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  1. BobK

    Appropriate Oscillator

    I agree with Colin. You cannot make it simpler than using a micro. You will get 1% accuracy without a crystal, and much higher with a crystal. With an SMT PIC and MOSFET you could fit this in 1 square cm. Bob
  2. BobK

    Drone (Help/Ideas)

    <post intended for another thread deleted> Bob
  3. BobK

    Need Electronics projects for 8 year old

    I would suggest one of these "101 projects" kits that come with a book telling you how to wire together various circuits. You could both work through the projects together. (or leave him on his own and he will probably get way ahead of you :)) Bob
  4. BobK

    12V to 230(400)V without transformer

    If you are assigned that project, and you are coming here asking us that question, you are in way over your head. What are your qualifications? If you do not have a degree in power engineering, they hired the wrong person. Bob
  5. BobK

    I need a charger for a power bank ...

    Charge it with a wall plug charger with a USB connector output. You need one with at least 2A capacity. Bob
  6. BobK

    Help Identifying a Battery

    Yes, that battery is just two cells put together like your other one. Bob
  7. BobK

    Radio waves question.

    From the AARL handbook: "The mixer, on the other hand, multiplies the instantaneous voltages of the two signals together to produce the output at each point in time" This is as opposed to an audio mixer which adds the two inputs. One way to do AM mixing is the have a variable gain amplifier...
  8. BobK

    Adding Aux input to older car stereo

    If I understand your question correctly, it does not matter which end of the cable the resistors are on. The corresponding lines at both ends are, after all, shorted together (hopefully) Bob
  9. BobK

    Replacing 3.7 lithium ion battery supply with permanent 3.7v power source

    Why not just run it off a power bank? Bob
  10. BobK

    Adding Aux input to older car stereo

    I think the problem might be that the phone is not sensing headphones because the impedance of the input to your car radio is too high. Headphones are typically 32Ω. A line input is typically 10KΩ. If this is the problem, you can correct it by placing a resistor from each channel output to...
  11. BobK

    78L33 regulator

    It will not shorten the life of the regulator as long as it is not overheating. More voltage means more heat. Do you know how much current is drawn? Is there a heat sink on the regulator? Bob
  12. BobK

    Help Identifying a Battery

    Have you tried removing the green wrapper? The cells might be marked underneath. In all likelihood, they are either NiCad or NimH cells. Bob
  13. BobK

    Newb wanting to BT my van

    Even the lovely wife Morticia is frightened by my driving. Bob
  14. BobK

    Supply for 30 LEDs

    Was it a 2 Watt? Bob
  15. BobK

    Circular Lights for Vehicle

    Here is a circuit that popped into my head, and it simulates well. You can add as many stages as you want, alternating between an NPN and PNP. Each stage after the first one connects to the previous stage's collector. Basically each stage is an RC delayed on switch. Once the first is on...
  16. BobK

    Supply for 30 LEDs

    Whoops, too early in the morning for me to do math. Previous post is totally wrong, I forgot to multiply the current by 30 when calculating the resistor. That would be the right resistor for 1 LED not 30. New calculation: (6 - 3.2) = 30 * 0.02 * R 2.8 = 0.6 R 4.66 = R Use a 4.7Ω. Power...
  17. BobK

    Supply for 30 LEDs

    It looks like they are all simply in parallel, which is not good, but it is what you have to work with. Unless you want to try to add a resistor to each one. Assuming 3.2V for the forward voltage, and 20mA current, I calculate a 140Ω resistor. Try a 150Ω. The power rating would be 0.6 *...
  18. BobK

    Supply for 30 LEDs

    If you cannot tell us how the LEDs are connected on the board, we cannot help you (or at best, we can only guess, as Sunnysky has done.) If you cannot determine this yourself, a least post a picture of the back of the LED board that we can see clearly. Bob
  19. BobK

    Trying to make a simple LED blinker but it doesn't work...

    Well, it does exactly what the paragraph you quoted says it will if the voltage is too high, so, I think yes. Why not try 12V. If you have a variable power supply, try that, varying it until you get it to blink. Bob
  20. BobK

    Supply for 30 LEDs

    A 1K resistor will allow no more than 6 mA of current through it from a 6V source. And white LEDs drop around 3.3V themselves, so that means 2.8 mA max through a white LED. Those LEDs are designed to handle at least 20 mA and probably more like 50mA to supply enough light for emergency...
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