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  1. AnalogKid

    Piezo sensor circuit

    I thought about that when I drew this up. Its never been a problem in the gazillion times I've used the circuit, but 10 uF is a bit larger than a typical monostable timing cap. Either a series resistor or the catch diode mentioned above will protect the input; the diode has the added advantage...
  2. AnalogKid

    Piezo sensor circuit

    Your analysis is correct as far as it goes. Two things. 1. On the very first positive edge out of the sensor (and negative edge out of U1A) U1C's output goes low. AND, it is fed back to the other input of U1A. This low holds the U1A output high no matter what happens at the sensor input...
  3. AnalogKid

    Piezo sensor circuit

    Schematics for two of the many alternate circuits to do this task. The upper one is a standard monostable followed by a logic-level N-channel power MOSFET, and everything runs on the lamp batteries. R3 can be changed to a pot for variable lamp on-time. The lower one is based on an...
  4. AnalogKid

    Piezo sensor circuit

    To turn a short input pulse into a multi-second output pulse, two methods are some form of R-C (resistor-capacitor) timer like a 555 or logic gate monostable, or a counter. The counter method is much more accurate and stable, but more difficult to adjust, An R-C timer is pretty simple, but has...
  5. AnalogKid

    Piezo sensor circuit

    Late to the party; some questions... How are you controlling the power to the lamp? What is the lamp voltage and current? What is a good adjustment range for the lamp ON time? Do you have any feel at all for the peak voltage out of the piezo sensor in this application? If the lamp can be...
  6. AnalogKid

    switching a relay - but on second switch. ( if that makes sense? )

    If you replace magnetic reed switch #1 with two reed switches very close together, the order in which they close will generate a pulse signal to the external circuit in one direction only without any logic circuits. Two switches, two resistors, and some DC power to create the output pulse. ak
  7. AnalogKid

    why would parasitic resonance defeat inductance?

    The capacitive and inductive reactances are in parallel, so the lower value dominates the combined value. As the frequency increases above the self-resonant frequency, the capacitive reactance continues to decrease, looking more and more like a capacitive short across the inductor. Once you...
  8. AnalogKid

    Current Amplification

    For precision you must have a feedback circuit that compares the current into the coil against a reference value. The forward gain of a single transistor varies significantly with temperature and with collector current. I don't think you can get "precise" current regulation out of any...
  9. AnalogKid

    Current Amplification

    I think you should check with the instructor about the requirement to change the frequency. That is very difficult. For example, if you have a 1.0 kHz input frequency and you want to change it to 1.2 kHz, you can heterodyne it with a 200 Hz signal in an analog multiplier. This sounds like it...
  10. AnalogKid

    child safety in cars

    1. Research CO2 gas sensors for sensitivity, size and mounting, power requirements, and output signal. 2. Research shopping sites for pre-fabricated CO2 sensor devices and assemblies. There might be one that does most of what you want, significantly reducing the overall design effort. 3...
  11. AnalogKid

    Connecting a signal generator to an amplifier

    My guess is that the amp and oscillator are powered by two separate batteries. In this case. there are several connection configurations that will work. but before that, there is an error in the amp schematic. You have the headphones connected directly across the battery, not to the output of...
  12. AnalogKid

    An IC for generating composite video signals

    It's an ok question, just 20 years late. Most of the analog video CG chips are out of production. You can search for old datasheets and app notes from companies like Mostek, National, SGS, etc.. Also, this and other fora have a flea market section for buy/sell/swap. You might find someone...
  13. AnalogKid

    video generator: guidance needed

    HDMI is a *digital* video interface. That means two signals cannot be mixed together as they can be with NTSC analog video. Combining two digital video streams means calculating the resultant pixel value for all pixels that are the result of combining; in your case, the pixels of the overlaid...
  14. AnalogKid

    Creating logic AND gate with 2N222 Transistor

    From memory, 1.8 V. This is the terminal voltage of a floating TTL input pin. ak
  15. AnalogKid

    Creating logic AND gate with 2N222 Transistor

    1. Separate 4.7K series resistors to each base. 2. Large resistor (100K to 470K) from each base to GND. ak
  16. AnalogKid

    Help with component choice / design in an alarm circuit

    LSI has a line of programmable digital lock ICs designed for exactly this task, no microcontroller needed. http://www.lsicsi.com/prog_digitallocks.htm ak
  17. AnalogKid

    Four way UK traffic lights

    The schematic in post #1 is a mess. The one in post #3 is much better. Note that a 4017 output is rated for only 4 mA, and will have significant output voltage sag at that level. Better to diode-OR the outputs into a small MOSFET like a 2N7000, switching the LEDs to GND. ak
  18. AnalogKid

    PNP Transistor Arrays.

    He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast. - Leonardo da Vinci, 1452 - 1519
  19. AnalogKid

    PNP Transistor Arrays.

    The UDN2981 is an 8-channel source driver. The output stage is an NPN darlington, so the max output voltage is about 2 V below the rail. 5 V in, up to 50 V out. If you need the output to pull all the way up to the + rail, then go discrete with a 2N4403 or 2N3906 PNP and two resistors per...
  20. AnalogKid

    Modify circuit

    Well, now you know.
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