Trouble with 4026B decade counter

Thread Starter

RoyCone

Joined Jul 15, 2022
21
I have a bistable 555 timer which works great (if connected to a led, it goes on when one button is pushed and off when the other button is pushed), I have a astable 555 timer which works great(if connected to an led, the led blinks on and off), problem is when I connect the outputs off the timers to the decade counter. Output of the astable counter goes to pin 1 of the 4026, okay. Output of the bistable 555 goes to pin 2. Okay, the decade starts counting. Normal, since the bistable is at low, but if I press the button to activate it (as I was doing to activate the led), the counter stops counting, but only as long as i keep the button pressed. If I let go, the counter starts counting again... But it's supposed to stay stopped because it's a bistable counter...
Why is it happening?
The circuit is from the book make electronics. It's experiment 19, page 185
Here is the schematic ( There's no picture of the complete schematic, sorry)
countertop.png
counterbottom.png
 

dl324

Joined Mar 30, 2015
14,905
Welcome to AAC!

Is this really homework? Or do you want it to be treated that way so no one just tells you what the problem(s) might be?

Since you're a beginner, it would be beneficial to post a picture of your actual breadboard. Many of us don't like tracing someone else's breadboard, especially if they're messy, but sometimes it's a necessary evil for newbies.

There's no picture of the complete schematic, sorry
Why don't you draw a proper one? The wiring diagram style used in that book is not conducive to being able to understand what the circuit is supposed to do. Not everyone has memorized the pin function of the 555 timer and even fewer will have bothered to memorize it for the CD4026.

I'll post a more conventional schematic later. If you can't follow it to wire the circuit, you shouldn't proceed any further in this hobby until you can. I suspect that many wouldn't bother to take the time to understand what the circuit you posted is intended to do.

EDIT: More conventional schematic:
1657981848215.png
The preferred flow in schematics is primarily left to right and top to bottom. I chose to not connect all of the power supply nodes together to make the schematic more readable. It makes more sense to show them explicitly connected in a wiring diagram.

The use of a single current limiting resistor for all segments of D1 is not something that should be done. Display brightness will change for different numbers. I understand that the author is trying to make wiring simpler for readers, but it's not an accepted design practice.

Using a 555 timer as a flip flop is a waste unless he taught you how it works. Did he?

Did he teach you how the astable works?

Even wiring diagram "schematics" should include component designators (e.g. R1, R2, C1, C2, etc) so you can talk intelligently about the circuit. He should have at least included pin numbers so people using his wiring diagrams don't have to keep counting the dots.

For clarity, power supply decoupling capacitors aren't shown. Did he tell you about them?
 
Last edited:

Ian0

Joined Aug 7, 2020
5,885
DO you have supply decoupling capacitors? Old-fashioned NE555 ICs are notorious to putting glitches on the power supply when they change state.
 

Thread Starter

RoyCone

Joined Jul 15, 2022
21
DO you have supply decoupling capacitors? Old-fashioned NE555 ICs are notorious to putting glitches on the power supply when they change state.
No i don't have that. What type of capacitors? How many farad would they be and where would I plug them?
 

Thread Starter

RoyCone

Joined Jul 15, 2022
21
Welcome to AAC!

Is this really homework? Or do you want it to be treated that way so no one just tells you what the problem(s) might be?

Since you're a beginner, it would be beneficial to post a picture of your actual breadboard. Many of us don't like tracing someone else's breadboard, especially if they're messy, but sometimes it's a necessary evil for newbies.


Why don't you draw a proper one? The wiring diagram style used in that book is not conducive to being able to understand what the circuit is supposed to do. Not everyone has memorized the pin function of the 555 timer and even fewer will have bothered to memorize it for the CD4026.

I'll post a more conventional schematic later. If you can't follow it to wire the circuit, you shouldn't proceed any further in this hobby until you can. I suspect that many wouldn't bother to take the time to understand what the circuit you posted is intended to do.

EDIT: More conventional schematic:
View attachment 271552
The preferred flow in schematics is primarily left to right and top to bottom. I chose to not connect all of the power supply nodes together to make the schematic more readable. It makes more sense to show them explicitly connected in a wiring diagram.

