Fredrik Eriksson wrote:
> On Wed, 19 May 2010 16:16:28 +0200, Invisible <voi### [at] devnull> wrote:
>> While we're here, does anybody comprehend what VCC, VSS, VDD and 
>> related symbols mean?
> 
> http://en.wikipedia.org/wiki/IC_power_supply_pin

OK, thanks for that...

Post a reply to this message

> Oh, and *don't* connect the LED to the 9V source at all. I did that once 
> by mistake... that particular LED doesn't do anything now.
>
> Ah, life seemed so much simpler back then. :-(

Reminds me of an interesting story.  We got a complaint from a customer that 
about 25% LCDs they have from us have a dark edge to the picture, either on 
the left or the right side.  When we checked the faulty ones we found that 
always the left or right LED was not working in the backlight (I think there 
were 8 in total).  This puzzled us for a long time, why would it always be 
the far left or far right LED that stopped working, and why were they 
breaking in the first place?

In the end we figured out what happened.  Actually *every* LCD we shipped 
had one broken LED, it's just they never noticed it when it was one of the 
central LEDs.  And it turned out the equipment at our outgoing inspection 
test was set to the wrong voltage, so the tester was just blowing one LED on 
every backlight that went out :-)

Post a reply to this message

Am 19.05.2010 16:04, schrieb Invisible:

> Most of the books I've seen only cover the 7400, 7401, 7402, etc., and
> don't mention things like the 741G00. Could be useful to know. (Except
> that Maplin don't seem to sell this stuff... *sigh*)

AFAIK they usually come in SMD packages only - which in turn means 
they'll usually be sold in bulk. And anyway - why would you buy, say, 
one 74x1G00 NAND and one 74x1G32 OR gate when you can get a 74x00 4xNAND 
IC for the same (or even lower) price, and wire up three of the gates to 
simulate the OR gate? (The 74x265 is also a neat beast - with its two 
(N)AND gates and two inverters/drivers it's an ideal candidate to 
simulate quite a wide variety of 2-gate combos you can imagine).

I guess the single-gate ICs are mainly targeted at applications where 
space, routing, speed or EMI constraints are serious enough to forbid 
sharing the gates of a single multi-gate IC among different sections of 
the circuitry.

Post a reply to this message

Am 19.05.2010 15:52, schrieb Invisible:

> http://www.maplin.co.uk/Media/PDFs/N24AZ.pdf
>

> content of this datasheet means! :-D

Ah yes, the typical cheap alphanumeric LCD.

I guess most of the datasheet information says, "this thing does exactly 
the same as other manufacturers' devices of this type".

Post a reply to this message

On 5/19/2010 7:31 AM, scott wrote:

> Why is that weird? The LED doesn't care which leg is connected to the
> logic output pin, it's just a voltage. You could even connect the LED
> between two output pins*, then it would only turn on when one was high
> and the other was low.


There's even a name for that trick: Charlieplexing.

The 3 state had to be simulated by switched, but here's a circuit for 
the Falstad simulator (http://www.falstad.com/circuit/):

$ 1 5.0E-6 10.20027730826997 50 5.0 50
L 224 176 176 176 0 1 false 5.0 0.0
L 224 224 176 224 0 1 false 5.0 0.0
162 352 176 352 224 1 2.1024259 1.0 0.0 0.0
162 384 224 384 176 1 2.1024259 1.0 0.0 0.0
w 352 176 336 176 0
w 384 176 368 176 0
w 352 224 336 224 0
w 384 224 352 224 0
w 368 176 352 176 0
L 224 272 176 272 0 1 false 5.0 0.0
w 384 272 352 272 0
162 416 176 416 272 1 2.1024259 1.0 0.0 0.0
w 416 272 448 272 0
w 416 176 448 176 0
162 448 272 448 176 1 2.1024259 1.0 0.0 0.0
w 416 176 384 176 0
w 352 272 336 272 0
162 384 272 384 224 1 2.1024259 1.0 0.0 0.0
s 272 176 336 176 0 0 false
s 272 224 336 224 0 0 false
s 272 272 336 272 0 0 false
w 384 272 416 272 0
162 352 224 352 272 1 2.1024259 1.0 0.0 0.0
r 272 176 224 176 0 100.0
r 272 224 224 224 0 100.0
r 272 272 224 272 0 100.0


-- 
~Mike

Post a reply to this message

On 5/19/2010 8:13 AM, clipka wrote:

> Texas Instruments has a nice collection of 74xx data sheets in a single
> proper PDF file at <http://focus.ti.com/lit/ug/scyd013b/scyd013b.pdf>

Ah, sweet! Thanks for that link! <Bookmarked>


-- 
~Mike

Post a reply to this message

scott wrote:
> have several devices all with their outputs connected to a data bus, 
> then only one device at a time must be driving the data lines to logic 
> low/high, the rest must set their outputs to floating.

Yep. Indeed, there are a lot of busses that are organized such that you have 
an output to it and an input, and you start putting your address on the bus 
bit by bit until you see a bit different than your address. That means 
someone else put on a 0 while you put on a 1 (assuming floating high). Every 
packet gets delivered with no contention, with lower addresses getting 
priority.  It's a kind of cool way to work it.

-- 
Darren New, San Diego CA, USA (PST)
    Ada - the programming language trying to avoid
    you literally shooting yourself in the foot.

Post a reply to this message

Invisible wrote:
> that particular LED doesn't do anything now.

It's a DED component. It emits dark.

-- 
Darren New, San Diego CA, USA (PST)
    Ada - the programming language trying to avoid
    you literally shooting yourself in the foot.

Post a reply to this message

Mike Raiford wrote:
> There's even a name for that trick: Charlieplexing.

Cute. Is there a name for when you have a red LED in one direction and a 
green LED in the other and you use AC to make it yellow? I want to use that 
around my colleges and sound like I know what I'm talking about. ;-)

-- 
Darren New, San Diego CA, USA (PST)
    Ada - the programming language trying to avoid
    you literally shooting yourself in the foot.

Post a reply to this message

>> that particular LED doesn't do anything now.
> 
> It's a DED component. It emits dark.

Hey, so long as it doesn't start emitting negative light...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message