HP's LED display

[Bo Kristoffersen]

In 1971 HP came out with the HP9810 with a three line LED display based on 7-segment LEDs developed in-house. In the same year Bowmar started selling their first LED pocket calculator model 901 (with LEDs manufactured by Bowmar), and Busicom introduced their first LED pocket calculator in mid 1971 (LEDs by Bowmar?). As we all know, in the beginning of 1972 the HP(35) was introduced.

By question is: as the 7-segment LEDs were not developed overnight, what was the initial reason for providing these rather small displays which mostly would make sense in small devices? When development was started, did the project managers really expect that the big-selling pocket sized calculator was just around the corner? Perhaps they had seen the TI Cal-Tech prototype and wanted to develop a display with this in mind.

Indeed, it may be argued that HP needed a small-sized display to show their three-level stack on a desktop calculator, however, was this the object of the LED developments at HP?

Therefore, is anyone aware of the objects behind the development of the first 7-segment LED display?

Regards, Bo Kristoffersen

[Andrés C. Rodríguez (Argentina)]

I may have some info on 1970's LED displays development.
(need to dig on my bookshelves...) Here is something from memory:

The usual LED display size was aroundnd 0.3". Monsanto was one of the most important manufacturers of such displays (MAN-1 was a medium size 7-segment; MAN-2 was an "incredible" 5 x 7 matrix for alphanumeric displays, MAN-3 were little size, about 0.15", etc).

Small size LED displays were used on calculators, wrist watches and were seen as the display choice for any portable applications. Larger LED displays were seen as displays for bench instruments, dashboards, appliances, table clocks, etc. Most LED displays were red, green was something special, and other colors were only dreamed about.

I think HP developed the displays as a semiconductor manufacturer, not only for its calculators.

BTW, most medium size displays were common anode at that time, and were driven by TTL circuits like the 7447; most small size displays were common-cathode, and were driven by TTL chip 7448. CMOS logic chips like the 4000 series were just being developed...

LCD were very new, with poor contrast and reliability, those years. And many pocket calculators used fluorescent displays. AC powered equipment, such as cash registers, office machines, weight scales, etc, sometimes used cold-cathode displays (Nixie tubes)

[Viktor Toth]

Here is a naive question, based primarily on the fact that most early calculator displays are actually even smaller than they appear, and use magnifying lenses... could it be that the reason why LED displays were small was that making them large was simply too difficult/expensive?

LCD technology didn't exactly begin with 21" high-resolution displays either.

Viktor

[Dave Hicks]

Small calculators were expected by 1970. The HP-35 project began before the HP-9100 was introduced in 1968. Most of the world was focused on getting prices of four function models under $100 but HP went in a different direction.

Hamilton was working on an all-electronic watch since at least 1966 and decided that it would have a digital LED display in 1968. It came on the market as the Pulsar in 1971 or 72.

[Andrés C. Rodríguez (Argentina)]

Interesting comments, thank you, Dave.

Andrés