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  1. Audioguru

    Need to find a cheaper part than this: Micro USB charger board

    A cheap Li-PO charger might be made wrong then set your home on fire or cause an explosion. Pay a little more and buy a good one that is certified to be safe. I buy my American-made certified to be safe Li-Po chargers at a local hobby store, not on adafruit, ebay, amazon or ali-express..
  2. Audioguru

    Voltage Controlled Voltage Source (VCVS) - Piezo Buzzer

    You should not use PWM on the alarm, you can use filtered PWM to set the voltage of an LM317 voltage regulator.
  3. Audioguru

    30W and 4x8W audio amplifier circuit?

    That was many years ago. Today most little amplifiers are class-D, use a single positive supply, are bridged and have no saturation voltage loss.
  4. Audioguru

    Determining LED values

    I did not say that a resistor is not needed. Of course a voltage should never be applied to an LED.
  5. Audioguru

    Determining LED values

    You must never apply a voltage to an LED because it is a diode, not a resistive light bulb. A small increase in the voltage will cause a very high increase in the current which will burn out the LED immediately. Besides each LED has a different voltage and the required voltage changes when the...
  6. Audioguru

    Voltage Controlled Voltage Source (VCVS) - Piezo Buzzer

    Does a medical person need to learn the 20 melodies to determine the medical problem? They all sound like a buzzer. Why not have the device speak the medical problem in words like airplanes do? Pull Up- Terrain; Bank Angle; Stall etc.
  7. Audioguru

    Determining LED values

    A white LED is a blue LED with a yellowish phosphor on top. A modern bright green LED uses the same technology and has the same forward voltage as a blue one.
  8. Audioguru

    Determining LED values

    The datasheet for an LED will show its range of forward voltages. If it is white, blue or bright green then it will have a voltage range from about 2.8V to about 3.5V and each one will be different even if they have the same part number. The voltage also changes when the temperature changes so...
  9. Audioguru

    Piezo Control voltage source

    When you amplify the signal from a piezo sensor then I think the input of the amplifier (transistor, jFet or opamp) should have diodes protection from the high voltage produced when a piezo is hit hard or is dropped. The high voltage can zap the input device. A piezo sensor produces a voltage...
  10. Audioguru

    Arduino RGB strip controller switching problem.

    Why do you show the datasheet for the IRFZ44 Mosfet that might barely turn on when the gate-source voltage is only 5V? The IRL3705 is fine since it is 'logic level". A Mosfet has a high gate-source capacitance and no gate current so when it is turned on and the gate is disconnected then it...
  11. Audioguru

    Piezo Control voltage source

    A tapped piezo has an output voltage that is "loaded down" by a load. Then the resistance of the load should be very high for the output voltage to be high. A tap causes a voltage with a very short duration that might be difficult for a meter to show (maybe an oscilloscope will show) and maybe...
  12. Audioguru

    Constant current circuit

    You did not understand what I said. You cannot buy an LED with a certain forward voltage.The forward voltage rating of an LED part number is not a single voltage, it is a range of voltages (an example is 2.8V to 3.2V) because an LED is not a certain length of very hot wire, it is a diode and...
  13. Audioguru

    Line splitter.

    Take an opamp that has negative feedback which causes its output impedance to be 0.1 ohm (it is probably less). Then "split" its output to drive ten 22k ohm loads. Does "splitting" cause a volume loss? How much is the level at each of the loads? The voltage divider is (22k/10) / [(22k/10) + 0.1...
  14. Audioguru

    Constant current circuit

    You said LEDs in plural. LEDs have different forward voltages even if they have the same part number. If you parallel a 2.8V white LED with a 3.2V white LED then the 2.8V LED will take all the current and might burn out but the 3.2V LED will not light until the other one has burned out then it...
  15. Audioguru

    12VDC Backup supply

    Calculate the resistor so that the battery has a trickle charge current not higher than 1300mAh/40= 32.5mA. But the battery will be 14V to 15V when fully charged so it will never be fully charged and it will never have a trickle charge. You can charge it through a resistor if the charging...
  16. Audioguru

    Line splitter.

    You have an opamp on the left driving three opamps that drive volume controls. The opamp on the left can drive many volume controls by itself without any additional opamps. But the additional opamps can have different gains if you want. I would simply increase the gain on the opamp on the left...
  17. Audioguru

    Line splitter.

    An audio splitter can have attenuation, gain or the same level outputs as the input. You can "split" one signal to feed hundreds of devices without using any parts. The signal source must have a low impedance (like the output of an opamp) and the devices must have a high input impedance (like...
  18. Audioguru

    12VDC Backup supply

    The Ni-MH battery shown in post #24 has 10 cells averaging 1.2V each and will be fully charged at 14V to 15V.
  19. Audioguru

    Signal mixer, voltage mixer.

    A control voltage would be a fixed or slowly changing DC voltage from a pot or a switch. A modulating AC waveform would quickly vary the tone (wah, wah, wah) or amplitude (burst, burst, burst) or frequency (like a siren).
  20. Audioguru

    Line splitter.

    The output from an opamp can drive hundreds of devices if their resistance is fairly high. Then a "splitter" is not needed. So you do not need a mixer and you do not need a splitter. Do you need an opamp? I am confused. You showed an AC circuit with one input and three outputs then talk about...
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