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  1. BobK

    Super capacitor phone battery

    The voltage drop is not the problem, a boost converter takes care of that. The problem is that the energy density of supercapacitors is way lower than that of a lithium ion battery. Bob
  2. BobK

    Quiz buzzer

    Put a 10K pot scross the two spaker wires and take the output from the slider, typically the middle connection. Bob
  3. BobK

    3V battery circuit / back lit rocker switches

    Where did you get the 250VAC 20 A specs? These are not listed in the doc you linked. Bob
  4. BobK

    Opamp to pic a/d

    Yes, very low compared ti the 10K max that the PIC specifies. BTW: you are the second person to state here recently that the PIC has an input impedance of 10K. That is incorrect. The datasheet specifies that the output impedance of the driving signal should be less than 10K, which is quite...
  5. BobK

    12v bipolar square wave oscillator

    Interesting solution. Looks like you got a bunch of 741s relabeled as TL072. Bob
  6. BobK

    Opamp to pic a/d

    If you use a 5V rail to rail op amp, Microchip makes some good ones, then you have no worries, the output signal of the opamp will be between 0 and 5V. The PIC inputs also have clamping diodes to Vss and Vdd, so, if you put a resistor, say 1K between the output and PIC you are well protected...
  7. BobK

    Bypassing TV's internal speakers to home-made aux input

    Using coupling capacitors and referencing one side of the bridged output to ground will produce 1/2 the voltage on the output. Going into the same load, they will produce 1/4 of the power. But the ear response is logarithmic. 1/4 of the power will not sound 1/4 as loud. Perhaps not even 1/2...
  8. BobK

    12v bipolar square wave oscillator

    The TL072 has a slew rate of 13V / uSec which should be plenty, i.e. the rise and fall times should be about 1 uSec. Show us the circuit you are using. I doubt that a 555 would be faster than that. Bob
  9. BobK

    T8 - LED shop lighting

    Aren't those two lines contradictory? Bob
  10. BobK

    POE 48vdc to 24-26 vdc

    You are right on the edge of having enough power. A linear converter will not work. the 48V at 15.4W supply can only supply 320 mA and you need 500 mA. A DC to DC converter with efficiency of 80% or more might work. Bob
  11. BobK

    Bypassing TV's internal speakers to home-made aux input

    Huh? He is trying to determine what to connect to the RCA ground terminal, which he added. Bob
  12. BobK

    Can minor fumes from old tubular lead acid batteries cause permanent damage to lungs

    That is a medical question that I am not qualified to answer. But... You might consider replacing them with newer sealed lead acid batteries, which would not emit fumes. Bob
  13. BobK

    DC step down

    However, you still cannot get 160W from a 144W power supply! Assuming you could find a buck converter that was 90% efficient, the most power you could get at 32V would be 129.6 Watts, which equates to just over 4A. Bob
  14. BobK

    Negative voltage

    Voltage is always a difference between two numbers called potentials. Depending on what you (arbitrarily) call zero, a higher potential will be a positive voltage with respect to zero (ground) and a lower potential will be negative. Look at the battery example a couple of posts up. Let's...
  15. BobK

    Measurement device

    Okay. I don't think the potentiometer will give you that kind of accuracy. Bob
  16. BobK

    Bypassing TV's internal speakers to home-made aux input

    Yes, any of those looks fine. One problem I have with TV shows that I watch from BBC is that I swear the enhance the amount of bass and treble, probably because they expect the TVs to have such bad sound. When played on my good sound system, this results in the musical score being outrageously...
  17. BobK

    T8 - LED shop lighting

    One of my more recent replacements was for 40W tubes in my basement workshop (is that T8?) They are great, much brighter than the fluorescent tubes they replaced.
  18. BobK

    Bypassing TV's internal speakers to home-made aux input

    Really? The isolation transformer would work perfectly well, all you have to do is place it between your already wired jacks and the headphones / speakers. It is not going to make your audio any worse than it already is in a cheap TV audio circuit. I had to use one of these between by...
  19. BobK

    Measurement device

    I don't think he is measuring anything. He is using a ruler as an input device, where you press the position on the ruler to input data in 1/32s of inches. However, unless you finger is very skinny, I think 1/32 in accuracy is quite impossible. Bob
  20. BobK

    T8 - LED shop lighting

    On the other hand, I have had most of my house running on LED lighting for years now (some as long as 10) and have never had to replace a bulb yet. Don't know why I am so lucky, others seem to have a different experience. Bob
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