This Project aims in reading the LCD screen of a scale so weight and body values can be transfered to a PC automatically over Ethernet
Datasheet for EEPROM
Adobe Portable Document Format - 82.28 kB - 09/22/2018 at 21:28
After a longer break we gave it another try and soldered the rainbow cable to the display of another scale. This time we were very careful and did only use as much solder as was really needed. After reassembling the scale the display still worked! Also the oscilloscope is displaying logic data, so the first step is done:
TODO: image of rainbow cable on the back of the scale
Now it's time to find the COM lines. First we need to find out which kind of LCD we have. The Display looks lilke this:
We have about ~80 segments but only about 19 data pins on the display. Therefore we clearly have a multiplexed display with multiple backplanes, which is controlled by so called COM-Lines. The question is now, how many COM lines we have. We also need to find out which Bias and Duty is used.
TOOD: images of COM lines
I am going to loose weight. Loosing weight takes time and can be very frustrating. Since I am a nerd and therefore interested in how electronics work, I was thinking about combining it with some hacking projects so beside improving my health, I have another reason to keep going.
At this moment I am logging my weight and my body fat values from time to time so I get on the scale and type the values from the screen by hand into a database. This is a bit annoying over time. It is not my first time that I try to loose weight but when I have learned one thing about loosing weight, than that you are trying to find excuses easily for not to log a meal, not to go to the gym etc. Finding excuses will get harder if the important tasks are comfortable and the hurdles are low.
The goal is very clear: I want to automate the process of weight logging. The first approach which came to my mind is to add a microcontroller which is equipped with an ethernet connection. This is then used to read the body values from the LCD screen of the scale and transmits them to a database over Ethernet automatically. Fortunately I am not the only person hwo has this idea in mind so due to a random talk with a cool guy called Akendo he joined me on that project and we started an initial hack weekend at c-base Berlin on 13th September 2018.
We both brought our scales to find out how hackable they are. We didn't know nothing about how digital scales work so we just disassembled our scales and took a first look.
First we opened my scale which is an AEG PW 5644 FA. I bought it for around 20€ on the web.
Since this scale consists of glass, the whole construction is glued together. After a while we managed to pry of the mainboard housing:
The housing holds, as expected, the LCD ...
... and the mainboard. The main controller chip is covered by an epoxy resin blob. On the right hand side to the chip is an I2C 24C02A EEPROM which has a capacity of 2kBits (250 bytes). On the scale you are able to store up to 10 profiles which consists of gender, height and age. The scale uses this values to calculate things like your Body Mass Index or Basal Metabolic Rate. I didn't read out the chip yet but I will do later.
The LCD is using a so called Elastomeric Connector which is also referred as ZEBRA connector in literature (Purple thingy in the picture below). This connector has very fine seperated contacts which are pressed against the contacts of the mainboard and some very thin contacts on the glass of the LCD. You have to be very careful not to rip off the ZEBRA connector from the LCD since it may very hard to align the stripe to the conducting traces on the LCDs glass again:
On the back side of the mainboard we find connectors which are going to the battery (red and black cable on the right hand side), the...Read more »