CD4026 based timer clock - how to reset the clock at startup and on demand

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Hello

I have made a timer clock based on CD4026 IC.
The clock is working normally as it should be.
The problem i am facing is that,
On initial start (supplying power), the third CD4026 IC from right (for minutes counting) jumps from '0' to '8' and then it continues to work normally.

So, I want to know how can I eliminate this random jump at starting, so that the clock starts at '0'.
Also, i am having problem in resetting the whole clock once it starts counting. All the CD4026 have to be resetted individually and cannot be reset together, as on doing that the normal counting also gets affected. So, is there a way i can reset all the IC together without affecting their individual reset settings.

 

Any tips/help are welcome.

 

have included the CD4026 pinout, timer schematic and PCB design for your reference.

 

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Schematic CAD drawing with nothing but net lists are NOT proper schematics, there is no way a person can follow that mess!

Produce a proper schematic with WIRES connecting all components if you want help!

I see not one bypass cap, every chip needs a bypass cap (100nf) from VCC/GND.  I'm not surprised you have glitches. 

PCB layout uses way too thin traces for the power needed to light up your LED's, suggest you use a gnd plane (maybe you do, but it does not show on layout), signal traces are carrying LED power and need to be bigger.

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Thu. Apr 16, 2020 - 03:30 PM
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So, how are you resetting the counters once the power supply has stabilised?

 

[EDIT]

 

I assume that since you are using a 555 as your master clock you don't really care if it keeps good time?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

Last Edited: Thu. Apr 16, 2020 - 03:29 PM
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I have added a single bypass capacitor at the input supply. far top right corner of the schematic.

 

With such a busy schematic its very difficult to connect all with wires as this would create a bigger mess and its difficult to manage.

 

1) Each IC has a one 7-segment display connecte which is placed next to it in the schematic.

2) Each IC has two 5-pin header which are in parallel with the 10 pins of the 7-segment display so all the headers in the schematic can be ignored.

3) the group of three NPN transistors form a 3-input-1-output AND gate to reset the IC individually.This way when the seconds timer reaches 60 the second IC is reset and third IC gets a high pulse. Similarly for 60 minutes and 24 hours.

4) the R9-R14 resistors are connected to reset pin of each IC and keep the reset pin pulled low, so when the reset pin gets high signal it resets the counter of that IC. I cannot have only one resistor for all IC as then all the IC will get reset every 60 seconds.

5) the 330ohm resistors in series with the ground are connected to the ground pin of the 7-segment display, one resistor for each display.

 

 

I hope this will clear a lot of questions about the schematic.

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puneet1984 wrote:
I have added a single bypass capacitor at the input supply.

Not just one for the whole board!

ki0bk wrote:
every chip needs a bypass cap (100nf) from VCC/GND.  I'm not surprised you have glitches. 

That's one per chip!

 

With such a busy schematic its very difficult to connect all with wires as this would create a bigger mess and its difficult to manage.

Not really - if you do it carefully.

 

one resistor for each display.

Not good!

 

That means the brightness will depend on the number of active segments!

 

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yeah you are correct, this is just a prototype and for rough time keeping (accurate upto minutes), i plan to connect the 555 output pin to RTC clock output (if possible) if everything works out and discard the 555 IC altogether.

 

Secondly, that's the problem, that i cannot reset all the IC together without affecting their counting function during normal working.

I need a solution "power on reset" that can reset all the IC at one go on startup but then do not interfere with rest of the reset function

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every chip needs a bypass cap (100nf) from VCC/GND.  I'm not surprised you have glitches. 

I can add the caps(0.1uF or 100nF)) to the PCB. Will try and will update. Will ceramic caps will work or electrolytics are required. 

 

one resistor for each display.

Not good!

 

That means the brightness will depend on the number of active segments!

 

I know each segment should have its own current limiting resistor, but i was low of components so decided to give it a try, and before i fabricated the PCB i tested it on breadboard and it was all working without any glitches. 

