Forgive me in advance... I'm a mechanical engineer, not an electrical...
[u]Project:[/u] Wearable thermometer for firefighting
[u]Background Info:[/u] Firefighting "bunker gear" has reached phenomenal levels of thermal protection. This thermal barrier, however, reaches an abrupt threshold where heat is no longer reflected and is instead absorbed. Unfortunately this thermal threshold is well above 500 degrees... meaning when the thermal liner of the gear becomes compromised, the firefighter is suddenly subjected to extremely high temps resulting in burns and even death. Current gear is so advanced, that firefighters generally have no idea how hot their environment really is. Old school firemen used the heat on their ears as indicators. Today's fireman are compromising their own safety by leaving key components of their ensemble off in order to expose bare skin to the environment in a burning building as a temp gauge.
[u]Project Synopsis:[/u] By using a platinum RTD, an Arduino Pro Mini, and an LED bar graph, create a temperature gauge inside the mask of a firefighter which will alert them to the ambient temp of their environment.
So here's the deal... I'm assembling parts and beginning to write my code for this. I bought a Nano to be my prototype (USB power & breadboardable) as well as a 1PT100KN1515CLA RTD element from Omega Engineering (100Ohm @ 0 degrees C). The RTD was chosen for its incredibly small size (since this mounts to the face piece of a firefighter)
I'm thinking more or less this... It's essentially the same as the bar graph tutorial with an RTD/thermistor instead of the potentiometer. The resistor on the other side of the RTD would be a 4k.
So... If I've done my math right...
V(divider) = (R2/(R1+R2)) V(divider) = (4000/(100+4000) V(divider) = .975v @ 0 degrees C
If I follow that the RTD will change resistance according to the Callendar-Van Dusen equation, then from 0-600 degrees there is a potential difference of .048v
So given that the resolution of the analog inputs is roughly .0049 volts per unit that gives me ROUGHLY 10 units ;D ... One for each LED on the bar graph.
Is my logic sound here?
Final note: I know the reaction time of the RTD is quite slow. This is intentional... this acts as a buffer for localized thermal events (i.e. the hosestream removes a radiant heat source, but the ambient temp will remain quite elevated)