555 timer issue - Page 1
Forum section: electronics / beginners

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 06:26:21 am
content: I'm testing a 555 circuit using this schematicshttp://waihung.net/wp-content/uploads/2012/02/circuit-flashing-led-schematic1.gif,the IC I'm using is NE555P (http://www.ti.com/lit/ds/slfs022h/slfs022h.pdf). The problem I'm having is the LED does not flash it stays on. Following is the reading that I took using multimeter when only connecting a battery to Pin 1 (GND) and Pin 8 (+)Pin-----1 - 7.512 - 0.01 (fluctate between 0.01 to 0.02)3 - 6.934 - 0.875 - 5.046 - 07 - 08 - 7.51I'm bit new so I'm attaching the picture of my multimeter with this post to show the kind of multimeter I'm using and also the way I took the reading is turning the knob to 20 and putting the GND to Pin 1 and move around the red cable around the different pins to take the reading (hope I'm doing this the right way in taking the reading).Can anybody help me ?Thanks

author: rexxar
author_rank: Frequent Contributor
timestamp: January 23, 2014, 06:40:34 am
content: You took those measurements without any other components attached? That's not particularly helpful. If you post a picture of your completed circuit, we can figure out what's wrong.

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 06:41:21 am
content: Quote from: rexxar on January 23, 2014, 06:40:34 amYes, I did not attach any components. Will take picture with the component attached

author: Rerouter
author_rank: Super Contributor
timestamp: January 23, 2014, 06:48:49 am
content: are you confident in your measurements, as that is saying your ground point is connected to battery + ?

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 06:51:09 am
content: Quote from: Rerouter on January 23, 2014, 06:48:49 amAccording to datasheet picture Pin 1 is GND and Pin 8 is to positive and that's what I've done to measure it.

author: Rerouter
author_rank: Super Contributor
timestamp: January 23, 2014, 06:57:45 am
content: Quote from: nicksydney on January 23, 2014, 06:26:21 am

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 07:06:49 am
content: Quote from: Rerouter on January 23, 2014, 06:57:45 amWhen I measure it I put the black cable on that pin 1 and red cable on pin 8 and that's the reading I get. Does this mean the IC is not spoilt ?

author: rexxar
author_rank: Frequent Contributor
timestamp: January 23, 2014, 07:13:07 am
content: Quote from: nicksydney on January 23, 2014, 07:06:49 amTo measure the voltage at pin 1, you need to connect your meter's common (black) probe to ground (the battery's negative terminal) and put the red probe on pin 1. Since pin 1 should be connected to ground, you should see 0 volts, as the probes are essentially connected to the same point.

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 07:18:19 am
content: Quote from: rexxar on January 23, 2014, 07:13:07 amTo measure the other pins (2-7) should I do the same for the connecting the black cable to the GND of the battery or I can use pin 1 for GND and red cable to connect to other pins for reading ?

author: rexxar
author_rank: Frequent Contributor
timestamp: January 23, 2014, 07:30:15 am
content: Quote from: nicksydney on January 23, 2014, 07:18:19 amYou can use pin 1 for your ground point, it's usually easier (I think) to probe that way. Like I said, if you've got it hooked up the right way, pin 1 is going to be at ground potential. For all intents and purposes, it's the same as connecting to the negative of the battery.

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 23, 2014, 07:45:20 am
content: Yes, keep your meter's black probe (GND) at the battery minus (-) terminal for measuring the rest of the pins on the IC.BTW, what type of battery are you using to supply the power to this circuit. 7.5 volts may be an exhausted 9 volt battery

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 23, 2014, 08:04:07 am
content: A ground lead attached to the breadboard ground or power supply ground (dotted line) are for your purposes, the same measurement point..

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:41:12 am
content: Hi,Following are measurement readings I took after connecting all the components to breadboard:Pin---1 - 02 - 0.7(*)3 - 2.074 - 3.55 - 2.346 - 1(*)7 - 2.25(*)8 - 3.54When I took measurement for the pin indicated with (*) I noticed that the voltage keep on dropping when the multimeter was attached to the pin - for example pin 2 when I took the measurement it reads at 0.7 and then keep on dropping 0.6, 0.54, 0.4 and so on.The component that I'm using and the connectionPin----1 - GND3 - connect to a LED and the LED to GND4 - connect to to 8 and 4 also connect to GND5 - connect to a C1 and than connect to GND6 - connect to R1 that connect to R2 which connect to Pin 7 and than R2 connect to C2 which connect to GND8 - connect to +R2 - 10kR1 - 1KC1 - written on it 101C2 - 10uF 25vBattery I'm using 9v but when I tested it with multimeter it was reading 7 something volt

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:41:54 am
content: More pics...

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:43:11 am
content: More pics....

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:44:06 am
content: Pics of capacitors I'm using...

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:44:33 am
content: Last pic...

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:46:56 am
content: Even when the battery is connected and if I remove any of the capacitors or resistors the LED still turns on.

author: andtfoot
author_rank: Unknown
timestamp: January 23, 2014, 12:19:55 pm
content: It looks like the breadboard is connected incorrectly.At a glance, you are missing R3, and the way C1 and the other resistors are hooked up looks wrong. One leg of the cap should be going to pin 2 or 6, but it looks like it goes through a resistor first.Edit: Also, it looks like the values of the resistors are wrong.