Last Edited: Thu. Apr 16, 2020 - 03:42 PM
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puneet1984 wrote:
I have added a single bypass capacitor at the input supply. far top right corner of the schematic.

100uf is NOT a bypass cap, it's a filter cap!  100nf caps are needed as close to each VCC/GND pin pair as possible!

puneet1984 wrote:
With such a busy schematic its very difficult to connect all with wires as this would create a bigger mess and its difficult to manage.

Nonsense! It just takes time and perhaps a "bus bar" here to there.

puneet1984 wrote:
the group of three NPN transistors form a 3-input-1-output AND gate

A 74ls11 3-input And gate would be a better choice!

puneet1984 wrote:
the R9-R14 resistors are connected to reset pin of each IC and keep the reset pin pulled low

Each reset pin should use an inverter gate (74ls04) with a pull up on its input here.

These added gates also need bypass caps (100nf) as well.

Question: can a 555 drive 4 LED's (20ma each) and the input to your LED driver too?

 

Jim

 

 

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Thu. Apr 16, 2020 - 03:43 PM
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Googling "CD4026 24 hour" gives loads of projects - have you looked to see how they did it ... ?

 

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puneet1984 wrote:
this is just a prototype

A prototype for what, exactly ?

 

Is this just a "for the fun of it" hobby project, or do you have some specific reason for implementing from discrete components & MSI chips?

 

As you're posting on AVRfreaks, the obvious question is: "why not just use an AVR?"

 

 

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I fail to understand why people don't just put their images inline, or at least attached to a post.  Don't force us to visit a third-party site.

 

 

 

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Hello

ki0bk wrote:

puneet1984 wrote:
I have added a single bypass capacitor at the input supply. far top right corner of the schematic.

100uf is NOT a bypass cap, it's a filter cap!  100nf caps are needed as close to each VCC/GND pin pair as possible!

puneet1984 wrote:
the group of three NPN transistors form a 3-input-1-output AND gate

A 74ls11 3-input And gate would be a better choice!

puneet1984 wrote:
the R9-R14 resistors are connected to reset pin of each IC and keep the reset pin pulled low

Each reset pin should use an inverter gate (74ls04) with a pull up on its input here.

These added gates also need bypass caps (100nf) as well.

Question: can a 555 drive 4 LED's (20ma each) and the input to your LED driver too?

Can you explain me how inverter gate -74ls04 (NOT gate) will work in this setup on reset pin. The datasheet of the CD4026 do not advise use of any other specific IC so I did not included in my prototype. 

Also, i tried sourcing the AND gate IC but due to Covid-19 most of the local shops were having no stocks. Would a NPN-transistor based-AND gate will have different results as compared to AND gate IC?

Sorry, i read filter cap as bypass cap, will add the capacitors for each IC and will test again.

awneil wrote:

puneet1984 wrote:
this is just a prototype

A prototype for what, exactly ?

Is this just a "for the fun of it" hobby project, or do you have some specific reason for implementing from discrete components & MSI chips?

As you're posting on AVRfreaks, the obvious question is: "why not just use an AVR?"

I have made as a hobby project and has no commerical purpose. I Plan to give it my doctor friend who can use it as per his needs.

Last Edited: Thu. Apr 16, 2020 - 05:13 PM
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I'd try something like this for power-on reset.

 

 

You'll need to increase the value of the 330R pull-downs to something more manageable like 47k. On power up the 100n has no voltage on it (discharged through the diode when no power applied) so the rest lines will all be high. The cap then charges through the 4k7 until the rest lines drops to 0V.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

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puneet1984 wrote:

Can you explain me how inverter gate -74ls04 (NOT gate) will work in this setup on reset pin. The datasheet of the CD4026 do not advise use of any other specific IC so I did not included in my prototype. 

Also, i tried sourcing the AND gate IC but due to Covid-19 most of the local shops were having no stocks. Would a NPN-transistor based-AND gate will have different results as compared to AND gate IC?

