Help With Spec Sheet: MM74C926

[Bigglez]

Hi,


Wow, 1000 piece pricing is up around 12 dollars US each.

Citation needed

[Bigglez]

I said "rotary". I meant thumwheel switch. About $5 and it is the only component you need. Seems to make sense to me.

Okay. But why the red ink?...

[Bigglez]

OK, you come out serial and then what?

Feed the serial data to an SR and latch the parallel
data into the LEDs. Simple, really.

Do you know of some real cheap LED display (four digit at least and nice BIG numbers like 1/2 inch) that incorporated serial input?

No.

Am I missing something? If a $3-4 uC will be dedicated to this task, what's the harm in dedicating six outs to doing the display?

Unless the LED display is small, requiring only 20mA or less
per segment, the uC will require a buffer (driver) stage.
I have driven dual seven segment displays in the 10mm
size directly from the uC port. For larger displays or
multi-digit ones the driver must pump more current,
so the SR with internal power drivers wins, and frees up
a bunch of uC IO pins.

Do you have any part numbers for "octal power logic SRs"?

TPIC6C595 Datasheet here

...

I'd need a schematic or at least a block diagram to get
my head around that idea.

Looking forward to seeing one.

[EPA III]

I said "rotary". I meant thumwheel switch. About $5 and it is the only component you need. Seems to make sense to me.

Okay. But why the red ink?...

Quotes within quotes within quotes. I thought the red color would make it easier to read: easier to tell what I was saying in the latest reply. Not an attempt at shouting.

Paul A.

[EPA III]

OK, you come out serial and then what?

Feed the serial data to an SR and latch the parallel
data into the LEDs. Simple, really.

So the serial data would be in seven segment code at the uc output?

Do you know of some real cheap LED display (four digit at least and nice BIG numbers like 1/2 inch) that incorporated serial input?

No.

Hence the SR chip.

Am I missing something? If a $3-4 uC will be dedicated to this task, what's the harm in dedicating six outs to doing the display?

Unless the LED display is small, requiring only 20mA or less
per segment, the uC will require a buffer (driver) stage.
I have driven dual seven segment displays in the 10mm
size directly from the uC port. For larger displays or
multi-digit ones the driver must pump more current,
so the SR with internal power drivers wins, and frees up
a bunch of uC IO pins.

That's what I thought. Even at 20 mA per segment, you can exceed the total current/power spec on an uC. 7 segments X 20 mA = 140 mA and then there's the decimal point. At least 150 mA.

In this device, I don't have any use for the "freeded up" pins. At least, not yet.

Do you have any part numbers for "octal power logic SRs"?

TPIC6C595 Datasheet here

Thanks, I am studying it.

...

I'd need a schematic or at least a block diagram to get
my head around that idea.

Looking forward to seeing one.

I will post a block diagram as soon as I put it to CAD.


Paul A.

[Bigglez]

Quotes within quotes within quotes. I thought the red color would make it easier to read: easier to tell what I was saying in the latest reply. Not an attempt at shouting.

How about editing the material for brevity?
Or, interleaving the quotes with their responses?