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I saw this project online for a simple binary clock:

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It's a very simple circuit. What I can't figure out, is how you can control each row separately.

The parts list is as follows:
1 - High Quality Lead-Free Professionally Printed Circuit Board 2"x2"
1 - ATTINY45 Microcontroller
1 - Socket for Microcontroller
12 - Red LEDS (1 extra)
2 - 25 pF Capacitors
1 - 16 Mhz Crystal
4 - 75 ohm Resistors
1 - Mini USB connector

The minicontroller is an ATTiny45 so I imaging it is using Arduino code. I have used PWM a bit for fading LEDs, but having a 4-bit value change which LEDs are on and which are off eludes me.

Can someone explain the process of what is going on in the software / hardware?

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We can't realistically answer this specifically without a circuit diagram. There are various techniques which exploit the fact that LEDs only light up if current flows in one direction, such as "Charliplexing". – pjc50 Apr 10 at 13:54
How do you want us to explain "what is going on in the software / hardware" when you don't give us the software / hardware? Or even a link to the project you found "online", where that may be. – Camil Staps Apr 10 at 14:19
the board is using charliplexing (en.wikipedia.org/wiki/Charlieplexing) to control the 11 LEDs via 4 I/O pins based on the way the traces are laid out – Gorloth Apr 10 at 14:49
An AtTiny45 does not at all imply Arduino code. – Anindo Ghosh Apr 10 at 20:02

closed as not a real question by Leon Heller, Brian Carlton, Nick Alexeev, Olin Lathrop, rawbrawb Apr 10 at 20:11

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

1 Answer

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By looking at the LED matrix of 11 positions, you can see that the bottom 4 and the top 4 have a similar pattern in the layout...4 are connected in common in both and add the middle left LED to their common trace. Therefore, you can deduce that these ride on a rail that can be pushed high or low based upon the output they are connected to. And 6 (2 bottom right, 2 center right, 2 top left) have a common trace. Then the other 6 (2 bottom left, 2 center right, 2 top right), share another common trace...the odd ball is the center left that is already configured by the first connections. So that makes 4 connection points on the matrix - that odd one on the middle left is a duplicate used for some interconnection. I suppose the 4 resistors are current limiters. Imagine a bridge rectifier circuit where the diodes are replaced by light emitting diodes. That equals 4 rail points that can be moved to high or low for 16 unique binary values. If the diodes are connected to other diodes in reverse connections, you'd have 8 possible values lighting up individual LEDs. Now if additional diodes are added "across" the tie points, you could have up to 4 more values but I assume one of those value "should" turn them all off leaving only 11 conducting values and 1 non-conducting value!

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