# Tagged Questions

99 views

### Which resistor for NPN transistor base?

Which is the way to choose a resistor for a NPN transistor base? I want to use P2N2222A as a switch, in a design as shown below. When I have voltage in base (1.8 V), I want a connection to be created ...
152 views

### Emitter resistor - why?

I was told to add an emitter resistor to the transistor T1. I'ver been researching the subject and could only find vague info about the E resistor and now I'm utterly confused. The transistor here ...
184 views

### Need help calculating resistance for transistor base

I have 3 12VDC/40A automotive relays (datasheet) that I want to use with my Arduino. Based on the tutorial I am following (link) I need transistor, resistor, and diode. I am not an electrical engineer ...
60 views

### measure resistance circuit when I have an lm334

I have a circuit simulate this circuit – Schematic created using CircuitLab this circuit without the lm334(current limiter) should produce some kind of voltage on R6 when R5 and R4 are ...
230 views

### Basic help with calculating values for PN2222A LED circuit

I'm gonna be adding an IR LED to my Arduino Uno and I'm trying to wrap my head around the math used to figure out the exact resistor values needed to use a PN2222A transistor to drive the LED. I know ...
821 views

### Single LED single transistor circuit not working

I was making a circuit with 1 LED and 1 transistor. pretty primarily i was trying to use the transistor as a normal switch. Here is the diagram below. So, this is an NPN transistor and i connected ...
828 views

### leds in parallel, switched with NPN transistors

I have the following circuit designed to drive 3 PWM pins off a 3v3 Arduino Pro Mini -- one pin for each of R, G, B in this set of 5 RGB LEDs. simulate this circuit – Schematic created ...
242 views

### Constructing a simple emergency light kit

This is my first adventure in the electronics world and, as I'm a CS student, you can expect a lot of associations that maybe aren't that right. The main feature of my circuit is: If there isn't ...
254 views

### Alternative to optocoupler? Other switching devices?

I have a part that classifies what kind of power I get on ethernet by presenting different loads. For example, the part needs to have a 100 Ohm resistor across two of its pins, and the part will ...
73 views

### NTE2013 base inputs

I have an NTE2013 which I want to use with an Arduino. I may be driving the base pins directly off of the Arduino or perhaps off of a 74HC595. Should I use resistors between the outputs and the base ...
384 views

### how to choose the transistor for following case?

I planned to use the following circuit to run unipolar motor. I got this circuit by surfing internet. I know how to choose the transistor for driver circuit by knowing the base current, but in this ...
1k views

### 1.8V to 5V, still not comfortable with transistors

I have a H-bridge IC L293DNE that needs 5V input signals to operate, however my available outputs are only 1.8V from a Gumstix Overo GPIO pin. I have a power supply that supplies me with +5V 1A. I've ...
924 views

### Transistors: why are resistors needed?

I have a solid state relay which needs at least 3V to activate, and I need to toggle with a 2.3V output from a microcontroller. I've also got a 6V 1A power supply which I can use to power the relay. ...
179 views

### How to properly store components efficiently and effectively [duplicate]

Possible Duplicate: What's the best way to store and categorise resistors/capacitors/ICs/etc? I have MANY resistors and many other components as well and currently I am using a very ...
2k views

### Why do you need 2 resistors when hooking up a transistor as a switch

What is the point of R2 in the following diagram: I get that R1 controls the current to the Base, but what does R2 do?
1k views

### Determine suitable resistor for the base of transistor as switch (NPN)

I have designed a program to count the frequency and time period of the pulse generated by a 555 timer IC using PC Parallel port. I’ve connected a base of BC547 (NPN) transistor to the output pin (no. ...
382 views

### Not use current limiting resistor for switching device on off using TIP122 possible?

I wanting to control MP3 player and amplifier box through PIC board. My project is doing announcement when person standing in near PIC board with proximity sensor. When proximity sensor detecting ...