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  1. BobK

    Horticultural led's

    LEDs are somewhat more efficient than fluorescents, but the main reason for using LEDs is that you can provide only the wavelengths needed by plants. Since plants appear green, this means that they are reflecting all the green light and absorbing the red and blue light. LED grow lights use...
  2. BobK

    Thermoeletric charging help?

    Look up :Joule Thief". It is a simple boost converter that will run off < 1V. Normally, it powers a LED, but if you replace it with a capacitor and a 5V zener diode, you should be able to get 5V out of it. That said, it would probably take days to charge your phone. Bob
  3. BobK

    Horticultural led's

    If you can find an LED that is 5800 lumens per Watt, don't buy it. The best ones available are in the range of 200 to 300 lumens per Watt. Bob
  4. BobK

    Command Script for Read/Write from USB Stick or SD Card

    A script for what? You need hardware to run a script on. Bob
  5. BobK

    Potentiometer Resistance ?

    Use Ohms law. If the motor is drawing 84mA at 5.5V then it has an effective resistance of V = I R R = V / I = 5.5 / 0.084 = 65.4 Ohms. A 100 Ohm pot would be therefore cut the voltage to the motor by a factor ofL 65.4 / 165.4 = 0.395 That should be enough to slow it down a bit...
  6. BobK

    Any advice or material to help make a box that makes a sound?

    Here is what you need: http://www.ebay.com/itm/USB-sound-voice-recording-module-PUSH-BUTTON-/250803983855?pt=LH_DefaultDomain_0&hash=item3a651515ef I am not reccommending this as I have not experience with it, I am posting it as an examaple. Bob
  7. BobK

    24EP256GP206 Running at 70MIPS

    The PIC24 series has a very flexible PLL that has a multiplier and divider allowing you to generate nearly any frequency you want. Typically you would use a 4 or 8 MHz crystal. Bob
  8. BobK

    LED science fair question

    2.4V and 20mA is just one point on the I/V curve of the LED. It will draw less current at lower voltages and more current at higher voltages. Bob
  9. BobK

    Any smart electricians out there know about power adapters?

    The voltage must match exactly, but the current can be anything higher than required, so a 9V 500mA or 1A adapter would be perfectly fine. Bob
  10. BobK

    Any smart electricians out there know about power adapters?

    Not to mention that a fixed 9V adapter would likely be cheaper. Bob
  11. BobK

    Li ion (2.7v to 4.2v) to regulated 3.3v

    At low discharge rates, most of the battery capacity has been used at 3.5V. So if you can find a 3.3V regulator with a dropout voltage of 0.2V you would be fine. Bob
  12. BobK

    LED Spectrum Analyzer Wall - College Project

    Or, for a lower cost alternative, use a 44-pin dsPIC to run an FFT algorithm and multiplex the 200 LEDs. Bob
  13. BobK

    Project design help needed

    Given your experience, I would look into Arduino and a relay shield for this. If you are not familiar, Arduino is a microcontroller based board and the shield are add ons that you can control with a simple programming language. Bob
  14. BobK

    Full-wave rectifier Smoking Issue

    I guess your sarcasm was too subtle for me. It looked like you meant it. Bob
  15. BobK

    Parallel LED Circuit

    Your calculation is wrong. The voltage across the resistors is not the full voltage, it is the fulll voltage minus the forward drops of the 3 LEDs. So the corrected calcuation is: I = (16.4 - 3*3.2) / 113.3 = 60mA Bob
  16. BobK

    timers

    Yep, this is a job for a micrcontroller with a crystal time base. Bob
  17. BobK

    Full-wave rectifier Smoking Issue

    The irony is about to make my head explode. You do realize that Steve's post was a joke, right? Bob
  18. BobK

    L.E.D battery capacity & charging indicator

    Usually, you would use a chip designed for the specific battery chemistry, so, no, you would be best to decide on that first, also the number of cells matters. You could build a microcontroller based charger then program it only after you know the specifics of the battery. Bob
  19. BobK

    Pic16f877a and lcd

    It can, but whether it makes sense or not depends on what kind of LCD you are talking about. Numeric display, alphanumeric, graphics? If you are talking about multiple graphics LCDs, I would use something like a raspberry PI rather than a microcontroller. Microcontrollers typically have...
  20. BobK

    L.E.D battery capacity & charging indicator

    Charger circuits are very specific to the battery chemistry, and the terminal voltage is really not a good measure of charge state. To get accurate charge state info you have to integrate the current in (during charging) and out (during discharge) with high accuracy. Bob
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