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  1. BobK

    (90-660) volt into (0-277) volt power supply

    If you have to ask, you should not be doing this. Bob
  2. BobK

    FET switch circuit - is it correct

    Is it? I get half that. See my calculation in the post above. (Of course, either of them is enough to saturate) Bob
  3. BobK

    FET switch circuit - is it correct

    The base to emitter voltage will be roughly 0.7V when Q3 is on. The midpoint of the voltage divider will be 1.17V as you state. The Thevenin equivalent at the base will be a 1.17V source through 7.7K. So the current will be (1.17 - 0.7) / 7.7K = 60uA. With a gain of 100 that will allow 6mA...
  4. BobK

    Aftermarket backup sensor - so LOUD!

    Yep, I am not a time traveler. :D I thought the same on first reading. Bob
  5. BobK

    Aftermarket backup sensor - so LOUD!

    Dave, It is a backup sensor intended to warn the driver when he is about to hit something, not the beeper intended to warn the person he is about to hit. Bob
  6. BobK

    FET switch circuit - is it correct

    I believe you finally have a circuit that will work. Bob
  7. BobK

    FET switch circuit - is it correct

    The 240R + 720R will be drawing over 5mA when the regulator is on, so it is not better than a 7805. Why so much resistance to using the correct part, which is low quiescent current, low dropout regulator with a shutdown function? Right now, you are just adding more and more complexity without...
  8. BobK

    Small Circuit needed for New Product Design - Help!

    Touch screens are not like the LCD you are using. The 1902 does nothing to help drive a touch screen. Touch screens are graphic and require more memory than any of the microcontrollers we have discussed. So I would not get a 1902 if that is where you are headed. A 16-bit PIC is probably more...
  9. BobK

    FET switch circuit - is it correct

    The wire going from Q1 to Q2 needs to be connected to drain of Q1, then I think it might work. With that change, you have a high-side switch + a level shifter. I would still use a modern low-dropout regulator with a shutdown pin to save on battery. The 7805 will use more quiescent current...
  10. BobK

    FET switch circuit - is it correct

    I don't think you can switch the COM terminal on the 7805 that way. I don't know what it will do, but I don't think it would be good. If you are going to use a regulator, why not use one with a shutdown pin? I don't know the part number off the top of my head, but I know they exist. Then you...
  11. BobK

    Potentiometer Burnout

    Did you see / smell any smoke? If not, maybe they did not burn out, but failed mechanically. Bob
  12. BobK

    Audio poweramp TDA2003

    You don't need a preamp. You can change the gain by changing R2. It is set for 10 now. Halve it and you will get a gain of 20. But notice the effect on Rx Cx to maintain the same frequency response. Edit: Actually the gain should be 100 now. That should be more than enough to drive the...
  13. BobK

    What is the best way to tun on and off a pic16f1847 using a microswitch?

    Or you can simply jump to the init code, but you must make certain you do not rely on the default values of any of the special function registers, i.e. init all of them that you are using. Bob
  14. BobK

    Are PICs still being used

    Yep, I bought 10 of these a while ago and have just designed a IR interrupter alarm using 3 of them. It's my favorite little PIC! For this project, you can think of it as a really fancy multiple 555 replacement. Bob
  15. BobK

    How do I decide what size motor to use as a generator?

    You specification is incomplete. You need to know both the current and the voltage. The voltage out of a generator will be high with no load and drop with a load (i.e. current). I am not an expert, but I think the place to start would be to choose a motor whose voltage and current are...
  16. BobK

    Carp fishing electronics

    I always thought the jerking of the rod was supposed to wake you up :) Bob
  17. BobK

    Small Circuit needed for New Product Design - Help!

    Kris: Yes, that looks right. D Hancock: When you say you are going to build 2 prototypes, what are you thinking? Do you mean that you will try each and determine which is better for the production model? The tradeoffs between the two are ease of programming, battery life, physical size...
  18. BobK

    What are the qualifications needed for a Project manager in an engineering firm?

    +1. Project managers are usually people who have already held a technical job at the company for a while and decide to take the "management track". Often, they are the ones that are not the technical stars, those tend to try to stay technical (as I have for 40 years.) I cannot see a company...
  19. BobK

    Solar Panels

    I expect that just connecting the cells as you have them through a diode to the two NiMH batteries in series would make a trickle charger. Measure the current in that configuration with fully discharged cells. I expect it will be 100mA or less which is fine for a trickle charge. Of course it...
  20. BobK

    Ceiling fan speed?

    Care to share what you found? Now I am curious. Bob
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