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  1. audioguru2

    white led

    Shocking! A white LED can have about 2.5V across it and not pass any current. You have 70 LEDs in series? Then the capacitor will be charged to at least 175V which will bite you.
  2. audioguru2

    Sound Level Indicator

    It is on the left side of the LM3915 and it connects to pin 1. It should be 22k for two LEDs in series but 10k also works to keep the first LED from lighting dimly when it should be off.
  3. audioguru2

    Wireless firework control

    Millions of people have those FRS radio walkie-talkies. You don't want to use something like that to ignite fieworks.
  4. audioguru2

    Creating a cheaply built (mostly out of slaughtered parts) mppt

    A switched-mode charger doesn't use switched relays. It uses Pulse-Width-Modulation. The power is switched with Mosfets. 17V at 9A is a power of 153W. There must be a powerful switched-mode charger circuit somewhere on the internet, designed forr solar cells as the source.
  5. audioguru2

    Wireless firework control

    I don't know of a transmitter/receiver that goes 1.5km. Garage door openers and keyless car remotes don't need such a long range. Test a little AA cell to see how many times it can heat the ignitor coil. Which gets hotter, the coil or the battery cell?
  6. audioguru2

    Wireless firework control

    There are transmitters and receivers that have a range of 100m. You would need to make a circuit to modulate the transmitter with a special code then another circuit at the receiver that would respond to only that code. I have seen 1.5V Duracell tiny watch battery cells and huge 1.5V cells. The...
  7. audioguru2

    Wireless firework control

    The voltage from a charged capacitor drops during discharge. If you charge a 0.5F (half a Farad) capacitor to 9V and discharge it for 2 seconds with an average of 1.1A then at first the current will be 1.65A, in 1 second the voltage will be 6V and the current will be 1.1A and in 2 seconds the...
  8. audioguru2

    SL100 & SK100 transistor

    I borrow some wisdom from parts manufacturers. They have very good reasons for the max allowed ratings and min and max spec's on their datasheets. In school I was taught about "typical" ratings but it was useless and obsolete knowledge. My experience gives me the wisdom to use min and max...
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    The OPA445 opamp is the only one I found with a high enough max supply voltage rating. It is made by the Burr-Brown division of Texas Instruments and is available through Farnell world-wide. NTE buys ICs and sells them as replacements.
  10. audioguru2

    DC Linear Gain Amplification

    The TL071 is a good audio opamp but it is inexpensive. Its max input offset voltage is 10mV but you can add a trimpot to null it if you want. Linear Technology and Analog Devices make some laser-trimmed opamps with extremely low input offset voltages.
  11. audioguru2

    Sound Level Indicator

    I am glad that you got it to work properly.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    The improved circuit is basically the same. The transformer has a higher voltage and current rating, the opamps have a higher voltage rating , One additional output transistor is added and they each have an emitter resistor, a couple of transistors are bigger and some resistors and capacitors...
  13. audioguru2

    How do I regulate voltage AND current?

    Make a circuit that will drain the capacitor. The pot can control how much current a transistor can drain and therefore how long it takes. The LED will also drain the capacitor so it should have its own power supply. A circuit can be made with a comparator to turn on the LED when the voltage...
  14. audioguru2

    DC Linear Gain Amplification

    The 741 and 324 are very old, noisy and have a high max input offset voltage. Newer opamps are laser-trimmed for very low input offset voltage and are much quieter.
  15. audioguru2

    Transistor Switch???

    If the circuit uses an opamp and not an open-collector comparator, then the output of the opamp will go up to 11V to turn on the NPN transistor and try to turn off the PNP. Then when the opamp output goes low to about 1V then the PNP turns on and the NPN turns off. The PNP transistor will turn...
  16. audioguru2

    Transistor Switch???

    Hi Tacamo, Welcome to our forum. ;D The PNP transistor turns on when the output of the opamp is low. Add an NPN transistor and it will be off when the output of the opamp is low.
  17. audioguru2

    Dual LM3886 Bridged Amp.

    You said "It doesn't work well on 4 ohm speakers" so it appeared that you didn't know why. Some people connect so many speakers in parallel to the output of an amplifier that it is driving nearly a dead short.
  18. audioguru2

    Dual LM3886 Bridged Amp.

    Hi Zombie, The peak current in the amplifiers is doubled with a 4 ohm load (compared to an 8 ohm load) and the current is doubled again when two amps are bridged. So the protection circuit in the LM3886 will drastically limit the power when bridged into a 4 ohm load. 
  19. audioguru2

    Electronic Eavesdropping Devices Detector

    P1 is the sensitivity control. AN920 recently showed his modofocation of changing R7 to an inductor and changing the values of C4 and C5 so they all make a highpass filter. Then the circuit won't be as sensitive to computers, their monitors, TV's and AM radio stations. In MS Paint, I took the IC...
  20. audioguru2

    Sound Level Indicator

    I made the circuit very sensitive. The LEDs bounce when the TV or stereo is playing. The automatic-gain-control reduces is sensitivity 20dB when there are loud sounds. If the R5 value of 100k is changed to 10k then it will be 20dB less sensitive.
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