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  1. BobK

    Can this be done?

    A constant current source does what you asking, only better, it reduces the resistance continuously, instead of a step. http://en.wikipedia.org/wiki/Current_source Check out the simple JFET circuit. Bob
  2. BobK

    Calculate the power supply for 10 LED Screen's

    1. If the lcd is rated for 1.2A at 19V, it might draw more current than that at 19.5V. 2. You have to multiply the current by 10 for th 10 displays, so 12A is required. So your laptop supply is not sufficient. Bon
  3. BobK

    A bit tricky..

    You cannot measiure a resistance without sending current thorugh it. If the resistance it already connected to the instrument cluster, it is probably sending current through the resistor. In this case, most likely one of the wires will be at ground and the other will show a different voltage...
  4. BobK

    Linear voltage regulator problem lm338

    Hmm. I gave that answer way back, but you insisted that it happened also on an LED that required only 2.5V. Bob
  5. BobK

    Idiot Question About RF burn

    No, such a transformer would respond very poorly to RF frequencies. Bob
  6. BobK

    Linear voltage regulator problem lm338

    Well, that all looks correct. I would suspect the LM338 then, have you tried replacing it? Bob
  7. BobK

    Linear voltage regulator problem lm338

    It looks to me like one side of the LED is connected to pin 1, and the other side is connected to the middle lug on your terminal block, which is connected to nothing. Is it actually connected to ground? Otherwise, the connections look right. Bob
  8. BobK

    Multiple pull-down inputs

    If they are unused inputs, yes. If you expect to use them as seperate inputs, you cannot connect them together. Bob
  9. BobK

    Linear voltage regulator problem lm338

    Is this on a breadboard? How about a photo so we can verify the circuit? Bob
  10. BobK

    Linear voltage regulator problem lm338

    Good point. I think there still must be something wrong with your circuit. The fact that you had a 0.1 Ohm resistance and it acted no different than with a 180 Ohm resistor says that something is not right. Bob
  11. BobK

    Linear voltage regulator problem lm338

    Well, there is your problem. If the LED is going to run at 12V, you need 14V mimimum input to the regulator. What is happening is that the regulator does not have the headroom it needs to regulate. Bob
  12. BobK

    Linear voltage regulator problem lm338

    Yes, a mistake is one of the easiest electronics projects to make! Bob
  13. BobK

    Looking for oscillator and frequency divider schematics

    And your extra flip-flop is the gold standard solutuion. Bob
  14. BobK

    Looking for oscillator and frequency divider schematics

    In the circuit posted, there is a suggestion on how to get a 50% duty cycle by bypassing the feedback reistor wtih another resistor and diode. Bob
  15. BobK

    Resistance-type gauges - controlling without sensors

    Harald, With these estimates, I would say you are about twice as talented as I am :) Bob
  16. BobK

    Knight Rider K.I.T.T. Scanner

    I would take the hardware minimalist approach. Looking at the datasheet, the Vss pin can sink up to 340mA. That would be 17 LEDs lit at 20ma -1 for the mA or two needed by the processor. So, I would keep the number lit LEDs down to 10 at any time (and socket the chip in case of software...
  17. BobK

    Help understanding SNR of a radio reciever

    However, I thought it was kind of cool to pick up a morse code beacon and have it tickle a feedback loop with the guitar. (If indeed that is what was really happening). If could see this worked into an indie rock hit. Bob
  18. BobK

    A bit tricky..

    If it truly is a pure resistance, AND, it is not connected to anything else, you can check for 160 Ohms by simply running a known current through it and testing the voltage with a comparator. If the sensor is already connected to something else, like the instrument cluster or the engine...
  19. BobK

    regulator/ charger design

    I would certainly use switch a switch mode regulator. Unless you are talking about saving a few dollars, they are far more efficient than linear regulators, and do not produce excessive heat. Bob
  20. BobK

    Knight Rider K.I.T.T. Scanner

    Yes, simple on / off status is what I was imagining when I suggested the 40-pin micro. If you want to build that first, you could still use the same micro for fading trails but the programming would get much more complicated. It might be reasonable to start with patterns that are only on / off...
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