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  1. Audioguru

    I buy am/fm radio kit but something i dont understand

    I am not a teacher but I found a real radio kit in Google. It is sold on Amazon and on Walmart online. The kit has the stages of the radios marked and comes with a training course appropriate for high school and university level curricular:
  2. Audioguru

    I have build a jk flip flop circuit from nand gate but it does not simulate, i need help ,

    When I saw this thread the first thing I did was lookup a CD4027 Cmos "Master-Slave JK flip Flop" and I have never used one. Its schematic is on its datasheet.
  3. Audioguru

    Capacitor charging

    Signetics invented the 555. Then Philips bought Signetics. Here is the article about why a coupling capacitor is required:
  4. Audioguru

    I buy am/fm radio kit but something i dont understand

    When I was about 15 years old, I built a real superheterodyne FM radio kit then later a stereo multiplex adapter kit for it. They worked perfectly. After using them for about 5 years I sold them for more than I paid for them. That was good value. I never ever made a simple Mickey Mouse...
  5. Audioguru

    I buy am/fm radio kit but something i dont understand

    The FM tuner is a Mickey Mouse "regenerative" circuit and the AM receiver is a Mickey Mouse "crystal" radio. A real radio is super heterodyne and is MUCH more complicated with MUCH Better Performance" than this garbage.
  6. Audioguru

    Clean square waves using a 555 timer?

    Get rid of the solderless breadboard with capacitance between its many rows of contacts and tangled long wires all over the place. Each wire has series inductance. The intermittent contacts are not designed to handle the 400mA shoot-through current of an ordinary 555 and a 9V battery also cannot...
  7. Audioguru

    LEDs powered from AAA battery

    You bought LEDs from Amazon who knows nothing about electronic parts so they did not specify the "viewing angle" of those cheap Chinese LEDs. Isn't the viewing angle (5 degrees?) so narrow that you cannot see the light unless the LEDs are shining directly at you? I always buy Name-Brand LEDs...
  8. Audioguru

    AM demodulation and DC offset

    C7 will charge when the input signal goes positive and it will not discharge so after a part of a second the AM detector will not work. If C& is used to block DC from the signal source then the anode of the diode needs a resistor to ground to discharge C7 each cycle.
  9. Audioguru

    AM demodulation and DC offset

    The capacitor goes to ground, it passes high carrier frequencies to ground, and it blocks the DC from shorting to ground.. The DC and audio from the diode passes on to the next stage. Look at this:
  10. Audioguru

    AM demodulation and DC offset

    You are correct, the resistor and capacitor are in parallel and are in series with the detector diode. Yes, the capacitor filters out the carrier frequency. No, the capacitor does not block the DC from the diode, the DC and audio frequencies pass on to the next stage.
  11. Audioguru

    1/4 inch mono jack 3 pins

    When you buy cheap Chinese junk from Amazon, ebay or AliExpress then you usually receive cheap junk with no information about it. A Name-Brand part made by a real manufacturer will have a long lifetime and has a detailed datasheet.
  12. Audioguru

    Woo-Woo MOSFET switch question

    Its maximum threshold voltage is 6V for some of them to conduct only 0.25mA. Then some of them will not do anything with a gate to source voltage of only 5V. It needs a gate-source voltage of 10V for it to turn on pretty well.
  13. Audioguru

    Can this PWM the amp burst ourput in this Nerf setup?

    It is cheap, Chinese and from ebay. Does anybody know anything about it??
  14. Audioguru

    Woo-Woo MOSFET switch question

    If a power supply has a positive voltage and a negative voltage then its common (called ground) is usually 0V.
  15. Audioguru

    Can this PWM the amp burst ourput in this Nerf setup?

    The PWM controller says 5a which is not 5 Amps. It says it controls up to 90W which at 7.4V is 12.5A. It does not say the current rating of the resettable fuse. The kit is made to use two AA batteries producing 3V when new. The two cells Li-PO battery is 8.4V when fully charged and it will...
  16. Audioguru

    Woo-Woo MOSFET switch question

    The video is wrong to show an IRF540 Mosfet with a gate to source voltge of only 5V. The datasheet for an IRF540 Mosfet shows a maximum threshold voltage of 4V when some of them barely conduct and shows 10V when it conducts well. The video should have shown an IRL540 (see the "L"?) that conducts...
  17. Audioguru

    Squawk Box

    You found a very cheap ebay Chinese amplifier with a fake LM386 IC on it. It shows the National Semi logo and says LM386N on it. But a real LM386N is a normal size dual inline IC with through hole pins, this one is a tiny surface mounted one that should be marked LM386MM. If it works it will...
  18. Audioguru

    Squawk Box

    Since the squawk box has an output transformer then it must be from the fifties. Its circuit uses either vacuum tubes or germanium transistors. An LM386 power amplifier IC has an output of 0.45W into 8 ohms (without a transformer) when it is powered by 9V. Here is a Philips audio amplifier from...
  19. Audioguru

    Newbie 12v meltdown, please help.

    You probably put the connector on with backwards polarity, the positive on the battery wrongly connected to the negative of the circuit and vice-versa. The circuitry is ruined.
  20. Audioguru

    Push button controlled LED decade counter ...

    If you use only one current-limiting resistor for all the LEDs to use then when the supply is 9V all of the LEDs receive a reverse voltage higher than their max allowed reverse voltage of only 5V.
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