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  1. BobK

    Help on blown transistor please

    If all it is doing is running an indicator, replace it with an LED and any general purpose NPN will do. In fact, if you use a high brightness LED you might be able to drive it directly from the output. Bob
  2. BobK

    Problem with positive pre-sensitized board exposure solved

    I had been using the positive presensitized PCBs for a while, using a kit I got from MG Chemicals, which included what is basically an under kitchen counter fluorescent light for exposure in a light box I made. I was getting really good results with a 12 minute exposure. Then, after not using...
  3. BobK

    Charge time for lithium batteries

    Your battery pack shows 1300 mAh capacity and a charge rate of 100 mA. If charging was 100% efficient it would take 13 hours. So, probably about 15 hours. Bob
  4. BobK

    250v switch

    I take back my reply. It is okay for switching the primary. Bob
  5. BobK

    250v switch

    No. DC current rating of switches is lower than the AC rating. Bob
  6. BobK

    Weather Station

    Are you sure you have that diagram right? It is odd. It give 2 separate 3V supplies with a common ground, not a split supply like @Bluejets said. Can't think of any reason they would do that. Bob
  7. BobK

    Teaching people to solder

    I know that, I am tweaking you! Here in the Boston area, we also do not pronounce "r"s (unless there is none and the word ends in an "a" sound) So it's "soddah" here in Worcester ("woosta") Massachusetts, get the "idear?" Bob
  8. BobK

    Teaching people to solder

    Did you manage to teach them not to pronounce the "l"? Bob
  9. BobK

    bridge 2 channels into one

    The cheap Chinese amplifier might already be bridged (class D) in which case the answer is no. If it is class AB, it might be possible, but you would have to invert the signal to one of the amps, which might be possible by a circuit modification or an external inverting gain 1 amp. Probably...
  10. BobK

    Light dimmer

    @Steve - I was thinking of the same explanation, but I saw your question and tried it out. It does happen on my dining room light, which has all LED bulbs, so filament resistance is not the answer. Bob
  11. BobK

    Converting an existing amplifier into a subwoofer amp

    Yes, the article goes on and on about how bad push-pull (class AB) amps are, and his solution is a push-pull circuit! Bob
  12. BobK

    Proximity sensor linked to cell phone?

    The stregth of the signal is affected by all kinds of things in the environment. In a controlled environment, such as in the middle of a huge flat empty parking lot, with the orientation of the two devices strictly controlled, it could work. In the real world, not so much. Both the...
  13. BobK

    Proximity sensor linked to cell phone?

    If I understand you, here is what you want. You have a cell phone. You have another object which holds some kind of sensor that can communicate with the cell phone. When that object is further than 2 meters from the cell phone, an alarm is activated on the cell phone. If this is not...
  14. BobK

    Denon UD_M30

    That was how I won over the lovely wife Morticia! Ah, I still remember that first date at the blood bank... What do you mean, “that's gross?” Bob
  15. BobK

    Drawing maximum amount of current from power supply ?

    :eek: Bob
  16. BobK

    Proximity sensor linked to cell phone?

    People ask for this sort of thing all the time. There answer is that there is no simple way to detect how far two objects are apart. If you want an accuracy of about 30 feet, a GPS could do it. Bob
  17. BobK

    hi fellow hobbyists.. ?about sensors

    An infrared LED would have Vf in that general range. Bob
  18. BobK

    ADC Values?

    Probably because they don't want to put more than 0.32V across the resistor. Think of how many Watts it would dissipate if you were to put 3.3V across a 1Ω resistor, compared to what it would be with 0.32V. (hint P = V^2 / R) Using 1/10 th of the range gives you roughly 1% accuracy while...
  19. BobK

    Drawing maximum amount of current from power supply ?

    Stop, now, before you hurt yourself. Connecting random things to a power supply capable of 288 Watts is dangerous! You are lucky you have not yet created an explosion, or at least a fire. Bob
  20. BobK

    Test Plan

    If you are needing to create a test plan, I presume that this is for a job, right? If so, ask for a copy of a test plan they have used for some other device to get an idea of what needs to be included. Bob
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