I have two HP82161A Digital Cassette Drives, the color of my first drive serial no. 2230A18882 is very similar to the HP-41 calculator where HP called Ink Brown (I would say it is more of black to my eyes!), the second unit - serial no. 2338A02973 is I guess I would call greenish brown and it is of the same color of my HP82162A Thermal Printer (serial no. 2341S20166)!

I wonder did HP change the color of both the drive and printer from Ink Brown to lighter color. Incidentally, I noticed that both the drive and printer in the picture in HP Series 40 brochure (5953-5557) seems to be Ink Brown (see below)


Yes, they changed the the colors at some time.
Compare to the LX palmtop series, where they changed from near black (95,100LX) to kinda blue (200LX, OmniGo)

The older versions of the printer (..43A) had the LED's looking out of the panel, where the newer versions of those IL devices hadd the LED's under the transparent plastic.
I think it was cheaper to produce (one production step less)



The reason for putting the LEDs under a translucent panel might have been for electrostatic discharge protection. I worked on a project that failed ESD testing because we had an LED passing through a hole in a panel. We tried different gaskets without success. The solution was to glue the LED in the panel with RTV. Apparently, if there is any air gap from the outside, a discharge can find the LED leads and get onto the PCB. A better design would have been to use a plastic light pipe to carry the light to the outside, so the LED could have sat down on the PCB far enough from the hole that it would not cause a problem.


Thanks for the info.
This seems reasonable.

In the past I thought they put the LED's under the panel because it's easier to clean the panel from dirt.

Now I get an idea why so many products have a kind of light pipe, instead of the LEDs directly near the surface.




Just to add that my 82143A has the translucent pannel and it is not an IL printer. I remember seeing some old 82143A with the pop-out LED's, and I used to believe the translucent pannel was for dust protection. Knowing it is for ESD protection is something new. Fresh knowledge to be kept in mind.

Good reading!



Another reason for a lightpipe is when the PCB isn't near enough to where you want the visible indication, as an alternative to adding a wire harness and a tiny PCB to hold the LED and fasteners to mount it where you want it. It also might help avoid a problem with radio frequency interference, since a wire harness would act as an antenna and even though it is carrying just a few milliamps DC for the LED, it might be necessary to add filtering components (at least to satisfy the compliance engineers!)


I think in the old days ESD was much less of a deal..other than mil spec assembly.

The most usage of LED covers was as a red panel, which gave a better background than clear, and passed thru the red LED light.
A dust-tight closure of course was also intended........


I think HP probably did take ESD into consideration primarily because the calculators are handheld devices and likely to be carried around and moved from place to place, while operating. I'm not talking about damage to components from ESD so much as disruption of operation. Also, while FCC Class B doesn't have ESD requirements, some European standards do. In the project I was working on, ESD testing was being done for European standards compliance, and the equipment (an IR communications interface) had data corruption when subjected to ESD.


Yeah, likely so, since I have never had an ESD failure or odd operation on any HP or other calculator, for that matter.

However, don't forget that many of the same considerations that come up with a handheld anyway also help ESD immunity. For one, the tough case implies thickness, and hence spacings. Also, dust sealing implies a relatively closed case which tesnds to reduce potential paths.
Finally, the usual type of clamshell case is generally accomplished with a tongue and groove closure, which lengthens the leakage or arc path.

We make all our equipment in export as well as domestic versions, and the basic design has to meet FCC/CE/C-tick, etc. I do EMC design evaluations and remediation as well as my regular design work. Part of that is ESD, although that tends to be inherent after the other items are satisfied. So I have some familiarity with the issues, and you are correct. I agree that if ANY company was interested in ESD back then, HP would have been it.

Now that they want to make nothing, I suspect they are less fussy.

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