https://www.thevespiary.org/rhodium/Rhodium/chemistry/equipment/scale.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/equipment/scale.html)
http://www.sciam.com/2000/1000issue/1000amsci.html (http://www.sciam.com/2000/1000issue/1000amsci.html)
Other ideas how to calibrate? (preferably OTC without involving a university or analytical lab)
hows about coins? ordinary old OTC change. in SWIGs neck of the forest, the information on the weights and contents of all the coins is readily available. jus need 2 dig up some newer ones!!.. but then again they not really easy to cut up ay..
A good additional resource for anyone seriously interested in making this scale is this follow-up article:
http://www.sciam.com/2000/1000issue/1000amsci.html (http://www.sciam.com/2000/1000issue/1000amsci.html)
geez that is a nice ref.some interesting ideas in there;
using pulse width modulation to increase sensitivity..
and a current mirror to increase stability and keep the current(in the coil) constant regardless of the temp of coil
SWIG might whip 2gether something with a PIC microprocessor.
as soon as a decent galvanometer can b loc8d.
http://www.sas.org/Membership/Membership.html (http://www.sas.org/Membership/Membership.html)
Re: SWIG might whip 2gether something with a PIC microprocessor... as soon as a decent galvanometer can b loc8d
A version of this scale was constructed using a Pic processor, breadboard, from scratch code, real time digital LCD output, two optosensors (for galv needle overload / underload). Added features such as "tare" button, more rapid PWM, voltage filters, fast binary-search response to rapidly changing weight.
Cost due to enhancements was $150 plus many hours of time...but, in the end it does work as advertised. The quality of the galvanometer is very important (and suitable ones are *very* delicate, bee careful ::) ). The galv-response is not really linear, so... making the sensitivity relevant, requires mucho calibration => nonlinearity adjustments in the code.
Measurements with final product matched those of a 0.1 mg analytic balance, with about 3x the resolution. But despite a plexi enclosure, scale was more fickle with the slightest vibration or air currents. The weighing range (~1 g max, with tiny foil tray) is not large enough to elevate the scale above novelty item status... tho, that might depend on what one would hypothetically be weighing.
http://www.balances.com/scientech/forcemotor.html (http://www.balances.com/scientech/forcemotor.html)