1985 era LED displays - ideas on how to drive? - Page 1
Forum section: electronics / projects

author: NickyDoes
author_rank: Contributor
timestamp: October 26, 2023, 07:50:05 pm
content: While I was cleaning up...I came across a cache of cool displays from the mid 80's and early 90's. These have the look of '85 from the technology and what looks like a date code (8513). The're pretty high quality, using Molex headers. No sign of SMD, unless you count the COB blob - which I don't. The display pattern is not the usual seven segment. It appears to be a 9-segment, with two vertical segments through the center of each digit.Here are all the numbers:(hand stamped in white ink)530265-185134507 APHILIPPINES(Back copper)43-0225-H(Front copper)0225-H(pin 1 and pin 7 markings)There are 7 pins. All go under the blob, except pin 7 - that goes through a 1K resistor, then across a 10 nF ceramic capacitor. The node between cap and resistor goes into the blob, and the other side of the cap also goes into the blob.Any thoughts on how to drive this? It sounds like something fun to try.If you'd like to see the other HP displays I found, let me know and I'll get some photos and part numbers up.

author: Gyro
author_rank: Super Contributor
timestamp: October 26, 2023, 08:58:00 pm
content: Sorry I can't help you with specific data but it's a National Semiconductor display. They produced a number of direct drive serial data LED driver chips and also produced displays such as these with the same ICs in COB form. They turned up on such things a early CD players (dead segments tend to be a risk). It will be 5V powered and probably Clk and Data interface, possibly with a strobe, but some of them used the last bit of the shift register to latch the data. It's possible that a couple of the pins might be outputs to drive external indicator LEDs.

author: floobydust
author_rank: Super Contributor
timestamp: October 27, 2023, 01:25:57 am
content: Late 1970's National Semiconductor went big, they went hard into optoelectronics. $10's millions on developing LED's, displays and chip-on-board products.I think an extension from the pocket calculator and games format - MSI driving LED's, bubble displays etc. They also did many custom products.MA1002, MA1003, MA1010 (1976), MA1020, MA1032 etc. clock modules and MA1026 clock/temperature module. NSM3914/15/16 has an LM3914/15/16 and 10 LED's integrated. III-IV Semi also made some later.I remember Digi-Key founding CEO saying that selling these N.S. (clock) modules kickstarted them into business - hobbyists would order them and other parts, this was the business that actually fueled them at the beginning.Unfortunately, the venture flopped - National Semiconductor pulled the plug and lost millions of dollars. I don't know exactly why. The modules were too expensive and you didn't actually save any money because you still needed headers and manual assembly of the module to your board. They didn't catch on.OP - your module looks custom for some OEM and with the RC oscillator the IC should have some neat function. Maybe an event counter or something.The very difficult part is ID'ing power and ground pins. You can use a multimeter on Diode-Test to get polarity right, some LEDs will light up. But I have never had great luck at least ID'ing ground. It's a big puzzle to get these up and running.

author: pqass
author_rank: Super Contributor
timestamp: October 27, 2023, 06:01:08 am
content: It's probably a variation on the NSM4000A display (see datasheet attached) from page 118 inthis National Handbook.The "Integrated Displays" introduction paragraph on page 111 says:"Currently, under develpment at National is a product line of integrated displays withcombines the state-of-the-art integrated circuits with the latest displays/readout devices. ... The following is a brief description ... 2) NSM4000A, A 0.3",4-digit array with National's MM5450 35-bit serial-input LED driveras the on-board driver. 3) NSM4001, Similar to the NSM4000 but with 0.5" 4-digit display."I couldn't find any other databook from National with integrated displays, although their driver ICs from 1988 (see page 4-44 onward fromthis databook) all seem to have the same kind of SPI interface (clock, data, /enable) except sometimes without the /enable pin.Based on your photo,pin 7 is very likely Vdd (+5V) since the resistor is tied to it,pin 6 is very likely Vled since it doesn't go into the COB, instead goes top-side (+5Vnot sure, maybe +3V with a 100R resistor just in case),the cap+resistor node is likely "brightness control" which can remain unconnected; buzz-out the pin,the other side of the cap is likely GND since it looks like it goes into the COB; buzz-out the pin,therefore, the other 3 pins must be clock, data, /enable.From my reading of the NSM4000A and MM5450 datasheets, for a quick test you may get away with using a low rate clock (<500KHz) and data rate half that while keeping /enable constantly low (6 possible combinations to try). This should light half of the display segments. Once life is confirmed, you can use your favourite MCU to generate an SPI stream that enables each bit to map-out the segments. I'm not sure what happens to the 4 extra bits on that last byte (of 5); probably ignored.Just in case I'm wrong about the pins, I would use a current limiting resistor on each: clock, data, /enable, Vdd, and Vled. Probably 100R initially; less for Vdd (draws <7mA), and Vled(draws 10 mA per segment).Good luck.

author: MathWizard
author_rank: Super Contributor
timestamp: October 29, 2023, 09:00:48 am
content: Quote from: floobydust on October 27, 2023, 01:25:57 amYears ago I had some little Business Tycoon type videogame. You could research things like computer tablets, mine and/or buy resources to make products, then sell them in stores. And you could even buy the stores and be like Apple store's of your products.Lets just say I always ran out of money and went bankrupt.

author: floobydust
author_rank: Super Contributor
timestamp: October 30, 2023, 06:19:12 pm
content: 1983 National Semiconductor merged with Data Terminal Systems (DTS) and went full bore into the cash-register business. The future was clearly grocery store barcodes, scanners and tills lol.I went for NS training in Boston on their Datachecker products, as a tech doing repairs on them at the time.CEO Charles Sporck (first to off-shore semi fab to Asia) - was it a good buy, a good business decision from making semi's to... cash registers and clunky mainframes?