Hey guys,
I have read and been told that I should place 0.1uF ceramic capacitor on Vcc pin 16 of the 595. Now I have three 595s do I have to place 3 capacitors 1 for each chip or only one is needed?
One more question, I was reading this tutorial here ( http://www.arduino.cc/en/Tutorial/ShiftOut ) and if you scroll down to part "2. Connect to Arduino" it says that I have to place the capacitor on the latch pin if I am having problems, but nothing about placing one on the Vcc.
Ideally, you would put 1 capacitor on each chip (3 caps total), each chip as close to the power/ground pins as possible. It may well work with just 1 chip for all 3, or it may not.
I don't think placing a capacitor on the latch pin is a good idea at all. Unfortunately, not everything on the Internet is true 
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Beat707: MIDI drum machine / sequencer / groove-box for Arduino
Got it thank you, but if i take out the latch capacitor the LED matrix goes berserk on me
That's a symptom of another problem then. Try putting a 220 ohm resistor in series with the latch signal (instead of the capacitor). Also make sure the grounds of the '595 chips go to the Arduino over as short a path as possible.
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The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins
We have been trying to get that capacitor removed from the tutorial for years because it is defiantly wrong and will damage your arduino because it causes excess current to flow in the pins many times above the absolute limit given in the data sheet. But for some reason all the requests get ignored.
For more on decoupling:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Can you tell me the name of the problem, so I can read about it. I will come home and give it a tr
Thank you
RuggedCircuits:
That's a symptom of another problem then. Try putting a 220 ohm resistor in series with the latch signal (instead of the capacitor). Also make sre the grounds of the '595 chips go to the Arduino over as short a path as possible.--
The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins
The problem is broadly one of "signal integrity"; my guess is that you are either seeing a bad case of overshoot/undershoot/ringing, or reflections due to long wires between the Arduino and the '595.
Here is some good bedtime reading:
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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected
Thank you for the link.
I have rewired the 595s on the breadboard to make sure that power and ground are as close as possible on the chips, and have implemented the 220ohm resister as you have recommended.
But the matrix was still flickering in places it shouldn't be. I managed to solve the problem but I am not sure why my solution works. If you could give me an explanation would be great.
I have a 9v wallwart going into a 5v regulated power supply circuit on the breadboard. I have connected my 3 595s to it as well as the LED matrix. My arduino is powerd by the USB cable running from my computer and from it I have 3 wire ( data, clock, and latch) going into the 595's that are located on the breadbaord. When I have it setup this way I have flikering in my matrix. But if i connect the ground rail of the breadboard to the arduino flickering stops and everything runs perfectly.
I am puzzled by this, since I have thought it doesn't matter where the ground connection is.
RuggedCircuits:
The problem is broadly one of "signal integrity"; my guess is that you are either seeing a bad case of overshoot/undershoot/ringing, or reflections due to long wires between the Arduino and the '595.Here is some good bedtime reading:
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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected
On paper it doesn't matter, but in real life it matters This is what I meant when I wrote:
Also make sure the grounds of the '595 chips go to the Arduino over as short a path as possible.
All electron flow must be in a loop, from the source, through various components, and back to the source. The wire you call "ground" is part of the loop, but it isn't anything terribly special, just a point in the circuit that we arbitrarily call "0 volts". By not connecting the grounds directly from the Arduino to the '595 chips you are creating a really big loop, running through the USB cable, to your computer, to the mains outlet on the wall, through the wall wart (which is probably isolated so doesn't even have a direct connection to ground), then to your breadboard. Through these long loops there can be voltage imbalances (all wires have resistance and inductance). By connecting the Arduino and breadboard grounds, the electrons flow over a much shorter loop.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
I have a 9v wallwart going into a 5v regulated power supply circuit on the breadboard. I have connected my 3 595s to it as well as the LED matrix. My arduino is powerd by the USB cable running from my computer and from it I have 3 wire ( data, clock, and latch) going into the 595's that are located on the breadbaord.
In my book that is not connecting the grounds together, see:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
Grumpy_Mike:
We have been trying to get that capacitor removed from the tutorial for years because it is defiantly wrong and will damage your arduino because it causes excess current to flow in the pins many times above the absolute limit given in the data sheet. But for some reason all the requests get ignored.For more on decoupling:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Forgive me for posting on this old topic :
As grumpy_mike said here and in many other places, capacitor is short when its empty, but this must be harmfull when connecting vcc of 595 to ground, when vcc comes from arduino tiny regulater with maximum 100ma(its about 200 for pro-mini but i use another LDO regulator) how its not bad for regulator with low output ability but damage chip with 40ma max output per pins. Please help me
In short voltage regulators expect capacitance on its output and have protection from overload inside.
Arduino is made to try to provide as much power as the load needs and it will die trying when you give it too heavy load.