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HP-45 With Shielding?
03-20-2020, 08:31 PM (This post was last modified: 03-21-2020 12:40 AM by JohnRausch.)
Post: #1
HP-45 With Shielding?
Has anyone seen an HP-45 with metal shielding under the back cover and surrounding the display?

The two pieces in the back cover are connected with a small wirw near the base and there is a spring connector that might be touching ground -- I haven't checked yet

[Image: hp45shielding.jpg]
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03-20-2020, 11:10 PM
Post: #2
RE: HP-45 With Shielding?
Hi, may you edit the post, please, actually I'm not able to see any pic
thank-you
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03-21-2020, 12:27 AM
Post: #3
RE: HP-45 With Shielding?
I think I have but can’t remember for sure at the moment.-kby
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03-21-2020, 01:15 AM
Post: #4
RE: HP-45 With Shielding?
Yes, I had some of those with metal shielding.
Maybe the ceramic body of some of the ICs on the CPU boards
in the earlier units caused more radio interference than the later versions.

-- Ray
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03-21-2020, 03:57 AM
Post: #5
RE: HP-45 With Shielding?
It is an early one, 1301A 07574. The circuit board is quite a bit different that others I have or have seen, on the side opposite the shielding. The contact does go to ground. I'm not sure the shield around the display makes contact with anything, but will check if anyone is curious. Right now the calculator is in pieces. Unbelievably dirty.

(03-21-2020 01:15 AM)Raymond Del Tondo Wrote:  Yes, I had some of those with metal shielding.
Maybe the ceramic body of some of the ICs on the CPU boards
in the earlier units caused more radio interference than the later versions.
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03-21-2020, 12:31 PM
Post: #6
RE: HP-45 With Shielding?
You may have discovered an interesting historical prototype/artifact!!!

Some background and historical notes follow:

The development of consumer electronics in the 1970s was regulated by the FCC (Federal Communications Commission). The FCC has strict regulations on the emitted electromagnetic fields of consumer devices. These regulations were to prevent interference with Radio and TV Commercial Broadcasting. (My experience is only with the USA - I presume there were similar regulations elsewhere on the planet).

Previous to this time, there were little (no) consumer electronics devices with (relatively) high speed clocks that would emit these potentially interfering electromagnetic fields. As I recall these early HP calculators have clock speeds approaching 1 MHz (1 million cycles per second). Given that these clock signals have relatively low rise times, the EMF (ElectroMagneticField) generated can be over 10 times this frequency.

https://en.wikipedia.org/wiki/Fourier_analysis

Keep in mind that AM broadcast receivers operate in the range of 0.5 to almost 2 MHz. FM radio operates in the range of 88 to 108 MHx. Television operated in the range of 30MHz to 300MHz.

https://en.wikipedia.org/wiki/FM_broadcasting
https://en.wikipedia.org/wiki/Analog_television

I am not aware that the early calculators were marketed as 'consumer devices', but it appears that this HP45 that you have may be an early prototype whereby the engineers took steps to shield the internal EMF fields. Certain metals, connected to a 'ground' or reference can significantly reduce the intensity of an EMF field. Those of us that were around in those early days would marvel at how the state of the LED display would produce varying and 'interesting' sounds from a nearby AM radio. Another historical note is that the HP35, in addition to being a truly revolutionary personal computing device is that it was Hewlett Packards first 'consumer' device - previous products were all developmental tools for industry.

On a related topic were the early home (consumer) computers - the Atari 400/800 home computer series of machine designers had worked at great lengths of designs to keep them 'quiet' - in a EMF sense. Open the cartridge slot of these machines and you will see the significant shielding. As these computers connected to the home Television, these computers were classified as consumer devices. Conversely, the early Apple ][ computers did not provide a television signal (the computer produced only a composite video signal thereby requiring the user to purchase a special monitor or use an external TV modulator) and as such were not considered consumer device; consequently not requiring shielding in their designs

As time progressed and clock speeds increased significantly, current consumption decreased significantly - no longer required the EMF shielding. Also, more recently some broadcasting (TV) have switched to narrow-band digital systems that are more less sensitive to interference.

Regards,
TomC

(03-21-2020 03:57 AM)JohnRausch Wrote:  It is an early one, 1301A 07574. The circuit board is quite a bit different that others I have or have seen, on the side opposite the shielding. The contact does go to ground. I'm not sure the shield around the display makes contact with anything, but will check if anyone is curious. Right now the calculator is in pieces. Unbelievably dirty.

(03-21-2020 01:15 AM)Raymond Del Tondo Wrote:  Yes, I had some of those with metal shielding.
Maybe the ceramic body of some of the ICs on the CPU boards
in the earlier units caused more radio interference than the later versions.
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03-21-2020, 07:51 PM
Post: #7
RE: HP-45 With Shielding?
Thankyou, John for sharing.
Very interesting, really
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03-22-2020, 03:49 PM
Post: #8
RE: HP-45 With Shielding?
On many consumer products the early versions had metal shield while later they sprayed a (usually grayish) conductive plastic layer on the inside of the case to save money.
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03-22-2020, 05:53 PM (This post was last modified: 03-22-2020 05:55 PM by JohnRausch.)
Post: #9
RE: HP-45 With Shielding?
Here is a comparison of the circuit boards. The one from the calculator with the shielding is on the left, one from 1350A 37499 is on the right,

[Image: hp45circuitboards.jpg]
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03-22-2020, 11:17 PM (This post was last modified: 03-22-2020 11:27 PM by Steve Simpkin.)
Post: #10
RE: HP-45 With Shielding?
(03-22-2020 05:53 PM)JohnRausch Wrote:  Here is a comparison of the circuit boards. The one from the calculator with the shielding is on the left, one from 1350A 37499 is on the right,

<image>

Very interesting that the one on the right has a mix of Mostek and AMI ICs as well as the 16 pin 1820-1128 clock/reset IC that replaced the 0855 and reduced the discrete parts count.

From Electronic, Feb 1973 regarding mixing of the two manufacturers for early production of the HP-35:
"Production models are either all-AMI or all-Mostek because the two suppliers' chips don't really run well together. Though the parts are the same electrically, the different locations of the precharge make it impossible for the Mostek A&R to operate with the AMI ROMs."
https://www.hpmuseum.org/forum/thread-3746.html

IC part numbers:
http://www.brouhaha.com/~eric/hpcalc/chips/
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