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  1. audioguru2

    inverter

    I just want to see their copy of ours! (but using vacc tubes [valves?]) Does anyone remember double-cotton-covered wire insulation? Where's our wizard, John will also know that stuff. I hope that he isn't in China. ;D
  2. audioguru2

    Question on the Plants Watering Watcher circuit

    Hi Oli, I'm not talking about us electronic genius's, but the average (stupid?) person probably won't be able to comprehend a flash rate change of only 10 to 1. Besides, a flash rate of 5 seconds is so slow that you could walk right by and not see it between flashes. I designed a communications...
  3. audioguru2

    Question on the Plants Watering Watcher circuit

    Hi Oli, In addition to using LEDs that have linear brighness vs current, make sure that they are wide-angle so that they can be seen when not pointing directly at you. Many "ultrabright" LEDs have a very narrow beam. Another problem with having a reverse resistance-to-flash-rate circuit would...
  4. audioguru2

    AA battery power rating

    Hi Jeff, Energizer has a pretty good web site. They have detailed datasheets for their batteries but be careful because a disclaimer says that they are subject to change. Their main site is here: www.energizer,com I am assuming a 20 degrees C temperature, its performance is poor when it is very...
  5. audioguru2

    inverter

    Their web site sure creates a language barrier. If anyone finds out about the inverter, please post english info here.
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Marek, Did you say that without U2, the voltage at its pin 6 is the same as its pin 3, that both pins adjust from 0V to 11.2V? Pin 6 shouldn't do that without U2. With U2 connected, it must be passing some of its output voltage of 27V to the pot to make it 25V instead of 0V to 11.2V. Your...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hey, is Smartkit sending all their customers who have problems over to here??? ;D ;D ;D
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Marek, You made good transistor substitutions. Your U2 is defective, replace it. It is feeding voltage to its input. Wait a minute, it could be that you have U2's pin 3 (input) and pin 6 (output) reversed! The top of the IC looks like this: 1* 8 2 7 3 6 4 5...
  9. audioguru2

    Question on the Plants Watering Watcher circuit

    Hi Oli, I am glad that your project works well. Is your soil different from mine? I have designed the circuit so that very wet soil that is only 47 ohms (with about 50mm of the probes in the soil and spaced 0.7" apart) turns off the LED. Very dry soil that is 100K or more makes the LED flash...
  10. audioguru2

    Mysterious Resistor?

    Hi Shahriar, I don't know why your original circuit doesn't work without Rx as a 1M resistor. The circuit is biased properly (with the non-inverting input connected to Mid) and its output voltage is correct. The opamp should work fine without Rx. As you measured, Rx doesn't seem to do anything...
  11. audioguru2

    inverter

    No link, no spec's, no price and not even any pictures. Maybe it is powered by watch batteries and they don't want to admit that a 1W load overloads it!
  12. audioguru2

    inverter

    Hmmmmm, No output power rating?
  13. audioguru2

    Stupid op-amp question

    Hi Darrin, The minimum output voltage of an LM324 opamp will be pulled down to about 10mVDC or less with a 2K load to ground. It is spec'd to be able to drive a 2K load nearly as high as it can drive a 10K load. With a 13V supply the IC and resistor will stay cool and you can use a 1.2K resistor...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Marek, Welcome to our forum. Let us fix your jumpy power supply project. First, some questions: 1) What are the output voltage and current or VA ratings of your transformer? 2) Did you build it like the original plans, or did you make any modifications that we discussed here? 3) Did you...
  15. audioguru2

    Stupid op-amp question

    Hi Darrin, Didn't I explain it well? Your LM34 sensor needs a high impedance load, like an opamp voltage follower, which can feed the 10K resistor of your diff amp. How much temperature accuracy do you need? The LM34 has an error, your diff amp resistors have error, the offset voltage of a...
  16. audioguru2

    Stupid op-amp question

    Hi GPG, It is all in the datasheet of the LM34 temp sensor that was linked earlier: http://www.national.com/ds/LM/LM34.pdf but they sure don't explain it very well. Their block diagram shows an emitter-follower output (I hate emitter followers because of their unequal pull-up and pull-down...
  17. audioguru2

    Mysterious Resistor?

    Hi Shahriar, Of course R4 and R5 are needed in your new circuit to provide a ground (mid) reference voltage for the non-inverting opamps. Without them, the output voltage of the opamps could be anywhere. Your other original circuit had an inverting opamp that was already Mid (ground) referenced...
  18. audioguru2

    Stupid op-amp question

    Hi GPG, 1) The gain of this diff amp depends on what you call its input. The entire circuit has a differential gain from between the inputs, V1 and V2, of exactly 22 (not 23). An input from the inverting input, V1, to ground has a gain of exactly 22. An input from the non-inverting input, V2...
  19. audioguru2

    Mysterious Resistor?

    Hi Shariar, Hey, isn't this the same IC that got hot in your other post? The one that was trying to operate without a negative supply? Then was when its input protection diode got fried. Injecting some mains hum with your finger was probably too much voltage for the input without a protection...
  20. audioguru2

    Mysterious Resistor?

    MP, All opamp circuits do not need an input coupling capacitor. Try amplifying a small DC voltage through a coupling cap. It won't work! Why are you talking about Cx? Of course it is needed. Shahriar was asking why he had to modify the circuit by adding Rx, to adjust the messed-up offset...
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