LED display for HP 3457A multimeter - I did it :-)

[TERRA Operative]

I wonder how hard it would be to get a Chinese manufacturer to make some replica LCD panels, along the lines of what Dave did for his uCurrent.
I wonder what the general minimum quantity is on this sort of thing?

Not as cool as the LED's, but maybe more easily accessible pending final cost.....

[bitseeker]

It seems getting them made isn't a problem. It just depends on the amount (cost and quantity) required.

[TERRA Operative]

Yeah, 100-odd is doable, but 1000 or more is stretching it whether you'd even sell them all...

[floobydust]

I think the deal breaker, as far as mass-producing this really neat retrofit, is milling the LED displays to get the width down by 1mm and leave room for discrete colons and comma.
Throwing numbers out there...

OP used Kingbright PSA39-21 0.39" displays about $1.15 each 1000-lot X 12 digits  = $14

For a custom LED display, I imagine it's the NRE to get a custom injection mold made and the custom LED die mounts.
Say it's $10,000 and good for a 4 digit module, need 3 per multimeter and you sell enough for 333 retrofits, total 1,000 pcs. of a custom 4-digit module.
That would make the NRE $10 per (4-digit) display module, and then add the LED module's cost to that, say $11 ea. so $21 per module ($63 per DMM) and $21,000 outlay then.

Someone would have to hit up some LED manufacturers and see if my guess is far off.

Kingbright SMT LED display ACPSA04 is 9.3mm wide vs the original through-hole 9.9mm-1mm milling... I wonder if that would work? It's not as thick too.

[texaspyro]

Use standard SMT LEDs on a PCB to make the segments.  3D print a housing for 7-seg digits.  Maybe fill segments with clear resin.

[fenugrec]

is milling the LED displays to get the width down by 1mm and leave room for discrete colons and comma.
Throwing numbers out there...

Indeed, but I think @TERRA meant manufacturing *LCD* panels, like Dave's multimeter with a custom vector drawing of the segments, etc.

[bitseeker]

Correct, fenugrec. Nevertheless, both possibilities are certainly interesting for the various HP equipment from this era.

[McBryce]

...
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.

You may want to look at taking the LCD from an hp 3488a - it think they are interchangeable (but you should verify).  You can usually find these pretty cheap on eBay.  However shipping it is sometimes more than the unit costs.  However you might see if the seller will just ship the front panel or display PCB since that would lower shipping cost.  There is not much in HP 3488A unit so you wouldn't be losing much junking the rest of the unit if you are just interested in the LCD.

I just saw two on ebay (unfortunately for Europe buyer it is in the US) for $15.00 but shipping in US about $20.00.

rastro

Can anyone here confirm that the 3488 LCD is compatible with the 3478?

McBryce.

Edit: Forget the question, they are not the same. The 3478 has text along the bottom row (SRQ, LSTN, TLK etc), the 3488 has just arrows.

[TERRA Operative]

Yeah, maybe discreet SMD LED's with a 3D printed frame for the segments sounds like a doable idea.
I wonder if a stack of a few PCB's could have the cutout shapes routed out and used the same way?

[rastro]

...
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.

You may want to look at taking the LCD from an hp 3488a - it think they are interchangeable (but you should verify).  You can usually find these pretty cheap on eBay.  However shipping it is sometimes more than the unit costs.  However you might see if the seller will just ship the front panel or display PCB since that would lower shipping cost.  There is not much in HP 3488A unit so you wouldn't be losing much junking the rest of the unit if you are just interested in the LCD.

I just saw two on ebay (unfortunately for Europe buyer it is in the US) for $15.00 but shipping in US about $20.00.

rastro

Can anyone here confirm that the 3488 LCD is compatible with the 3478?

McBryce.

Edit: Forget the question, they are not the same. The 3478 has text along the bottom row (SRQ, LSTN, TLK etc), the 3488 has just arrows.

You are correct.  I was thinking it is a possible replacement for the HP 3457 which does use arrows like the 3488. 

It slipped by me you were taking about an HP 3478; a different meter from the one of the OP referenced.  Sorry for the confusion.

rastro

[enochRoot]

Hello Xi,

Not sure if you saw but I sent you a PM.  Interested in any progress on the kit for this.  Would love to inject some visibility into my 3457!

[coldframe]

Shut Up And Take My Money!

