Wanna hear about the time that I bought four LM3909Ns?

  • October 9, 2016
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Mucking About With Things Spitting Images The Diary of Lupin Pooter
Unboxing my LM3909Ns.

… and they came wrapped in sock-foam-mesh fruit wrappers?

Above: My four itty bitty LM3909Ns came sandwiched between two rectangular bits of pink (possibly anti-static) foam, wound inside a chrysalis of plastic wrap (UK: cling film) which was, in turn, lovingly cocooned within a mass of sock-foam-mesh fruit wrappers. And they’re older than you, assuming you were born after the fall of the Berlin Wall.

What is an LM3909N? Why did I want some? Why did I buy ’em on Taobao? How much did I pay for them?

It’s an oscillator IC formerly manufactured by National Semiconductor (absorbed into Texas Instruments in 2011). The LM3909N can be used to flash an LED (on ≤ 1.5V) or drive an 8Ω speaker and there’s a two-page spread of fun 3909-based circuits in Forrest Mims Engineer’s Notebook [ISBN 9781878707031] (see pages 104-105). The LM3909N has been discontinued (no later than 2000, judging from the timestamps on forum posts by folks requesting suggestions for alternatives) and was not readily available from the usual online electronics suppliers, though I’ve seen some listed on Ebay for about US $5 apiece. I paid ¥13 (currently about US $1.95) per chip but shipping from the seller in Shantou, Guangdong, PRC to Hong Kong added ¥8 to the order (bringing it to ¥56) and home delivery cost an extra HK $30 (US $3.87), yielding a total of about US $12.26. That’s US $3.065 apiece.

Snapshot of part of the two-page spread of DC circuits utilizing the 3909 IC in Mims's book.

Mims’s book refers simply to 3909s (described as the “easiest to use IC in this notebook” — see above photo), but I bought a specific type of 3909, the LM3909N, and there’s another code (M8936) printed on each chip above the model number. To satisfy my own curiosity, I Googled around and found a report from National Semi (last revised in 2005 but with a TI logo and a 2012 TI copyright at the bottom) that elucidates theese markings: SNOA039C: Device Marking Conventions.

The LM signifies that it’s from National Semi’s Linear (Monolithic) device family and the N indicates the package type: Molded Dual-In-Line Package (DIP). Near as I can tell, the M8936 printed on the chips indicates that they were assembled at a facility in Malaysia in YYWW, in 1989, between the 36th and 41st weeks of that year. That appears to correspond to a period between early September and early October 1989, shortly before the Berlin Wall “fell” in November 1989.

I’ve seen the NTE876 mentioned (e.g. here: Nostalgic LED Driver – An Upshot) as a substitute for the LM3909N but neither Mouser nor Digi-Key seem to carry it either.