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  1. BobK

    Understanding Buck Converters

    Another way of thinking about the inductor in a buck converter is that it reduces the voltage without loss. The voltage across the inductor is proportional to the rate of change of the current. So If the current is always changing, i.e. the inductor is not saturated, then there is a voltage...
  2. BobK

    Do I understand OpAmps wrong?

    I think you are exceeding the allowable voltage at the inputs. These are normally limited to the supply voltages. Please measure the voltages on the + and - input pins. Bob
  3. BobK

    Microcontroller beginner

    As far as I can tell, that is the only through-hole ARM core available. If you are choosing it because it is through-hole, you have no where to go when you need more pins (which you will). I would think PIC or AVR would be a better starting point. Is there a reason you want an ARM core or...
  4. BobK

    how to find resistor value ?

    The version I heard from my physics teacher was much more politically incorrect. Hint: The first one was the actual color. Bob
  5. BobK

    what should consider when design motor speed controller

    The trouble with that chip is, that it loses between 1.2 and 1.8V on each side, so 2.4 to 3.6V total. A bridge made of 4 MOSFETs would cost less and perform better. I am starting a robot project next week, and I have chosen these...
  6. BobK

    Two inputs simultaneously

    Assuming the outputs are capable of driving and LED, you can do it with one transistor:
  7. BobK

    Power source help

    That might be because you wired it incorrectly. Some power sockets are designed to short two contacts then a plug is inserted. Bob
  8. BobK

    DAC and ADC Simutaneous Testing

    It sounds like you are saying the line called "send out DAC data" is sending all 300 values in sequence. Is that the case? Bob
  9. BobK

    temperature measurement

    I think some of the 16-bit PICs have a differential mode for ADC. But, that really is not necessary. Look at your Wheatstone bridge. One side is always going to read a fixed voltage, so what is the sense of measuring it? The bridge is good when you want a differential signal, but that is...
  10. BobK

    how to find resistor value ?

    Yes, just go to your supermarket and dump them all in the Ohm counter. It will count up all the Ohms, and give you back a resistor that has 95% of the Ohms you put in. Bob
  11. BobK

    Find Fault in my built amplifier

    That resistor should have limited the current to about 30mA which would probably not be enough to blow anything out. Had you connected the other leg, it would have been a problem. I take it the amp was wired incorrectly from the start, so the amp was never working, right? For starters, I...
  12. BobK

    Fuel Gauge converted to Volt Meter

    I think you should determine how the meter responds to a voltage. I assume that if you put 12V on it, you will get full. What happens at lower voltages, with no resistor. Bob
  13. BobK

    Resistor & Capacitor Identification

    The first band is yellow, no? So 47.5 Bob
  14. BobK

    Fuel Gauge converted to Volt Meter

    Hey, I do my best work when I am asleep! :) Bob
  15. BobK

    Fuel Gauge converted to Volt Meter

    Thanks, Adam. I tried to do this right after you asked, and I kept getting the wrong answer. I woke up at 3 AM thinking about it, so I had to get up and work it out. Turns out I was flipping a sign before and once I fixed this, the example worked. Bob
  16. BobK

    Fuel Gauge converted to Volt Meter

    Start with the differential amp configuration of an opamp. The equation for a differential amp is: Vout = (Vin+ - Vin-) * g So if you want to convert the range (V1 to V2) to the range (V3 to V4), put in the two endpoints to the equation above to get two equations: Because the voltage range...
  17. BobK

    12V - 36V 30mA Converter using LT1173

    Just curious, what does the simulation show? Bob
  18. BobK

    Power source help

    I always think of the analogy to height and mass. You have 1 Kg mass and your raise it 10 m. That takes a specific amount of energy. When you drop it, it gives up the same amount of energy. The difference in height x the mass is called potential energy. The difference in height is called a...
  19. BobK

    12V - 36V 30mA Converter using LT1173

    I see what you did there. Bob
  20. BobK

    Fuel Gauge converted to Volt Meter

    You don't need to do that. A single op amp can change any voltage range into any other voltage range, linearly. That and a single resistor would do it. Bob
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