistor. The equivalent resistance of the pump is 12...
  16. AnalogKid

    Beep once Circuit

    Please post your schematic. ak
  17. AnalogKid

    Voltage rating of Capacitors.

    A general rule of thumb for capacitor reliability is to use a voltage rating that is at least twice the peak voltage the part is likely to see. In this case, a 6.3V cap is close for a 3.3V application. Not exactly following the rule, but motherboards are notorious for squeezing every micro-...
  18. AnalogKid

    Circuit trigger on specific preset sound

    Tone activated switching is very different from, and much easier than picking a particular sound out of voice audio (for example). This is an outgrowth of touch-tone dial circuits. Signetics (then Phillips then NXP?) and National (now TI) used to make a cute little phase-locked loop tone...
  19. AnalogKid

    detecting shaft rotation

    I've done a lot of motor and fan sensing. There are about 19 ways to do this, so more data is required to get to a good solution for your application. Shaft speed in rpm or rps Shaft diameter Environment (wet, humid, dry, dusty, medical, food processing, etc.) Output signal (transistor switch...
  20. AnalogKid

    Alternative for 8 2N3904 transistors in a single chip?

    " The real question here is finding a transistor array which has a gain near to 20. " There isn't one. At a collector current of 20 mA, all commonly available transistor arrays have a DC forward gain much greater than 20. I don't understand why a transistor with a gain of 20 is the real...
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