Alt-BEAM Archive
Message #13794
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@telus.net
Date: Fri, 21 Apr 2000 11:27:03 -0700
Subject: Re: The sensitivity of a 74XX240
Jason - wrote:
>
> Hie all,
>
> i have been very frustrated with all those broken chips i have ,
> the problem is they are very fragile esspecially the 74xx240...the is one
> time which i fried it just by connecting the wrong polarities of the chip to
> a 4V battery..........so i would like to know is there any special way for
> me to look after them.....and will direct soldering when i am free forming a
> circuit make it become bad too......thanks
Hi, Jason.
When I'm experimenting off the breadboard, I stick a little piece of red
electrical tape next to the positive supply pin (which is the higest
numbered pin on a 74-series chip). A dab of nail polish will work too.
The important thing is to be consistant. The negative supply pin is
always diagonally opposite the positive pin (on a 74-series chip).
I also put a piece of red tape next to the positive terminal on my
battery pack, AND on the wires I connect to it. This seems to be a bit
excessive to many people, but it's saved me more than one chip when I
was in a hurry :)
Static is always a concern with CMOS chips (e.g. 74HCxxx). Nowadays the
chips have static protection built in, but they won't withstand a heavy
zap. If the conditions in your work area produce static (dry air,
carpets, plastic/rubber soled shoes), be sure to touch something that's
electrically grounded before touch your chips.
The specifications for most chips say you can heat a pin to 260 degrees
Celsius for 8 to 10 seconds at a distance of 1 mm or more from the chip.
Most solders melt at about 220 degrees or less, so if you heat a pin
until the solder just flows, you should be OK. I try to avoid soldering
pins next to each other all at one time -- this prevents the heat from
getting too concentrated in one spot.
Lots of people recommend freeforming using a socket. This lets you
solder away without overheating the chip. It may be tough to insert the
chip later without damaging the circuit.
Bruce
13795 Fri, 21 Apr 2000 14:33:17 EDT Re: Wheels beam@sgiblab.sgi.com Meabadboy@aol.com In a message dated 4/21/2000 1:58:17 PM Eastern Daylight Time,
jester96beam@iname.com writes:
<< About 2 inch in diametre or larger will be great, and they should have
treads of some sort. >>
cheep small toy cars from Wal-Mart/K-Mart ~ ect. have sim type of tires on
them that you are looking for ~ I baught a bunch of toy construction vehicles
for around $6 (3 in a bag) and took the tires off ~ I had to hot glue them on
to my bot ~ usually they are on a 1/8" axle ~ but they work great for bots
and verty cheep.
Steve
13796 Fri, 21 Apr 2000 11:50:45 PDT Re: efficient launcher? beam@sgiblab.sgi.com "Timothy Flytch" >
>what happens when it decides you are a large aject it needs to get over
>
In that case you would not need a grapple... Just a barbed skewer...
"Oh look... It's look at me... Ouch!!! my eye!!!"
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