Sanity check on project plan

Greetings, all.

I thought I might post some general ideas for the implementation of a "vintage/retro" model scoreboard project I'm working on, just to see if there might be glaring errors or suggestions in general.

First, this scoreboard is going to be a faithful, working reproduction of an mid-70's/early-80's era college stadium football (American football, that is) scoreboard, with a pretty standard home/visitor score, working countdown clock, and a space for current quarter, time outs left for each side, as well as down, yards to go, and "ball on" indicator.

The score and clock digits will be .8" yellow seven-segment LED's; all remaining digits will be .56" yellow seven-segment LED's. The score and clock will consist of four two-digit LED's; the others will be four single-digit LED's and two double-digit LED's, totalling 8 "large" digits and 8 "smaller" digits.

I plan to drive the LED's with a pair of daisy-chained MAX7219's; one for the smaller LED's, the other for the larger ones. With those drivers handling the multiplexing, the max draw should be at most 100-120mA for each bank of LED's being driven, with the whole schmear hosted on an Arduino Uno. I plan to wire up a bunch of momentary contact pushbuttons on a separate small console to control the digits through a script in the Uno. So far, that doesn't seem very complex or complicated.

The part I'm not yet sure about are the matrix regions I plan to build for the team name "badges" over their score sections. I plan to use 8 5x7 LED matrix displays in what would become 40x7 display region. I should be able to drive these with two MAX6953's (one per four matrix displays). Since I need two such badges, I'll need four total 6953's to drive 16 5x7 matrix displays.

My question is whether its realistic to put two MAX7219's and the four 6953's off a single Arduino. I'm confident the Uno could handle the two 7219's and the 16 LED's they will drive for the basic scorekeeping, but I'm not at all sure I could push the additional matrix drivers/displays on there as well. I've all-but resigned myself to a dedicated power supply; should I be looking at a second Uno to run the name badges? The intent for the badges is to do nothing more than statically display each team's name; no animation or graphic images; set it once and forget it.

I may well be overthinking this, and underestimating the Uno, but I thought it more wise to ask than wonder. Apologies if the question is dumb or the answer obvious to the rest of the world; just isn't to me :slight_smile:

Thanks.

The MAX6953 chip uses the i2c protocol (e.g. "Wire" library in Arduino) so you just need to connect it up to the Uno SCL/SDA pins (A4/A5). Since you will be using 2 of these chips, you will have to make them respond to different addresses on the bus by wiring the A0/A1 pins differently (one has both tied to ground, one has one tied high, one to ground)

I am wondering what is so good about the MAX6953s?

Five MAX7219 matrix modules (you can get them in groups of four) would make a 40 by 8 unit, so ten modules would do your matrix displays. What colour did you want it?

For any practical project, you would be better to use a Nano than a UNO.

Paul__B:
I am wondering what is so good about the MAX6953s?

Five MAX7219 matrix modules (you can get them in groups of four) would make a 40 by 8 unit, so ten modules would do your matrix displays. What colour did you want it?

For any practical project, you would be better to use a Nano than a UNO.

The pre-built 4-by-8x8 were very intriguing and would have been a perfect choice had I been able to find them in a small enough configuration. I found only 1.2" sizes which are too large for my project, and even then none were in yellow.

What makes the Nano preferable/more practical than the Uno? Sorry for the naive question.

Thanks.

like this? mini 8x8 LED

0.7" I2C

Found doing a search for "miniature 8x8 Yellow LED"

Per that link, only four remain. I'd need 10. The closest matches I could find were sold out or were selling at something like $59 each. I found an .8" version, which is really still too large vertically (.7" is ideal given my constraints) and a proper multiple would be too narrow (4 @0.8" is 3.2") while an oddball 5 is 4" - and that's too wide. My badge region is constrained to .7" x 3.5"

Thanks for the idea, nonetheless!

soonerdave:
What makes the Nano preferable/more practical than the Uno? Sorry for the naive question.

Size. They both use the AT328 chip. With the nano, since it uses the SMD version of the chip, you do get A6 and A7 if you need two more analog inputs.

Size is an advantage, but the overall form factor is more practical. Two straight line of pins with a smaller connector on the end (advisable to re-solder the pads that hold it on with some real solder), generally supplied with the pins not soldered so you can solder your own leads directly, using the pins you can mount it to a solderless breadboard, a "screw shield" or as a daughter board to your own custom PCB.

And generally cheaper. Yes, it also has the last two Analog pins. :sunglasses:

Well, as I've read through these replies (thanks) and done some checking, I've found the 6953's are nearly out of stock everywhere (obsolete) and the places that have them ask $30 each. That'd be $120 for my project. Yikes. For a hobby/fun project, that's getting a little steep. I've got nearly everything else I need for this project, and I don't believe I've spent that much.

