Feedback on how this works?

Sep 12, 2009
4
Hello, I'm relatively knew to the world of electronics and totally new to this forum. I have a VERY simple LED blinker circuit diagram but I cant post it here because I don't have 10 posts yet. If you search for my user name (RaleTheBlade) on Photobucket it should guide you to my very small recently uploaded album of three pictures regarding this circuit.

I'm just wondering if someone could take the time to explain it to me a bit better. What I don't understand is the gates. When the circuit has power, are they both open at the same time initially? How are they closed by the circuit? How is the capacitor charged and then discharged to illuminate the LED? I understand how the NOR gates work, ground to the both gate pins and the gate is closed (allows current through), more than a certain voltage to at least one of the pins and its open (no current flow.) But I don't understand how they work together in this circuit to make the LED blink.

I was guessing that the 6 volts from pin 4 of the 4001 IC would charge the capacitor, but I cant really see how pin 3 on the IC comes into play...

Thanks

Last edited:

amdNRA

Sep 3, 2009
50
Some points: Basically, the oscillator is formed by creating unstable states and by feeding back around an inverter gate.
The rate of feedback is controlled by the capacitor charge and discharge cycles, ie. RC circuit. Try changing the values and see how the flashing rate is different.
Do not think of gates as having current or no current flow but rather as having at the output either a logic 0 or close to ground potential and 1 or close to the power supply. You are thinking that a gate can only supply current at the output when it is high but this is not the case. Think of an led and dropping resistor hooked up to the positive end of the power supply; now connect the cathode to the output of the gate and the led will come on when the output is 0 or low(or 0 volts). This is called sink; the other way around is called source. This demonstrates that you can draw current in both situations; it all depends. Read about totem pole output configuration at
http://www.physics.mcmaster.ca/phy4d6/Lab/chapter6.htm#Totem
The inputs to the gates are connected together(pins 1-2, 5-6); this makes it an inverter. Meaning if you have a 1 at the input, then this makes a 0 at the output and viceversa. Follow the circuit around by using this
At power up, the cap is discharged. Cap starts to charge and discharge as the gates switch states over and over again.
Hope this helps, Gil.

Sep 12, 2009
4
Awesome, thanks for the help =D Ill take a look at it when I get home from work. I'm trying to learn everything I can from the base most level but the materials I'm using doesn't cover things that way unfortunately. Its more of a "OK, the circuit works? Good, moving on to the next example" kind of book.

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