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I am trying to learn basic oscillator circuits with the help of this link.

But when I connected the components, my LED is not blinking. Rather, it is giving bright light. The components I have used are 1K resistor 18V battery 200uF capacittor 2N2222 transistor and LED with 100 ohm resistance.

Here is the circuit:

enter image description here


From above page:

enter image description here

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  • \$\begingroup\$ Are you sure you connected the transistor exactly as in the diagram? I assume you are using the first diagram? What voltages are you measuring across the capacitor and the LED? I have built the circuit myself couple times, it works as intended. 18V may be a bit on the high side, maybe increase the resistor to 1k5. \$\endgroup\$
    – jippie
    Mar 27, 2015 at 20:54
  • \$\begingroup\$ When I measured voltage across capacittor it was 1.5V ,But suddenly led stopped lighting and I am sure led is working properly and there is no loose connection \$\endgroup\$
    – user70739
    Mar 27, 2015 at 21:01
  • \$\begingroup\$ is the voltage increasing from 1V5 up? \$\endgroup\$
    – jippie
    Mar 27, 2015 at 21:16
  • \$\begingroup\$ When disconnected the battery it decreased from 5V,When I reconnected the battery it suddenly jumped to 5V from 1V \$\endgroup\$
    – user70739
    Mar 27, 2015 at 21:25
  • \$\begingroup\$ Hard to troubleshoot without the circuit in front of me. Maybe a good picture will help. \$\endgroup\$
    – jippie
    Mar 27, 2015 at 21:30

3 Answers 3

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IF the pinout is the same as the

OR this

then you have the transistor C & E reversed.

That alone would completely prevent the circuit working as intended.


Your photo is reasonably well taken (although you could have arranged it so that ALL connections were unambiguously visible) BUT it is very poorly presented.

Just by cropping it to show only the relevant part you give people a much better idea of what you are doing. Rotating it to be "square" on is a bonus.
If you cannot do that look at fabulous free Irfanview - from here

Thusly:

enter image description here


Adding a few labels to show where eg power connects.
Showing where you THINK C & E are, may help people see that they are not.

enter image description here


Finally [ :-) ], your enthusiasm in investigating such an unusual and interesting aspect of electronics is commendable, but your construction methods are unnecessarily untidy and it will take you LESS effort and give better results if you improve them. More could be said, but a few suggestions:

  • The transistor could have had all 3 leads plugged into the breadboard with the base not connected.

  • Twisting the capacitor wires together is not advisable.

  • Even if you do not cut the leads, bending resistor leads square so they sit flat and with an obvious orientation to where you are connecting you will be better able to see what you have done and to be sure it is what you intended.

  • Connecting links for the power supply or battery to the horizontal "power rails" lets people see where power comes from ad allows you to know what is and connected to power and to disconnect and connect things easily and rapidly.


Note:

Circuit operation is somewhat component critical.
Note their comment: "If the resistor that charges the capacitor is too low in value (or if the power supply voltage is too high), the current through the transistor will not become low enough for the transistor to turn off. If the resistor that charges the capacitor is too high in value (or the power supply voltage is too low), the capacitor will not be able to charge to a high enough voltage to enable the transistor to turn on. This is because the transistor draws as small amount of current before switching on."

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Try to be just a little less messy with your circuits and don't trust protoboards, mainly old and dirty ones. Remove - at all - the 100 ohm resistor. Use a higher value for the 1k resistor 10k or 47k maybe. Do not let the base touch ANYTHING, even plastic, if possible, rip it off. Try reversing C and E. Check your capacitor leakage. Use a larger and good brand capacitor. Try another transistor, this one may be fried up or leaky.

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I tried the same circuit with 2N2222 (not 2N2222A) it did not work. Then I measured the voltage across the capapacitor, it was not rising more than 8.8 volts with source voltage at 14 volts. I disconnected emitter lead and voltage went up, that means the voltage leaked through transistor and did not allow to rise to expected level across the capacitor. I think if a better transistor is used it may work, try better transistors. I tried with 2N5551 NPN and TIP132 power transistor, even though voltage across capacitor went up but it did not go into oscillation.

If you want to see one working watch this video.

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