Maker Pro
Maker Pro

Working around garbled LCD display on a blood-pressure monitor

gk1089

Sep 27, 2022
1
Joined
Sep 27, 2022
Messages
1
I have a digital blood-pressure monitor that shows the readings (current BP, Current Pulse-rate, last 100 BP readings from memory) on a LCD that has some 7 segment sections (it is not pixel based). Currently, the machine is working fine but the output on the LCD is garbled (it seems to be changing like it would do while taking the readings so I am assuming the readings are being taken just fine):

IMG_20220927_110338.jpg

I opened the thing up and tried to give some percussive 'repair' and even applied some heat to the LCD contacts but it did not help. The LCD has a 28 wire ribbon attached to it and has no obvious brand markings. I assume it would be an LCD created specifically for this device and impossible to find in the open market anyway.

IMG_20220920_163210.jpg

The LCD is being driven by the circuit seen below:

IMG_20220927_092112.jpg

The chip driving the LCD is seen below:

chipOnly.jpg

I tried looking for datasheet for the chip using the markings but came up with nothing.

Is there anyway I can attach a simple series of 7 segment displays and display just the current BP reading? I don't really care for the pulse-rate or the memory part.

The device itself is not very expensive and this is more of a learning/side project for me to reverse engineer (if I may say so) the display. If I can avoid adding to the eWaste, that would be a big plus too. So, how would you go about figuring the display logic. Is it possible to connect all these pins to a microcontroller like Arduino and try to figure out what set of pins is showing the relevant output?

Any pointers would be highly appreciated.
Cheers!

PS: Not sure why the image/text in this post is getting misaligned. It appears just fine in the edit mode.
 
Last edited:

danadak

Feb 19, 2021
205
Joined
Feb 19, 2021
Messages
205
Usually the display cable is compression attached via zebra strip.
You can clean that interface, if it exists, I have recovered several
dirtbag consumer items that way.

1664276723720.png



Regards, Dana.
 

73's de Edd

Aug 21, 2015
3,436
Joined
Aug 21, 2015
Messages
3,436
Sir gk1089 . . . . .

In examining photos 2 and 3 and it is seen that NO zebra strips are even being involved with THIS unit.
It uses 28 strips of printed on carbon/ graphite ink onto a paper like sheet and extreme end connections are made with individual micro drops of the same slurry.
There ¿ may ? may be a long clip that surrounds the PCB end and pressure clamps that end.
The other LCD display end is DELICATE CITY !, so handle gently and don't overflex .
Since the LCD displays contacts onto its glass blank are electro deposited metal tabs of just mini microns of thickness onto each ground glass divot..
What you might try is to have the unit naked, as it is shown now , and the unit into an operational state such that digits may be displayed then.
Use a pincer action with curved thumb to index finger to work from both ends directions to see if any or all digits transition to full readability as you work towards the center . . . and its a lo o o o o o ng stretch to reach into the middle.
This should tell you if the problem is either a loss of contact pressure or fracturing of the now very dried slurry.

Considering the handling of the LCD cable end . . . .be extwemely ( Elmer P. Fudd ) cawefull.

If you find success . . . . finding all of them to intermittently work with applied pressure, check back and I will tell you how I have fixed small calculators using the same rabbit ass connections and your like, now experienced conditions.

Thaaaaaaaaaassit. . . . . .

73's de Edd . . . . . .



You know when you buy a bag of salad and then it gets all soggy and brown . . . . .

well, cookies don't do that . .
Mmmmmmmm . . . . . . .c o o o o o k i e s !


.
 

danadak

Feb 19, 2021
205
Joined
Feb 19, 2021
Messages
205
I could not tell in pic of display with ribbon exiting left if on backside there
is a zebra strip between ribbon and display .....

But no expert here am I.


Regards, Dana.
 

kellys_eye

Jun 25, 2010
5,134
Joined
Jun 25, 2010
Messages
5,134
Any break in the ribbon connections to the LCD or the PCB will be a real PITA to fix. Such measuring devices as you show are commonly available and not worth repairing (sadly, all too often the case these days).
 
Top