Simulation of 555 timer circuit in KiCad

555 Timer.pdf (13.1 KB)

hello i have been trying to simulate this timer circuit, when i try to simulate it keeps saying the circuit is not loaded. Can someone mention the steps in details also the time periods which have to be given as inputs. Any other key points is also requested for simulation in KiCad.

My experience with spice in general is very limited, though I have managed to get a simple opamp amplifier working. It was one of the example projects, but still needed some tinkering to get it to work.

I found this page useful:

Have you read the chapter about spice in the Eeschema manual?
Eeschema / [F1] and then search for “spice”.

Also: if someone here wants to have a look at your 555 circuit, it’s much better if you zip the whole project and upload it instead of a .pdf.

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I’ve had numerous problems with simulations in KiCad - 90% of the time it’s with finding good parts to load into schematic.

My ‘goto’ app for 99.9% reliability is LTspice and making 555 timer took about 3 sips of black coffee and it was done.

I’m not suggesting a direction to explore, only saying what works best for me…

So true , Eeschema in kicad requires some extra info which i couldn’t figure out, I too shifted to LTspice so much easier to simulate.

In the video linked to by Paru, he goes to some website, fills in some form to download a complete simulation package and then goes on to copy the LM555 sub circuit.

As an alternative I spent about 2 hours searching the web, tried some 10+ different LM, NE, TLC, and other 555 variants and could not get to a blinking led.

I will also not resort to commercial software, even if they give it away for “free”.
So for me it’s back to my breadboard and oscilloscope.

LTspice’s educational examples folder includes NE555.asc, which is a full transistor-level model of the 555 timer.

I removed the external components that allow this example to simulate, and saved out the netlist of just the internal 555 structure into a subcircuit library:
NE555.lib (1.2 KB)

You can use this LIB file within KiCad. I had no idea what you were trying to do with your original circuit in the PDF, so I just built a simple astable circuit and successfully simulated that. I attached a ZIP of this example project. (5.1 KB)


Thanks Ste. Finally a 555 circuit that works.
I was a bit surprised that changing the battery voltage did not change anything in the simulator, and then discovered it had an extra (hidden) spice parameter.
I replaced it with a battery with RefDes V1 and a value of “DC 15”, in the same way as in the video linked by paru.

Now I also noticed the pdf of Rohit_Kumar.
I see at least 2 errors in the pdf.
First. You have to annotate the schematic, so the question marks in the RefDes’s go away.
Then Voltage sources (such as your battery) need to have a Refdes starting with “V”, or the simulator will not recognize it as a voltage source.

For an estimate of simulation time constants. Take some ball park figure for a RC constant, and divide that time with a factor of at least 10. (50 to 100 or so is usually better, higher resolution often just adds more simulation time) For example, you have a 150k resistor on Q with a capacitor of 4.7uF.
1.5e5 * 5e-6 = 7.5 e-1
Which is just below a second, so simulation resolution should be well below 100ms resolution. Starting with 10ms is probably better.
Note that too high a resolution just slows down simulation, while a too coarse a resolution completely *&^%$#@! the whole simulation and the results do not make sense anymore.

In the screenshot below the resolution clearly is too low.
The output pulse widht (red) is not stable anymore, and the voltage over the timing capacitor (green) becomes chunky.