next topic »

[on:]

Greetings Peeps....

I want to start dabbling in SPI, and am wondering where's a good place to start?

My thought is to get a MAX7221 and a couple of 7-seg LEDs a la this playground tut, since that would teach me about a few things at once, as well as being useful.

Or maybe the digital pot example?

Any thoughts?

[Reply #1 on:]

That'd be a good start.
Use basic idea of:

Code:

digitalWrite(ssPin, LOW);
SPI.transfer(MAX7221register);
SPI.transfer(dataByte);
digitalWrite(ssPin, HIGH);

to write to all the registers with the default SPI settings.  Be sure to have decoupling caps on the MAX7221.
D10 must be an output, even if you use a different pin for SS to the MAX part.

I also use direct port manipulation to go even faster:

PORTD = PORTD & B11111011;  // example to clear bit 2
PORTD = PORTD | B00000100;  // set bit 2

MAX7219 will work the same way and are less expensive, $1.25 at www.taydaelectronics.com with inexpensive shipping (to the US anyway).
Boffin1 is also in SA, you could PM him to see if he has shipping experience with them.
I think they have displays also (smaller units) while futurlec over in Australia have larger ones available.
Make sure you get common cathode 7-segment displays.
8x8 matrix you can use either common anode or common cathode, they are the same matrix with different pin orientations that you can work around.

[Reply #2 on:]

Thanks CR....

I've got three suppliers close by, one within 5mins walking distance in fact; I'm sure one of them will have the chip.

[Reply #3 on:]

That's convenient.  5 minutes only gets me to the parking lot at work, or maybe to the end of my street from home.
I do have a dozen of the chips in my workshop upstairs at home tho - I buy some extra bits of stuff when I place orders to have some parts to experiment with.

[Reply #4 on:]

I've got three suppliers close by....

And....

Supplier #1 doesn't have it (or similar) on their web-site
Supplier #2 doesn't have it on their web-site, but it shows a couple of surface mount ones, so I'll email to see exactly what they have
Supplier #3 doesn't have a web-site (well, not a real one) and said to me on the phone "What's a digital potentiometer?"

[Reply #5 on:]

Be sure to have decoupling caps on the MAX7221

I'm pretty sure I should know the answer to this, but what's the diffs between the 2 capacitor symbols in the playground schematic?

Edit... I found the answer... the one with the white and black is polarised and the white bar is +ve.

So supplementary question... what do I ask for in the shop?- a polarised capacitor?

[Reply #6 on:]

10uF are usually aluminum electrolytic caps, and polarized. Look like little cans with leads out the bottom.
You can get them as non-polarized ceramic surface mount too, probably not what you want here tho.
A regular, 10uF, 16V or 25V, would be fine.