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  1. audioguru2

    latching

    Here's a simple circuit that uses a capacitor to debounce the pushbutton's contacts and is a master, and a couple of inverters as a slave. Push for on, push again for off like a JK flip-flop.
  2. audioguru2

    4W FM Transmitter

    Down Under? D'day mate! Are you near Oz? How do you like it to be upside down all the time? With kangaroos and wallabees running around all over the place! I have snow when you are sweating. Go to www.farnell.com and click on your flag. Farnell has nearly everything except refrigerators. Dick...
  3. audioguru2

    Temp. Compensation for linear power supply

    Maybe you used an LM138 and its 240 ohm resistor (half the current).
  4. audioguru2

    Re: Alun's low voltage alarm

    Maybe you should tell National Semi to raise their minimum spec rating because you breadboarded a single circuit and it worked! They will raise their spec only when their production yield is good enough for them to throw away the weak ones.  :P What would you do with the assemblies with LM339's...
  5. audioguru2

    Re: Alun's low voltage alarm

    Thanks Alun, MP and I have had many disagreements about spec's like this.  ;D
  6. audioguru2

    Temp. Compensation for linear power supply

    The datasheet shows an LM338 circuit for up to a 25V output. With its 5K pot adjusted about halfway for a 25V output, it dissipates 238mW which is very close to its max if it has a 1/2W rating to be dissipated along its entire resistive element. It is also very close to the max rating of a 1/4W...
  7. audioguru2

    Re: Alun's low voltage alarm

    You don't believe what is stated in datasheets and you operate ICs above their ratings. If the ICs improved over the years, don't you think that the manufacturer would uprate their minimum spec's? Circuits that I design and have seen operate components within their ratings. Only? It has a...
  8. audioguru2

    FSK.............. project

    Frequency Shift Keying: 2 frequencies, one is a logic high and the other is a logic low. Google has 295,000 articles about it.  ;D
  9. audioguru2

    4W FM Transmitter

    The project's author would expect you to fasten a refrigerator to it.  ;D Otherwise operating it at 1.8W would exceed its storage and operating temps. A big high-velocity fan would do wonders for it!
  10. audioguru2

    4W FM Transmitter

    Hi Alun, Philips and a few others rate it at 1/2W. They dont talk about using a heatsink on such a small transistor. I wonder if a heatsink could be soldered to their metal case, not the plastic one though, duh! That's a good idea to parallel them.
  11. audioguru2

    4W FM Transmitter

    Hi Alun, How are you going to cool the poor little 2N2222A?  ??? It's rated for a maximum of only 1/2W.  ::)
  12. audioguru2

    Temp. Compensation for linear power supply

    Hi Smart, Your resistor from the adjust pin to ground is probably getting hot (nearly 1/4W) and decreasing in value which reduces the output voltage. Use a bigger resistor that won't heat as much and will be more temp-stable. If it is a pot then replace it with a stable cermet pot.  ;D
  13. audioguru2

    Re: Alun's low voltage alarm

    Yes MP, The LM339 has a flea-power output that is guaranteed to sink a current of only 6mA with a saturation voltage of no more than 1.5V. The factory has already sorted them for you by passing the 6mA ones, but you can test a bunch yourself and you might find some that sink 16mA. They are...
  14. audioguru2

    Help: I want to build my own Intercom.

    Hi Masterleous, Your preamp is designed for an electret mic. It should have only two wires (some have 3 wires) and one of its wires is connected to its metal case which connects to ground at the preamp. Measure the DC voltage across your mic with a multimeter. It should be a few volts. If it...
  15. audioguru2

    small current amplifiers

    Kevin, You missed the decimal point. 1% of 10 isn't a spread of 2, it's a spread of 0.2. Let's compare the gain accuracy of an opamp circuit that has a gain of 10 with negative feedback: 1) The opamp has its minimum gain of only 25,000. According to the attached tutorial, the circuit's gain...
  16. audioguru2

    Re: Alun's low voltage alarm

    Hey Alun, The project has its "opamp" called a comparator (but not a quad) and its + and - input polarities corrected now. I forgot to mention that the LM339 quad comparator is low-power, so doesn't have enough output current to work in this circuit. A typical "piezo buzzer" is the 23.4mm...
  17. audioguru2

    small current amplifiers

    Kevin, The input transistors in opamps use high beta for an extremely low bias current and an extremely high impedance, not for voltage gain. The input transistors use emitter-degeneration resistors to straighten their linearity which reduces their voltage gain a lot. Opamps use very high...
  18. audioguru2

    New Server

    Hi Guys, Our new server or our site seems to breakdown for many hours every day. "Cannot find server, DNS error" or "Web site found, waiting for reply". It is very frustrating! When it works it's great! Compounding the problem is that the home page's "Recent Topics Details" doesn't work. So...
  19. audioguru2

    fm tranismiter

    Hi Alun, A TL081 isn't spec'd for noise. It is the same as a TL071 but the quiet ones are labelled and sold as "TL071" and the lousy ones "TL081". Maybe a TL081 is made late on a Friday or early on a Monday, and whatever makes it noisy might affect its reliability. Try your TL081. Maybe its...
  20. audioguru2

    Help: I want to build my own Intercom.

    Hi Masterleous, There is no such a thing as "an Electric MIC". What kind of mic, electret or dynamic? It might even be a carbon mic from an old telephone, or a crystal mic from a toy. They are all different. You didn't describe the noise. If it is coming from the wiring then you need a shielded...
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