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  1. BobK

    Floating pins on Microcontroller

    If the operation of the bootloader requires that the serial in pin must be an input (the chip does not), then it must be pulled up or down. So I think we are in agreement. Bob
  2. BobK

    Voltage Drop across NPN BJT C&E?

    You are making some assumptions there about how I calculate bias, which are incorrect. First of all, one does not want a stiff divider, this will lower the input impedance too much. One wants the biasing resistors to be as large as possible while still supplying the required base current...
  3. BobK

    Voltage Drop across NPN BJT C&E?

    Yes, and you cannot see that it does not matter whether it is base current or Vbe that controls the collector current. The two are precisely related, and using a black box model it is equally correct to consider either one controlling the collector current. Bob
  4. BobK

    Voltage Drop across NPN BJT C&E?

    LvW, We all know that it is actually the voltage that controls the collector current. We also know that the voltage controls the base current. Both of these functions are exponential. When you compose them, you get a linear relationship between the base current and the collector current...
  5. BobK

    Floating pins on Microcontroller

    A picaxe is just a normal PIC microcontroller with a bootloader programmed in, same as an Arduino is just a ATMega. Typically, the only pin that is only an input is the reset pin, which must have an external pullup always. On the Microchip forum, a common question is "My program works when...
  6. BobK

    Charging/Discharging circuit for multiple 18650 batteries

    If this is just a prototype needed to demonstrate your software, why do you have such specific requirements for it? And, if there is a Raspberry PI in there and presumably a display of some kind, why not put the battery indicator on the display? Bob
  7. BobK

    Floating pins on Microcontroller

    Microchip says all floating pins should be outputs. If an floating pin is an input and it floats to about 1/2 Vcc it can turn on both of the complementary MOSFETs on and a large current can flow. Bob
  8. BobK

    Charging/Discharging circuit for multiple 18650 batteries

    Hmm. Pretty much all of the power banks I have seen (I own 3 of them) have 4 LEDs to indicate state of charge. Bob
  9. BobK

    Floating pins on Microcontroller

    Not true. Floating input pins are a problem. Make any unused pin an output. Bob
  10. BobK

    Can you help me test a transistor

    Are you sure you are identifying the pins correctly? What kind of transistor? Bob
  11. BobK

    Can you help me test a transistor

    I assume you mean using the diode test function of your multimeter, correct? If so, you should get something like 0.6V on both of those connections. If you get nothing with the base positive and emitter negative, the transistor is bad. Oh, and welcome to E.P. Bob
  12. BobK

    Voltage Drop across NPN BJT C&E?

    Static sensitivity of MOSFETs is easily handled by having a resistor (even 1M) from gate to source. The gate should never be floating. Bob
  13. BobK

    High side MOSFET not working @ IR2104 driver

    The amplitude will not be the same. The HO signal goes above Vcc. That is what the boost circuit is for. Bob
  14. BobK

    Winter down under time

    Well, melting ice (latent heat) sucks up a lot more heat than just heating water. And our power outages tend to be during blizzards. I glued a U shaped piece of sheet metal to the bottom of the Peltier so the flame would not be directly on it. I might have to try this again. Bob
  15. BobK

    My final Electricity Generator Idea?

    Well, you missed the most important part of the opportunity here. Why not use malted barley instead of just sugar, then it will make beer at the same time! Bob Edited: Damn, you beat me too it. I had actually typed this a couple of hours ago and failed to push the button.
  16. BobK

    Charging/Discharging circuit for multiple 18650 batteries

    Take the guts our of the power bank's enclosure? If you can't do that, you can get the controller boards for these things on Ali Baba Express. Bob
  17. BobK

    Charging/Discharging circuit for multiple 18650 batteries

    Just buy a power bank. It already does everything you need. And it is likely cheaper than you can make it. Bob
  18. BobK

    Winter down under time

    I had this same idea, but my plan was to epoxy the Peltier to to bottom of a tin can, and fill the can with snow. I actually made it, but I used a clamp to hold the Peltier to the can while gluing and the pressure destroyed it. I have not tried it again, but I might. It is an intriguing idea...
  19. BobK

    Help with N-Channel Mosfet as a switch at low voltages.

    Yes, that one looks good. They characterize the on resistance at even 1.8V (max 375mΩ) and it can handle 300mA at that gate voltage. Bob
  20. BobK

    Help with N-Channel Mosfet as a switch at low voltages.

    Okay. That's better. It sounds like 3V is not enough to turn the MOSFET on fully. I looked up the datasheet for it, and it is only characterized for on resistance at 4.5V, which means anything below that is undefined. The threshold voltage can be as high as 3V, which means it would only...
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