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  1. audioguru2

    ringing detection circuit

    The telephone ringing signal in North America is 90VAC. Your zener diodes are only 3.3V and the 330 ohm resistor creates a huge current with a peak of 370mA. I am amazed that your opto-isolator didn't burn out. Look at all the ringing detector circuits in Google that use 15V zener diodes and a...
  2. audioguru2

    Far-distance remotely controllable rectifier with back-up battery

    You need to select a type of rechargable battery, its voltage and its capacity. Then you need to learn about how a battery charger circuit works and how to design one. The fuzzy JPG is very hard to see. It should have been saved as a clear PNG file type. The first circuit is a dual polarity...
  3. audioguru2

    Simple Unipolar Stepper Driver

    A TIP31 is rated for a max of 3A. At 1.5A its minimum current gain is only about 20 so it will need a max base current of 75mA. The current in the diodes should be at least twice as much which is too high. Your 24V power supply has a voltage way too high for this little motor. If the supply...
  4. audioguru2

    Momentary switch

    I have never seen a switch before that doesn't have a voltage and current rating and doesn't say what is the material of its contacts. Switches that size usually have 2A to 10A silver contacts.
  5. audioguru2

    Simple Unipolar Stepper Driver

    The 2V zener diode is a very poor voltage regulator. Use forward biased diodes instead.
  6. audioguru2

    very simple PS

    Hi Ante, Electronics-Lab "lost" my avatar so I changed its address to another electronics chat forum and now it works fine.
  7. audioguru2

    Far-distance remotely controllable rectifier with back-up battery

    Q1 and U1 with 3 resistors forms a voltage regulator. R6 is a current limiter that charges the battery. D1 stops the main power from overcharging the battery but allows the battery to power the circuit when the main power doesn't work. We can design a similar charging circuit for you if you...
  8. audioguru2

    Momentary switch

    For electronic circuits I use switches with gold plated contacts that are made for switching low currents. "Industrial" switches are made with silver plated high current contacts that rely on the spark to break through the silver oxide insulating film that quickly forms on them, so they are not...
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    With an 18VAC transformer, the max regulated output voltage at 3A is about only 16.5VDC. If the max output current is 3A then a single transformer should be rated for 76VA so yours is fine.
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    The very old LM301A is 33 times slower than a newer TL081 so the circuit might oscillate. It also has a high input bias current. It has a high input bias current. The TL081 and OPA445 have FET inputs. Where in the world are you? You are being ripped off! Digikey sell them for "only" $9.50US.
  11. audioguru2

    very simple PS

    Hi Walid, Nope. You forgot that the full-wave bridge has two 0.75V diodes in series for each polarity of the AC. So the DC output is 8,49V - 1,5V= 6.99VDC. The current in the diodes is very high for short duration pulses, so the forward voltage of each diode is a little higher than 0.7V.
  12. audioguru2

    high wattage resistor in batt charger?

    The resistor will limit the current when the battery voltage is low.
  13. audioguru2

    transistor as a switch

    Hi Walid, You have a very good point. ;D The circuit can't work if R8 is there! The supply voltage is 6.8V if the battery is fully charged. Then the output high of the 555 is about only +5.6V. R5 and R8 form a divide by 11 voltage divider so the base voltage of T2 is only 0.51V and so T2 never...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Subumann, It is good to hear that your original circuit works great. Other people have found that its max output is about only 25VDC and about only 2.5A at the same time. They also found that the transistors and rectifier diodes get very hot when the voltage is set low and the current is...
  15. audioguru2

    IC controlled emergency lamp with charger

    The Mosfets are a push-pull amplifier that drive the transformer. They work best if the waveform is a 50-50 square-wave. A 555 without the diode produces a rectangular waveform because the capacitor is charged slowly by R3 and R4 in series, but is discharged quicker by only R4. The diode shorts...
  16. audioguru2

    audioguru fm transmitter

    C2 and R6 are on the bottom of the circuit board. I didn't make a new circuit board but I modified the mod3 circuit into the final mod 4 circuit instead. All resistors are 1/4W, 5% carbon film. My 220 ohm resistor is longer because it is about 40 years old. I used two 5pF to 35pF trimmer...
  17. audioguru2

    IC controlled emergency lamp with charger

    Hi Walid, The article says that D5 adds to the zener's voltage for a 6.9V reference which is higher than the battery. D8 bypasses R4 when the 555 timing capacitor charges so it charges quickly.
  18. audioguru2

    Got a couple questions regarding this fm transmitter

    I thought I explained that Canada uses 75us pre-emphasis. I explained that a 50us transmitter (made for Europe) will sound muffled on a radio made for Canada.
  19. audioguru2

    Got a couple questions regarding this fm transmitter

    Hi Dot-com, Canada and the US use 75us pre-emphasis (a big mistake). The US started FM broadcasting with plenty of pre-emphasis (too much) to reduce hiss but audio sources in those days didn't have as much high frequencies as better sources did a little later when Europe began FM broadcasts. So...
  20. audioguru2

    Adjustable precision shunt regulators, TL431

    Don't use 1 ohm and 4 ohms as a voltage divider for a little TL431. At 12.5V then their current will be 2.5A and the little TL431 will melt if the source voltage rises. The reference input current is only typically only 2uA and doesn't change much when the temperature changes, so the current in...
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