The use of a single current limiting resistor for all segments of D1 is not something that should be done. Display brightness will change for different numbers. I understand that the author is trying to make wiring simpler for readers, but it's not an accepted design practice.

Using a 555 timer as a flip flop is a waste unless he taught you how it works. Did he?

Did he teach you how the astable works?

Even wiring diagram "schematics" should include component designators (e.g. R1, R2, C1, C2, etc) so you can talk intelligently about the circuit. He should have at least included pin numbers so people using his wiring diagrams don't have to keep counting the dots.

For clarity, power supply decoupling capacitors aren't shown. Did he tell you about them?
Hum, it's not homework. I'm just trying to learn on my own so please tell me what's the problem. I started a month ago so bare with me. I know how an astable and bistable work and mine work. I tested them separately with LEDs. Yes there are pictures explaining the pins from the chips. I can add them if you want. No he didn't talk about supply decoupling capacitors.
Here are pictures from my circuit (everything after the right most 7 segment digit is not in the circuit(the two switches and capacitors)). 20220716_175054.jpg
20220716_175112.jpg))
20220716_175142.jpg
 

dl324

Joined Mar 30, 2015
14,905
I'm just trying to learn on my own so please tell me what's the problem.
Your post is in homework help, so members shouldn't be just giving you answers. Now that you've told us it isn't homework and your objective, we know how to proceed.
Yes there are pictures explaining the pins from the chips. I can add them if you want.
Don't need them. You should be aware that most well drawn schematics are self-documenting.
No he didn't talk about supply decoupling capacitors.
Until you've learned how to troubleshoot circuits on your own, you should use them. 555 timers and switching CMOS logic are known to put glitches on the power rail. Putting decoupling capacitors on the supply will let you avoid some problems.
Here are pictures from my circuit (everything after the right most 7 segment digit is not in the circuit(the two switches and capacitors)).
Give me some time to look at your wiring. Are the power rails on the breadboard continuous? Some have a break in the middle of the 4 rails. Is the CD4026 known to be working?

I'm not a neat freak when it comes to breadboarding, but there are some commonsense things to do.
  1. You should form the leads of the components as much as possible. Some components can be damaged if their leads are abused.
  2. You have several jumper lengths. Use them appropriately. I have around half a dozen different lengths.

Here's an example with multiple independent circuits:
breadboardExampleColorAdjusted.jpg
 

Thread Starter

RoyCone

Joined Jul 15, 2022
21
Your post is in homework help, so members shouldn't be just giving you answers. Now that you've told us it isn't homework and your objective, we know how to proceed.
Don't need them. You should be aware that most well drawn schematics are self-documenting.
Until you've learned how to troubleshoot circuits on your own, you should use them. 555 timers and switching CMOS logic are known to put glitches on the power rail. Putting decoupling capacitors on the supply will let you avoid some problems.
Give me some time to look at your wiring. Are the power rails on the breadboard continuous? Some have a break in the middle of the 4 rails. Is the CD4026 known to be working?

I'm not a neat freak when it comes to breadboarding, but there are some commonsense things to do.
  1. You should form the leads of the components as much as possible. Some components can be damaged if their leads are abused.
  2. You have several jumper lengths. Use them appropriately. I have around half a dozen different lengths.

Here's an example with multiple independent circuits:
View attachment 271588
The breadboard rails are continuous and the 4026 is, from what i know, working. I have a couple of them and i changed them to see if there was a problem with the one I was using, but there was no change in the circuit.
Where do I put the supply capacitors? What should their capacitance be?
I'm trying my best for the circuits, but I need more practice...
 

djsfantasi

Joined Apr 11, 2010
8,447
Also, using long wires on a breadboard is another source of trouble and can make even a properly connected circuit not work. The long wires act as antennas, changing signals apparently via a ghost.