Sorry, i read filter cap as bypass cap, will add the capacitors for each IC and will test again.

Sorry I now see your using cmos parts, so hex inverter cd4069, 3 input and cd4073:

Inverter plus r/c input will auto gen a reset pulse when power is applied, or you can add a reset button to gnd to the /RST_in for a manual reset.

Jiim

 

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

Last Edited: Thu. Apr 16, 2020 - 06:50 PM
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I dont have the CD4069 or CD4073 on hand and will take at least next 2 months for the shops in my city to get them due to country wide lockdown since a month now and will continue for another 3 weeks. so i am stuck with the PCB i have and will have to make modifications on the PCB itself.

 

So, what i try with

1) add bypass caps to all my CD4026 and see if that resolves the issue.

2) try to make a reset on power circuit on perf board using diodes, resistors and caps, will share the schematic before actually soldering the components.

 

But i want to know why the same problem was not there on breadboard with same circuit layout.

 

Hope it works.

Also fabricating another PCB for this would not be feasible.

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puneet1984 wrote:
shops in my city

Don't you have online ordering ?

 

https://in.element14.com/

 

https://in.rsdelivers.com/

 

https://www.digikey.in/

 

 

breadboard with same circuit layout

It wouldn't the same layout in a breadboard as a PCB!

 

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With such a busy schematic its very difficult to connect all with wires as this would create a bigger mess and its difficult to manage.

This has to be about one of the worst schematics I've seen in many years.   If anyone "drew" such a thing (it barely qualifies as a drawing) at our company, they'd be promptly fired. You might as well forget drawing & just use an excel sheet to list the connections instead.  The purpose of the schematic is to show an easy visualization of how things are connected together, just like a roadmap.

 

Have you ever seen a roadmap that looks like this?

 

Red interconnect dots connect to wires NOT component pins.   Component pins ONLY connect to wires (not other component pins). 

Each pin of r2 should go to a wire, then to the other components.

 

 

Time for round two!   You will get experience in making a real schematic.  

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Fri. Apr 17, 2020 - 01:43 AM
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0.1uF (== 100nF) axial monolithic caps can be very prettily tacked diagonally across the chip on the back of the board.

 

I'm not quite as down on 'netlists as schematics' as some - I've got entire boards whose schematics are "a bit that way"; they used a lot of programmable logic and were organized in ways that made sense.  Drawing all the lines would have just made a mess.

 

However, I do kinda agree with avrcandies, your schematic's a disaster area.  The first post was to an image link that was so fuzzy I couldn't read a thing, until it got reposted properly as a .png that I could zoom in on, and even then it was a mess.  Overlapping text, random blocks of this and that splattered all over the place, no visible organization nor flow...  Your board layout was significantly neater.  Do what you did to the board to the schematic, as a starting point.

 

Anyhow, carry on!  Learning by practice is an excellent way.  S.

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Hello,

have cleaned the schematic a bit and uploaded it again. Hope it helps.

 

 

awneil wrote:

puneet1984 wrote:
shops in my city

Don't you have online ordering ?

 

https://in.element14.com/

 

https://in.rsdelivers.com/

 

https://www.digikey.in/

 

 

breadboard with same circuit layout

It wouldn't the same layout in a breadboard as a PCB!

 

 

whole country is in lockdown, all the shops,industries and e-commerce throughout the country are closed. Only essential services like grocery and hospitals are allowed to be open. stepping out of home is prohibited and if found legal action is being taken including arrest.

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Interesting power wiring on the pcb - did you use the autorouter?  The led current is being sourced via the 4026 ics and these are fed by a skinny power track. What current is being drawn and what is the voltage drop across the track? Bypass caps might help - you might have to run a bit of tinned wire to supplement the pcb.

 

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Yes, i used autorouter.

The input signal is from the 555 timer IC. the signal is in parallel to the first 4026 and to the four LEDs. Have not checked the voltage drop on the tracks. And yes the bypass cap should help a lot.

