# 4 way traffic light using 555 timer

I'm trying to build a 4-way traffic light controller in NI Multisim, using the 555 timer and a decade counter (no microcontrollers allowed). I used this as reference: https://circuits-diy.com/four-way-traffic-light-circuit-using-555-timer-ic/

Upon simulating this circuit, the 4 LEDs farthest to the right lit up, and then the simulation stopped due to a "convergence issue".

Upon analysing, I came to the conclusion that the connections of the 555 IC weren't correct for it to be used as an astable multivibrator. There should be a capacitor between pin 5 (control pin) and ground, instead of a capacitor between Vcc and ground.

I made this correction, and the exact same error is still occurring: LEDs 7,8,9,10 light up for a brief moment , after which the convergence issue error arises.

I tried to isolate the Multivibrator circuit and tested it's output with a scope, and I get:

Is the large initial pulse the cause for the error? It has a time period of about 190 ms. Subsequent pulses have a period of about 148 ms, which matches with the formula $$0.693(R1+2R2)C$$

If yes, how exactly can we fix this?

LEDs 7,8,9,10 light up successfully because upon generation of the first pulse, Q0 is high. But something seems to be wrong subsequently.

Also, the materials required section of the website states that 3 1k and 3 10k resistors are required, but the diagram only uses 1 of each....is the diagram missing resistors?

Edit: Something I noticed with the scope: Magnitude wise , the initial pulse seems correct (10v),and the subsequent pulses are significantly less than 10v. But time period-wise, the first pulse seems incorrect (~190 seconds), and the rest (~147 seconds) seem to be within agreement of the theoretical calculation...

• The capacitors and resistors are not causing your problem. The capacitors (other than the timing cap) have no effect in a simulation. Maybe just get the 555 working first (remove the rest of the circuit). It could be a problem with the 555 model or some simulation parameter. Commented Oct 29, 2021 at 13:10
• I have attached the output of just the 555 circuit ...what do you think about that? Commented Oct 29, 2021 at 13:12
• If you deleted everything else, I would say something is wrong with the model or some simulation parameter. Commented Oct 29, 2021 at 13:59
• Can you suggest a platform where this could be simulated successfully? Commented Oct 29, 2021 at 14:20
• Why no 1N4007 diode at output Q4 ? Commented Oct 29, 2021 at 14:37

Simulated with microcap v12 ... Seems ok. Updated to 12V.

Search the Components ... Digital primitives ... Stimulus generator ... Stim 1 ..., take it and drop it in the schematic window. Stim 1:1 will open automatically.

Fill the text in the Stim1:1-bit Digital Stimulus (or double-click on the icon "Sim digital generator" in the schematic window) ... and what is in window "Value" in "blue".

.define _1HZ +label=start +0m 1 +500m 0 +1 goto start -1 times

For the .param directive (as for adding the labels in the schematic, same rule, no CR),

click on T icon, fill exactly what in blue (no carriage return !), then click OK.

Here the "Transient Analysis limits" window ...

And finally the results of simulation

You can then measure what you want (with the good "icon"). :-)

• what component are you using as the input to the clock pin? and to the reset pin? Commented Oct 29, 2021 at 18:14
• Square wave 1 Hz for clock input. Digital animated level by switch. Commented Oct 30, 2021 at 8:13
• and how exactly are you getting these output graphs? Just transient analysis? I'm sorry, I haven't used this software before.. Commented Oct 30, 2021 at 8:14
• Just transient analysis. Be aware that I think the simulation is made with a voltage supply of 5 V. It does not mean that at 10 or 12V, it will have same behavior. Just try. Commented Oct 30, 2021 at 8:18
• For trying ( I have tried. It is ok) at 12V just add this Text in the schematic : .param CD4000_VDD=12V Commented Oct 30, 2021 at 9:08

The cap from pin 5 to GND is a noise filter on an internal voltage divider. Both in simulation and in real life, it is not required for standard operation.

The cap from Vcc to GND is for power supply decoupling, a combination of noise filter and energy reserve for output current transients. this is strongly recommended ion real life, but has zero effect on simulations.

R3 can be deleted.

• The error still persists after removing R3.. Commented Oct 29, 2021 at 13:35