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How do IC chips work? Answered

Do you need to prgram them, or are they standard enough to where you buy certain ones for a given project? Also where's a good place to find cheap IC chips, specifically a LM3915 ?



11 years ago

Most ICs (with the exception of microcontrollers and some other relatively uncommon parts) are NOT "programmable" in the sense of needing some sort of special programmer to use them, and part numbers are relatively standardized. An lm3915 is an LED bar-graph chip; relatively uncommon. See the other forum posting about good online vendors. BG Micro has them. Also check eBay; some vendors there will sell small orders with less than the usual $7 minimum shipping charge (which is what UPS actually charges for packages under 1lb...)

I don't see the LM3915 being uncommon, I have lots of them,
and they are still in full production according to the manufacturer.

It's the LM3909 I miss. When I was young I made blinky lights out
of them, and they're all still going like perpetual motion machines.
They have a LOT of weird obscure uses, such as I've seen a
schematic for a toy walkie talkie that used 2 of them to transmit
and receive. Probably in a book called "101 uses for the LM3909".
They also probably made a loud siren run on a watch battery.

Nachomamma is thinking about the LM7815 regulator.

Agreed... LM3909 need to be revived. I found a source and bought a few, but they aren't cheap for what they are.

. Wow! I was waaayyyy off on the 3915. Sorry about that.


11 years ago

The 7400 and 4000 series logic seems to be very standard, having been around for around 40 years and seen others come and go. They are generally named for what they do, but there is a lot of room for circuit bending, such as I once had a PONG game made entirely out of the 7400 chips which are supposed to be 4 NAND GATES. Binary counters can make musical notes... Eleven or Twelve 4060's can make a musical organ which probably makes ALL of the key notes. And most of the 7400 and 4000 series costs less than a buck.

. Oh yeah, back when I was experimenting with ICs, there was a fellow named Forrest Mims who wrote a lot of excellent articles and books on basic IC circuits. I highly recommend him.

. In a nutshell, Integrated Circuits have their components (transistors, diodes, etc) etched onto a piece of semiconducting material. Instead of having to mount hundreds to millions of components on a Printed Circuit Board (PCB), you cram them all into one small package. Search for "transistor theory" or something similar if you really need to know how they do what they do. . Some ICs are programmable, eg, controllers, processors (your computer's CPU is an IC), some not, eg, LM3915 (that's a -15V regulator, IIRC). Some can be "programmed" by using external components (555 timer). . Very standard. For most DIY projects, who made your LM3915 isn't terribly important; they will all work the same. . Most local electronics stores will have a 3915 (if it's what I think it is). I've used DigiKey with good results. Search for "electronic supplier" or some such. Ebay.