PaulRB:
Those displays require 20mA per segment, or 30mA if multiplexing.If not multiplexing, that's 20 x 8 x 6 = 960mA.
If multiplexing, you would need 30 x 8 x 6 x n where n is your multiplexing ratio. So with a multiplex ratio of 1 in 2 (=0.5) that would be 720mA, or with a multiplex ratio of 1 in 6 (=0.167) it would be only 240mA. But the higher the multiplex ratio (lower value of n), the lower the brightness of the displays.
My main concern is not the current output of your supply (although 960mA is a little too close for comfort), but the voltage. As I said before, you always need more than the forward voltage of the display, for switching/current limiting etc.
You should never connect leds to power without some kind of current limiting. Even if the led forward voltage matches the power supply. if you want to know why, I think Grumpy_Mike gives an explanation on his web site.There are two ways to limit the current. One is to use resistors, the other is to use a chip who's outputs have "constant current circuits". Most chips (e.g. Arduinos, shift registers) don't have those. But some chips like max7219 and saa1064 do, so you don't need current limiting resistors.
Definitely worth a go. I've used this chip before to drive 1.5" blue 4-digit 7-seg displays with a forward voltage of 6.5V from a 9V supply, so I had an extra 2.5V than I needed. You have virtually no extra voltage, so I don't know, try it. I will draw you up a diagram. What kind of Arduino are you using?
Test sketch:
#include <Wire.h>
#define SAA1064ADDRESS 0x70
void setup() {
Wire.begin();
Wire.beginTransmission(SAA1064ADDRESS);
Wire.write(0); //Update control register
Wire.write(0b01110110); // No multiplexing, max segment current
Wire.endTransmission();
}
void loop() {
for (int i=0; i<=255; i++) {
Wire.beginTransmission(SAA1064ADDRESS);
Wire.write(1); //Update digit 1
Wire.write(i);
Wire.endTransmission();
delay(100);
}
}
Thank you SO MUCH! You are a scholar and a gentleman! I'll try my best to pick up a power supply later at a store. I might have to read up a little more on multiplexing later again. I believe I've done multiplexing before but I kind of did it my own way with 4 digit segment displays. Heres what I did if you're interested.
Every time I switch numbers, I added a delay of around 100ms. The program was just a timer that incremented in seconds. So every 1000ms, I updated the numbers. I just summed up the delays in the loop and every time it reached 1000ms I updated each value.
I will read up more on multiplexing and multiplexing ratios. My current power supply has 1A and 12V but like you said perhaps it would be best if I had some more voltage. I think I have a 15V charger lying around somewhere if I'm too lazy to run to Frys Electronics.
I'm using an Arduino UNO R3. Is that enough information? I'm still new to this and arduino so I'm not sure if theres any other specifications you need. Thank you again so much for the code and the sketch and all the help. I'll give it a go with the 12V Power supply I have if not I'll try something a little bit higher. What would you recommend if I wanted to power six of these? a 60V power supply?
Can I ask what program you used to draw the circuit connections? I really really appreciate it also its really pretty.
So I was looking at your schematic....shouldnt there be current limiting resistors anywhere? Or is this case fine since I'm using the SAA1064 chip like you said?
P.S - OH And you were right back a few posts, I did blow the fuses on my multimeter. But I have had them replaced so the mA and microA ammeters work good now 