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  1. Audioguru

    Confusion about led's forward voltage

    All white LEDs I have measured use a blue LED (2.8V to 3.5V) and a yellowish phosphor.
  2. Audioguru

    LED Circuit Question

    The website you found says no details. The LED has a maximum allowed current and has a range of forward voltage that are shown on its datasheet. If the forward voltage of the blue LED is 3.3V then the current in the LED and in the 10 ohms resistor is (3V - 3.3V)/10 ohms= ZERO and the LED will...
  3. Audioguru

    Need help resistor values

    Hee, hee. You have bats in your bedroom? Then do you live in a cave or in a tree? With pin 2, pin 6 and the capacitor of the 555 connected together then you have made an oscillator, not a timer. Why do you use two transistors for the relay coil when the datasheet of a 555 says it can produce up...
  4. Audioguru

    6v LED brighter with 3v battery

    How many people buy 2016 coin cell batteries? Stores probably keep them for at least a few years then they are hardly ever new. Sellers on ebay probably also keep very cheap no-name-brand ones for years.
  5. Audioguru

    battery switch over help?

    The very high current rating of the Chinese switch indicates that it has silver contacts that tarnish when switching low current. Then the switching fails soon. I have always used American or European switches with low current gold contacts that last forever when switching low current. The high...
  6. Audioguru

    Lets take a look at a linear amplifier

    Maybe the thing you want to make does not use an audio power amplifier.
  7. Audioguru

    5 volts 1000 mA from 12 volts

    You will probably end up with the output voltage changing when the ambient temperature changes (even as it warms up) and if the load current changes. You mentioned "simple" then its performance will be horrible. That is why we use an IC or zener. An inexpensive 7805 IC works well and has 16...
  8. Audioguru

    Charging different types of batteries ?

    Since a "12V" lead-acid battery needs about 14.5V to charge quickly then a 14.5V or 15V power supply would probably melt because it would have nothing to limit the current. The battery might try to take 10A or 20A without a current limiter. A cheap 2A power supply will have nothing in it to...
  9. Audioguru

    Need help adding a Line-in to a Roland MT-300s (MIDI Music Player)

    I have found that ordinary high current power switches have silver contacts that fail in a short time when used with very low power audio signals because the silver tarnishes (high power cleans away the tarnish). Therefore I always use switches with gold contacts (they cost the same as power...
  10. Audioguru

    Charging different types of batteries ?

    Charger One is a 12V, 2A power supply, not a battery charger. Its voltage is too low to charge a "12V" lead-acid battery with 14.5V and its 2A of current is so low that charging a battery the size of a car battery will take a very long time. Charger Two is designed to charge a "12V" large car...
  11. Audioguru

    USA wall wart in the UK

    If the wall wart is lightweight and small then it does not have an old fashioned large and heavy low frequency transformer in it and instead it is a modern electronic circuit that uses a lightweight high frequency transformer. The modern ones work from a wide range of supply voltages.
  12. Audioguru

    Reducing voltage for a driver driven LED strip

    Is the humming produced by a bee in the little box connected to the red and black wires? Do you need the little box? The value for a resistor is calculated from the current you want when your supply was 3.3V and the voltage that will be across the resistor. The power wasted by the resistor...
  13. Audioguru

    Can I use 78l05 replace lm2931?

    The LM2931 low dropout regulator was probably in the original circuit so that a 6V battery can be used. Your 78L05 might shut down when it gets too hot since it must throw away the power of the 12V - 5V= 7V difference that causes heat. The LM358 was used because its datasheet shows a minimum...
  14. Audioguru

    Variable Power supply circuit

    Why didn't your teacher teach you how to design it properly like this:
  15. Audioguru

    Protection of Lithium Batteries

    Ordinary little CR2032 disposable lithium battery cells are 3V at low current. If you need more current or duration then simply connect a few of them directly in parallel.
  16. Audioguru

    FM oscillator/mixer

    A best circuit is completely different to a simplest circuit. The best circuit works well but the other one has poor performance.
  17. Audioguru

    What are these?

    If you connect the resistor across the battery like you said without an LED in series then the current is what you calculated. Are you trying to light up the resistor? An LED has voltage across it that reduces the voltage across the series resistor so that the current is less than you...
  18. Audioguru

    Lets take a look at a linear amplifier

    The schematic you posted is class-AB and it wastes a lot of power making heat. A class-D amplifier is completely different. You did not say the frequencies or load impedance.
  19. Audioguru

    What is the proper way to use 1 cell lipo batteries in parallel?

    Battery Management System ICs are designed to charge a high quality Lithium battery fairly quickly at a reasonable current of 0.5C. The Li-PO batteries I buy can be charged 10 times faster at 5C. Since the current from your solar panel is weak then it can charge parallel batteries fine but a...
  20. Audioguru

    Where could I salvage an LM317 Voltage regulator?

    Modern electronic products use extremely small ICs and a robot is used to connect them to a circuit. Fairly old products used "normal" size ICs that are easy to connect to. I have not looked inside many products so I do not know which ones would have an old normal size LM317 IC. I hope that...
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