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Topic: Daisy chained shift register problem :( (Read 1 time) previous topic - next topic

lastchancename

#15
Mar 09, 2018, 04:05 am Last Edit: Mar 09, 2018, 04:08 am by lastchancename
Quote
The problem is not the design or something else.
Then why are we here?

Does anyone else see this could have been addressed 12 posts ago with an accurate schematic?  There may still be underlying design issues in the circuit as-built.
Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

nurimo

"ABSOLUTE MAXIMUM RATINGS (1)
Continuous output current +/-35mA


Continuous current through VCC or GND  +/- 70mA


(1) Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratingsonly, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied. <b>Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.</b>"

So 35mA rating is not recommended long term.
And the power supply pin  only supports 2 pins at that current.

Further design questions:
Do you have 0.1uF cap on the Vcc pin of each shift register?

Are you sinking current (low outputs) to turn things on? I would use TPIC6C595 (100mA per output) or TPUC6B595 (150mA per output).



Your recommendations are really good but i just want to ask this, 10 mA each output makes 80 mA total output. Isnt this in safe range ? or I should i use something else ?

CrossRoads

Well, 80mA is greater than 70mA.  As an engineer I would suggest something else.  And did, if your load can work with the shift register sinking current from it to activate it.  LEDs and motors work great that way.

I even offer a board with a '328P and 1 to 12 shift registers to control up to 96 outputs.
http://www.crossroadsfencing.com/BobuinoRev17/#LED-Driver
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nurimo

Well, 80mA is greater than 70mA.  As an engineer I would suggest something else.  And did, if your load can work with the shift register sinking current from it to activate it.  LEDs and motors work great that way.

I even offer a board with a '328P and 1 to 12 shift registers to control up to 96 outputs.
http://www.crossroadsfencing.com/BobuinoRev17/#LED-Driver

That is great idea. Im just asking to confirm. TPICB595 does not source they sink right ? then I need to change my design by connecting anode to its drain pins. My solution is this , I will connect jumper to the anode and cathode of the leds, if 74hc595 does not work like this time, I will remove the jumpers from ground side and connect them to kathode side. This way I will have 2 shift register on board for fail safe. I just want to as what is the value of ceramic capacitors in your circuit ? I did not use any ceramic capacitors in mine. Is is better for high frequency operations ?

nurimo

Well, 80mA is greater than 70mA.  As an engineer I would suggest something else.  And did, if your load can work with the shift register sinking current from it to activate it.  LEDs and motors work great that way.

I even offer a board with a '328P and 1 to 12 shift registers to control up to 96 outputs.
http://www.crossroadsfencing.com/BobuinoRev17/#LED-Driver

It later occured to me, if the problem caused by shift register overload, it would be go away when i changed the whole shift registers right ? im not opening all of tbe outputs at all times. It consumes max 50 ma at a time. I have disassemled the fried pcbs. There is no visual problem other than fried power rail. I will post pics after I shop some components today.

lastchancename

#20
Mar 09, 2018, 10:47 pm Last Edit: Mar 09, 2018, 10:47 pm by lastchancename
ZZzzzz...
I'm losing interest without absolute references. (Schematic of as-built) !
Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

TomGeorge

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..... :)
Everything runs on smoke, let the smoke out, it stops running....

nurimo

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

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.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nurimo

"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 ?

nurimo

"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 ?

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
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.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nurimo

"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.


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

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

nurimo

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 ?

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