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  1. dorke

    Transistor as a constant current source to variable DC input

    The most important parameter is missing. What is the LED current needed?
  2. dorke

    Replacement Transistor

    You can get it here . In order for it to be the same, you need to buy the K grade( from YCK) The big question is why did it fail ...
  3. dorke

    FSK Demodulator using a PLL

    Javier , This can be very helpful: FSK Modulation and Demodulation using CD74HC4046A
  4. dorke

    Question in 555 timer circuit

    Your understanding is correct. The inputs of the 2 comparators inside the 555 have very high resistance, i.e no current flows into pins 2 and 6 (blue arrows). The capacitor charging current is the red arrow.
  5. dorke

    Checking Battery rating

    Bob, I think you should see this video...
  6. dorke

    How to turn off a LED with 3.7v

    Well, You can actually use any diode(have you got any?). From Ebay, buy 100PCS of 1N4007 they sell for less than 1$ (same price as 10PCS). You will have a general purpose rectifier diode for future use.
  7. dorke

    D Flip Flop Question

    Your welcome.:cool: Another issue is decoupling capacitors. From your photo I see you don't use any. It is a good practice to use 0.1uF ceramic caps on the VCC and GND pins, use one with shortest leads possible for the 74LS74. And, better use decoupling on the voltage regulator as well...
  8. dorke

    reducing 5V to 4v or 4.2v MAX

    Heat generation is power dissipation related. Using 2 *1N5822 will make each diode less hot than a single 1N5408. 1N5408- @3A the max voltage drop is 1V (that is 3W on a single diode). 1N5822 -@3A the max voltage drop is 0.525V (that is 1.6W on a single diode). I think the 2 1N5822 diodes...
  9. dorke

    reducing 5V to 4v or 4.2v MAX

    John, 1.If possible ,the best way is to set the voltage of the "12v to 5V 3A converter" internaly. Many of them have that capability with a dedicated trimmer on them. 2.The voltage drop of a 1N5822 for 10mA-3A would be 0.25-0.525V. If you take that approach use 2 diodes in series.
  10. dorke

    Need Help Creating a digital display that counts and saves numbers

    Oran, When the battery is totally empty or being replaced(not simply "on/off"). Is it important for the "count" to be saved and reused or can it be discarded?
  11. dorke

    How to turn off a LED with 3.7v

    Nick, Here is the magic you asked for... ;) This little circuit simply popped in my mind(thanks for stimulating it). All you need is add a little diode... As you say the LED is 1.2V, while the diode is 0.7V... that is all it takes.
  12. dorke

    D Flip Flop Question

    Here is a simple and common switch de-bouncing circuit:
  13. dorke

    Questions about Oscilloscope

    What is the scope you have(brand and model)?
  14. dorke

    Simple Button and Ethernet Interface Schematic

    Well, That depends of is it you like to achieve... The way you connected it D1-D4 have logic level "0" normally. pressing the push-button of an input will change that to logic "1" (as long as the button is pressed). Don't try to count "events" with that connection !!! ;)
  15. dorke

    Need Help Creating a digital display that counts and saves numbers

    You need to provide more info( " device requirements "). "...that counts and saves numbers, a digit can be added by pressing a button on the top..." Counts numbers?- what numbers? Saves?- where ? a digit can be added ?- not clear what you mean. there are lot more things like : What is the power...
  16. dorke

    Questions about Oscilloscope

    1. "periodic signal" and "repetitive signal" are the same thing. "repetitive signal changes over time" is a figure of speech meaning: "the signal is mostly repetitive with small changes over time". The correct term is the Jitter and Wander of the signal. 2. Is your scope in the "Auto" mode?
  17. dorke

    Energy Lost Due To Friction

    I wonder, what does that friction issue have to do with Electronics?o_O maybe something like this: A capacitor C1 charged to an initial voltage e connects to another capacitor C2 through wire resistance R.
  18. dorke

    Samsung LED TV UN39FH5000F screen issues

    Sound like it is a worming related problem. It could be the T-con or the Main-board or the flat connectors, even the PS-board. The TV should have a "self test mode" to help you troubleshot(need manual to find out how about the service menu ). How skilled are you in electronics repair ?
  19. dorke

    Temperature Control SSR Help

    No such thing as a silly question here...;) Can you make a drawing of the exact way you connected the devices? possibly add clear photos as well.
  20. dorke

    D Flip Flop Question

    A floating input with LS logic is possible and yields a "logic '1' interpretation" by the IC. In general it is not recommended,better use a proper pull up resistor (1k ohm). The 74 is a positive edge triggered DFF:a rise in the CLK signal from '0' to '1' will cause Q=D. Using a "mechanical...
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