LED Matrix completed !

LED Matrix completed !

Postby Janke » Wed Mar 29, 2017 1:16 pm


Now, the LED matrix has grown to 30 modules, i.e. a display of 16 x 120 pixels.

I've installed it above the background panorama on my model railroad, where it shows departures & arrivals, as well as running a Quiz game for the exhibit visitors - see photo.

The large font is readable from very far away, see a sample in the other photo!

A few notes to anyone planning to use the MAX7219 LED Matrix modules:

- the modules generate a lot of electrical noise, so add a decoupling cap (100 uF) on each module (they only have 100 nF built-in).
- Preferably have a separate power line for the modules. (I use two "buck" step-down 3-amp boards from 12 volts, one for the EzSBC, the other for the LED modules.)
- Make sure the module's data lines are kept LOW during power-up. If not, the modules may power on with all LEDS at full brightness! At 40 mA each, that's asking a lot of the power supply!

My own solution is to power on the LED Matrix buck board from within the Basic code, using one output pin, a simple current booster and a small relay. I also have the daisy-chained module data input line pulled low with 4.7 KOhm, and then sending the display data with signals on other EzSBC pins. (The modules need three pins for data, clock and load.) This prevents any annoying start-up, full brightness flashing of the displays.

Oh, one more thing: During testing, don't connect the project's power to the PC/Mac through the USB cable! I cut the read lead in the cable, and can safely program and debug the display running on its own power.

Good luck with all your projects!

PS: The MAX7219 data sheet is easily found on Google.
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