Electronics > Beginners

Traffic light circuit with 556 timer?

<< < (6/15) > >>

james_s:
Why are you obsessing about doing it with a single IC and avoiding a microcontroller? What is the goal exactly? Are you trying to learn a specific aspect of electronics? I microcontroller is the single IC solution, it's the smallest, easiest, cheapest way to go. A $2 attiny85 Arduino can do it with code that can be written in literally 2 minutes.

Otherwise most solutions are going to take multiple ICs, or a single IC and some transistors and diodes, you can build a astable mulivibrator out of two transistors, two capacitors and 4 resistors. You might also try a ring oscillator out of transistors, or you could try the CD4060B which is an integrated counter/oscillator IC. You're going to have to experiment, that's part of the hobby.

SmokeyTheElectrician:

--- Quote from: phennessey on December 22, 2019, 07:35:22 pm ---Besides a microcontroller, what’s a single simple IC that could do this? There are many 555 variants out there (like the 556), would any of those achieve this effect?

--- End quote ---

Wow and Holy Cow!,
 there is a ton of awesome advice here
in all of these posts and replies.

Thanks for sharing EEVBlog!

I'll bet once the OP achieves success with 555
type timers, you all have opened up an entire
universe of discovery should the OP decide to
further persue their interest in futzing around
with electronic circuitry.

Now getting back to trying to follow the OP's initial and insistent request:

Please redraw the circuit you originally shared with shared with us,
according to my prior suggestions and post the new circuit so we
are able to make sure we are on the same page.

( even better, if you do not already have it downloaded and install
. LT SPICE {or any other free SPICE version} and use that for
. schematic capture and you will be able to also simulate the
. circuit {and share those results} )

Next take a look at the 555's and 556's pin assignments
.. ( you already have a diagram for the 555 in the OP ).
.. ( hint go on your favorite search engine and search LM556 Pinout )


and construct a table as follows:
( actually, here, I'll help you out a little more by getting the table started
. just fill in the pin numbers from the 556 -- hint: since Vcc and Gnd are
. share between the 2 556 timers, just repeat the 556's Vcc and Gnd
   assignments  in the below table for each timer )

Function               555     556tmr1      556tmr2
------------------   -----     ----------     ----------
Ground                  1
Trigger                 2
Output                  3
Reset                   4
Control Voltage         5
Threshold               6
Discharge               7
Vcc                     8


Then re-redraw the circuit using the 556 in place of the 555s
according to the above pin cross-reference map that you created.

&&& again,
share your results so we can help keep you on track,
(as well as gloat with you once you achieve success....)

.  ( BTW the ultimate goal here is to help you to learn to answer your own questions
.... at which point you will start to be able to help noobier noobs on these forums
.... as well as share the clever things you come up with the rest of us  )

Cheers to all!


SmokeyTheElectrician:

--- Quote from: james_s on December 22, 2019, 06:59:26 pm ---I don't see how. You'd need to add at least something to allow you to hold the second timer in reset and also prevent either LED from lighting while the first one is on. As I mentioned earlier, this is an unusual way of doing a traffic light.

--- End quote ---
With the circuit redrawn according to my earlier suggestions:
.
Timer 1 free runs

&&&

When timer 1's output is low:
a) The Red LED lights
......12v---/\/\/\---->|-------TMR2out(low)
and
b) timer 2 is held in reset where by
b.1)the discharge transistor is off
...(the Orange LED will be off  :   12v---/\/\/\---->|-------disCHRg2(open) )
and
b.2)the output is low
...(the Green LED will be off  :   TMR2out(low)-----/\/\/\--->|-------GND  )

Then when timer 1's output goes high:
a) The Red LED will be off
......12v---/\/\/\---->|-------TMR2out(high)
and
b) timer 2 can free run
b.1) during the phase where TMR2output is low ( actually TMR2's 2nd half cycle )
the discharge transistor will be on
...(the Orange LED will be on  :   12v---/\/\/\---->|-------disCHRg2(GND+Vsat -i.e. low) )
...(the Green LED will be off  :   TMR2out(low)-----/\/\/\--->|-------GND  )
and
b.2) during the phase where the TMR2output is High ( actually TMR2's 1st half cycle )
the discharge transistor will now be off
...(the Orange LED will be off  :   12v---/\/\/\---->|-------disCHRg2(open) )
...(the Green LED will be on  :   TMR2out(low)-----/\/\/\--->|-------GND  )
and
c) the time constant for timer 2 is long enough such that timer 1 puts
it back in reset before timer 2 starts on a second cycle.

Cheers to all!

SmokeyTheElectrician:
PS
circuit diagrams are compliments of ASCIICAD

SmokeyTheElectrician:
Corrections:
a) I have typos where TMR2 should be TMR1
b) the orange diode powers off of the Timer output
+ c) some clarification in the operation of Timer2
 
so lets see if I can spell out the circuit's operation
without any more ooopsies:

~~~~~~~~~~~~~

Timer 1 free runs

&&&

When timer 1's output is low:
a) The Red LED lights
......12v---/\/\/\---->|-------TMR1out(low)
and
b) timer 2 is held in reset where by
b.1) the 555's internal discharge transistor's state does not matter (it is either low or open)
...(the Orange LED will be off  :   TMR1out(low)---/\/\/\---->|-------disCHRg2(do not care) )
and
b.2)the output is low
...(the Green LED will be off  :   TMR2out(low)-----/\/\/\--->|-------GND  )

Then when timer 1's output goes high:
a) The Red LED will be off
......12v---/\/\/\---->|-------TMR1out(high)
and
b) timer 2 can free run
b.1) during the phase where TMR2output is low ( actually TMR2's 2nd half cycle )
the discharge transistor will be on
...(the Orange LED will be on  :   TMR1out(high)---/\/\/\---->|-------disCHRg2(GND+Vsat -i.e. low) )
...(the Green LED will be off  :   TMR2out(low)-----/\/\/\--->|-------GND  )
and
b.2) during the phase where the TMR2output is High ( actually TMR2's 1st half cycle )
the discharge transistor will now be off
...(the Orange LED will be off  :   TMR1out(high)---/\/\/\---->|-------disCHRg2(open) )
...(the Green LED will be on  :   TMR2out(high)----/\/\/\--->|-------GND  )

~~~~~~~~~~~~~

sorry for the additional confusion

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod