A project log for Heartbeat Logger

A portable device that logs a snippet of your heart at the push of a button.

Ole Andreas UtstumoOle Andreas Utstumo 12/04/2019 at 23:410 Comments

Ok, no measurements have been done to verify the functionality, but that doesn't mean we cannot be allowed to get ahead of ourselves... Discussing the casing with my great colleague Borut we had some ideas on plastic casings and then soft casings made out of silicone. It turns out, of course it does, that there is a kind of silicone resin to be bought that is "medical grade". According to Wikipedia:

Medical grade silicones are silicones tested for biocompatibility and are appropriate to be used for medical applications. (...) Medical grade silicones are generally grouped into three categories: non implantable, short term implantable, and long-term implantable.

The list of examples given are

Some fun examples here :-)

So Borut came back the next day with some pretty well thought out ideas on how the casing should work, how the edges should bevel with a shallow angle so the casing can integrate better with the skin of the user, how the PCB can be slid into the elastic casing with the USB port still accessible, how the mold would look in detail with a insert as negative space for the PCB and how the leads for the logger would also need to be printed on the insert. Few days later and he's made CAD models for the mold!

Botton half of the mold
Top half of the mold
Botton half of the mold
USS Enterpr... I mean the insert

Brilliant! There's even a small indentation for the tactile button to be felt on the outside of the soft casing :-)

And what do you know, some other great colleague by the name Börje recently purchased a cheap SLA printer and a ultrasonic cleaner, and presented us with an amazingly sharp print of the mold over the weekend.

I opted for some "food and skin grade" silicone resin (shure A 15, ebay link) and got down to business with syringes free from the pharmacy.

To be continued..