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  1. BobK

    Wiring pot as voltage divider across polarities

    You do not need the two regulators. A pot and 2 fixed resistors can be used. Bob
  2. BobK

    Please tell can mobile with 3.7V battery run fine on 3.8V battery ?

    A 3.7V LiIon battery actually charges to 4.2V and discharges to under 3V. The 3.7 is just a nominal value for the average voltage over the discharge cycle. I would like to see a link to two batteries. It is likely the 3.8V is the same type of battery as the 3.7 with the manufacturer using a...
  3. BobK

    Getting additional voltage/power to pc water pump

    If you want to run the pump at lower power use 12V and PWM. Bob
  4. BobK

    Need help with voltage for custom speaker

    According to Wiki, here are the typical capacities of Alkaline batteries; AAA 1200mAH AA 2700mAH C 8000mAH D 12000mAH So a D battery has about 10X the capacity of an AAA. https://en.wikipedia.org/wiki/List_of_battery_sizes Bob
  5. BobK

    voltage output slowly decreasing by .01 why?

    I am with Analog Kid. I think the part is heating up and the reference voltage inside the LM317 is being affected. It will stabilize eventually when it gets to thermal equilibrium. This is well within the expected behavior. Bob
  6. BobK

    Need Help w/ Custom Portable Speaker Schematic

    Here are some alternatives: I used to deal with Madisound years ago when I built my own speakers and they are very knowledgeable and helpful. https://www.madisoundspeakerstore.com/approx-3-fullrange/ Bob
  7. BobK

    What component to use to keep multiple pins high

    You can use either a port extender or a shift register / latch to get 8 outputs from 2. Bob
  8. BobK

    Membrane and/or tactile switches for 3 way hi/low/off settings?

    How is the heater wired? Are there two positive leads, one for low and both activated for high? Assuming it is like that: What you would need is some logic and two relays. The switch would pulse the logic to advance to the next state: off -> low -> high -> off. The switch needs to be...
  9. BobK

    Need Help w/ Custom Portable Speaker Schematic

    Did you read the one review of that speaker? He said it only sounds good up to 2V, which equates to 1/2W in an 8Ω speaker. I think you can do better. Bob
  10. BobK

    LED light driver

    You cannot use a 1000mA constant current driver with 700mA LEDs, it will overdrive them and shorten their life dramatically (though they will be very bright while they last.) You need a driver at 700mA or less. You may have heard that you can use a power supply at the right voltage but with...
  11. BobK

    Drill bits for homemade PCBs?

    At 10000 RPM how long do you think it takes a drill bit to cut through a PCB? I don't force it and there is never any burning, it is just that it really drills that fast. Seeing as I have not broken or worn out any bits over thousands of holes, I think my method works adequately. Bob
  12. BobK

    Drill bits for homemade PCBs?

    Mine (Dremel model 220) moves the drill, so you must not have the same model. Here is a link to the one I have: http://www.amazon.com/Dremel-220-01-Rotary-Tool-Station/dp/B00068P48O/ref=sr_1_1?ie=UTF8&qid=1443464552&sr=8-1&keywords=dremel+220-01+rotary+tool Bob
  13. BobK

    Drill bits for homemade PCBs?

    I use a Dremel tool and an Dremel drill press. I have never broken a bit while drilling. Unlike Martaine, I go really fast, a fraction of a of a second to drill a hole. I use double sided tape to fasten the PCB to a backing block of wood. I set the drill height so that it just barely clears...
  14. BobK

    motor driver 12v .. 2a... fail~

    Welcome to the forum! First of all, that is not a MOSFET, it is a Darlington pair. Second, you need to heat sink it. What is the input voltage? Assuming 15V, which is the minimum needed to get 12V out, the pass transistor will dissipate 5.4 Watts, which would require a hefty heat sink. If...
  15. BobK

    My amplifier!

    It does sound like the power supply has lost its filtering. Check the output with a multimeter in AC mode. It should read in the millivolt region, if it reads volts, the filter capacitor is probably open. Bob
  16. BobK

    PWM led without timer

    What are you trying to achieve with this code? What the code will do is cause a PWM with a duty cycle that increases from 0 to 100% then repeats. If you just want a PWM with a fixed duty cycle, you should have 2 variables, period and duty_cycle, then while(true) { turn_on()...
  17. BobK

    Power supply circuit question - Transformerless good idea? Still pass certification?

    Transformerless power supplies are practical for a few milliwatts, not 360W! And they can only be used when completely enclosed with no part of the circuit exposed since the entire circuit is at line potential and therefore a shock hazard. Bob
  18. BobK

    Multi-input D flip-flop?

    I use only the free tools from Microchip. Bob
  19. BobK

    Multi-input D flip-flop?

    Or you could buy the more powerful 16F1826 direct from Microchip for $1.43, unit quantity. Or the less powerful 16F54, which would be fine for this purpose, at $0.55. The 16F84A is an outdated chip that costs more than newer alternatives. Bob
  20. BobK

    Multi-input D flip-flop?

    It is not at all clear how you want this to act. Here is my guess: You have 3 inputs, 3 clk pins and 1 output. When any clk pin goes high (or whatever), the data from the corresponding input is latched. Is this right? Bob
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