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  1. BobK

    Need advice for 100 watt led power supply

    Hmm. That is barely better than a 100W incandescent (1700 lumens.) Bob
  2. BobK

    Need advice for 100 watt led power supply

    You just need to choose a supply that can supply a little more than the forward voltage and the current desired. Operating them in constant current mode is the right way to go. By the way, how many lumens do these put out? At 100W they ought to be seriously bright! Let me guess, grow...
  3. BobK

    Beginner question: diodes?

    Or, your could connect the variable resistor to a current source and then run the voltage across it into an anlog input on the raspberry pi and control the volume in software... Bob
  4. BobK

    Help Needed: Building 18V Power Supply for Power Tools

    Big heatsink + cooling fan I think. Oh, and I keep forgetting to mention. You are going to have to use a capacitor with a higher voltage rating. 35V would be good. Bob
  5. BobK

    Help Needed: Building 18V Power Supply for Power Tools

    The problem is that you have to disspate over 200W to drop the voltage from 29 to 18V. This will produce a lot of head (think of 2 100W light bulbs, that much heat). It doesn't matter whether you use resistors, diodes, or a linear regulator, all will have to dissapate the same amount of power...
  6. BobK

    Need help with LED Circuit

    Not as simple a circuit as you think. For one thing, a pushbutton will turn on and off multiple times each time you press it. This is known as "bounce" and you need a debouncing circuit. Next, you need some memory. The circuit has to remember how many times the button has been pushed...
  7. BobK

    Help Needed: Building 18V Power Supply for Power Tools

    Do the tools really take 20A? That seems quite high for battery powered tools. Dropping the voltage by resistor or linear regulator would not be good. To go from 29 to 18V at 20A would be 210 Watts. Your only hope would be a switching regulator, but finding (or building) one that can...
  8. BobK

    3V,7.7mA supply from 12V battery

    Hi Olin, We were both posting actively on Microchip forum for a while. Bob
  9. BobK

    Help:Replace manual switch with mcu controlled device.

    Harald, I was just questioning his two statements. 1. The input draws not current. 2. Connecting it through a resistor does not work. What I was headed for, was to verify the connecting it through a resistor does work , then use an NPN to pull it down to turn off, controlled by the...
  10. BobK

    using MOSFET to drive sensor signal to PIC

    MOSFET gates draw current for a short time when they are switched. They act like a capacitor. Some high powered MOSFETs can draw gate current measured in Amps (and require such current in order to switch quickly) The pulldown resistor is needed to ensure that the MOSFET is off when there is...
  11. BobK

    Voltage increase with arduino?

    You might find this helpful. I am not endorsing this, as I have not used it, but the idea is sound. http://www.inmojo.com/store/inmojo-market/item/digital-ac-dimmer-module/ Bob
  12. BobK

    3V,7.7mA supply from 12V battery

    Hey Olin, Welcome to the forum! Haven't seen you in a while :) Bob
  13. BobK

    Help:Replace manual switch with mcu controlled device.

    If it draws no current, a resistor must work! What value were you using? Bob
  14. BobK

    using MOSFET to drive sensor signal to PIC

    Look at circuit 1 again, the source does go to ground. And the 10K resistor is from ground to the pickup. The diode is to block negative pulses, and the resistor is to limit current to the gate, which is probably not necessary. Bob
  15. BobK

    12v LED Strobe Controller

    Too busy right now, but retirement is coming up soon. bob
  16. BobK

    12v LED Strobe Controller

    Sounds like a business opportunity to me. Bob
  17. BobK

    120 LED indication device

    I presume the 74HCT574s are used as shift registers by connecting each Q out ot the next D in. But a 74HCT575 would be better, as it has fewer pins, is already set up as a shift register and has a seperate output latch so that you can switch all 120 outputs at the same time, vs. getting...
  18. BobK

    Altoids Phone Charger

    Just curious, how much of a charge were you able to get from 1 9V battery? I would think a full charge would be impossible. Bob
  19. BobK

    Signal help

    +1 I vote that Steve does not get the free ice cream at the next top-secret world domination conspiracy meeting. Bob
  20. BobK

    Signal help

    Steve, Shhhhh.. You are putting us all in danger! Bob
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