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  1. Audioguru

    Board design help! Some buttons and led on a perfboard

    About an hour or two.
  2. Audioguru

    Amplify signal from piezoeletric

    There you go, 10k ohms. Then the capacitor feeding it must be 26uF for a cutoff at 0.66Hz.
  3. Audioguru

    Amplify signal from piezoeletric

    Then the output capacitor on the opamp circuit feeds the input resistance of the Arduino. What is its resistance? The Arduino input might already have a series capacitor that does not pass your extremely low frequencies.
  4. Audioguru

    Amplify signal from piezoeletric

    If your feedback to ground resistor is 100k then the Rf must be an extremely high value to have any gain. You still did not say what resistance this circuit is feeding so the value of the output capacitor cannot be calculated.
  5. Audioguru

    Mosfet Buffer Amp Circuit Help

    An amplifier has a certain maximum output voltage and maximum output current. You failed to say what they must be.
  6. Audioguru

    LED Timer

    Why are you talking about an "input"? The 555 does not have an input, instead it has a trigger input. The output of the 555 goes high when the trigger input goes low and times out only when the trigger input is high during the timeout. If the trigger input is still low after the timeout then the...
  7. Audioguru

    Board design help! Some buttons and led on a perfboard

    I like to use my noggin to do Vero-stripboard layouts.
  8. Audioguru

    Diy multi bank battery charger

    It looks like your "charger" has no filter capacitor. Are your batteries 12V lead-acid? A full wave bridge rectifier has two silicon diodes in series for both phases. A silicon diode has a voltage drop of about 0.7V at low current and about 1V at the high peak current in this circuit...
  9. Audioguru

    Board design help! Some buttons and led on a perfboard

    My bare jumper wires are almost always at right angles to the copper strips and are soldered on the component side from one strip to a nearby strip. Here is my layout and a photo. Each red X is where a strip was cut:
  10. Audioguru

    Amplify signal from piezoeletric

    I have never applied a voltage to the input of an opamp that is higher than its supply voltage so I do not know if the input is destroyed if you limit the over-voltage with a Schottky diode to about 300mV too high.The datasheets of most opamps do not say to use Schottky diodes, the datasheets...
  11. Audioguru

    Board design help! Some buttons and led on a perfboard

    I use Vero perforated-stripboard for all my circuits. The strips are cut to length with a drill bit and form half of the wiring of a pcb and the parts and a few short jumper wires form the other half. It looks so good that all of my prototypes were sold as the final product where only a few were...
  12. Audioguru

    Amplify signal from piezoeletric

    Here is a simple non-inverting opamp with a single positive power supply:
  13. Audioguru

    Homemade capacitors, that hold a charge?

    Your home-made capacitor has such a low capacitance that your voltmeter discharges it instantly. Can your multimeter measure its very low capacitance?
  14. Audioguru

    Amplify signal from piezoeletric

    I did not see the video when I first replied. I thought the piezo was used as a microphone but the video shows it used to show breathing pressure on it. Maybe you are using it to show the pressures caused by coughing? The video shows ordinary wires as a cable which will pickup mains hum and...
  15. Audioguru

    Amplify signal from piezoeletric

    You said you are making a cough sensor with only low frequencies no higher than 4Hz. But a cough contains many higher frequencies. Your circuit shows a lowpass filter of R with Cf in parallel creating its cutoff frequency. The circuit I showed with a non-inverting opamp does not and cannot have...
  16. Audioguru

    Amplify signal from piezoeletric

    The load resistor is whatever this preamp opamp drives. Maybe its load is the high value bias resistor of a second opamp that is your lowpass filter. A non-inverting opamp makes a poor lowpass filter when its negative feedback resistor has a capacitor in parallel because it can only reduce its...
  17. Audioguru

    Amplify signal from piezoeletric

    The input capacitor is not needed if the input is from a piezo because a piezo is already a capacitor. The C2 capacitor from the negative feedback divider to ground blocks DC but passes AC so that the opamp does not amplify its DC input offset voltage. Yes, R6 and C2 are a highpass filter...
  18. Audioguru

    Amplify signal from piezoeletric

    A resistor in series with the non-inverting input if a non-inverting opamp amplifier is useless. The non-inverting input must be biased at half the supply voltage with a high value resistor. If the supply is plus and minus then the bias resistor connects to 0V.
  19. Audioguru

    Does this power supply seem safe

    A power supply has many detailed spec's. This cheap Chinese junk has no detailed spec's. But it is very cheeeep. It is not a charger circuit for a lithium-ion battery.
  20. Audioguru

    Amplify signal from piezoeletric

    The piezo produces a voltage output with almost no current. Your opamp is inverting with an extremely low input resistance so its input is a current, not a voltage. If you make the opamp non-inverting with a high input resistance then the piezo will work fine until it is dropped then its very...
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