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

[xi]

First of all, thanks everyone for all your nice comments and everything else about my mod




After a loooooong pause for my home improvement, I ended up making electronic again I have worked on my LED display for the HP3457A kit, and for everyone who previously asked: I have now one complete display to sell

Don't be too excited though, it won't be cheap, because it costs a lot to build (expensive BOM & time consuming machining / soldering). Just for the Bill Of Material, cost is now more than Eur 110 (approx the same in $).
The BOM's cost was much lower before the crisis, but some people are taking advantage of this situation to increase their component's price unreasonably. (For example: the kingbright red high luminosity display PSA39-21 cost including VAT was 1€548 in 2019 and now it is 4€607. So for 12 digits, the BOM cost - just for the 14 segments LED displays - increased from 18€60 to more than 55€ ...)

Anyway, I have one kit fully assembled available now, and given the BOM cost, the milling time (PCBs + LED displays + acrylic sheet) and the hand soldering, I will sell this first kit for Eur 175 (preferably inside Europe, to avoid any complicated customs declaration); contact me if you are interested.

After that, I will have 4 more PCBs sets left ; depending on the interest for this first display, I could:
- either provide a fully assembled display like the first one,
- or provide a complete kit to be soldered & assembled,
- or even just provide the PCBs + the digits + the plastic sheet machined (and possibly a programmed ATMEGA 162),
- or just do nothing if there is no interest in it 

(For the kits to be soldered, be careful, the punctuation board requires high soldering skills (a binocular microscope is almost mandatory because of the "coma" LEDs which must be mounted vertically with the legs bent at 180° angle)).

What do you think?

Some more pictures of this "kit" below:

[TERRA Operative]

Nice work, I still want one or two, but this chip shortage is killing the pricing of parts...

Are you willing to release source code and schematics etc so we can build our own versions?
I have an idea to construct the display from SMD LED's and milled PCB instead of the 14 segment LED modules. I can do mechanical design no worries, but software is way beyond me.

[xi]

Are you willing to release source code and schematics etc so we can build our own versions?
I have an idea to construct the display from SMD LED's and milled PCB instead of the 14 segment LED modules. I can do mechanical design no worries, but software is way beyond me.

See my previous posts: I have already released the source code (GPL), the HP LCD protocol, the schematics, ... the only thing I didn't released is the PCBs because I wanted to try to sell them before; but I think I will release them too in a near future.

[TERRA Operative]

Ah, I should have checked! Thanks!

[dietert1]

Can you offer a kit, like boards, LEDs and programmed MCU, maybe special connectors? For me it would be fun to build this and hopefully i can make it work. We have three 3457A, including one spare unit that i could use for a test.

Regards, Dieter

[The Bootloader]

Hi,

There is one reason why so many Kickstarter projects fail. Lack of DFM (Design For Manufacturing).

As we are seeing here, designing a prototype is one thing - but having a design that can be produced "en masse" in a cost-effective way is another thing.
Very often, companies do a complete redesign.

The situation with the Kingbright displays at 4 euros each is ridiculous and is a great example of this issue.

Take a look at these: https://www.aliexpress.us/item/3256803078161467.html
Around $8 for 30 modules of 4 digits, that's $0.24 per module, you need 3 per display, that's less than one dollar. They are also much simpler to assemble as they are already multiplexed.

My suggestion: just redo your two top PCBs to use these modules. It should reduce your BOM cost substantially, potentially dropping your list price from 170 euros to 115 euros. If you can find other savings to drop it below 100 euros, it should be much easier to sell (remember the relative value of the display cannot be too high relative to the value of the instrument)

I suspect there are many ways to reduce the cost. I can't see how this can cost more than 50 euros if produced with DFM in mind, leveraging proper assembly facilities.

You could leverage the SMT assembly service of JLCPCB (or others) to pre-assemble all the passives. Using an ATmega microcontroller might not be a good idea either - go with something chinese and commonly available for cheap, maybe an ESP32? An ESP32-S2 is available from LCSC for less than $1.3, and they can solder it for you too! You can base your design on this dev board, and you would get free wifi capabilities (could be neat for data logging).

Try finding all your components on LCSC. I'm sure you can be sub-50 euros when produced in sufficient volume (100 units). I am sure you can sell 100 units based on the responses in this forum. 175 euros is prototype-level price.

Hope this helps and hope it gives you good pointers

[DavidKo]

You need to pick up 14 segment display for 3457A like https://www.aliexpress.com/item/32584509522.html

[The Bootloader]

Haha, you're right! I was tired it seems.

I remember this old video from Dave about getting custom LCDs manufactured. I wonder if it would not be a good avenue to explore :


It would be possible to have them assemble everything, with the right dimensions, and make a drop-in replacement.
But this time around, with backlight...

Could probably also find OLED display manufacturers, or simply custom LED modules. There are a lot of suppliers for custom LED modules on Alibaba, and the MOQ and prices seems really affordable (<$1 each, MOQ 100-1000).

Dave was able to get 5 custom LCD displays delivered for $100, so it seems to me that it is definitely something to explore

[dietert1]

The 3457A native display is LCD and it is quite easy to supplement background illumination, except there doesn't seem to be a kit.
I once modded a 3478A, that has the same or a very similar display unit. Bought some transparent acryl boards with different surfaces like one side glossy, one side dim, laser cut to the proper side. Then i added six green LEDs, three on each end. Result after first try was useful and remained. For a revision i would increas the length of the acrylic sheet some mm in order to somewhat reduce direct light from the LEDs.
In 2013 there was this thread:
https://www.eevblog.com/forum/projects/hp-3457a-lcd-backlight-mod-(also-for-3478a)/msg227880/#msg227880

Regards, Dieter

[rsbonini]

Superb work on this. 

Any word on either kits availability or complete manufacturing documentation so we can roll our own?