555 timer - failed at the first hurdle [FIXED]

Even before I get to do anything with my 555 timer I thought I'd play with it and already I have fallen at the first hurdle (perhaps even before getting to the starting gate) :(

It wired up as per http://www.instructables.com/file/F0UNQNHH742SU5Y for an astable timer (or so I hope).

I've plugged in a PC scope that I think I've gotten to grips with and have pin 3 on the scope and it grounded.

I have a 5v power supply which I use to power my breadboard Arduino plugged in (no MEGA328 or anything).

I have lovely square wave output... that doesn't change when I change the resistor values, pull out the capacitors.... WTF?!

And the thing that really bothers me though is the 555 is getting very hot! Is this normal or am I stoking up a little BBQ.

Changing briefly to a 9v battery and the square wave goes away to be replaced by nothing useful looking. So I deduce the square wave signal is something to do with the 5v regulated power supply (which is powered by a 10v DC plug in the wall thingy) although that defeats my logic as well.

Obviously I'm looking for the wiring cock-up but don't see it so will have to plug it back in soon sometime but I'm worried I may just burn all my sausages and burgers before I get it sorted.

The speaker is probably 8 ohms so drive it with a power transistor not the 555

I'm not driving the speaker... I'm driving nothing but the scope on pin 3

Show us a picture of your wiring.

If you are using a 100K pot as the schematic shows, insure you do not turn it to zero ohms. I usually use a 1K resistor in series just to prevent overloading the discharge FET. Without a little resistance, that would be a short circuit.

Well here we go...

Yellow wire is pin3 to scope. both scope channels plugged into it.

capacitors are 103 and 104 respectively towards the top right. have had a 470uF in place of the 104

variable resistors are now 207k upper and 110k lower set to max by plugging into outer pins but I have had them using centre pin and end pins to vary the resistance.

sorry its in a pickle but i've been tearing it apart and...

Sorry re-read that 4.7uF instead...

Rig it up with resistors first. (It looks like the pot wipers aren't connected anyway.)

In this photo they aren't connected - I did this to ensure that I didn't have zero resistance in error by a wiper being at the wrong end.

Confirm with a DVM you have +v on pin 8 to pin 1
Double check the red wire going to the top Pot, is it going to the lead of the Pot?

I think that an 8? speaker on the output is not a great idea. I'd put a resistor in series; 100?, 220?, something like that.

I have no speaker o the output. I have only a scope

Have some load on the output.

got "2K"?

What is written on the capacitor connected to pin 6 and ground?

Proto boards may need 22 gauge wire to fit in the hole. If the jumpers are 20 gauge and the pot is 24 gauge, a loose connection may exist which places a gap between wires instead of a node. A cap may use thin wire and a jumper may have fat wire that spreads the internal metal strips.
The power decoupling cap is not seen.

5.27 v on source 3.9v across pin1-8

sticking the the 2k on the output does this to the scope


and just to make the point about the 9v here is the scope output

If you have the parts try this combination.

capacitor 1 say 104

swapped out with another saying


sorry can’t closer and focus

By the way, nobody has commented on the fact that the 555 gets very hot

Pin 4 should be = supply volts Pin 8 should be = supply volts or there's a problem.

You should jumper the Gnd bus on the one side over to the one on the other side. Then ground your caps on that rail/bus instead of running the jumper leads as you are.

If this is a CMOS 555 (7555 or LMC555) then it should run from a 9V battery OK. If it's an [u]LM[/u]555, a bipolar device, then it will suck (big transients on transitions) and will get hot depending on the load.

Placate the bypass crowd by placing a 0.1uF, from +V to Gnd on your power bus.