My 1924 mercury vacuum barometer left to me by my grand […]
My 1924 mercury vacuum barometer left to me by my grandfather broke in transit from the United Kingdom to Australia. The original operating principle is an evacuated glass tube in a U shape that holds mercury in the base of the U. As the pressure changes, the mercury pushes back against the evacuated air in the closed end of the tube, meaning the height of the mercury surface on the open end changes. Since mercury is dense, a small glass weight is balanced on this surface, and attached to a string that loops over a pulley wheel, and which is counterbalanced by another lighter weight to provide tension.
Aside from this history lesson, having broken this tubeChina Wash motor Manufacturers I would have had to pay a glass blower to custom make a new China Wash motor Manufacturersone (approx $200). I would then need to break the law and purchase mercury to store in an unsealed location in a domestic building,violating the safe handling of chemicals act. Not to mention it would have been really fiddly to evacuate and fill the tube myself.
Instead, I used an Electric Imp attached to a servo motor in place of the pulley wheel. It connects to my WiFi network, geo- locates its IP address, downloads the local weather for that location, parses out the pressure value, converts that to a servo rotation, and drives the indicator on the front. Total cost approx $30.
More recently, I just reprogrammed a MakeyMakey (which is built around an Arduino core) to output multimedia keycodes for volume, start/stop/pause, etc. I've started drilling holes in my coffee table, and am about to install coins or brass discs that will then become the buttons to control my media centre.