# Digital thermometer

#### JoyAm

Joined Aug 21, 2014
126
I am supposed to be able to calculate the room temperature using this two diode circuit but i have no idea how, can you give me some hints ?

#### dalam

Joined Aug 9, 2014
58
Voltage drop across diodes depends on temperature.

#### JoyAm

Joined Aug 21, 2014
126
Voltage drop across diodes depends on temperature.
By the factor VT=K*T/q ?
and i will use this VD=VT*ln(ID/IS)
in that case idk what the value of IS is

#### MikeML

Joined Oct 2, 2009
5,444
Not sure that V(x)-V(y) is any better than V(x) or V(y) by itself...

#### JoyAm

Joined Aug 21, 2014
126

#### MikeML

Joined Oct 2, 2009
5,444
The V(x)-V(y) represents the Vp .But well i still dont know how can i solve it
Start here...

The simulation shows the temperature dependence of the forward voltage drop of two ideal diodes with different forward currents. Vp = V(x)-V(y)

#### JoyAm

Joined Aug 21, 2014
126
Start here...

The simulation shows the temperature dependence of the forward voltage drop of two ideal diodes with different forward currents. Vp = V(x)-V(y)
T=vp*q/(ln(I1-I2)*k) is that right ?
Oh i think i got it just give me some minutes

#### JoyAm

Joined Aug 21, 2014
126
Or not...
Vp=(k*T/q)*ln(I1/I2)
dVp/dT=0.139=(k/q)*ln(I1/I2)
so from that we can calculate the k/q
and then i dont know