I am planning to cut the LED track from the IC and feed it through a NPN transistor base and power the LED directly from the Vcc.

The max current output (recommended) from a 555 IC is about 200mA (as per datasheet), so 4 LEDS each around 25mA will be 100mA total, still 100mA is there to generate the pulse for the first 4026 IC.

 

 

555 IC datasheet for reference

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Where are your led resistors?   You only show 1 resistor (improperly)  for each display!!!  Why is the resistor (ex:  r3) not actually shown connected to the display?  A schematic is not a game of hide & seek.

 

also why are all of these reset resistors in the bottom of the lower left corner....obviously that is not where they belong.

 

Stacking 3 transistors is a poor way to make an and gate...why not use an actual  and gate or some nand gates (one can invert)....also when the transistors are off, the chip pin will float, which is not a good idea.

 

You are missing all of your caps for each of your chips....where are they?

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Here is one that looks somewhat meaningful...not a giant mess.

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Fri. Apr 17, 2020 - 08:00 AM
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avrcandies wrote:
 You only show 1 resistor (improperly)  for each display!!! 

See #5 & #7

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avrcandies wrote:

Here is one that looks somewhat meaningful...not a giant mess.

 

But with curious errors. For instance why is MR on U6 and U7 connected together but not to anything else? And I would still like to see something to reset the counters into a known state at power up.

 

TBH, even using the 4026s, I'd be inclined to do away with the AND gates and all the wired counter interconnects and just drive the counters from an AVR.

 

[EDIT]

 

You'd only need 6 pins from an AVR plus whatever you need for buttons and buzzers.

 

1 sec clock and reset

1 min clock and reset

1 hour clock and reset

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Last Edited: Fri. Apr 17, 2020 - 08:41 AM
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avrcandies wrote:

Where are your led resistors?   You only show 1 resistor (improperly)  for each display!!!  Why is the resistor (ex:  r3) not actually shown connected to the display?  A schematic is not a game of hide & seek

also why are all of these reset resistors in the bottom of the lower left corner....obviously that is not where they belong.

Stacking 3 transistors is a poor way to make an and gate...why not use an actual and gate or some nand gates (one can invert)....also when the transistors are off, the chip pin will float, which is not a good idea.

You are missing all of your caps for each of your chips....where are they?

These are already discussed in the previous posts.

 

--the group of three NPN transistors form a 3-input-1-output AND gate to reset the IC individually.This way when the seconds timer reaches 60 the second IC is reset and third IC gets a high pulse. Similarly for 60 minutes and 24 hours. due to covid-19 infection all shops and ecommerce are closed in my country.

--the R9-R14 resistors are connected to reset pin of each IC and keep the reset pin pulled low, so when the reset pin gets high signal it resets the counter of that IC. I cannot have only one resistor for all IC as then all the IC will get reset every 60 seconds.

--the 330ohm resistors in series with the ground are connected to the ground pin of the 7-segment display, one resistor for each display, to save on components.

-- the pins of the cd4026 are connected to the 7-segment display, so when the respective segment is off, the pins of that segment are pulled low by the chip, as if they are floating then the segment will light-up with variable intensity. if you are referring to the reset pin as chip pin then they are already pulled low using R9-R14 resistors.

--as already discussed and pointed out, i will add the bypass caps on all the chips.

-- the R3 resistor is connected to the m1 net and m1 net is connected to ground(G2) of the LED3  as shown in the schematic. I have used nets instead of wire connections in my schematic.

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Brian Fairchild wrote:
with curious errors.

and some push buttons with no debouncing !

 

 

drive the counters from an AVR.

Indeed:

 

in #10, I wrote:
As you're posting on AVRfreaks, the obvious question is: "why not just use an AVR?"

 

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Don't use the autorouter!

 

You really would want to use a cmos 555 ic - the old bipolar ones have some interesting issues which I dare say you're going to learn about.

