I guess I don't want you to lose sight of the fact that a voltage does, in fact, control the collector current of a BJT. I should also say that I got this idea for this circuit from the following schematic:Īnd I notice that mine has the 9v source and the sparkfun one has both at 5v and maybe this is where I've messed up the biasing. Simulate this circuit – Schematic created using CircuitLab Later that will be a pin from an Arduino board which will put 5v on that line. I threw in the SW1 to show how I am testing the circuit. Would you expect that to be true?Īt how many volts on base of Q1 do you believe would it take for current to flow and LED to light? What do you believe the lowest voltage that would activate the LED would be? An NPN ( N egative- P ositive- N egative) configuration and a PNP ( P ositive- N egative- P ositive) configuration. The design of the 2N2222 transistor allows it to be used in a variety of electronic circuits. When used as a switch, the 2N2222 can control the flow of current to other components such as LEDs, motors, and relays. This 600-Volt, grounded, jacketed cable wire is used primarily in residential wiring, including branch circuits for outlets, switches, etc. This table is set out like a typical data sheet for BJT transistors: Extension Box. It seems that the LED lights even when the 5v source is down to 1v and less. NPN Transistors are three-terminal, three-layer devices that can function as either amplifiers or electronic switches In the previous tutorial we saw that the standard Bipolar Transistor or BJT, comes in two basic forms. The 2N2222 can be used as an amplifier or a switch, depending on the circuit design. In real life I have built this circuit and the LED does light. Note: If my battery is backwards or something in the schematic that is just because I couldn't get it right on there. To test out the circuit, I figured I'd substitute an LED for the time being. Obviously the Arduino I'm using doesn't have the voltage to drive the 5V relay, so that's where the 2N2222 comes in. If not, can you provide details about what needs to be changed? 6 I'm looking to drive a relay on a 5V rail from an Arduino 3.3V pin. I'm attempting to use the transistor as a switch so that only when an outside source voltage appears on its base then the secondary circuit will be turned on.ĭoes this circuit seem properly wired? (in basic theory) If anyone has any ideas on how to get this to work or if they notice something I've wired backwards (highly embarrassing) please let me know.I have the circuit drawn below and I'm expecting the circuit to only light the LED when 5v appears on the base. Thought the relay might be fried, swapped it out for a different one then connected it directly to 12V.NPN 2N2222 transistor (or similar) SPST Switch LED 3 AA Batteries or DC power supply 330. The parts we need to run this circuit are shown below. We use the transistor to supply the amplification necessary so that the LED can be driven. Thought I might be losing my mind and had wired the transistor in backwards. This circuit exploits the fact that transistors can function as current amplifiers in circuits.I tried all of the above with a 330 ohm resistor instead of a 1k (R1) to increase the current through the transistor, no luck there either.I thought maybe for some crazy reason 3.3V just wasn't cutting it so I tried a 5V signal instead, no luck there either.I thought maybe the 2N2222 (TR1) base wasn't draining properly so I tried connecting it to ground via a 10k ohm resistor as well as the 1k ohm, no luck there.I've tested all of the voltages and they're fine. The only way I can get the relay to turn off again is to disconnect the 12V power source. When I push the tactile pushbutton the relay turns on, when I let the button go, the relay stays on. External Circuitry Eliminates Calibration External circuitry can be designed to utilize the inherent sensing capability of low - cost transistors without. In reality the 3.3V signal will come from an ESP8266 but on my breadboard setup its coming from a power supply. I have a very standard NPN low side switch setup to turn a relay on/off from a 3.3V signal. I've been pulling my hair out over this for weeks and I can not for love nor money work out why it's not working.
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