a bit of context: i'm new to arduino and to coding (learning c++ right now), i've been playing with electronics (old fashion stuff like 555 timers etc...) for a few years now, im quite poor and this is not going to change anytime soon unfortunately so my budget for hobby is quite low.
i have an idea for a project but im not sure its even possible.
What would be the best way (or would it be possible) to drive 40, 7 ssegments small led display with arduino cheaply and efficiently?
-can involve many atmega chips,
-need to display letters and numbers
-cannot be too expansive
for instance after some google research i found the Max6951(and other similar chips from the same company) that can drive 8, 7-segment display..
but the problem is the price.
they go for $11+ each, so thats about $60 right there not counting anything else. very expansive.
can any of you amazing creative mind help me figure this out??
Maybe you could make an Atmega328 do the job (that the MAX7219 does) with suitable programming, however the other chips like the MAX7219 have built-in current limiting. Without that you are going to need a lot of resistors.
You would still need 10 of them (the MAX7219 handles 4x 7-segment displays), and thus you would have to connect them together somehow. The extra capacitors, resistors, resonators, etc. might start pushing the price up to what you would pay for a dedicated chip.
I've not used that so can't comment, but if you're okay with a lot of wires, MAX7219 is something I've found effective. If you already have the 7-segment LED digits then MAX7219 should be around $1.50 or less each, depending on where you shop.
Alternatively you can get pre-built 8 and 16 digit 7 segment arrays with the driver chip inbuilt from the likes of deal extreme for under $10 delivered worldwide. A nice review on Tronixstuff explains how to drive a couple of different versions of that.
MAX7219 is available for $1.25 from taydaelectronics.com. I ordered 12 of them earlier today, $1.87 for shipping.
Each will drive 8 7-segment displays + decimal point, (or 64 LEDs). Just need 1 current limit resistor per chip, ~22K, and a 0.1uF and 1uF cap per chip.
40 digits, need 5 chips.
Single arduino can drive them easily.
[quote author=Nick Gammon link=topic=131520.msg988840#msg988840 date=1352438392]
You would still need 10 of them (the MAX7219 handles 4x 7-segment displays), and thus you would have to connect them together somehow. [/quote]
Sorry to disagree but the MAX7219 handles 8x 7-segments so only 5 needed
I'm new to arduino as well, but I got a similar project: drive 52 7-segment displays (10-20mA each).
What I'm worried about is the amount of current that would be required. If I use MAX7219 ICs, will I be able to keep inside the 500mA limit ? (imposed by the USB connector as I understand).
The other line of thought is to use TIP6B595 IC to drain some external power source.
regards, krajo
ps: obviously I could go with a couple of LCDs, but LEDs would look cool
If you hav 52 digits, that's 7 MAX7219s.
Each MAX7219 only has the equivalent of 1 digit on at a time, 7 segments @ 20mA would be 140mA.
So theoretically you would be hard pressed to support more than 3 at once from a USB source.
I would suggest an external 5V source to power the MAX7219s.
Connect its ground to the Arduino ground.
