Picture of Arduino Based Meter - a many LED Driver
As the direct result of a question in the Instructables forum, for a bargraph to display data on the dashboard of a car, a custom electronics instructable.

Here, for your delectation is the Car-barDuino, a simple display system for analog and digital stuff, for a car, for a timer, for a thermometer, for whatever. I built it for a manifold pressure meter for friends car, I'm going to use it at work for some monitors in a research instrument.

Under the hood, it uses a micro configured to run "Arduino" sketches, so anyone can play with the code. All the spare I/O has been brought out to connectors to play with.

Enjoy and employ.

Step 1: What it can (and can't) do

Picture of What it can (and can't) do
In its current form, we can drive 2,  7 segment displays and a 30 element bargraph. We can mix LEDs from red/green/yellow, but it can't drive white or blue. If there was enough interest, I'd redo the design to allow higher voltage LED technology to be used. The current design is open ended, since each MAX7221 can be connected to the next over just 5 wires, and each can drive 64 LEDs at once.

There are 15 levels of digital control of LED brightness, and a SINGLE resistor to set the maximum brightness of all of the LEDs on one chip.

The processor can be any standard Arduino (Atmega 168 or 328) and with the ICSP connector, you can burn your own bootloaders.

The input interface uses a simple current limiting resistor and two diode clamps to the 5V rail. DON'T make a habit of driving into the clamps !

There are no input scaling resistors on the circuit at the moment.

DillyDog2 months ago

Great concept! I'm thinking of a sleek wall clock showing the time in a bargraph. Will this easily expand to 2 bars of 60 LEDs each (making 120 LEDs)? I don't immediately see why not.

steveastrouk (author)  DillyDog2 months ago

Yes. use 2 boards. You only need the processor on one of the boards. They were designed to be cascadable.

rendermatt4 years ago
Very nice. I'm sure I will find use for one of these one day! Haha, the reset mode reminds me of my knight rider scanner
Llamarama5 years ago
Minimalist design at it's very finest! Is it possible to connect an external sensor, somthing like a hall sensor, and use this as a speedometer/tachometer?

Either way an interesting concept!
steveastrouk (author)  Llamarama5 years ago
Yep, its eminently possible.

Listen carefully, because this spec even confuses me ;-)

The new board I have done (ready for a prototype or two) has TWO rows. You can use 2 digits on the top row, and 20 bars, or you can have no digits and 30 bars.

The 2nd row has provision for none,  2 or 4 digits. no digits 30 bars, 2 digits 20 bars and 4 digits no bars.

The board is standalone arduino....or it will work as a shield, if you don't populate the board, or it can accept shields.

AND it has expansion slots, so you can extend the display to EIGHT 7221s.

Its only very slightly wider than the MK1 board in the article.

Very confusing, but I think I have it. :)

So in theory I could have 2 Digits for 99MPH then the 20 bars for a tachometer, or 4 digits for MPH and RPM.

If I chose to extend I could have 8 digits and 40 bars? Or would I have to use 2 boards with 4 digits and 20 bars.

Or some variation thereof, I think, perhaps, sort of, mabey...

Regardless thoroughly intrigued and I will follow with great interest! :)
steveastrouk (author)  Llamarama5 years ago
See ? Now I'M confused, and I designed it ROFL.

I could have 2 Digits for 99MPH then the 20 bars for a tachometer, or 4 digits for MPH and RPM.


I could have 8 digits and 40 bars? Or would I have to use 2 boards with 4 digits and 20 bars.

Only on two boards.

Looking at OBD functionality at the moment as well, as a shield board.

Oh well, that would simplify programming greatly, 1 board for the speedo and one for the tacho!

Now to get a grip on programming! How I long for a world of logic gates and PROMs! LOL!
steveastrouk (author)  Llamarama5 years ago
Here'e the latest board design. Hope you can see the idea.

I see what you mean now! Looks like a good board! Can't wait to see the final product!
steveastrouk (author)  Llamarama4 years ago
Final board is in my hands now. More news when I put the chips on. ...

I am now extremely excited! :) Can't wait to build this myself!
Jeffrey G C4 years ago
i cant get it to download, ive tried to save it, but it wont let me save it as anything other than .tmp
steveastrouk (author)  Jeffrey G C4 years ago
Save it and rename it.
neutron75 years ago
Hi i am trying to download your code, i want to have a look at how you use a bargraph and 7 segment separately on max 7221 (im doing 7 seg + LED indicators) it points to a temp file.
steveastrouk (author)  neutron75 years ago
Save the file as a .pde file and open in Arduino.

Jayefuu5 years ago
When are you adding the videos? :)
steveastrouk (author)  Jayefuu5 years ago
When I reshoot with the other 10 leds on the bar.

steveastrouk (author)  steveastrouk5 years ago
Video is up now.
Where? Are you shure? There is a blank space where the video should have been.
steveastrouk (author)  mhkabir5 years ago
Hi Kabir,
Yep, first step :-)
If you can't see them, let me know and I'll send you the links.