Daisy chained shift register problem :(

ZZzzzz...
I'm losing interest without absolute references. (Schematic of as-built) !

nurimo:
there are 15 pcb cards in system. Every 5 of them connected to a 40 A 12 V switching power supply.

Okay so you have PCBs.
So PLEASE post your schematic and your pcb pattern.
You are asking us to help, so please provide us with the information we need to help.
Tom..... :slight_smile:

Hi everyone, i have noticed something with my pcbs. I have a 0.1 uf cap between latch pin and the ground pin. I suddenly realised that 10 of the pcbs were not so bad and it was really noisy after 10. So I have 15 daisy chained 74HC595 IC with connected bare clock line and bare data lines. There is no cap on data and clock lines. And I have 0.1 uF cap as i said earlier. In theory and accourding to datasheet, it is recommended using a 1 uF cap between latch and gnd. So, I mistakenly used 0.1 for each IC. In this case if I daisy chain 10 boards, they must work due to parallel 10*0.1 uF caps. After that, the value goes up and filterin the noise become filtering the actual signals and it scrumbles again. Am I correct ? And if I am, what should I do ? there are a lot of suggestions on this post but dont know which one is safer and reliable.

https://forum.arduino.cc/index.php?topic=408135.30

"I have a 0.1 uf cap between latch pin and the ground pin."

Get rid of it. Digital control lines should never have caps on them. There is an Ardiuno page in the Playground showing a cap like that; we have complained about it for years.

0.1uF and 1.0uF from VCC to Gnd is needed tho.

CrossRoads:
"I have a 0.1 uf cap between latch pin and the ground pin."

Get rid of it. Digital control lines should never have caps on them. There is an Ardiuno page in the Playground showing a cap like that; we have complained about it for years.

0.1uF and 1.0uF from VCC to Gnd is needed tho.

In fact i have seen your complains about it and got rid of it. I already have 0.1 uF cap on output of 7805 regulator and 33 uF on input. I have 100 nF and 470 uf caps on 12V input. But a strange thing is when I touch the ground and latch line at the end of the line and squize it, scrumbling effect fade %60 approximately. It is still scrumbling but not so much. I thought, it is parasitic noise maybe ? And if you think the same what can be done ?

CrossRoads:
"I have a 0.1 uf cap between latch pin and the ground pin."

Get rid of it. Digital control lines should never have caps on them. There is an Ardiuno page in the Playground showing a cap like that; we have complained about it for years.

0.1uF and 1.0uF from VCC to Gnd is needed tho.

I have 12 V 30 A Power supply and every 4 shift register board connected to 1 power supply the outputs of shift register controls optocouplers and they opens and closes switches to power 12 V motors. Do you think problem might be the instant change of power supply ? since 7805 regulator feeds from same power supply ?

"Do you think problem might be the instant change of power supply ? since 7805 regulator feeds from same power supply ?"

Could be. Depends on how much of a current hit each motor is taking off the 12V line.

Can you try adding a separate 5V to your system to power the shift registers?
Example
http://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520+PS/

Keep the Gnds connected.
I still strongly suggest a 0.1uF cap at Each shift register.

CrossRoads:
"Do you think problem might be the instant change of power supply ? since 7805 regulator feeds from same power supply ?"

Could be. Depends on how much of a current hit each motor is taking off the 12V line.

Can you try adding a separate 5V to your system to power the shift registers?
Example
5V 4A Power Adapter OPENPEAK OP-20004

Keep the Gnds connected.
I still strongly suggest a 0.1uF cap at Each shift register.

How can I monitor the voltage level of power supply at aproximatelly 200 Hz ?

Use an oscilloscope.

CrossRoads:
Use an oscilloscope.

Okey here what I will do, I will power shiftregisters from a seperate power source and see if it gets better. And if it doesnt, my previous post was about parasitic decoupling. How can I apply to my project that ?

Perhaps add a termination resistor to the end of the clock and latch lines. 500 ohm, 270 ohm, something in that range, to Gnd.

Hi,
Post#31 and we still have no schematic or PCB pattern.
If we had them when asked, the cap to the signal line would have been picked up long ago. :o

Please some diagrams....

Thanks.. Tom.. :slight_smile:

TomGeorge:
Hi,
Post#31 and we still have no schematic or PCB pattern.
If we had them when asked, the cap to the signal line would have been picked up long ago. :o

Please some diagrams....