Switching to 7219s doesn't help much; I'd need one for each matrix, and even those are a bit scarce. I happen to have to 7219's on hand, but those are already allocated.

Not sure what to do; I don't see many alternatives. I see Adafruit still offers 16x8 "featherwing" backpacks, although I'd have to wire the LED rather than solder it; I need to mount the LEDs side-by-side. Even then, the final dimensions of .8" x 3.2" aren't a very good fit for my project :frowning:. Alas.

Guess I'm going to have to make one of those tradeoffs or leave this part of the project out. If there are better suggestions out there, I'm open to them.

soonerdave:
Switching to 7219s doesn't help much; I'd need one for each matrix, and even those are a bit scarce. I happen to have to 7219's on hand, but those are already allocated.

I hope you are not suggesting that MAX7219s are scarce. :astonished: The small matrices may be,

Paul__B:
I hope you are not suggesting that MAX7219s are scarce. :astonished: The small matrices may be,

Nono I was just referring to the fact I'd need one per matrix....going from four 6953's to 14 7219's

Greetings, all. I wanted to post an update to this project.

I have the board about 85% functional, with a 18-button control panel working to control the main clock, quarter, timeouts, score, and down-and-distance numbers. It has run in testing for considerable time with only a minor power I discuss below.

I initially wanted to explore using hardware interrupts for driving one-second ticks on the clock, but I realized the Arduino isn't the ideal place for that kind of code (even though it could be done). I opted to implement the scoreboard software as a finite state machine, going from an IDLE state to one of various control-input states. That has worked out extremely well, and allowed me to write the.clock as a measure of millisecond intervals between loop() execution; when more than a second has passed, tick the clock - perhaps not atomic accuracy, but more than adequate for this purpose.

The only issue I have regards power consumption. I am driving right .7" seven segment LEDs with one 7221, and another set of 8 .4" LEDs with a second (cascaded) 7221. The second set of LED's will, at times shimmer/shudder.or.go completely dark. Because I speculated power, I purposely tested the idea by driving "8" values to all digits - and sure enough, that induced the second MAX shimmer/shutdown. So I'm off to build a separate power source that can deliver more than the 500ma the Arduino can provide, esp considering I still have to wire up four 6593's to power a series of 5x7 matrices for the team name badges.

If nothing else, I'm getting much better at soldering and rediscovering interest in an old hobby. Thanks for the prior support.

soonerdave:
So I'm off to build a separate power source that can deliver more than the 500ma the Arduino can provide,

That is a most bizarre statement!

The Arduino can not "provide" anything! It is not a power supply, it is a microcontroller board.

Of course you need to power it from the same regulated 5 V power supply that you use to power your MAX7219/ 7221 modules; you connect that power to the "5V" pin (and ground).

A practical power supply for the Nano (or UNO, Pro Mini, Leonardo etc.) is a "phone charger" with a USB output connector for 5 V, generally up to a couple of Amps though you can not feed more than 500 mA through the USB connection.

A real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" and "Vin" connections to the on-board regulator is a usable source of 5 V power. This is absolutely not the case. It is essentially only for demonstration use of the bare board back in the very beginning of the Arduino project when "9V" transformer-rectifier-capacitor power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.

Paul__B:
That is a most bizarre statement!

The Arduino can not "provide" anything! It is not a power supply, it is a microcontroller board.

Okay, sorry if I said something stupid.

I just tried to power the chips/LEDs from the 5V source on the Arduino. I guess that was a stupid thing to do, and I'm sorry. It was not clear to me that trying that was obviously dumb. As I said, I'm going about taking an existing external power supply and using it to power the project.

Again, sorry for saying something stupid. Was just kinda proud of my progress and thought I'd share, but now I feel kinda dumb. Live and learn.

Hey, don't take it so hard! :astonished:

My concern is that a lot of Arduino tutorials, both on the site and elsewhere, seem to imply that the on-board regulator on the UNO/ Nano/ Mega2560/ Pro Mini/ Leonardo/ Pro Micro is actually useful. Then innocent people try to use it in a project and turn up here when it goes belly-up.

Now powering through the USB connector is also limited, by a "polyfuse" on the UNO and a diode on the Nano, so you lose voltage and are constrained to 500 mA or so.

Current "phone chargers" provide regulated 5 V (though some contributors here express doubts about that) to either 1 A or 2.1 A and have a USB connector as output - and are generally quite cheap. (Avoid dodgy Chinese products from eBay; best purchased locally as you have a degree of warranty, even if they are all made in China.) You either chop the end off a USB cable to wire it to your 5 V devices and the "5V" pin on the Arduino, or maybe if that is not neat enough, get a USB "spill" board like this:

This avoids any losses or interruptions between power source and active components.

soonerdave:
Per that link, only four remain. I'd need 10.

You just have to check the source. They have many more LED matrix displays available.