Hi,
I am making a pedometer with an Arduino micro and am using a shift register to drive a 4 digit 7 segment display which displays the number of steps. Just wondering if I need a ceramic capacitor on the clock pin of the shift register to protect it.
Thanks in advance
Adding a capacitor to the clock pin will most likely prevent your circuit from working.
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Connect the capacitors between Vcc and GND.
Have you thought about clocking a decade counter chip instead of a shift register? The decoding from BCD to 7-seg display would be easier, I think.
A MAX7219 using SPI might be the best option for a 7 segment display.
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Thanks everyone for your help. It is very much appreciated.
Hi @LarryD , thanks for the detailed information. Is there a variant of the Max7219 that has only 4 digits on the display as that is the only size that will fit in my enclosure?
Thanks
The MAX7219 can be used with 4 seven segment digits.
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Hi LarryD, thanks for that information. I've had a look online and when I search for the Max 7219 I only get results for boards with an integrated 8 digit display. I would be grateful if you could post me a link of a site I could purchase a Max 7219 from.
Thanks
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Hi Larry@D,
thanks very much for all of your help. It 's very much appreciated.
Remember the 7219 drives a common cathode seven segment display.
Here is a sketch to get you started with the MAX7219:
/*
SPI_Max7221/7219
*/
#include <SPI.h>
const int slaveSelect = 10; //pin used to enable the active slave
const int numberOfDigits = 4; // change to match the number of digits wired up
const int maxCount = 9999;
int count;
//**********************************************************************
void setup()
{
SPI.begin(); // initialize SPI
pinMode(slaveSelect, OUTPUT);
digitalWrite(slaveSelect, LOW); //select slave
//prepare the 7221/7219 to display 7-segment data - see data sheet
sendCommand(15, 0); //Display test off
sendCommand(12, 1); //normal mode (default is shutdown mode);
sendCommand(11, numberOfDigits - 1); //7221 digit scan limit command, 0 relative
sendCommand(10, 8); //set medium intensity (range is 0-15)
sendCommand(9, 255); //decode command, use standard 7-segment digits
digitalWrite(slaveSelect, HIGH); //deselect slave
//displayNumber(count);
} //END of setup()
//**********************************************************************
void loop()
{
count = count + 1;
if (count > maxCount)
{
count = 0;
}
//send the current count to the MAX7219
displayNumber(count);
delay(100);
} //END of loop()
//**********************************************************************
//function to display up to four digits on a 7-segment display
void displayNumber( int number)
{
//sending all the digits to the display
for (int i = 0; i < numberOfDigits; i++)
{
//get the value of the rightmost decade
byte character = number % 10;
//sendCommand(reg,data)
sendCommand(numberOfDigits - i, character);
//next digit
number = number / 10;
}
} //END of displayNumber()
//**********************************************************************
void sendCommand( int reg, int data)
{
digitalWrite(slaveSelect, LOW); //chip select is active low
//2 byte data transfer to the 7221/7219
SPI.transfer(reg);
SPI.transfer(data);
digitalWrite(slaveSelect, HIGH); //release chip, signal end transfer
} //END of sendCommand()
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I’m driving 8 x 8x8 matrices with mkr zero and I found that SPI very temperamental not to mention that default SPI.begin() just breaks it, only beginTransaction with SPISetting works, and even that gets wierd trying to run all 8 in cascade. ShiftOut on the other hand is as solid as a rock.
Yes, but that is somewhat misleading to say.
It drives common anode displays perfectly well. 
This is a misunderstanding resulting from a particularly stupid blunder in the Arduino tutorials.
I use 8 and 4 digit all the time with SPI, I’ve never experienced that problem.
Yes CA can be used but with software contortion 
Not familiar with mkr zero, what voltage is the controller ?
If 3v, I believe there is a special 3v version of the 7219.
3.3v, I have no idea what version of controller, it is under the led matrix which is not removable. the seller indicated it needs 5v and it seems ok
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