# 555 timer ciruit errors

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

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)

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

• The resistor or led may not touch each other, I advise you double check your circuit with ohm-meter. Nov 30, 2014 at 19:26
• Does everything else look correct? Nov 30, 2014 at 19:28
• Did you do what I asked? Nov 30, 2014 at 19:32
• I don't have an ohmmeter Nov 30, 2014 at 19:43
• I'll buy one and try later, for now, I want to make sure my entire circuit is correct Nov 30, 2014 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?

• I'll try that.. Mar 1, 2015 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!

• 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? Nov 30, 2014 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.

• I will check my led polarity though Nov 30, 2014 at 19:31
• @irishpatrick I know the colours mean nothing, the large image helps to see the wiring though ;)
– RSM
Nov 30, 2014 at 19:32
• I checked my polarity, the blue line is vcc and red is gnd , I'll fix that Nov 30, 2014 at 19:34
• Ok then if it was like that your LED was origionaly reverse polarized, if you change power around ensure you change IC connections
– RSM
Nov 30, 2014 at 19:36
• How do I make sure that it doesn't stay in reset? Nov 30, 2014 at 19:41