talking to mikroelektronika 2x 4 7-segment display

hello,

i purchased https://shop.mikroe.com/serial-7-seg-display-2-board - as it's using max7219 i did not expect any issue. yet.. the examples do do not really work.

i wired it like this (espruino pico):
cs = b14
sck = b13
mosi = b15
gnd = gnd
vcc = 3.3v

can someone please advise if there's something that can prevent from the configuration to work? currently the display seem to be either on and off, or flashes randomly.

thank you!

jose

Looking at the MAX7291 and family datasheet, I see 5V operation (minimum 4V). Trying to run it with 3.3V does for sure call for trouble... also the power consumption could be an issue.

What Espruino Board are you using to drive the display board?

hi, i am using espruino pico. what would be your recommendation? test it with arduino uno first to rule out wiring issues?

That's odd - if it's MAX7219 it should work easily as you say.

It's worth trying 5v, however I've run MAX7219 displays off of 3.3v before without problems. Sometimes the default configuration turns all the LEDs on bright which draws a lot of power, but even then I don't think it'd be a big deal on the Pico.

When does the flashing happen? And how fast is it? I'd noticed that happening on MAX7219 before uploading code, as the data lines are floating by default and can input random data.

In the past I'd had problems with that random data setting the 'displayTest' flag inside the MAX7219, but I added code recently to fix that.

You could try setting the SPI baud rate to something lower and seeing if that helps: SPI2.setup({baud:10000,mosi:B15, sck:B13});

You could also try calling displayTest(false), scanLimit(8) and on() just to try and reset values if they had got confused.

However if you're getting flickering even after uploading code, I'd check the connections - in my case flickering was always caused by disconnected data lines (or lines connected to pins that were floating).

hello,

i've experienced flickering at random times and often after code upload. also, sometimes code upload results in all segments on or off, or just some being lit up (but never the correct ones).

the question is whether i should question the connectors (see pics) if apparently vcc and gnd are wired up (leds light up).

br, jose

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ok, let me answer that. these connects really ARE INCOMPATIBLE. going around the gray 2x5 to-slot connector worked. so now i need to find some compatible prototyping-friendly connector. ideas welcome and thank you for a great hint ;-)

Great! glad you got it sorted! It's amazing how often it's the simple things that go wrong :)