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  1. BobK

    How can i add a LED with the same time as the buzzer where it will be flashing on and off.

    Hi, and welcome to the forum. The easiest way is to get a flashing LED (they come that way) and wire it, with a proper resistor, in parallel with the buzzer. Bob
  2. BobK

    38Hz flash

    If you are using a TSOP 38KHz IR sensor, be aware that it will reject a steady signal. Look at the datasheet carefully. You need to send bursts of 38KHz followed by a silent period. Bob
  3. BobK

    Amps measurement of a battery

    You can't. A battery does not produce a certain current, the current depends on the load that it is driving. If you were to measure the maximum current it could supply, it would depend highly on the state of charge and would decrease rapidly if the battery was fully charged to begin with. Do...
  4. BobK

    LED array, quick question

    Assuming the resistors were chosen to give the same current through the LEDs, the two are equally efficient. Let's say I is the current through the LEDs and V is the voltage of one battery. For the one battery case you can compute the power as follows: P = (2 * I) * V For the two battery...
  5. BobK

    Current variations.

    Yes, you misunderstand. If you are talking about a cell phone charger, say rated at 5V 1A, the voltage is held constant, the current is the maximum current it can put out, and it varies with the load. Bob
  6. BobK

    I need to power a synthesizer with a battery...Please Help :)

    Thanks, glad it worked out for you. And I learned a new word (busking.) Bob
  7. BobK

    Controling DC Fan Speed via Voltage

    Then the answer is no, you cannot reduce the heat produced. You could use a larger potentiometer which would not rise in temperature as much, but the same amount heat would still be produced. This is only one of the reasons a potentiometer (actually a variable resistor) is not the way to do...
  8. BobK

    Pizero or arduino nano?

    45mA is not a small standby current. Microcontrollers can use < 1uA in sleep mode and can run for years off a coin cell if they are sleeping nearly all the time. And they can communicate with SD cards. Bob
  9. BobK

    iPhone 7 headphones connection

    Did it not come with an adapter? From what I have read, there is one included with the iPhone 7. Bob
  10. BobK

    GT-511C3 (ADH TECH) Fingerprint scanner getting hot while connected to pl2303 usb to ttl converter

    Can you point us to a datasheet or at least a description of the fingerprint reader. It sure looks to me like it is a USB client device, which should simply be plugged into a USB host via a standard cable. Bob
  11. BobK

    Buck converter help

    Did you test the voltage under load? It may turn out to be way lower than you think. Bob
  12. BobK

    charging a supercap through a transistor

    With the switch in position 1, the lower side of the capacitor is at ground and the emitter of Q3 is at Vc WRT ground. This will set up a current through Q2 based on Vc and the 15Ω resistor. When the switch is in position 2, and the cap is discharging there will be a drop of Vce of Q3 in...
  13. BobK

    Joining NiCd batteries - conducting glue

    Capacity is not the whole story though. NiCads can produce a lot more current than NiMH cells that may have much higher capacity. I tried replacing the worn out NiCads in a drill / driver with NIMH and, even though they had twice the capacity, they would not run the drill because they could...
  14. BobK

    I need to power a synthesizer with a battery...Please Help :)

    Hey, once you get out there performing, a video would be good! Bob
  15. BobK

    Voltage Drop across NPN BJT C&E?

    Show me how I can calculate that from parameters I find in the datasheet. Bob
  16. BobK

    Voltage Drop across NPN BJT C&E?

    I originally stated that I know that is is Vbe that controls the current, so no, I have never claimed that Ib controls Ic, only that pretending it does produces the correct results. And I have no idea what you are talking about with the class A and class AB example. I would not tell anyone...
  17. BobK

    Voltage Drop across NPN BJT C&E?

    And I started my response in this thread by saying that I do know that it is actually controlled by Vbe, which I have never disputed. So I guess we are in agreement. Bob
  18. BobK

    Voltage Drop across NPN BJT C&E?

    Really? So next time I design a BJT switch I should just apply a stiff 3V to the base with the emitter grounded? I just looked at the PN2222A datasheet. The Vbe at saturation is anywhere from 0.6V to 1.2V. Please tell me what voltage I should put on the base to saturate it. "Some forward...
  19. BobK

    Voltage Drop across NPN BJT C&E?

    I have never seen a datasheet that gives any relationship between Vbe and Ic much less a precise one. So how is trying to control the current by controlling Vbe any easier? We all know that the BJT transistors must be designed to be insensitive to the exact beta. Bob
  20. BobK

    I need to power a synthesizer with a battery...Please Help :)

    I think he is talking about bypassing the wall wart shown, and using a 12V to 5V converter commonly used to charge phones in a car to power the equipment with 5V. Bob
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