I hang out on the discussion forum for the hpmuseum.org Web site, mostly to soak up the ambiance of people who really love old HP calculators. I own an original HP 35 (the world’s first pocket scientific calculator) that I bought as a college junior, which I used to plow through Circuits 3 exams and iterate on the problems while my peers slaved over their slide rules just to run through one set of calculations. I also own an HP 41CX, given to me by a good friend, which is way too capable for my computational needs these days but it was a landmark pocket calculator in its day. Once in a while, I find a gem of a discussion that I like to share in my blogs and such a gem just appeared.
It’s about a member of the HP Voyager series of small, credit-card-sized calculators with CMOS guts (that’s what the “C” means in “HP 10C”). The earliest HP calculators pre-dated CMOS LSI and used LEDs rather than low-powered LCD displays so they employed rechargeable NiCd batteries that lasted a few days rather than decades. The most famous Voyager calculator from HP was the HP 12C financial calculator, which is still being manufactured after three decades because it’s the de facto calculator for financial calculations. Voyager machines were powered by primary coin cells.
Here’s the conversation that seemed blog-worthy to me:
“It struck me that my HP10c (SN 2247A02668) is now 30 yrs old. It has lived all these years on the original batteries! Anybody else experienced a long battery life?”
“Yes, some (a few?) users have witnessed about 3 decades of battery life in their Voyagers, something closer to what you have. Indeed, these are somehow rare experiences and I believe some factors, when happening together, are the most important:
- calculator chipset – probably one amongst a set is tunned this way;
- battery set – the three ones you just choose, together with the calculator chipset;
- battery contacts – if the calculator has a power supply control that compensates battery voltage drop with current increasing (SMPS), having the battery contacts clean and with very low resistance leads to lower current drain and batteries will live longer;
- usage – the way you use your calculator and how often you do that;
- climate conditions;
- as many others as needed (geographic location for magnetic fields?)
Or else it is just something that happens…
Cheers. And congratulations! Your HP10C is one of a kind!”
“The coin batteries are awesome. I wish rechargeable batteries lasted that long.”
Now for today’s question. With 30 years of VLSI advancements and Moore’s Law progress, do you think you could design anything that might still be operating off of its original coin cell batteries 30 years after being manufactured and sold. That seems like a really large order to me.
In the intervening three decades, devices geometries have shrunk, leakage has gone up, and clock rates have risen significantly as well. According to the hpmuseum.org Web site, HP had developed a new processor used in the Voyager series that was “an 85,000-transistor circuit, which drew 0.25 milliwatts and had a standby leakage of 5 – 10 nanoamperes. The process was meant to allow calculators to run for a year from a set of small batteries but several owners have reported that they are still running on their original batteries after 20-22 years.”
Apparently, those words were written a few years ago because the forum discussion above puts one set of batteries at 30 years and still going. Quite an accomplishment! Try finding a microcontroller with a sleep-current rating of 5-10 nanoamps. The new Freescale Kinetis L series of 32-bit microcontrollers, which is really very good, is rated at 381 nanoamps typical (943nA max) in deep sleep mode and 40µA/MHz in run mode. So the run mode seems like it could perform better but that low-current sleep mode in the old, old HP calculator chip seems pretty darn good even today.
That 1981 semiconductor technology was nothing to sneer at, was it?