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Brian Fairchild wrote:

avrcandies wrote:

Here is one that looks somewhat meaningful...not a giant mess.

 

But with curious errors. For instance why is MR on U6 and U7 connected together but not to anything else? And I would still like to see something to reset the counters into a known state at power up.

 

TBH, even using the 4026s, I'd be inclined to do away with the AND gates and all the wired counter interconnects and just drive the counters from an AVR.

 

[EDIT]

 

You'd only need 6 pins from an AVR plus whatever you need for buttons and buzzers.

 

1 sec clock and reset

1 min clock and reset

1 hour clock and reset

 

Also they have not included the bypass cap on any of the ICs.

I wanted to build a timer clock using only basic components without any microcontrollers.

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thank for the info.

Will try to route my PCBs manually next time.

Also can you please provide me with some links about the interesting issues you mentioned about the 555IC.

Will need to check at my local store if they have CMOS 555 chips.

 

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The 555 ic has been around nearly as long as I have so there's no secrets.

 

https://www.eevblog.com/forum/be...

and there's more. The designer of the chip points out some more shortcomings. Just a Google away.

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--the R9-R14 resistors are connected to reset pin of each IC and keep the reset pin pulled low, so when the reset pin gets high signal it resets the counter of that IC. I

You seem completely oblivious, or just a complete lack of basic understanding. WHY are these resistors not shown AT THE PIN OF THE IC or at the transistors???...There is NO REASON they are off in some corner, that is goofball, to say the least.

 

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When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:

when  you         words do

 write     the    you  around??

             all   

 scatter  

1+

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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I think people are getting their knickers in a twist about nothing here. Schematic style is a bit like coding style. There are plenty of ways to do it and it's down to personal choice. Consider one of mine...

 

 

Yes, it's neat but, and here's the thing, even though I use busses they are nothing more than a drawing element. They have no 'electrical' function to them. All I have is a pile of stubs connected to pins which have a net name attached. And there are plenty of schematics from major companies who do it exactly that way.

 

It's really not necessary to show every single interconnection as a line between two pins.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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And there are plenty of schematics from major companies who do it exactly that way.

Many schematics at our company use busses, however, they are used judiciously (as in: when needed due to lack of drawing space). Also, they are not allowed to become dumping grounds. Typically, we want to keep the schematic information resolution high, unless it is desired to present more of a block diagram effect (50000 foot view).

Separate busses should be used to clarify groupings of connections.  For example, a grouping of multiple elements connect from region A to B and perhaps onwards to C, D, etc.

If a separable set of elements goes from location X to Y, Z, etc it will be indicated using a separate & distinct bus, not dumped into the bus going from A to B (since they have nothing in common).

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sat. Apr 18, 2020 - 11:25 AM
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The use of the bus does guide one's eye to follow the signals to where they connect. Whereas, without the bus, one must meticulously scan the schematic sheet to find all of the connections. I much prefer buses over just plopping components down and providing a signal name on a pin with no indication of where or how many places it goes or if it is even used at all elsewhere in the schematic.

 

edit: typo

David

Last Edited: Sat. Apr 18, 2020 - 11:54 AM
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Brian Fairchild wrote:

I think people are getting their knickers in a twist about nothing here. Schematic style is a bit like coding style. There are plenty of ways to do it and it's down to personal choice. Consider one of mine...

Yes, it's neat but, and here's the thing, even though I use busses they are nothing more than a drawing element. They have no 'electrical' function to them. All I have is a pile of stubs connected to pins which have a net name attached. And there are plenty of schematics from major companies who do it exactly that way.

 

It's really not necessary to show every single interconnection as a line between two pins.

 

Exactly my point. Pointing on the way someone makes his/her schematic actually defeats the purpose of the the forum of finding the real solution to the problem. style of drawing/coding is a personal choice and everyone has his own and are most comfortable in. I know mine is not beautiful but it gets the job done for me. I am trying to improve but it takes time for everyone. You all have years of experience in this and i am just starting now. I would request you to please give tips and tricks regarding laying out a good schematic rather than criticising it. Let it be a constructive criticism.

