555 Astable Circuit on Thingiverse

Thread Starter

jspring111

Joined Oct 20, 2020
11
I was trying to put together a 555 Astable circuit on a breadboard and ran into problems so I built it on thingiverse and it doesn't seem to work as it should. The lower LED lights up and as the voltage across the 47 uf capacitor rises, the LED shuts off and the upper LED lights as it should.

But in the descriptions I've found online, as I understand it, the voltage should then drop making the upper LED go off and the lower one come back on. This does not happen. The voltage climbs to 12v and the upper LED stays on.

Am I missing something? Is my wiring correct?

Thanks for looking at this.

https://www.tinkercad.com/things/4d...e=mFnZyDiwSfegqobsMOjctQGiX1PNN1CD76tHvL4afQw
 

dl324

Joined Mar 30, 2015
16,846
Welcome to AAC!

The link you provided requires membership and this forum prefers that information be posted on this site. Post you schematic.
 

Thread Starter

jspring111

Joined Oct 20, 2020
11
I posted the Tinkercad link so it could be tested but here is a view of the circuit. The second attachment is the schamitic i was trying to duplicate.
 

Dodgydave

Joined Jun 22, 2012
11,285
You can get the same result using pin3 as the charge and discharge feed instead of pin 7, this will save one 10K resistor and give you an approximate 50/50 mark space time.

ba963403ed847105735206175e69488e.png
 

dl324

Joined Mar 30, 2015
16,846
I posted the Tinkercad link so it could be tested but here is a view of the circuit. The second attachment is the schamitic i was trying to duplicate.
That's one of the saddest wiring diagrams I've seen. Whenever you see something like the attachment you posted, ignore them; they probably have no idea what they're talking about.

A proper schematic:
1603227851420.png
 

MisterBill2

Joined Jan 23, 2018
18,176
I agree with d1324, that was a wiring diagram, not a circuit schematic. And a rather poor wiring diagram at that. With the discharge connected correctly the circuit will continue to oscillate.
There are many sources of incorrect information around, you have located one of them.
 

Thread Starter

jspring111

Joined Oct 20, 2020
11
Sorry, I was changing the values of the resistors as i was tinkering, changing the voltage then changing the LED resistors appropriately. Alsh the cap and resistor to change the timing. I know my Tinkercad drawing doesn't match the design I was copying. After I moved the resistor as bertus pointed out, the circuit worked correctly.

I tried to build it on a breadboard but the LED just stays on. I think my 555 is bad.
Anyway thanks for all the help and interest. Just trying to learn.
 

dl324

Joined Mar 30, 2015
16,846
I tried to build it on a breadboard but the LED just stays on. I think my 555 is bad.
Anyway thanks for all the help and interest. Just trying to learn.
An astable is simple to debug, even without an oscilloscope. Post the voltages on the trigger, threshold, and discharge pins.

I know pins 2 and 6 should be the same net, but on a solderless breadboard, things might not actually be connected.
 

MisterBill2

Joined Jan 23, 2018
18,176
An astable is simple to debug, even without an oscilloscope. Post the voltages on the trigger, threshold, and discharge pins.

I know pins 2 and 6 should be the same net, but on a solderless breadboard, things might not actually be connected.
Dennis is certainly correct about those solderless breadboards. They are subject to a number of problems, including not connecting to things plugged in. also they sometimes have poor connections in some holes.
 
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