Greetings,
I'm trying to make a simple robot. (Rolls around and whatnot) I've done it before, but this time I wanted want to make my own circuitry where I used a pre-made board last time. Which is turning out to be way much more complicated than I initially thought.
I'm stuck on giving the 2 wheel motors the ability to operate in both directions. After looking online, I decided to try an H-Bride circuit which should allow me to switch the polarity.
I took a used prototype I had, which was just some transistors on cardboard, and then rearranged the leads. I think the resistors used are 220 ohm. I write them all off. Then I write S1 and S4 on, and the motor doesn't spin. I haven't been able to come to any conclusion checking voltages only that the transistor are receiving the signal. I don't even know if this circuit will work with transistors so I thought I'd ask.
Here is a gallery of images trying to show what I ended up with (Negate the stuff above the top transistor. Not being used.) -> Gallery
You better use MOS-FETs. They work like transistors but have very little internal resistance (down to 0.1 ohms).
If you are not familiar with MOS-FETs just think of a relay: switch-ON / switch-OFF.
If your device consumes more than 100 mA i would prefer a MOS-FET.
You will find lots of information on MOS-FETs in the Arduino forum.
However, be careful, the Gate-Source voltage (basis-emitter voltage for transistor people) required for higher currents (required by some motors) might be higher then the Arduino output voltage.
arduinoaleman:
You better use MOS-FETs. They work like transistors but have very little internal resistance (down to 0.1 ohms).
If you are not familiar with MOS-FETs just think of a relay: switch-ON / switch-OFF.
If your device consumes more than 100 mA i would prefer a MOS-FET.
You will find lots of information on MOS-FETs in the Arduino forum.
However, be careful, the Gate-Source voltage (basis-emitter voltage for transistor people) required for higher currents (required by some motors) might be higher then the Arduino output voltage.
Look for "logic level" FETs.
arduinoaleman
I'm going to be using two of those tiny motors that are in the pics above @ sub 4v. I'm my tests previously using these transistors for powering those motors, they did just fine. I think they are rated for 5v. They didn't get hot at all.
If you really really just have to make an H-bridge using transistors, here's a really good walk-through from Robot Room. Everything is pretty well broken down and explained. RobotRoom Transistor H-bridge
If you just want to build a motor driver yourself, a good place to start is the L293D. This is a dual H-bridge integrated circuit. It's an inexpensive solution that will allow you to drive two DC motors in both directions or a single stepper motor. You can use it to control your motors individually in both directions with it and can control their speed with the addition of PWM. This is one I use a lot for DC motors rated at around 6v and it works great. If you want something more flexible, say a driver that can control DC motors ranging from 1.5 to 11 volts, I would recommend looking into the Texas instruments DRV8835. It's a much smaller surface mount IC but there are lots of packages already put together. Pololu even makes a few different Arduino shields that use it. Here's the one I'm going to order this Friday for my current bench project. DRV8835 Motor driver
As you can see it's very small. Could you build your own H-bridge from this? Sure, there are a few companies that make breakout boards that the IC can be soldered to, but when it's this small, I would rather leave the soldering up to the robot.
dritchie:
Read through that .. and came out with nothing. Sorry.
It was illustrating, as it were, certain realities.
People, "n00bs", get this deal where they're going to make an H-bridge (never done much, gonna make a h-bridge), and they fail.
They fail because they know next to nothing and assume way too much.
They fail because there's a lot of misinformation and the agendas of the distractors.
They fail because too many cooks spoil the soup.
MOSFETs are transistors. Do you mean BJT? Bipolar Junction Transistors?
High side drive with NPNs are tricky, so for simplicity sake I'd suggest high side are PNP, low side NPN.
Do NOT use darlington pair, they drop out around 1V.
Read the spec sheet of your transistors, but generally for saturated switching, base current needs to be no less than 1/10th the maximum collector current. Some newer transistors can reliably saturate with 1/20th, but read the data sheet.
polymorph:
MOSFETs are transistors. Do you mean BJT? Bipolar Junction Transistors?
High side drive with NPNs are tricky, so for simplicity sake I'd suggest high side are PNP, low side NPN.
Do NOT use darlington pair, they drop out around 1V.
Read the spec sheet of your transistors, but generally for saturated switching, base current needs to be no less than 1/10th the maximum collector current. Some newer transistors can reliably saturate with 1/20th, but read the data sheet.
I re-did my H-Bridge circuit/layout to make it 1:1 to the basic schematic. And I can now get a motor to spin in one direction. However, I can't get it to spin in the opposite direction when changing pins.
Testing the resistances of all the transistors it appears one has a very slight different resistance than all the others. I'm not sure if its a bad transistor somewhere, or I have the right current going in the wrong direction.
dritchie:
Thank you everyone who tried to help. Except Runaway Pancake, you really aren't as funny as you think you are.
I can't see where I was injecting any humor, so I don't get you.
I guess I went wrong: agreeing to "assist" you in "getting this thing to work" and by not trying to take the subject off in another direction ("your Dad's transistors, PNP, and all the other junk), respecting your decision.
Nice that you checked your wiring.
FYI, the 2N4403 is rated for not more than 600 mA. What could you possible drive with an H-bridge made with such low rated BJT (BIPOLAR JUNCTION TRANSISTORS (Junction-1: collector, Junction-2: emitter).
See Reply#6 of this post for a DIY mosfet H-BRIDGE
It helps to tell us your electronic background (if any).
This:
I'm stuck on giving the 2 wheel motors the ability to operate in both directions. After looking online, I decided to try an H-Bride circuit which should allow me to switch the polarity.
tells us nothing about your background (or lack thereof).
This:
You guys are speaking another language and it's going right over my head
however, speaks volumes.
You might start by asking why EVERYONE is trying to steer you AWAY from transistors for an H-BRIDGE
application. That's a question you should definitely be asking. It is not a coincidence. The fact that you have not asked that question tells us alot.
You came here for advice. We are trying to give it. You are trying to tell us what you want (or don't want ) to hear.
POP QUIZ
I'm aware of the short circuit risk. Luckily, I haven't experienced any as of yet; fingers crossed. I'm using an external power source of 18650s.
If you aware of the "risk" (as you call it), then what is the name for the condition that results in the short circuit in an H-BRIDGE ?
18650 cells can EXPLODE. I have 4 of them wired up series-parallel, and if I touch together (very briefly) the + and - wires, I get sparks. It is great! Now imagine that shorted through a 2N4403. BOOM!
I, for one, would really like to see a schematic for this "h-bridge" - an all-PNP h-bridge?
We've all seen (generally poorly functioning) all-NPN (and all N-channel) h-bridges before - but I don't think I've ever seen an all PNP h-bridge...
Seriously, dritchie - you've gotten lucky (and using cardboard too - just where in the world are you that proper PCB perfboard material can't be easily bought?).
A proper h-bridge, when constructed from transistors, usually consists of PNP (BJT) or P-channel (FET) transistors on the high side, and NPN (NJT) or N-channel (FET) transistors on the low side; you can also get away with an all NPN or N-channel design, but usually with FETs you need your high-side transistors to be several volts higher than your supply voltage to get them to properly turn on and off - this is usually effected by using a high-side driver chip or circuit of some sort, and/or a voltage booster circuit on the high side of things (in such a case, the bridge is driven using PWM, and the signal can never go above about a 90-95% ratio, otherwise the boost in voltage is lost).
Now that you have something working, you owe it to yourself to understand why it is working - and why it (likely) isn't very efficient - and how to construct a much better working h-bridge in the future...
