Research
Features using IR323/HO-A
- Infrared LED IR323/H0-A
- Peak wavelength λp=940nm
- Max continuous forward current 100mA
- Typical radiant intensity at 20mA continuous current 3.5mW/sr
- 60˚ beam angle
- Performance graphs can be seen on datasheet
Features using 2N2222A
- 2N2222A NPN switching transistor
- Max collector current 800mA
- Min transition frequency 300MHz
- Max emitter-base voltage 6V
- Three terminal through hole
- Included in circuits lab kit
- Performance graphs can be seen on datasheet
Circuit Diagram
Simulation Results
- Green is 5V 56 kHz square wave
- Red is BJT emitter voltage
Distance Equation
The maximum distance the IR needs to travel is 1.5 meters. The maximum current needed can be calculated using the equation below.
- I_e=emitter intensity
- Emitter intensity of IR323/HO-A at 20mA: 3.5mW/sr
- E(e,min)=irradiance of the reciever
- TSOP36256 minimum irradiance (56 kHz) (receiver on the headband) when Vs=3V
- Pulse width tolerance: t pi- 5/fo< tpo< tpi+ 6/fo. Typical: 0.4W/m2
- d_max=maxdistance = 1.5 meters
- Using the above information, the maximum current needed is 5.145mA
- Therefore, if there are 9 IR LEDs mounted on the cup, the total current used by the system is 46.3mA
Block Diagram
Alternatives
Features of MTE9440M3A
- Peak wavelength λp=940nm
- Max continuous forward current 60mA
- 160˚ beam angle
- Through hole
- $3.00 each
The reason we didn't use these is because they are $3.00 a piece.
Features of IR25-21C/TR8
- Peak wavelength λp=940nm
- Max continuous forward current 65mA
- Typical radiant intensity at 20mA continuous current 1.5mW/sr
- 160˚ beam angle
- Surface mount IR LED
It would be more difficult to mount surface mount components on the outside of the cups.
Features of ZVN2110G
- N-channel DMOS FET
- Max collector current 500mA
- Fast switching speed
- Max gate source voltage 20V
- Min gate source threshold voltage 0.8V
- SOT 223 package
- Pulse drain current 6A
- Fall time 8ns
- Rise time 4ns
I didn’t want to use a MOSFET because I am more familiar with BJTs.
Features of BC817
- NPN general purpose BJT
- Max collector current 500mA
- Min transition frequency 100MHz
- Max collector base voltage 50V
- Max emitter base voltage 5V
- SOT 323 package(surface mount)
- Pulse drain current 1A
Suitable replacement of 2N2222A if it fails for unforeseen reasons.
References
- 1. Discrete Semiconductors, “2N2222; 2N2222A NPN switching transistors,” 2N2222A datasheet, May 1997.
- 2. Everlight, “5mm Infrared LED IR323/H0-A,” IR323/H0-A datasheet, May 2013.
- 3. Vishay, “Standard Thick Film Chip Resistors,” D/CRCW e3 datasheet, June 2012.
- 4. Everlight, “Technical Data Sheet Reverse Package Infrared LED,” IR25-21C/TR8 datasheet, Nov. 2005.
- 5. Marktech, “Infrared Emitter,” MTE9440M3A datasheet, Aug 2011.
- 6. Diodes Inc., “SOT223 N-CHANNEL ENHANCEMENT MODE VERTICAL DMOS FET,” ZVN2110G datasheet, Oct. 1995.
- 7. NXP, “BC817; BC817W; BC337 45 V, 500 mA NPN general-purpose transistors,” BC817 datasheet, Nov. 2009.