Tipping the scales
Really neat PCB, locking molex connectors, cables, the lot. It is working well. Marsden kindly sent the service manual so I can set to "kg" and "st/lb" modes for those that like old-school weights.
The system has a QR code on the scales, which allows you to register any card against your email address. You then weigh yourself and tap the card on the scales to record the weight.
When you tap the card it beeps to confirm it is working, and keep beeping until a stable weight is recorded over WiFi to the server. Simple UI if ever I made one!
Sadly, I have fried a couple of boards whilst doing these upgrades, but Marsden do spare parts (not cheap) and whilst I have a few clues what I may have done, I am not 100% sure of how I killed them. I think, with care, and anti-static, and being neat (avoiding any shorts, or diodes backwards) I can do this reliably now. Obviously very unofficial so I cannot expect any help from Marsden. They do make very nice scales though.
The next challenge is to make the web site that holds the data have graphs and sharing options and so on. At present it is just a list of weights. But even that is working for relatives using this solution.
This is turning in to the new fat-shamers club or something, not sure.