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  1. audioguru2

    4511 bcd to 7 segment help needed

    Hi Johnny, Welcome to our forum. The 4511 can drive up to 25mA on each output so your 720 ohm relays (12V?) are no problem with your 12.5V supply. The outputs of the 4511 are active-high, so the other end of your relay's coil should connect to ground. It is good that you have pull-down...
  2. audioguru2

    Temperature:Speed Timer Circuit?

    Hi Ante, No, I think a thermistor is any resistor that changes its value with temp changes, even an incandescent light bulb. Most thermistors change value very little with temp change, measured in parts per million per degrees C. BTW, I just got back from the store where I bought my new...
  3. audioguru2

    Temperature:Speed Timer Circuit?

    Hi Guys, The 555 works fine when connected with just a single timing resistor to its output. It makes the timing capacitor's charge and discharge times the same, producing a symmetrical output, especially with a Cmos 555 and if the value of the timing resistor isn't too low. ::) Twizted's...
  4. audioguru2

    Electronic Stethoscope 2

    Hi Hakyman, Welcome to our forum. 1) Your ADC probably has an input voltage range of 0V to +5V. The output of the Stethoscope-2 project swings about +3.5V to -3.5V. If you use the output pin of the LM386, the voltage will swing about from +1V to +8V, no longer negative but still too high for...
  5. audioguru2

    Oxodized Sodering iron

    Hi Tweak, I have used temperature-controlled soldering irons for most of my long life. They heatup to operating temperature very quickly, don't cause overheating damage to components, heat more at full power to solder something that is big, and allow the tips to last almost forever. No...
  6. audioguru2

    Negative charge pump

    Hi again, In your more detailed schematic, the opamp used to feed CL1 is driving two 100 ohm resistors with a total output current of about 226mA, much too high a current for an ordinary opamp. If you use a power audio amp to provide the required current, its output swing certainly wouldn't be...
  7. audioguru2

    Negative charge pump

    Hi Kevin, I am glad that your circuit worked with a +5V supply. However, I have analysed the 1st half of your last circuit and found 2 serious problems if it is used with a higher supply voltage: 1) When the capacitor is charging, nothing limits the current. The transistors might be destroyed...
  8. audioguru2

    Maximum current for AC/DC adaptors

    Hi Autir, Sorry, I locked the other topic by mistake, it's unlocked now. I don't think that an unregulated AC/DC adapter should ever be operated with a load current beyond its nominal rating. Its maximum current isn't listed and it usually must dissipate more power when the mains voltage is...
  9. audioguru2

    Voltage regulator + current amplifier?

    Hi Autir, Only linear voltage regulators heat-up because of the power they must dissipate due to the voltage across them and the current through them (P = V X I). Switching voltage regulators heat much less. Look at the high efficiency of the switching regulators in your computer, delivering...
  10. audioguru2

    Digital multimeter powered by adaptor?

    Hi Ante, My computer salesman was smiling, even though he didn't get any commission because he is paid salary only. When big computer stores buy in vast quantities they must make a huge profit, except for the sale price that I found. ;D My workshop has flourescent lights and my soldering...
  11. audioguru2

    Digital multimeter powered by adaptor?

    Hi Guys, Here's my new Pentium4. I got a really good deal. ;D My battery-powered multimeters can measure very small AC or DC voltages and fairly high frequencies (20KHz) differentially, so it doesn't even matter which lead is connected to common, without much interference pickup. If my meter...
  12. audioguru2

    measurement

    Hi Kevin, You don't need a dual supply to power a transistor. A single supply with a resistive voltage divider for the base will work fine. Why do you vary the collector voltage? The transistor circuit that you show has the transistor as a constant current sink, therefore changing the collector...
  13. audioguru2

    Digital multimeter powered by adaptor?

    Hi Autir, I have 2 multimeters so I can measure voltage and current at the same time. They have LCD screens (not high-current LEDs) so use very little current from their 9V alkaline batteries. Their batteries therefore last for many hours and years. I can hardly measure how little their accuracy...
  14. audioguru2

    AC/DC adaptors: voltage over normal?

    Kevin, You don't have to put regulators in series to get "better" regulation, a regulator operating by itself within its ratings provides excellent regulaion. Look at the datasheet for a 7805 regulator. Its line (input voltage change) and load (output current change) regulation and ripple...
  15. audioguru2

    Negative charge pump

    Hi Kevin, Like I said in your other post about a simple amplifier, your 3 left side transistors will work well making -12V pulses, when it is driven with a square-wave oscillator like a 555. I don't know what the right side transistors will do. I think that the PNP transistor at the extreme...
  16. audioguru2

    The simplest audio amplifier

    Hi Kevin, Your 3 left side transistors will work well making -12V pulses, when it is driven with a square-wave oscillator like a 555. I don't know what the right side transistors will do. I think that the PNP transistor at the extreme right side will do nothing but breakdown since it base is...
  17. audioguru2

    3V LED Chaser project

    You will notice that a new capacitor has been added at the transistor. It is used to attenuate extremely narrow PWM pulses at minimum brightness. Both the original 3V circuit and the new 6V circuit need it when using ultra-bright LEDs, because they are so bright. You should see the new 1.8V...
  18. audioguru2

    3V LED Chaser project

    Hi Guys, I was wondering why my original 3V LED Chaser project looks as bright as the new circuit I designed for ultra-bright LEDs and a 6V battery. The original circuit produces 15mA current pulses in its LEDs but the effective current is reduced to about 10.5mA by the max duty-cycle limit of...
  19. audioguru2

    pulse detecotr type circuit

    Hi Wingman, Welcome to our forum. Do you use an amplitude modulated carrier, like an AM radio? To quickly store the amplitude of a pulse, then quickly change its voltage to the amplitude of the next pulse, you need a sample-and-hold circuit. It is made with a low-impedance buffer that charges or...
  20. audioguru2

    Bass-boost

    Hi Mukhalled, That amp has built-in feedback so you can't change it to give bass-boost. You must add a boost circuit to its input. Over the years I built 2 audio amps with bass-boost that I use at the beach. They both use a 2nd-order Sallen and Key high-pass filter at the input of each amp that...
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