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  1. BobK

    How does an IR pen scanner work? Need to know now, ie before Christmas

    I WILL say something about your fear of EMF. You are doing your children more damage by promoting this kind of irrational fear that is contradicted by research than they would ever suffer from EMF. Bob
  2. BobK

    I need a motor setup so that it will turn ~1lb of material once every 24 hours

    It the wheel is balanced it should not take any significant torque to rotate it. I think a hefty clock movement would do the trick since they are able to move a hand, which is anything but balanced. Bob
  3. BobK

    help with adjustable power supply

    If your breadboard is like the one I use, the top and bottom rails do not connect all the way across. The middle gap is open and needs a jumper across it to connect the rail all the way across. Bob
  4. BobK

    Alternative to multiple shift registers?

    Look up multiplexing 7 segment displays. Bob
  5. BobK

    LED vs Diodes

    An LED is a diode. Connected to AC it will simply light during the positive half of the cycle and not during the negative half. However, this is not the full story. There is also a max reverse voltage that it can take without being destroyed. Apparently, the resistor you have in there is...
  6. BobK

    Can someone tell me how to read this Trifield Broadband Meter?

    Any reading other than zero indicates the presence of ghosts. :D Bob
  7. BobK

    Relay or similar between 5v dc - 240v ac.

    I find literally hundreds of relays with a 5V coil and 240V AC contacts on Mouser.com There are also solid state releays, and raw opto-isolated triac ICs that would do the job. Bob
  8. BobK

    need help on the dsPIC33FJ64GP802

    You do need to connect AVss and Avdd and all Vss and Vdd pins in order to program dsPIC's. Also you should have a 100nF capacitor near each pair. Looik at the "Minimum Connections" section of the datasheet. Bob
  9. BobK

    Running a LED off a capacitor

    Well, I was thinking of a lot more then 8 hours when you said and "extended period of time". So I think it is feasible to use supercapacitors for this purpose. You want to run the LED off a current-controlled DC-DC converter. The converter should be of the buck-boost topology so that it...
  10. BobK

    Running a LED off a capacitor

    Of course I could be grossly misinterpreting what you mean be an extended period of time. Why don't you tell us: How much current the LED willl draw and How long it needs to run. Bob
  11. BobK

    Running a LED off a capacitor

    You are going to need a lot more than 1F to do what you want. Given a current draw of 5ma, your 1F capacitor will lose 1V every 200 seconds. And the highest voltage I could find on a 1F capacitor was 5.5 volts so 1100 seconds if you could use all the energy in it. If you can find and LED that...
  12. BobK

    Run an mp3 player on a car battery?

    Agree with duke37, you want a deep cycle battery for this purpose. Bob
  13. BobK

    Ideal Transistor for battery discharger

    It is probably oscillating as someone suggested earlier when the voltage gets near the cutoff. This would cause the MOSFET to heat because it would be switching rapidly, faster than it could be fully turned on or off and therefore operating in the linear region. A possible solution is to add...
  14. BobK

    I want to learn

    In the U.S. digikey and mouser are the two big on-line sellers where you can get practically any electronic parts. If you are talking about programming microcontrollers, I am partial to PIC microcontrollers from Microchip, but that is an accident of how I got started. If you want to go the...
  15. BobK

    Run an mp3 player on a car battery?

    The battery rating is amp hours, not amps per hour. A rating of 1 amp hour means that the battery can provide 1 amp for 1 hour or 1/10th A for 10 hours, or 2 amps for 1/2hour. If you expect the music to be heard by someone walking or bicycling by, you will need amplfication, and this will...
  16. BobK

    Project: Wireless transmitters

    To send a single piece of analog data, the simplest way I can think of is to modulate the carrier with a frequency that depends on the data, any transmitter that could send audio could do this. Bob
  17. BobK

    device to tap people's conversation

    Whoops, my previous post was wrong, it is not most states, it is only 12 states where it is illegal to record any conversation without consent of all parties. http://www.callcorder.com/phone-recording-law-america.htm I just happen to live in one of them. Bob
  18. BobK

    device to tap people's conversation

    It the U.S. it is illegal in most states to record your own telephone conversations without informing the other party. It is even illegal to record a conversation in person without informing the other party. I have never quite uderstood who this law is protecting, the only answer I can come up...
  19. BobK

    Ideal Transistor for battery discharger

    You are computing the power dissapated by the transistor wrong. Only the voltage across C to E of the transistor should be used. This better not be 15V! The Vce at saturation for an 2N3055 is listed as 1.1V at 4 amps, and 400ma Ibe. So at 2 amps, the power dissapated should be about 2W...
  20. BobK

    rectifer issues

    Yep. If you draw a diagram you will see that you are just using 2 of the rectifiers in the bridge, and the other two are just connected (internally) back to back, so no current flows through them. Bob
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