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  1. BobK

    NPN and relay

    So let me see if I have this right. You have access to the + power lead and the non-grounded lead of the relay coil, and the 1.2V signal, but no ground? Bob
  2. BobK

    AC-DC mA adapter changes

    When matching a power supply to a device, the voltage must match, the current must be equal or higher than the device requires. A device will not take more current just because a supply will provide it. So there is no problem in using a 9V 300ma supply in place of a 9V 30ma supply. Do swap...
  3. BobK

    Car Accident App? lol

    I am afraid you are too late: http://en.wikipedia.org/wiki/Advanced_Automatic_Collision_Notification
  4. BobK

    NPN and relay

    Why can't the transistor be between the relay coil and ground? If the signal that you want to drive it is at 1.2V this is the better way to do it. Bob
  5. BobK

    10 watt LED

    In electronics we do a smoke test, in plumbing its the water test. In my last plumbing effort, everything worked fine except the one joint I forgot to solder, so I failed the water test miserably. Bob
  6. BobK

    Cut heatsink tab off 7805

    You can get a 78L05 in T092 if you want to save space. Bob
  7. BobK

    LED powered by AC. Already read the sticky stuff about LEDs

    Did you read Harald Kapp's post? If you do not have an antiparallel diode you are most likely exceeding the peak reverse voltage on the LED. Bob
  8. BobK

    Help with motor comparison

    If the RPMs are the same and the wattage close, I think the motor will likely work. I do not understand your concern about the LEDs. They should not be affected by the motor. Also, why no replacing the LEDs? Bob
  9. BobK

    Rotating Laser Lever Receiver / Detector

    Wow, I guess I was way off on this one :o I guess it makes sense that you could not see the line when it is going by that fast, but the pulse would be plenty strong to be picked up by a photo-diode which would respond much faster than they eye. Always good to learn something new. Bob
  10. BobK

    PIC COMPILERS

    HiTech. Now supplied by Microchip. Bob
  11. BobK

    bridge rectifier help

    Well, I got tired of building power supplies when I was in high school, over 40 years ago. I still have a +- 12 V supply I built back then that uses zener diodes and a pass transistor for each supply and it still works fine. I am a programmer at heart (and by profession) so I spend most of my...
  12. BobK

    Help with motor comparison

    You would also want to know the torque and RPMs of the motors to find a replacement, voltage and wattage is not enough. If the new motor spins twice as fast, you might have some hyper skaters! Bob
  13. BobK

    bridge rectifier help

    Or you could pick up a wall wart that outputs 5V at a flea market for $2 like I do :-)
  14. BobK

    Rotating Laser Lever Receiver / Detector

    I presume you cannot see the laser on a white target in this environment, or else you would not need the detectors / LEDs. If that is the case, it is pretty challenging, because the ambient light is going to overwhelm the detectors. The first thing I would try is putting the detectors at...
  15. BobK

    DIY PCB

    It you are planning on transferring the printed image to the copper clad board, it has to be a laser printer. Ink will not trasfer and would not act as resist if it did. Laser printer toner is essentially a plastic that is melted onto the paper. Bob
  16. BobK

    what happens if emitter-base & base-collector junctions are forward biased with 0.7V?

    Well, you could do it. Just connect the base of and NPN to positive supply and both the emitter and collector to ground. In this case you would be shorting the supply with two parallel diodes, and your transistor will not last long. In a normal configuration, the voltage on the collector is...
  17. BobK

    Digital counter project

    Yeah, I was thinking the same, but I suspect that the LCD's you would find are "bare glass" and the clock chip itself has all the segment driving logic. You would need a large (64-pin) PIC to drive all the segments without and additional driver chip. Bob
  18. BobK

    Digital counter project

    That is going to be challenging. I cannot find any 4 digit displays that are less than about 2 inches wide from mouser or digikey. And LCD numeric displays are not easy to deal with, they have a lead for each segment (32 for 4 digits), and need to driven by an AC signal. I take back my...
  19. BobK

    Digital counter project

    I assume you are doing a study on how many diaper changes a baby requires :) An LCD numeric display can be very small and light and uses very little power. It would not even be a stretch to make this 1" across. Think of the little stick on clocks that are about that size. Are you thinking...
  20. BobK

    Hard Wiring Garage Door Opener (12v)

    It looks to me like the battery contacts are somewhat corroded. Try using some sandpaper on them until they are shiny at the point of contact to the battery. That said. You problem might not be the battery at all, but the switch. Have you tried operating it with the case open and pressing...
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