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How to control conventional and charlieplexed matrices
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How to control conventional and charlieplexed matrices

by Smart_celery on Thu Nov 19, 2020 5:24 am

How about it, this is my second post in this forum

I need to design a system that allows me to control a led array which can be either a conventional array (nxn) or a charlieplexed array (CP).

For now the power stage and the microcontroller are not yet defined since the most important thing is basically to achieve the task outlined above.

The arrays usually have a maximum of 50 LEDs, they can be 7x7 or 8 pins in CP. The LEDs are usually supplied with 10V to get a current of 10mA which is the physical limit of the technology, a higher current basically melts the conductor wire (yes, we are talking about very very small).

The LEDs are turned ON one by one, no complex patterns, figures, or dimming are required, nothing. Just ON and OFF with a frequency not exceeding 100kHz.

Before explaining my first idea I just want to reiterate that the system must control only one configuration at a time, this means that through an HMI/GUI you define the topology of the array and act on it, not that you have two different LED arrays connected at the same time and you must act on them. NOPE.

My first idea (failed) was to use the -already know around here- IS31FL3731 chip from Lumissil Microsystems.
This is an array driver that is specific for crossplex (charlieplex) topologies, which allows you to control two arrays with a total of 144 LEDs (much more than I need). However my idea was to share the first 8 available pins (CA1 - CA8) to control the Charlieplexed array, and for the conventional one use the same CA1 - CA7 and CB1 - CB7, thus that way I thought I can control rows and columns.

However, contacting the manufacturer, the registers 00h - 11h which are responsible for defining the ON-OFF status of individual LEDs, to be defined as OFF leave the pin in a floating state, not GND. That's why the whole idea went to hell.

Thanks in advance for any idea or help.

IS31FL3731 Datasheet:

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Please be positive and constructive with your questions and comments.