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 I would request you to please give tips and tricks regarding laying out a good schematic

Never have wires join as a 4-way connection, only at a 3 way intersection

Component pins ONLY connect to wires,  never other component pins or connection intersection dots

Wires leaving component pins go straight out, not at 90 deg

Connection intersection dots are only applied to wires

Show connections to the extent possible, if not possible or the distance is large, a connection label may be used instead.

If many connections go from one area to another, a bus may be advisable if room is lacking.

Component text must not overlap wires or symbols..nothing should obscur it.

Circuit paths should generally flow left to right, inputs on left, outputs on right.

opamps should point to the right,  transistor base, gates should typically be on the left.

Connectors on page left should face left (wires to the right), opposite for page right   

opamps  typically have the - terminal above the + terminal.

Gnd symbol always points downwards

Use gnd symbols where possible, balancing out having too many in one area.

Wires leading to gnd should only traverse downwards

Don't use gnd symbols for connections needing tightly grounded together--show a gnd wire, or a unique gnd designator  

Components that form a circuit block are preferably located together to the extent logically possible.

Organize blocks of circuitry so they flow from beginning to end as the schematic is viewed from beginning to end.

 

 

I found this interesting comment on the web:

There is no “New Standard” for showing the connection of two wires (lines) that cross. The Rule is that an offset is applied to avoid a “Dotted Cross Connection”. Placing a dot on a cross is simply WRONG, not just “not recommended”.

The fact that component manufacturers are increasingly showing the cross with a dot does not mean that it is OK or a new standard. It means that newbie engineers with a only scant 15 or 20 years of experience have never been properly trained in schematic design. Component manufactures do not set standards.

Before CAD systems all schematics were drawn by professional draftsmen. Engineers were not ALLOWED to render a schematic for publication. They simply did not have the skill or training. CAD tools then came out. .......

 

Be aware that if you present a dot on a cross as a connection, the Old Masters of Electronic Engineering are silently watching you and questioning your skills.

 

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sat. Apr 18, 2020 - 04:06 PM
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Thanks a lot avrcandies.

This is be of great help and a good starting point to many new people like me.

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In my humble opinion, this entire concept for a working clock is wrong.  While yes it is possible to make a clock with these parts, it must be accepted that this is a completely obsolete design.  No one has built a clock like this since 1972.  This design assumes that one can get an accurate 1Hz signal from 555 timer.  Simply not possible.  

 

  A modern clock design that displays time on six 7-segment displays will have three module boards:  the microcontroller base,  the Real Time Clock, and the 7-segment display.   The cheapest and fastest way to make a modern 7-seg clock is to use an Arduino Nano (or Pro Mini) for the CPU base, a DS3231 RTC module, and a MAX7219 module with integrated LEDs.  On eBay, you would buy a $3 Nano, like this: https://www.ebay.com/itm/New-Dev...

then get the clock engine, like this: https://www.ebay.com/itm/DS3231-... Try and find one that includes the coin-cell battery.

And finally, the 7-seg display module:  like this one: https://www.ebay.com/itm/MAX7219...

 

Then you use Arduino libraries to tie everything together.   Total cost:  about five Euros  [ about 500 Indian Rupees ]  and 12-15!!! total wiring connections.

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avrcandies wrote:
... I found this interesting comment on the web:

 

There is no “New Standard” for showing the connection of two wires (lines) that cross. The Rule is that an offset is applied to avoid a “Dotted Cross Connection”. Placing a dot on a cross is simply WRONG, not just “not recommended”.

The fact that component manufacturers are increasingly showing the cross with a dot does not mean that it is OK or a new standard. It means that newbie engineers with a only scant 15 or 20 years of experience have never been properly trained in schematic design. Component manufactures do not set standards.