Thanks.. Tom.. :slight_smile:

As you know, it happened just after pcb fry incident. I just assumed it is connected to that. But it seems the problem is some noize in latch pin. Some suggestions were made on forum but not every one of them has good explaination. My problem originates from instant change of power supply load. Since i open 32 motors per power supply with different order in 10 ms interval. But here is what i cannot understand, cant i just have a big cap on vcc of the 74hc595 so that big power changes do not affect the ic ? I already have 0.1 uf

Hi, problem was my power supplies. I have changed them. Problem is mostly gone. I havent set all 4 power supply to same voltage by their pot but they are parallel connectable mean well brand 12 V 29 A power supplys. Do I need to set each of their voltages to the same or approximate values ? Can this be the cause of a little parasitic behavior "not setting them all to the same voltace "

nurimo:
Hi, problem was my power supplies. I have changed them. Problem is mostly gone. I havent set all 4 power supply to same voltage by their pot but they are parallel connectable mean well brand 12 V 29 A power supplys. Do I need to set each of their voltages to the same or approximate values ? Can this be the cause of a little parasitic behavior "not setting them all to the same voltace "

Hi, what do you mean "parallel connectable" ?
Please at least a power supply connection diagram!!! :o :o

PLEASE.....Tom.. :slight_smile:

TomGeorge:
Hi, what do you mean "parallel connectable" ?
Please at least a power supply connection diagram!!! :o :o

PLEASE.....Tom.. :slight_smile:

I can connect all V+ outputs of power supplies together and do the same for V-. I can do better, brand is meanwell and model is LRS-350-12KO

Check out the link below.

nurimo:
I can connect all V+ outputs of power supplies together and do the same for V-. I can do better, brand is meanwell and model is LRS-350-12KO

Check out the link below.
Connecting Mean Well Power Supplies in Parallel | Power Supplies Australia

You told us this;

Every 5 of them connected to a 40 A 12 V switching power supply

Your powersupply is not included in the list of current sharing SWMP that the link supplies!!!!!!

You do not connect all the V+ together, the gnds YES, but NOT the V+.

You connect the V+ to groups of your boards.
As in;

Every 5 of them connected to a 40 A 12 V switching power supply

The sharing diagram there will not work unless you have them ALL exactly the same voltage, not possible.

As they do not monitor each others current, they cannot evenly share current.

The noise could quite easily be the supplies interacting with each other.

Please at least a power supply connection diagram!!! :o :o

PLEASE.....Tom.. :)
PS. Are aware that if you supplied the schematics we requested 7 DAYS and over 30 posts ago, your problem could have been solved.

I want to share the connection diagram but its too complicated to understand from pictures and I didnt use wires to connect the components, I used NETs to do it. So I will send pics of pcb instead

TomGeorge:
You told us this;
Your powersupply is not included in the list of current sharing SWMP that the link supplies!!!!!!

You do not connect all the V+ together, the gnds YES, but NOT the V+.

You connect the V+ to groups of your boards.
As in;

The sharing diagram there will not work unless you have them ALL exactly the same voltage, not possible.

As they do not monitor each others current, they cannot evenly share current.

The noise could quite easily be the supplies interacting with each other.

Please at least a power supply connection diagram!!! :o :o

PLEASE.....Tom.. :)
PS. Are aware that if you supplied the schematics we requested 7 DAYS and over 30 posts ago, your problem could have been solved.

As you can see 7805 regulator has 2 capacitors 0.1 and 33 uf. The 0.1 cap at the top is not connected anymore. It was connected to Latch line. 12V supply connected to 1000 uf and 100 uf. But I added another one 100 nf. Also changed the smd resistors from 220 to 470 since I need only 2-3 ma per output. But the noise still there not much but there.

As I said in previous post, powersupplies are connected parallel right now. They have a name for this feature " current sharing." mean well powersupplies have this feature. So I connected V+ terminals together. Still every 5 board connected to 1 power supply but since they all connected together pcb boards connected together all ofcourse. But before you say anything, I tried to do it by seperating the power supplies and supply the 5 boards each. It didnt work, a little noise is still there, this is why I used current sharing feature.

I know they should be at exactly same voltage level or the higher one will be overloade and noise will still be there. I just followed the manufacturers suggestion on current sharing.

Hi,
What don't you understand with this statement?

Your powersupply is not included in the list of current sharing SWMP that the link supplies!!!!!!

Don't just copy and paste!!

Please read..

Also, why don't you have a fuse on each of your PCBs?

Tom... :slight_smile:
PS Please at least a power supply connection diagram!!! :o :o
An image of your PCB pattern and a schematic will help!!!!!!!