555 timer: why won't this work

I can't see much from your picture. If I assume pin one is in the lower right corner and Vcc is at the bottom it looks like you messed up the pin connections. Look at the pinout from the top of the IC. Tom

Pin 1 is either in the upper right (from the viewer's POV) or the lower left, unless the chip is mounted dead-bug, which it isn't in a protoboard.

Cheers! Rich

I thought it was round the other way ! That would explain a lot !

Graham

Now that's something easy to forget about for us oldtimers, but yes, it can be unclear for the beginner.

Looking from the top:

8 7 6 5 1 2 3 4

And there will be something, a dot or a dimple at the 1/8 side to indicate the orientation. For that matter, I can't recall seeing an DIP IC that didn't have pin 1 on the lower left when the writing was oriented for proper reading.

Michael

You are of course correct, I got distracted by the proto upside down and the power connections crossed. He gets his money back. Tom

It's hard to tell which way round the 555 is, but it looks to me like it's in backwards - the notch needs to be on the right, looking at your photo.

Either way the schematic shows a capacitor from pin 5 to ground, which you don't have. This is merely 'recommended' rather than 'required', but if it aint working you should do everything as recommended. You can start changing stuff *after* it works.

Tim

--- Try this:

1. Unplug the chip and turn the power on. Both LEDs should light up. If they don't, there's probably something wrong with your breadboard.

1. If they _do_ light up, turn off the power, plug in the chip making sure not to plug it in backwards, pull out the wire going to pin 3, and turn the power on. Both LEDs should light up. If they do, reconnect the pin 3 wire. The thing should start flashing.

You _do_ have battery negative connected to the bottom rail (in your picture) and battery positive connected to the top rail, (The one with US PATENT DES NO. 235554 closest to it) no?

-- John Fields Professional Circuit Designer

Pin one needs to be grounded. Pin five must not be grounded. Five can be connected through a capacitor to ground or left open for this application. Bob

snipped-for-privacy@gmail.com wrote in news:1155670084.115533.84170 @h48g2000cwc.googlegroups.com:

It looks like the LED's are in backwards. The flat side of the plastic case is the cathode (negative side)

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! 120,000+ Newsgroups

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

hi sam in the image,if i am not wrong i see resistors as 15kohms and

10kohms. but i can"t see the capacitor's value.i cant find which schematic you've tried on in the site you provided.if you have changed the resistor values,then it would be problem with the frequency.first calculate the frequency and timeperiod .to see the leds glow you will require a minimum 0.5 sec time period. if i am right tell me the reason

if i am not right tell me the reason