Search results

Search Forums New Posts
  1. Audioguru

    Adding an LED display to an FM radio kit?

    I can buy a finished radio with that TDA7088 circuit at The Dollar Store for $1.00 and it comes with earphones and a battery so the radio is free. It works poorly. It is overloaded by strong local stations and cannot pickup weak distant stations that better radios receive perfectly. Its scanning...
  2. Audioguru

    Heating coils with a 9v, why doesn't this work?

    I think your shorted battery will produce more heat than your nichrome wire or twist tie. But only a brand new alkaline battery and only for a minute or two. I forgot to say that a new 9V alkaline battery will heat itself to about 12W for a few seconds when shorted then it will be dead in about...
  3. Audioguru

    Christmas Tree LED lights

    With a supply that is only 3V then an ordinary Mosfet will not turn the LEDs on and off, even a "logic level" Mosfet will not work. Some small Mosfets used in radio controlled toys work from 3V. Then make a Cmos oscillator to turn the Mosfet on and off. A PWM circuit can fade the little Mosfet...
  4. Audioguru

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

    The BD139 is an NPN little power transistor that needs a heatsink and is Q2, not Q3. Q3 in the original project is a little BC557 or BC327 PNP transistor driven through R20 and it has a fairly low current to turn on the LED so it does not need a heatsink. Maybe the Chinese kit labelled Q2 and Q3...
  5. Audioguru

    Amplification to a constant Vpp

    I hate the effect of an audio compressor on pop music when it causes the background music volume to pump up and down with the beat. Also when a TV news announcer is talking on the street then his voice level disappears when a loud truck drives past due to the audio compressor.
  6. Audioguru

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

    The BD139 is European, the 2SD9015 is Oriental and of course they are different. If going from one side of the earth to the other side you should look at the datasheet of what you are using.
  7. Audioguru

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

    Pin 2 voltage is too high. What connects to pin 2 that is doing it? U3 or C8 or some conductive crud on the pcb.
  8. Audioguru

    Amplification to a constant Vpp

    Why does Electro Schematics dot com always make every schematic wrong? The NPN transistor has its collector load wrongly negative instead of positive.
  9. Audioguru

    Trying to get this circuit to work on breadboard

    Even if the polarity of the receiving LED is reversed, the maximum allowed reverse voltage of most LEDs is only 5V but this circuit gives it 9V.
  10. Audioguru

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

    First, you need to fix whatever is causing the voltage on pin 2 of U3 to be a positive voltage higher than almost 0V.
  11. Audioguru

    Amplification to a constant Vpp

    A signal limiter or compressor keeps the signal level from exceeding a certain amount. A Wien Bridge oscillator has its compressor circuit rectify the output signal and uses the resulting DC to turn on a Jfet attenuator at the input. It is designed to produce very low distortion, not clipping.
  12. Audioguru

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

    That was needed to test U2 by itself.
  13. Audioguru

    Fm transmitter data pins, what are they for?

    The jack plug shorts left and right stereo signal source channels together which might destroy the signal source. The simple transmitter is mono, not stereo.
  14. Audioguru

    Homemade light-bar (LED query)

    Isn't 600W of LED light enough to blind everybody for miles around? How will you cool 600W?
  15. Audioguru

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

    The way the current regulation works is using U3 to reduce the output voltage by using D9 to reduce the input voltage of U2. Then if you set the current setting at 1A but the voltage is set to 10V and the load is 5 ohms then U3 senses way more than 1A and reduces the input voltage of U2 so that...
  16. Audioguru

    Bone conduction low frequency speaker

    A piezo is a squeaker and cannot produce low frequencies with any force. A small speaker has a high resonant frequency and also cannot produce low frequencies. I agree that a relay might work.
  17. Audioguru

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

    Good, you are almost finished fixing its problems.:)
  18. Audioguru

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

    It is a good idea to replace all the cheap Chinese junk (Bangnogood). The output of U2 is its pin 6 that should be 2.7V higher than its input pin 3: 0V in = 0V out. 2V in= 5.4V out. 10V in= 27V out. 11.2V in (max)= 30V out. Pin 3 of U2 is fed through R8 and R9 from the slider of the voltage...
  19. Audioguru

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

    Another problem. P1 is supposed to feed 0V to 11.2V to pin 3 of U2 (measure it) and U2 has a voltage gain of about 2.7 times so its output should go from 0V to about +30V. But if the LED lights then the input of U2 is reduced by U3 driving D9. Then the U3 problem with its pin 2 voltage being too...
  20. Audioguru

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

    If R7 measures 0.002V and pin 2 of U3 connects to R7 through R21 then how can pin 2 of U3 be 0.94V? Does the output of the project measure +0.93V? Then something is shorting it to the positive voltage. R7 is 0.47 ohms. 0.94V/0.47 ohms= 2.0A which is a lot of current and where is it coming from...
Top