HP / Agilent 34401A VFD to LED Display Conversion

[KungFuJosh]

"ERR" , "-ERR-" no?
as well as ERROR to ERR0R , if it NOT monospace font

It's a printed screen; they can use whatever font they want. Hopefully, they won't choose Papyrus.

[Zucca]

Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

Anyway you will sell a lot of those bicolor LED for the legendary 34401A... regardless this "error" discussion.... It is not so important.

[dimmog]

Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.

[coromonadalix]

for zucca   add an i/o port of the mcu to drive an big 10mm red led  loll   you'll see your error status


i would be satisfied with the last shown photo of the display, error status is visible   

[BillyO]

One could put a little bit of red filter over the "ERROR" annunciator.  That would make it 'eye catching'.

[Zoli]

Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.

There's no room for two in series?
Edit:typo

[dimmog]

Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.

There's no room for two in series?
Edit:typo

= uneven brightness

[edavid]

There are "PC red" LEDs which have a blue die + phosphor.

(Not that I think you need to bother with that. I don't even think you should have the ERROR label reversed. As you pointed out, it's rarely used.)

[Zucca]

for zucca   add an i/o port of the mcu to drive an big 10mm red led  loll

No, I will then trigger this:

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Your Price:  $49,284.54 / ea

[Zoli]

There's no room for two in series?
Edit:typo

= uneven brightness

It meant to be a joke, so let's carry on: just place the uneven one on the back of the PCB 

[Miti]

Just curious, why so much space between the 45 degree segments and the vertical and horizontal ones? If you look at the VFD display on 34401 they are much closer. I’m guessing mechanical limitations?

[dimmog]

Just curious, why so much space between the 45 degree segments and the vertical and horizontal ones? If you look at the VFD display on 34401 they are much closer. I’m guessing mechanical limitations?

In short, yes.

[dimmog]

Just a quick update: we're now testing the production prototype.
The supplier change set us back a bit, but we're almost there now.

[the Chris]

Thanks for the update. Looking forward to it.

Strickly speaking, I haven't been unhappy with the brightness of my 34401A, but once my 34410A arrived last year, I could see that the 01A is noticeably dimmer. Now that a 34411A with a nearly-new display joined the two others, I definitively want to treat my 34401A to one of those LED displays.

[dimmog]

Thanks for the update. Looking forward to it.

Strickly speaking, I haven't been unhappy with the brightness of my 34401A, but once my 34410A arrived last year, I could see that the 01A is noticeably dimmer. Now that a 34411A with a nearly-new display joined the two others, I definitively want to treat my 34401A to one of those LED displays.

The original Agilent 34401A VFD was quite bright when new. In fact, they added two current limiting resistors in the latest revision of the display board to reduce the brightness. The Chinese clone VFDs currently available on eBay and AliExpress are noticeably dimmer. The brightness of our LED display is somewhere between the original Agilent VFD and Chinese replacement clones.

[Smile2016]

Great! Agree the red "ERROR" would probably look really cool. I might struggle a bit to squeeze in a small resistor there to make it work though. I also tend to prefer slightly bolder fonts, but that’s just a personal preference.

Any idea what the overall BOM would come out to, & the selling price & availability?

[dimmog]

Great! Agree the red "ERROR" would probably look really cool. I might struggle a bit to squeeze in a small resistor there to make it work though. I also tend to prefer slightly bolder fonts, but that’s just a personal preference.

Any idea what the overall BOM would come out to, & the selling price & availability?

Expected availability is in about two weeks and it will be priced at $69.

[dimmog]

A few photos for you to enjoy 

This is the first unit featuring the upgraded dual color LED display, and it's now available on eBay. Sold

[dimmog]

Preorders are now open! Shipping is expected to start on June 25, 2026.

https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion-preorder

[dimmog]

The dual color LED display replacement for the HP / Agilent 34401A is finally ready, and we started shipping orders today!

Hubequip website: https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion
eBay: https://www.ebay.com/itm/325714571683
eBay listing for UK buyers: https://www.ebay.com/itm/327219091572

[dimmog]

I'd like to point out that the new 34401A LED display is a true drop in replacement.
No additional wires need to be soldered to the display board, making the installation process quick and straightforward.

Simply desolder the original VFD display along with its mounting brackets, then solder the new dual color LED display in its place.