I recommend getting a wire kit for breadboards and neatly route all wires.
 

dl324

Joined Mar 30, 2015
14,905
Where do I put the supply capacitors? What should their capacitance be?
Put them on the supply rails. I'd use an electrolytic of 100-470uF (make sure the voltage rating is at least 20% higher than your supply voltage) and a 0.01uF ceramic (or two). It would be best to distribute multiple ceramic capacitors along the rails. Since you're not using both rails on the same side of the breadboard, you'll need to use jumpers; that will impact the high frequency bypass capability of the ceramic caps. Since you're not using the power rails as they'd normally be used, you could also put them from the power pin on one or more of the ICs to ground. You should be using the + rail near pin 8 on the timers as power and using the - rail near pin 1 on the timers as ground. If you use both of the "top" rails, you can use a jumper between the two ground rails. That will make mounting decoupling caps more convenient.

Is the yellow wire to the white switch making good contact? Are you moving the wire when you press that switch?

Press and release the white button and measure the output of the bistable.
 
Last edited:

Thread Starter

RoyCone

Joined Jul 15, 2022
21
Put them on the supply rails. I'd use an electrolytic of 100-470uF (make sure the voltage rating is at least 20% higher than your supply voltage) and a 0.01uF ceramic (or two). It would be best to distribute multiple ceramic capacitors along the rails. Since you're not using both rails on the same side of the breadboard, you'll need to use jumpers; that will impact the high frequency bypass capability of the ceramic caps. Since you're not using the power rails as they'd normally be used, you could also put them from the power pin on one or more of the ICs to ground. You should be using the + rail near pin 8 on the timers as power and using the - rail near pin 1 on the timers as ground. If you use both of the "top" rails, you can use a jumper between the two ground rails. That will make mounting decoupling caps more convenient.

Is the yellow wire to the white switch making good contact? Are you moving the wire when you press that switch?

Press and release the white button and measure the output of the bistable.
The yellow wire to the white switch is making good contact. I have 20 AWG wires so they're pretty solid and I'm careful while pressing the switch. I placed a multimeter probe at the yellow wire of the white switch, it goes 8.2 V depressed to 0.02mV pressed. The output of the bistable 555 is 0.02mV. IF I press the white button nothing changes. If I press the blue one, it goes up to 7.7V. If I wait, it drops automatically to 0.02mV after a couple or second, or I can press the white button to drop the voltage to 0.02mV immediately.
Do you have a schematic for the supply capacitor using a jumper wire from the right (-) rail to the left (-)? I have trouble seeing how many capacitors and of what type go where
 

Thread Starter

RoyCone

Joined Jul 15, 2022
21
Put them on the supply rails. I'd use an electrolytic of 100-470uF (make sure the voltage rating is at least 20% higher than your supply voltage) and a 0.01uF ceramic (or two). It would be best to distribute multiple ceramic capacitors along the rails. Since you're not using both rails on the same side of the breadboard, you'll need to use jumpers; that will impact the high frequency bypass capability of the ceramic caps. Since you're not using the power rails as they'd normally be used, you could also put them from the power pin on one or more of the ICs to ground. You should be using the + rail near pin 8 on the timers as power and using the - rail near pin 1 on the timers as ground. If you use both of the "top" rails, you can use a jumper between the two ground rails. That will make mounting decoupling caps more convenient.

Is the yellow wire to the white switch making good contact? Are you moving the wire when you press that switch?

Press and release the white button and measure the output of the bistable.
Oh shit, it works!!!! I placed a 100 microfarad at the base and 3x10 nano farad on the rails and now it works!!! I would've never found that by myself!!! Why is that happening? Just some inner chip circuitry thing? Anyway thanks a lot!!! I've been on this everyday for 2 weeks... Should I placed supply capacitors on every futur circuit with chips? IT's going to be weird to solder this on circuit board...
 

dl324

Joined Mar 30, 2015
14,905
Why is that happening? Just some inner chip circuitry thing?
This is the timer output stage from National Semiconductor's datasheet:
1658019170271.png
It's possible for both output transistors to be on (briefly) when the output switches state.

