Hi! The title says it all, I need to build a 10 digit 7 segment common anode high voltage countdown. I don't know much about electronics and have been looking online for info on how I could make this for over a year and now I need your help!
I work with 2,3" 6,5 V common anodes (view specs in attachment). I made two graphs, could anyone tell me if there is a possibility that it could work?
Thanks!
14881? 5600 x 2550? Can't see enough of that to make sense.
Rescale to not much over 1000 wide.
What does the "Arduino?" label mean?
Does the Arduino have anything else much to do? It should be able to do this without the need for the 7218 driver chips.
Also those chips multiplex the displays but you aren't muxing, all the anodes are connected directly to 6v5.
And another also, if Vf of the displays is 6v5 you need a higher voltage to drive them because how do you calculate the resistor value if V (VCC-Vf) is 0?
And yes the pic is too large, it forces people to download it and view in another package.
Rob
Hi..
Look at this for 4 digits and get it going.
Then migrate to large number of digits, do this in stages especially if
I don't know much about electronics and have been looking online for info on how I could make this for over a year and now I need your help!
You will learn as you go, for someone who
I don't know much about electronics and have been looking online for info on how I could make this for over a year and now I need your help!
that is quite a pair of circuit diagrams.
Tom...... 
Hi marlene,
That first diagram seems like a lot of chips! 20 altogether. Each digit is driven by a 74hc575 shift register combined with a uln2803 to boost the current. You could reduce that down to 10 chips by using tipc6b595 instead. Those chips are like a combination of the 74hc595 and uln2803 in a single chip. You will also need 80 series resistors, and you will have no ability to change the brightness depending on the ambient light level (although that could be achieved by connecting a PWM output from the Arduino to the Output Enable pins on the 595s). The advantage of this type of design is that there is no multiplexing, so the display will be maximum brightness. If used outdoors this could be a big advantage. Having said that, in bright sunlight, led displays are pretty useless however you drive them.
The second diagram uses two maxim 7218 chips and, again, uln2803. I had never heard of these 7218 chips before. 7219 are far more common. But max7219 can't work with the 6.5+ volts you will need for the displays, and I suspect 7218 would be no different, even if you could find some.
The other problem with that second circuit is you could not wire the segment outputs of the max7218/9 direct to the 6.5V supply like that anyway. Also, one chip is running 8 digits and the other is only running 2, so it would be difficult to match the brightness (even though the 7219 has 16-level brightness control). 5 and 5 would be a better idea, but like I said, I don't think these chips will work at the voltage you need.
A third option would be to use 3 saa1064 chips. These can cope with the 6.5V displays and each chip can run 4 digits with a couple of extra transistors. This would mean the digits would be multiplexed with a 1:2 ratio, so some loss of brightness, but still fine for indoors and maybe outdoors. Other advantages include no need for 80 current limiting resistors (only 3) and built-in brightness control.
Paul
I can't see the first pic, it just disappears when I click on it. But yes using a 74hc595 (oops, tipc6b595) would be a very simple way to do this.
Rob
Ok sorry for the huge image! Ans thank you all for your comments! I will work on this and give you news of how it developed!
Wire up my board with current limit resistors & your display, will be all set:
http://www.crossroadsfencing.com/BobuinoRev17/