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 23, 2014, 12:25:54 pm
content: Quote from: nicksydney on January 23, 2014, 11:41:12 amPin 1 is now reading only 3.54 volts and should be your battery voltage. Either you need to replace the 9 volt battery due to exhaustion (can not supply 7 volts to circuit due to high internal resistance in the battery)orthe circuit is wired incorrectly.Next step is to measure directly across the battery terminals while you are powering the circuit. If the voltage present at the battery terminals reads around 3.5 volts, the battery most likely needs to be replaced.

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:03:31 pm
content: After following Joule Thief advice I search for new battery and found 8 x 1.5v so I use that to make 12v battery and this time it's the same the LED still stays on but the reading is bit differentPin----1 - 02 - 9.53 - 9.34 -12.15 - 11.96 - 9.57 - 9.58 - 12.3Previously I notice few pins were dropping in voltage when measuring but now none of the pin give a voltage reading that dropped...it consistenly stays at approximately same level.I tried rearranging the pin to connect 2 to 6 and connect the capacitor from pin 2 to GND and then the resistor from pin 6 to 7 and from pin 7 to GND it still doesn't make any difference

author: tstanford
author_rank: Newbie
timestamp: January 23, 2014, 01:18:45 pm
content: Can't really see the colors on the resistors that well, but here's how i checked color codes when I started.Code:Black Brown Red Orange Yellow Green Blue Violet Gray White0 1 2 3 4 5 6 7 8 9If you get out your calculator or number pad, counting along as you say the colors helps.First stripe - most significant digit (example in a 10,000 ohm resistor it would be the 1, brown)Second stripe - next digit (In a 2700 ohm resistor this would be the 7, violet)Third stripe - the power ten is raised too, or the number of zeros following the first two digits whichever is an easier way to think of. (in a 3300 ohm resistor this would be a 2, red)Fourth stripe - tolerance. (gold silver or missing unless its a precision resistor. gold is +- 5%. silver +-10%, none is +-15%Pneumonic device big boys race our young girls but violet goes wild works (theres a politically incorrect one we used).

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:52:10 pm
content: Did a bit of rearrangement to make it easier to take photos for pin 5-8

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:52:52 pm
content: Another pics

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:53:39 pm
content: Another pics

author: nicksydney
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:54:08 pm
content: Pin 7

author: andtfoot
author_rank: Unknown
timestamp: January 23, 2014, 02:53:17 pm
content: It looks like you have gotten yourself confused a bit.Looking quickly, I can see that the connection for pin 7 is in the wrong spot. It is meant to be between R1 and R2, not where R1 should be connecting to +V.I have just quickly chucked together the circuit that you posted on a breadboard here and it works fine for me (the only change was a 2.2uF capacitor, because I didn't have a 1uF). Here are some photos (sorry for the blurry phone pics):

author: rexxar
author_rank: Frequent Contributor
timestamp: January 23, 2014, 03:14:47 pm
content: Here, maybe this will help.

author: Fluxed Matter
author_rank: Regular Contributor
timestamp: January 23, 2014, 07:07:42 pm
content: Quote from: nicksydney on January 23, 2014, 11:41:12 amCheck your connections again. Pin 4 indicates its connected to pin 8 and GND, and then down below you show pin 8 connected to +V. Basically your shorting power to ground.Use rexxar circuit. It should work for you just fine.

author: nicksydney
author_rank: Regular Contributor
timestamp: January 24, 2014, 06:02:45 am
content: Hi andtfoot,Thanks for the pics. Do you mind taking a clearer one so I can compare with mine as no matter what I do it's still not flashing.CheersQuote from: andtfoot on January 23, 2014, 02:53:17 pm

author: andtfoot
author_rank: Unknown
timestamp: January 24, 2014, 06:28:48 am
content: Quote from: nicksydney on January 24, 2014, 06:02:45 amNo worries. I have taken some more, but instead of filling the thread with giant pictures here is a link to the gallery:andtfoot.smugmug.com/Electronics/555-Timer/36223656_T97vTVIf you hold your mouse cursor over the picture, a bar will popup on the right that allows selection of a larger size.

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 24, 2014, 11:17:45 am
content: this is a little rough but the bird's eye view might be helpful.

author: nicksydney
author_rank: Regular Contributor
timestamp: January 24, 2014, 02:24:51 pm
content: Finally! I've fixed the problem. The issue is got to do with the 555 IC, it's faulty, after changing to another 555 timer with same model it works. The LED is now blinkingThank you to all that has helped me diagnose this problem. Lesson learned here make sure you have backup of any of the components that you are using in case of faulty issue.Here is a video to share with you all the resulthttp://videopasteus.s3.amazonaws.com/videos/21b3f11afd864c1fb0f736baca430dc1.htmlCheers

author: Rigby
author_rank: Super Contributor
timestamp: January 24, 2014, 03:13:53 pm
content: Did your incorrect wiring botch it up at some point?

author: nicksydney
author_rank: Regular Contributor
timestamp: January 24, 2014, 11:23:46 pm
content: I think so I'm not really sure to be frank. It could be that or I use a different power source and didn't pay attention too much about it.Quote from: Rigby on January 24, 2014, 03:13:53 pm

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 25, 2014, 08:11:13 am
content: Good to see everything worked out. The 9 volt battery can still provide a bit more learning opportunity.Devise a simple experiment for battery terminal voltage versus current output and solve for the approximate equivalent series resistance inside the battery itself. You will become familiar with the concept of ESR and discharged batteries.Once the ESR experiment is finished... take the battery apart. Observe the construction and materials used.Tear everything apart before before it leaves your bench for the trash can!