The outputs of CD4026 are "high" current inverters. Both of the MOSFETs in an inverter can be on (briefly) when the output switches state. This is from RCA:
1658020039826.png

This is a CD4069 inverter from an RCA datasheet:
1658019420675.png
Should I placed supply capacitors on every futur circuit with chips?
A conservative rule of thumb for decoupling capacitors is one ceramic cap per IC. That's usually overkill, but it will usually prevent problems with spikes being introduced on the power rails.

IT's going to be weird to solder this on circuit board...
If you enter your circuit in a schematic editor, you can use the editor to make a board layout.

Here's the flywire view from my schematic editor:
1658019774177.png
I do board layouts even when I'm going to wire point to point. It lets me use bare wires for most of the wiring.

I'll work up a placement for this circuit when I have time.

I'm not a fan of the book your using. It wouldn't have taken much time or space to advice the usage of decoupling capacitors. Using conventional schematics and teaching readers how to use them would be time well spent because, believe me, competent people don't use pin order diagrams in schematics. They're only useful for indicating wire congestion and that's what we use board layout programs for.

If the author didn't mention decoupling caps, that's a huge omission.
 

Thread Starter

RoyCone

Joined Jul 15, 2022
21
This is the timer output stage from National Semiconductor's datasheet:
View attachment 271591
It's possible for both output transistors to be on (briefly) when the output switches state.

The outputs of CD4026 are "high" current inverters. Both of the MOSFETs in an inverter can be on (briefly) when the output switches state. This is from RCA:
View attachment 271596

This is a CD4069 inverter from an RCA datasheet:
View attachment 271594
A conservative rule of thumb for decoupling capacitors is one ceramic cap per IC. That's usually overkill, but it will usually prevent problems with spikes being introduced on the power rails.

If you enter your circuit in a schematic editor, you can use the editor to make a board layout.

Here's the flywire view from my schematic editor:
View attachment 271595
I do board layouts even when I'm going to wire point to point. It lets me use bare wires for most of the wiring.

I'll work up a placement for this circuit when I have time.

I'm not a fan of the book your using. It wouldn't have taken much time or space to advice the usage of decoupling capacitors. Using conventional schematics and teaching readers how to use them would be time well spent because, believe me, competent people don't use pin order diagrams in schematics. They're only useful for indicating wire congestion and that's what we use board layout programs for.

If the author didn't mention decoupling caps, that's a huge omission.
I'm not at the level to understand the details of why the outputs are both on at the same time, so this will be sufficient for me now.
Yeah, I should learn a computer program to help me with my projects, but right now i'm just trying to make a habit of doing electronics, but it's hard when you face a problem like that. The book should have mentionned supply capacitors! But what do you want, that's what happens when you learn something by yourself...
Thanks a lot for the time and effort! I hope I'll get better fast, that way my question will be clearer : )
 

dl324

Joined Mar 30, 2015
14,905
But what do you want, that's what happens when you learn something by yourself...
You should expect more from the book you bought. I think I read somewhere that the author tried all of the circuits. If that's the case, he should have seen, or anticipated, one or more cases where decoupling caps were required and take the time to add a discussion because it could have saved you a significant amount of time and grief.

I added a power header, decoupling capacitors, and another digit:
1658024319130.png
The yellow lines are called fly wires. They show where things need to be connected. I highlighted the 9V net to give you an idea of why I placed components where I did.

It just occurred to me that the switch component I used in the schematic wasn't associated with an actual component, so the three switches are missing.

Putting the counters under the digits would reduce the X dimension, but I'm worried about routing congestion to the segments.

The grid is 0.1" and the board is 3.1"x2.2".
1658024461360.png
 
Last edited:

Audioguru again

Joined Oct 21, 2019
4,945
You re using the old fashioned NE555 that is based on antique TTL circuitry. Intersil makes the newer Cmos 555 (ICM7555, LMC555 and TLC555) and its datasheet shows the massive almost 400mA power supply current pulse caused each time the old 555 switches but the Cmos version does not do that. a pretty big supply decoupling capacitor is needed to keep the positive supply from dropping during each 400mA pulse. Or use a Cmos 555.
 

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