problems with 555 timer.

Thanks for your input.. I'm new to google groups and just joined the first one that sounded like it made sense.... didn't notice the basics one.

I build the figure 5 circuit about 10 times and each time nothing happens. My previous post has a link to the photo.

This is driving me nuts. I just want to make an LED blink.

-sam

My tongue, and LEDs.

-sam

A couple of tests:

If i remove pin 1, the red LED lights up.

I put pin 1 back, then added the following to the end of the board:

• 100Ohm .. yellow LED -

Nothing happens... meaning that it's getting shorted somewhere, I guess.

When I removed pin 8. Both the Red and Yellow LEDs light up.

-sam

The LEDs appear to be in backwards -- if they're in correctly and you pull the wire going to pin 3 they should both light up. If they light up the way they are now then you have your battery in backwards.

Get a cheap volt meter! At this rate it'll pay for itself in timer chips, and you'll have a voltmeter when you're done.

Ok, the bottom one was in backwards. Whoops. So I fixed that.

Then I pulled the wire to pin 3 and nothing happened. After that i pulled the wire going to pin 1 and they both lit up. Then I put pin 1 back, and pulled the wire going to pin 8 and they both lit up.

Still, this thing isnt working.

In message , dated Mon, 14 Aug 2006, snipped-for-privacy@gmail.com writes

Your layout is very untidy, and it's difficult to see whether there is an error. There may be none, but the 555 is dead.

I'll try to make a better layout and put a picture on my web site.

I always put the IC in so that pin 1 is at the lower left. OK, I can invert your picture.

A capacitor marked '561' is a 560 pF capacitor. The '1' means 'one zero'.

Buy a cheap digital multimeter from Maplin. Will save you hours of frustration.

Are those LEDs the wrong way round ?

Graham

I've seen some very cheap DMMs on ebay btw ( and bought one as a cheapy backup ) .

Graham

I hope this photo is really the circuit you are trying to trouble shoot.

If you are trying to build the circuit in figure 5.

Please have someone else re-check your wiring and post another pic.

Hint: What does pin 4 do?

Look more closely.

It appears that both LED's are backwards -- the side with the flat spot should point toward the neg rail on both LED's. Pin 4 is going to the wrong voltage rail. The electrolytic cap is backwards. Looks like R3 and R4 are 100 ohms rather than 220 -- that will drive the LED's pretty hard (about 75 mA).

Interesting schematic of the 555 chip itself.

Probably copyrighted because it has several mistakes ;-)

...Jim Thompson

In message , dated Mon, 14 Aug 2006, snipped-for-privacy@gmail.com writes

I've put a picture of my build of Figure 5 on my web site

with a link from 'Current Topics'.

I used a 10 uF capacitor from pin 2 to earth (negative battery)[1] so as to slow down the blink rate. With a smaller value, the green LED may flash so briefly that you don't easily see it.

With this circuit, you can't get the two LEDs to flash for equal times. There are ways of fixing that.

The common rail may not be the same as 'negative battery' - it isn't in most op-amp circuits.

Did you ever get this thing working ?

What did you find was wrong with it ?

Please post another pic.

I don't think anyone mentioned this: Your electrolytic capacitor is installed backwards. The big black stripe should be the negative side.

As others have noted, your LEDs are backwards, too. And your

It is *best* to start with a circuit that is 100% identical to what is in figure 5, even if it takes some time to get the parts. As someone pointed out, the 100 ohm resistors will allow about 75 mA through the LEDs - that's way too much, and may damage them. Once you get it working with

So here's your shopping list:

Ed