[k007007]

Hello!
Really nice job by Xi on both decoding the protocol and building the replacement display!
However, as long as no kit for a LED display appears to be available, this solution might be too consuming for some of us.
A compromise way might be a graphical LCD or OLED.
There is another hurdle though at this way: apparently both 3457A and 3478A send O and S instead of 0 and 5 to LCD. This will make alphanumeric messages look ugly on any display, which presents S and 5 differently; probably there is no chance to "guess" between 5 and S (respectively 0 and O) in the display's controller.
Fenugrec's (https://www.eevblog.com/forum/testgear/hp-3478a-rom-modification-relative-mode/msg2048623/#msg2048623) excellent disasm of 3478A makes chances better at least for 3478A:
hier https://github.com/fenugrec/hp3478a_utils/blob/master/ROM_disasm/dc118.d48#L3965 might be the routine substituting those two bytes.
Though it is not quite clear, why or how 5 is passed to that routine as number 0x05 rather than as symbol 0x35.
Any thoughts or deeper insights greatly appreciated.
 

[fenugrec]

might be the routine substituting those two bytes.
Though it is not quite clear, why or how 5 is passed to that routine as number 0x05 rather than as symbol 0x35.
Any thoughts or deeper insights greatly appreciated.

You must also look at the code for "render_reading" around 18AD, which takes the packed-BCD reading and prepares the "string" to be sent to the LCD.
Now keep in mind I haven't looked at 8039 asm and this project in a while -
but see how it calls "append_hsdigit" or _lsdigit to go through both upper and lower nibbles of each byte containing packed-BCD.

And later in the implementation of those :

Code: [Select]

append_digit:
anl a,#0xf ; 1d25 - 53 0f S.
orl a,#0x30 ; 1d27 - 43 30 C0
append_tail:
jc X1d2e ; 1d29 - f6 2e v.
mov @r1,a ; 1d2b - a1 !
inc r1 ; 1d2c - 19 .
ret ; 1d2d - 83 .
;
X1d2e: mov r7,a ; 1d2e - af /
xrl a,#0x30 ; 1d2f - d3 30 S0
jz X1d3e ; 1d31 - c6 3e F>
xrl a,#0x5 ; 1d33 - d3 05 S.
jnz X1d39 ; 1d35 - 96 39 .9
mov r7,#0x13 ; 1d37 - bf 13 ?.
X1d39: sel mb0 ; 1d39 - e5 e
call X17ca ; 1d3a - f4 ca tJ
sel mb1 ; 1d3c - f5 u
ret ; 1d3d - 83 .
;
X1d3e: mov r7,#0xf ; 1d3e - bf 0f ?.
jmp X1d39

see how "orl   a,#0x30" would appear to transform digits to "ASCII" numbers (0x30-0x39), but immediately after, you have two XOR operations with 0x30 and 0x05 which seem to do exactly as you describe: check if =='0' or '5' and replace with O/S. (keep in mind the LCD character map has 0x01-0x1A mapped as uppercase letters. (?? see detailed charmap that someone posted earlier)

I still think it would be a better project to emulate some of the code from a modern mcu and replace the display + cal code with something easier to work with. Luckily  my display still works so I don't need to worry about that !

[k007007]

Ok, thank you!
now it's clear.

[graybeard]

excellent work!

[dietert1]

Today i found this quick fix using pieces of 24 V LED strip. These meters will be in a stationary setup for a long time and i needed illumination for debugging GPIB control.

Regards, Dieter

[Xyphro]

In case you look for an Oled variant of this, check this out:

https://www.eevblog.com/forum/testgear/hp3548-hp3457-oled-display/

Credits to XI for sharing his protocol reverseengineering details!

[dxl]

Very nice work reverse engineering the protocol. Many thanks for that. I started wiring up the 3457A based on the 3478a code in mame. It is showing signs of life, but i haven't implemented the keyboard yet which is a bit larger. And i'm not sure whether i can do anything with the Keyboard when it is in that 'FAILED' state.

[dxl]

Does anyone have the schematics of the Keyboard matrix? I haven't found that in the Service Manual which has all the other schematics.

[fenugrec]

I started wiring up the 3457A based on the 3478a code in mame

Awesome ! I was wondering if anyone would ever reuse that code. I never split out the LCD emulation as a separate class, but it's probably worth doing now.
Can't help with your keypad schematics sorry - I would probably just give up, disconnect the keypad and continuity test the key matrix ...

[dxl]

I started wiring up the 3457A based on the 3478a code in mame

Can't help with your keypad schematics sorry - I would probably just give up, disconnect the keypad and continuity test the key matrix ...

Unfortunately i don't have a 3457a (yet). I had two several years ago, but sold them because... because of the crappy Display. 

[dxl]

This looks like a nice display for the 3457A: https://www.ebay.de/itm/201694165598?epid=1648365133&hash=item2ef5e8ba5e:g:ogsAAOSwRp5iYURz

[oz2cpu]

i am a bit impressed :-)
specially about the home etched and home milled and all that home DIY
I must admit, i would have ordered pcb's from jlc or similar places.
great to save them old top class DMM

[wizard69]

Thanks for this thread!   I really like this sort of post, as even an old man like myself can learn a bit.   Beyond all of that there is enough info here so that people can easily come up with their own solutions.  Impressive work!