20th May
"But there are alternatives.."
As not to encroach on Nick's work with load cell interfaces, I have interfaced a set of digital scales in a completely different way to retain its original functionality and appearance.
My scale has an ASIC with I2C ROM that does all the work and I'm letting it do all the load cell management.
Like my previously mentioned mystery device I have reverse engineered the digital scales to find suitable interface points to tap.
At this moment I am purely using the scales as a pressure switch.
When a preset threshold pressure is reached (either in a positive or negative sense) it will assert a digital signal which the SimpleLink Wi-FI C3300 can process such as send a twitter message or SMS.
This is accomplished using just 3 wires;
Ground
On/Off and Zero Function
"minus" LCD signal
Depending upon the circumstance, an additional actuator may be necessary to reset the threshold pressure setting or prevent the unit from automatically turning off.
This is to lift or place a calibration weight on the scales to either zero the setting or present signs of activity.
All that is going on is under program control, setting the Zero point to the threshold setting and checking the display for a positive or negative reading.
The On/OFF LCD signal is used to turn the scales on and if necessary reset the desired threshold setting.
The "minus" LCD signal is not a digital logic level signal but an AC multi level LCD drive signal.
With a bit of decoding of this signal can be interpreted as either "minus" segment on or off.