Before CAD systems all schematics were drawn by professional draftsmen. Engineers were not ALLOWED to render a schematic for publication. They simply did not have the skill or training. CAD tools then came out....

Could this be a North American thing? IEC 60617:1996 (international graphical symbols for use in electrotechnical diagrams) allows two undotted offset three-way connections (cf. 03-02-06) or a single dotted four-way cross connection (cf. 03-02-07).

 

Quote:

Be aware that if you present a dot on a cross as a connection, the Old Masters of Electronic Engineering are silently watching you and questioning your skills.

If I remember the old (American?) masters, they would question you if you crossed two signals at right angles – with a dot or without. For the latter case, one line should hop over the other to avoid a four-way intersection.

- John

Last Edited: Sat. Apr 18, 2020 - 05:36 PM
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Simonetta wrote:
This design assumes that one can get an accurate 1Hz signal from 555 timer.  Simply not possible.
You need to read more carefully:

puneet1984 wrote:
i plan to connect the 555 output pin to RTC clock output (if possible) if everything works out and discard the 555 IC altogether.

 

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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I wonder if this standard was drafted to accommodate "religious" differences.

- John

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I wonder if this standard was drafted to accommodate "religious" differences.

Well engineers do say the devil is in the details 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Hi Simonetta,

You are absolutely right, this is not the right way to create a timer clock in year 2020, when we have uC and other active components. But i wanted to build one using non programmable components or semi active components.

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Simonetta, the fallacy in your post is that the Arduino was, and is, all about the 'maker' community. A community which is all about making things that you can usually buy off the shelf. Sometimes people make things just 'because'.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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Brian Fairchild wrote:

I think people are getting their knickers in a twist about nothing here. Schematic style is a bit like coding style. There are plenty of ways to do it and it's down to personal choice. Consider one of mine...

 

 

Or one of mine:

 

This moves essential clutter (power and decoupling) to the bottom left, and uses a mix of  point to point and labelled bus connections to get the point across. I used to use Brian's approach with visible decorative busses, but it became clear that on my designs they were just eating real estate without providing any information that wasn't there before... This is one page of about twenty for this circuit; there are two internal eight bit common busses, as well as 24 bits of external bus and perhaps another 32 bits used internally, as well as an awful lot of 'only go to one or two places' wires.

 

Power is implicit throughout; this is a single rail design.

 

Neil

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Now that is a neat & clear schematic! It has a wonderful balance, and to top it off, all gnd symbols are pointing downwards.  

Some productive time was obviously spent to get there...too many people just throw down some unorganized mess and never touch it thereafter.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Thank you. I firmly believe that ground symbols should always go downwards, and power symbols up, if possible.

 

What is missing (mea culpa) is a table explaining mode:

mode    result
0       BusB = BusA + Treg
1       BusB = BusA + Treg + CarryFlag
2       BusB = BusA - Treg
3       BusB = BusA - Treg - CarryFlag
4       BusB = BusA & Treg
5       BusB = BusA | Treg
6       BusB = BusA ^ Treg
7       BusB = BusA (pass through)

The zero flag is set whatever the operation; the carry flag is valid after arithmetics only. Latch one operand into T on one clock cycle; perform the other and read the result on the next.

 

Neil

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Yes, you could add a bus for treg & another bus for Bus B & one for BusA...but this is nice and clean & easy to digest.

What is really hateful, is some fools will combine all of those into ONE bus...which makes the bus rather useless for quickly visualizing where things connect.  It's like drawing an entire schematic as one node.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sun. Apr 19, 2020 - 04:24 PM
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(For those unfamiliar with kikad: signal names written in a flag are global; visible on any other sheet without explicit connections - e.g. BusA, BusB go to about two dozen chips. Those written without a flag are local to the drawing they're in and can only get out via a mechanism I haven't bothered to learn :) e.g. Treg. Unlabeled point to point links are all local).

 

Neil