Learning about H-bridges and transistors

Wow, I didn't expect this much interaction to my question. Thank you everybody.

My direction was to control a stepper motor (Mitsumi M49SP-2K and KH42JM2) and I got mislead somewhere (here, it says H-Bridge on the IC) that I need an H bridge, so I tried to learn about them and about transistors. I'm still a noob in electronics, and I know bits and pieces of it. Your answers have been most helpful, especially the criticism on my schematic. I know it's terrible.

I haven't studied in any field related to electronics. I'm a software developer, with very limited knowledge about electronics, and I'm trying to learn about it.

For controlling the KH42JM2 I've made this with the help of a friend some time ago.

And the code:

int led1 = 13; int led2 = 12; int led3 = 11; int led4 = 10; int button = 2;  int pause = 50; bool forward = true;  void setup() {     pinMode(led1, OUTPUT);     pinMode(led2, OUTPUT);     pinMode(led3, OUTPUT);     pinMode(led4, OUTPUT);     pinMode(button, INPUT);           digitalWrite(led1, HIGH);     digitalWrite(led2, HIGH);     digitalWrite(led3, HIGH);     digitalWrite(led4, HIGH); }  void step1() {     digitalWrite(led1, LOW);     digitalWrite(led2, LOW);     digitalWrite(led3, HIGH);     digitalWrite(led4, HIGH); }  void step2() {     digitalWrite(led1, HIGH);     digitalWrite(led2, LOW);     digitalWrite(led3, LOW);     digitalWrite(led4, HIGH); }  void step3() {     digitalWrite(led1, HIGH);     digitalWrite(led2, HIGH);     digitalWrite(led3, LOW);     digitalWrite(led4, LOW); }  void step4() {     digitalWrite(led1, LOW);     digitalWrite(led2, HIGH);     digitalWrite(led3, HIGH);     digitalWrite(led4, LOW); }  void goForward() {      step1();      delay(pause);      step2();      delay(pause);      step3();      delay(pause);      step4();      delay(pause); }  void goBackwards() {      step4();      delay(pause);      step3();      delay(pause);      step2();      delay(pause);      step1();      delay(pause); }  void loop() {     if (digitalRead(button))           forward = !forward;      if (forward)           goForward();      else           goBackwards(); }

But now I tried to go on my own. I have some salvaged parts, and I'm willing to destroy them in the name of learning.

I will eventually use an IC for future projects, but first I want to understand how components work, and how to make a circuit to achieve this.

I've recently got a book about transistors: Romanian translation from "Questions and answers on Transistors" by Clement Brown - Butterworth & Co (Publishers) Ltd. 1969. I quite like it as it explains in very much depth. But my free time is scarce so progress is slow. Anyway, until I finish this book, further questions about transistors would be useless. I'll make a list of questions I have, and If I don't get an answer later in the book or from Google I'll come back.

Thank you very much for all your help and shared knowledge. I haven't read through all the links you've gave me yet, but I've bookmarked them, and I will look at all of them.

If you are new to electronics then your diagrams are not that bad... wrong perhaps but pretty good start for a newcomer and you will only get better over time

In the diagram above i would suggest a small resistor in series with the LEDs as they are in parallel with the coils and so will limit the volts to the coil and conversely when the transistors switch off there will be a back EMF that could destroy them. You should have a protection diode (NOT an LED) across each transistors load to minimize the impact of this

The diagram you have above btw is not an H Bridge, the stepper you're using in the diagram has 5 or 6 wires with the center taps of each coil going to +Vcc, the rest are sequenced to ground by the controller, you can also simplify the components by using an LM2003 darlington driver chip, it will handle steppers of this kind when they're not too big, it will also handle motors of more than 5V if needed, LEDs with series resistors can easily be added to give visual indication of operation, you could also put them on the input of the chip rather than the output, then just use a 330R to 1K Ohm resistor in series with an LED to 5V and it should not load the output of the arduino too much

btw, here is a more readable version of the H bridge schematic (The bit with the transistors anyway, you just need to add your IC back to it. Any NPN  transistors that have the required specifications will work, it all depends on the load your switching and the drive your using (The chip in the case of the diagram above). This diagram is also the more traditional way of showing the H Bridge, yours is not wrong, just harder to follow. I would also use 1N4001 ot better diodes than a 1n4148 as those are just signalling diodes and may not last long with any but a tiny motor

If you are new to electronics then your diagrams are not that bad... wrong perhaps but pretty good start for a newcomer and you will only get better over time

In the diagram above i would suggest a small resistor in series with the LEDs as they are in parallel with the coils and so will limit the volts to the coil and conversely when the transistors switch off there will be a back EMF that could destroy them. You should have a protection diode (NOT an LED) across each transistors load to minimize the impact of this

The diagram you have above btw is not an H Bridge, the stepper you're using in the diagram has 5 or 6 wires with the center taps of each coil going to +Vcc, the rest are sequenced to ground by the controller, you can also simplify the components by using an LM2003 darlington driver chip, it will handle steppers of this kind when they're not too big, it will also handle motors of more than 5V if needed, LEDs with series resistors can easily be added to give visual indication of operation, you could also put them on the input of the chip rather than the output, then just use a 330R to 1K Ohm resistor in series with an LED to 5V and it should not load the output of the arduino too much

btw, here is a more readable version of the H bridge schematic (The bit with the transistors anyway, you just need to add your IC back to it. Any NPN  transistors that have the required specifications will work, it all depends on the load your switching and the drive your using (The chip in the case of the diagram above). This diagram is also the more traditional way of showing the H Bridge, yours is not wrong, just harder to follow. I would also use 1N4001 ot better diodes than a 1n4148 as those are just signalling diodes and may not last long with any but a tiny motor

Not sure I'd use 1N4148 diodes.

I tend to prefer 1N4001  to 1N4004 as they handle the current a little better.

Mark

That's exactly what I said in my comment with the Diagram and I completely agree... It was a Stock Diagram I found

what I said in my comment

oops I should have read all the words .....

Sorry.

I do the same from time to time, no apology necessary , but thanks anyway

Peter