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  1. Audioguru

    Strange Chinese battery. Need help finding charger.

    The battery voltage is 25.9V which is 7 Lithium cells in series that average 3.7V each. Each cell is charged to 4.20V with a specified current then the charger is disconnected when the charging current becomes low. The total charging voltage is 7 x 4.2V= 29.4V but usually a multi-cell Lithium...
  2. Audioguru

    Powering an LED from a triboelectric nanogenerator

    Google links a video of a triboelectric nanogenerator providing a weak current that is harvested. But the Oriental student making the video has horrible Engrish.
  3. Audioguru

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

    The fuse should be in series with the electrical input and the on-off switch that feeds the transformer.
  4. Audioguru

    Power supply output voltage

    Of course it is faulty.
  5. Audioguru

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

    The heatsinks need air circulation. I can't remember if you are mounting the heatsinks outside the box or if you are using a fan.
  6. Audioguru

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

    Your meter looks nice and bright and your voltages are good and normal. U3 pin7 is fine at the unregulated voltage of 42V minus the 10V of zener diode D13. U3 pin5 is fine because it does not have an offset adjustment pot.
  7. Audioguru

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

    220uF will be fine as a filter for the 15.7V pulses. Connect its (-) wire to the (-) wire of the bridge rectifier and connect its other wire to the +15.7VDC that you are smoothing.
  8. Audioguru

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

    When you feed 12.1VAC to a bridge rectifier then at a low current the output of the bridge rectifier is pulses of about 15.7VDC. The meter probably needs smooth DC so add a 100uF/35V capacitor to the output to smooth it.
  9. Audioguru

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

    The photo shows the cathodes of the diodes at the cathode end of the old Zener diode D7. But a Zener diode is used in reverse mode, ordinary diodes are used in forward mode. Yours are backwards so turn them around. Use an ohm meter to measure the pcb trace that connects the anode of the D7...
  10. Audioguru

    ws2812b ledstrip as motorcycle indicator

    Red, green and blue LEDs at maximum allowed current do not produce white light, maybe it is yellow. Two of the color levels must be reduced to produce white. Then their total current is less than half of the current if they are at maximum current. What indicator? Vehicle laws say the required...
  11. Audioguru

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

    The Chinese kit had a 5V1 Zener diode for D7 since it used TL081 opamps. The new opamps use two diodes in series instead. A Zener diode is used with reverse polarity but you installed the two diodes backwards also with reverse polarity. Reverse the two diodes so that their cathode ends are at...
  12. Audioguru

    Microphone advise for monitoring heart sounds in animals under anesthesia

    Don't use cheap Chinese ebay products for medical applications. ebay sells manufacturer's rejects and fakes. Also they might be contaminated with poisons and/or diseases.
  13. Audioguru

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

    D7 is two silicon diodes in series. If they have the correct polarity (the bar on them is the negative cathode end) then each one limits the voltage to 0.65V so the two in series limit the negative voltage to about -1.3V. Maybe yours are burned out or are mounted backwards.
  14. Audioguru

    Capacitive reactance affecting voltage divider output

    A piezo transducer is a speaker or microphone. It is fed AC or produces AC. It has two wires. A piezo beeper has a built-in transistor oscillator. It is fed DC. Its piezo crystal has three connections: output, ground and feedback. We do not understand what you say your friend is doing. If he...
  15. Audioguru

    Microphone advise for monitoring heart sounds in animals under anesthesia

    Use an electret mic. Most have a very flat frequency response to less than 20Hz.
  16. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    One cheap speaker sounds like a cheap speaker: 1) A high resonant frequency with no deep bass. 2) A peak in the upper midrange with no highs. A network of these speakers will sound the same but can be louder than just one speaker. A large "super diaphragm" will be very directional.
  17. Audioguru

    Regenerative Receivers-explanation

    A super-regen quenches and automatically works but an ordinary regen receiver needs you to fiddle with a regen potentiometer for it to work poorly. Guess what? The change in current draw is AM (amplitude modulation). In addition to having poor sensitivity and poor selectivity, a regen or...
  18. Audioguru

    Capacitive reactance affecting voltage divider output

    A piezo beeper has its own oscillator built into it. It oscillates at its resonant frequency when it is powered from DC. But you said the piezo is driven from a PIC (40kHz signal, not DC?) then the piezo is a transducer. A piezo transducer has one capacitance, not two like you show. Your...
  19. Audioguru

    Design of a transistor curve tracer

    But it has a low input impedance. A non-inverting opamp can have an extremely high input impedance. did you understand that your schematic had the opamp feedback connected to the wrong input?
  20. Audioguru

    Design of a transistor curve tracer

    Google Images shows hundreds of opamp. All inverting have the Positive input on the bottom and all non-inverting have the Negative input on the bottom like this:
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