1. ECE 102 Engineering Computation Chapter 10 LabJack LED Interface Dr. Herbert G. Mayer, PSU Status 9/2/2015 For use at CCUT Fall 2015

2. Syllabus Light Emitting Diode Connect LED to digital FIO Channel Connect LED to DAQ Channel

3. 2 Light Emitting Diode A diode is a semiconductor device that primarily conducts current in only one direction. Symbol: I - V relationship (non-linear): i(t)i(t) v(t)v(t) anode (+)cathode (-) Standard Diode anode (+)cathode (-) Light Emitting Diode (LED)

4. 3 A diode is created when a semiconductor is doped with impurities to create a p-n junction. When fully conducting, the voltage drop across the diode is a fixed value ( ≈ V D ). A difference in energy exists at the junction (called the band gap). When charge carriers recombine at the junction, they can release energy in the form of photons. The band gap determines the wavelength (and color) of light emitted by the diode. Courtesy Wikimedia Commons

5. 4 Connect LED to digital FIO Channel Type #1:Source current from FIO LED specs: V D = 2 V, I Dmax = 20 mA Is an external current limiting resistor needed? –(3.3 V) + V R + V D = 0 V R = (3.3 V) – (2 V) = 1.3 V R min = V R / I Dmax = 65 Ω Since R > R min, the internal resistor is enough to limit current by itself. Write FIO: 0 → Turns LED OFF 1 → Turns LED ON FIO: R = 550 Ω EIO/CIO: R = 180 Ω 3.3 V R IDID VDVD VRVR LabJack Internal circuit – You do not need to build this. FIO

6. 5 Connect LED to digital FIO Channel Type #2:Sink current to FIO LED specs: V D = 2 V, I Dmax = 20 mA Is an external current limiting resistor needed? – VS + V D + V R = 0 V R = VS – V D = (5 – 2) V = 3 V R min = V R / I Dmax = 150 Ω Since R > R min, the internal resistor is enough to limit current by itself. Write FIO: 0 → Turns LED ON 1 → Turns LED OFF FIO: R = 550 Ω EIO/CIO: R = 180 Ω VDVD LabJack Internal circuit – You do not need to build this. FIO GND R VS = +5 V IDID VRVR

7. 6 Connect LED to DAQ Channel L ED specs: V D = 2 V, I Dmax = 20 mA What is the safe V DAC range? V Rmax = R∙I Dmax = (50 Ω)(0.02 A) = 1 V – V DACmax + V Rmax + V D = 0 V DACmax = V Rmax + V D = (1 + 2 ) V = 3 V Hence, 0 V ≤ V DAC ≤ 3 V will ensure that 0 ≤ I D ≤ 20 mA. DAC: R = 50 Ω V DAC R IDID VDVD VRVR LabJack Internal circuit – You do not need to build this. DAC