I have set up a 555 Timer circuit on my breadboard following this diagram.555 Timer Circuit

These are the values I use:

R1: 1k

R2: 1k

C: 0.1uf

Vcc: 9V

The only problem is, on pin 5, I have a 0.001uf capacitor. When I connect the circuit, the led I have on pin 3 (normally I have an 8 ohm speaker but I wanted to see if any current was being produced) doesn't light up. Here is a picture of my breadboard. (Sorry for the horrible wiring... And the extremely large image)

Breadboard circuit

The bigger capacitor is 0.1uf and the smaller is 0.001uf. Also, wire colors don't mean a thing (again... sorry).

Thanks in advance for your help.

  • \$\begingroup\$ The resistor or led may not touch each other, I advise you double check your circuit with ohm-meter. \$\endgroup\$ – electro103 Nov 30 '14 at 19:26
  • \$\begingroup\$ Does everything else look correct? \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:28
  • \$\begingroup\$ Did you do what I asked? \$\endgroup\$ – electro103 Nov 30 '14 at 19:32
  • \$\begingroup\$ I don't have an ohmmeter \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:43
  • \$\begingroup\$ I'll buy one and try later, for now, I want to make sure my entire circuit is correct \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:44

I can't see from your picture: does the yellow wire go to pin 8 and the white wire go to pin 7?

The easiest way to troubleshoot this is to use your LED as a test light.

Disconnect the lead that goes from pin 3 and connect it to your +V rail. Does the LED light?

Now take that lead and check pins 4 & 8. Does the LED light?

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  • \$\begingroup\$ I'll try that.. \$\endgroup\$ – irishpatrick Mar 1 '15 at 2:42

The schematic you provided can be found on http://www.robotix.in/tutorials/categ/auto/ic555 where it gives you the calculations for high and low times.

So, high time is \$T = 0.693 \times (R_1 + R_2) \times C\$. Replacing with your component values:

\$T = 0.693 \times 2 \times 10^3 \times 10^{-7} = 0.0001386\$ seconds.

And low time is \$T = 0.693 \times R_2 \times C = 0.693 \times 10^3 \times 10^{-7} = 0.0000693\$ seconds.

The frequency is about 4.8 kHz. You won't see the LED flickering at this frequency, but because high time is double than low time you should see it on all the time but at a lower intensity.

Double check the connections and the LED polarity!

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  • \$\begingroup\$ I just checked the polarity, it all looks correct, do you think that I got a bad 555 and I should try a new one? \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:40

Welcome to EE.SE. Your circuit is reversed polarized, assuming that you have done this: Red line = Vcc/positive Blue line = ground

First the LED, from the image you can see the flat side is connected to positive, flip it around and that should light up.

Second you need to switch pin 8 to positive and pin 1 to negative, then to make sure the 555 doesn't stay in reset put the pin 4 to positive.

Third R1 needs to be connected to positive and the 0.1uf should go to ground.
enter image description here

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  • \$\begingroup\$ I will check my led polarity though \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:31
  • \$\begingroup\$ @irishpatrick I know the colours mean nothing, the large image helps to see the wiring though ;) \$\endgroup\$ – RSM Nov 30 '14 at 19:32
  • \$\begingroup\$ I checked my polarity, the blue line is vcc and red is gnd , I'll fix that \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:34
  • \$\begingroup\$ Ok then if it was like that your LED was origionaly reverse polarized, if you change power around ensure you change IC connections \$\endgroup\$ – RSM Nov 30 '14 at 19:36
  • \$\begingroup\$ How do I make sure that it doesn't stay in reset? \$\endgroup\$ – irishpatrick Nov 30 '14 at 19:41

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