Intro and Functions:
The 2N2222 is a general purpose bipolar junction NPN transistor. It is commonly used for low power amplifying or switching. This transistor is actually designed for low as well as medium voltage and current values. However it works on moderately high values. Originally it was made in TO casing or package as shown here
2N2222 is a very common transistor and usually referred as an example of NPN transistors. Usually it serves as a small signal transistor and has a long lasting fame for being small general purpose transistor.
2N2222 Transistor Circuit
One 2N2222 Transistor Code Lock System:
One 2N2222 transistor code lock system is a simplest electronic code lock system. It consists of a relay, a transistor and some passive devices like resistors, capacitors and switches. The circuit is simple but really efficient and works the best.
The circuit has only one transistor with a relay as load at its collector. A current limiting resistor R2 is connected across the positive supply rail and base of the transistor along with five switches (S0 to S4) in series. Other five parallel arranged switches (S5 to S9) are connected between transistor’s base and ground. The only case when the transistor Q1 becomes ON and the relay is activated when all the first five switches S0 to S4 are ON and the last five i.e. S5 to S9 are OFF. The switches are arranged on the panel in a shuffle manner and so the relay works only when the switches are ON or OFF in the pre-described manner.
Here power supply section consists of transformer T1, capacitor C1, and bridge D1. D2 is freewheeling diode. The resistor R1 confirms to keep the transistor OFF when positive supply rail and base are not in contact with eachother. S1 is the power switch for the lock.
2N2222 Transistor Equivalent:
Alternatives for the 2N2222 are now commonly available in TO-92 packaging e.g. P2N2222 which has alike specifications excluding lower max collector current Ic. However the pins order for P2N2222 is different from 2N2222. Actually the collector and emitter pins are interchanged.
2N2907 is also a complementary general purpose PNP transistor with equal popularity.
2N2222 v/s 2N3904:
The 2N3904 is also an NPN transistor with same characteristics like 2N2222 but with one difference. It can control only one third of the current of 2N2222. As compared with 2N2222 it shows forward gain at lower current. 2N3904 is more useful in amplifier applications with fewer collectors current. For example 2N3904 exhibits gain peak at 10mA while 2N2222 at 150mA.
2N2222 Transistor Pinout:
2N2222 Transistor with Arduino:
For the time being, arduino is the Nano-technology with almost 40mA input or output current. This value of current is enough to light a single LED but you may need to light several LEDs using a single pin. For this purpose one may use a transistor as a switch while controlled with arduino.
Here the 2N2222 transistor is used which can endure upto 800mA current and 40V voltage. A single 2A2222 transistor can withstand with 40 LEDs but for test here we put just 5 LEDs. You may widen the range but going above 40 LEDs per 2N2222 is not recommended.
Here the 6V battery is corresponding to four double batteries each of 1.5V. However to mount the supply upto 7.5V, five such batteries are recommended.