So I am building a remote control car for physics class and I have written code to run it and successfully tested it. I am using an h-bridge to switch the current back and forth in order to reverse the direction and the two motors driving it. The problem in having now is that everything originally worked correctly but now one side of the h-bridge won't work in reverse. In running 12v through the h-bridge and when I set both motors to forward both leads read positive 12v but when I reverse this one lead reads negative 12v and the other reads negative 0.9v. This is causing the one motor to not function in reverse. Has anyone else had this problem or can anyone else help me with this problem?
"H-bridge" is a generic term, like "car" or "truck". It tells us nothing about the specifics about your hardware. If you want specific answers, ask specific questions.
1- (what kind of H-bridge?
2- what kind of motors (probably not necessary)
3- what kind of power source ? (batteries ?)
4-When did this symptom start ?
5- What was the LAST thing you did with the project before it changed ?
raschemmel:
"H-bridge" is a generic term, like "car" or "truck". It tells us nothing about the specifics about your hardware. If you want specific answers, ask specific questions.
1- (what kind of H-bridge?
2- what kind of motors (probably not necessary)
3- what kind of power source ? (batteries ?)
4-When did this symptom start ?
5- What was the LAST thing you did with the project before it changed ?
The h-bridge model is an L923DNE (I believe it's made by Texas Instruments). The motors are medium sized dc motors that can handle about 12v or so. The power source is a dc power supply that is plugged into a wall outlet and has a knob for adjusting voltage. The symptom started today when I hooked everything up to the power supply. Originally I was running the bottom right input of the h-bridge (the motor power supply) through the arduino which provided only about 4.45 volts to the wheels. This was not enough to drive the car so I connected the positive lead of the power supply to that bottom right input of the h-bridge and the negative lead to ground. I am running the power supply at 12v.
You need to provide pin numbers if you are using the chip . The chip has a logic power supply input pin (+5V) and a motor supply input pin. You should have the datasheet.
Originally I was running the bottom right input of the h-bridge (the motor power supply) through the arduino which provided only about 4.45 volts to the wheels.
This is incorrect. There should be no connection between the arduino and the motor supply or it's connection to the L293. It sounds like you miswired something. Draw a schematic, post a photo of it
and refer to datasheet pin numbers in all future posts.
raschemmel:
You need to provide pin numbers if you are using the chip . The chip has a logic power supply input pin (+5V) and a motor supply input pin. You should have the datasheet.
This is incorrect. There should be no connection between the arduino and the motor supply or it's connection to the L293. It sounds like you miswired something. Draw a schematic, post a photo of it
and refer to datasheet pin numbers in all future posts.
Here is a photo of my setup. The yellow wire all the way to the right is connected to ground. The other yellow wire in pin 8 of the h-bridge (it's on row "D" of the breadboard) is the positive input for my power supply. I also attached a picture of the power supply. I have the red lead attached the the yellow wire in pin 8 on the h-bridge and the black lead attached to the yellow wire hooked up to ground. Everything else should be wired correctly I cross checked my wiring with multiple sites.
Originally I was running the bottom right input of the h-bridge (the motor power supply) through the arduino which provided only about 4.45 volts to the wheels.
I have no idea what this means. If you are trying to say you used the arduino +5V pin as your L293
Motor Power Supply, then please say so.
By this point I am becoming convinced you do not know how to draw a schematic. Is that a safe assumption ? (since you didn't draw a schematic and post the photo of it). Your photo confirms that your 12V supply is connected to the Motor Power Supply (Vcc2) pin of the L293. That's about all it tells us.
Have you tried swapping motor connections to see if the problem follows the motors or follows the pin numbers of the L293 ? Do you have a spare chip (since you seem to have damaged yours)
(FYI, never buy just one of anything) At this point it looks like you need to categorize the different components of your system and try to eliminate them one by one as the cause. (including the wiring).
Have you measured the resistance of your motors ?
ComponentResistanceStatus
1- motors Motor-A = ____ ?
Motor-B = ____ ?
2- L293 chip Pin3 to PIn6 = -____ ?
Pin11 to Pin14 =____ ?
3- Wiring Motor wires (from chip to motor) replaced ?
4- Code Posted ? (probably not S/W issue)
raschemmel:
I have no idea what this means. If you are trying to say you used the arduino +5V pin as your L293
Motor Power Supply, then please say so.
By this point I am becoming convinced you do not know how to draw a schematic. Is that a safe assumption ? (since you didn't draw a schematic and post the photo of it). Your photo confirms that your 12V supply is connected to the Motor Power Supply (Vcc2) pin of the L293. That's about all it tells us.
Have you tried swapping motor connections to see if the problem follows the motors or follows the pin numbers of the L293 ? Do you have a spare chip (since you seem to have damaged yours)
(FYI, never buy just one of anything) At this point it looks like you need to categorize the different components of your system and try to eliminate them one by one as the cause. (including the wiring).
Have you measured the resistance of your motors ?
ComponentResistanceStatus
1- motors Motor-A = ____ ?
Motor-B = ____ ?
2- L293 chip Pin3 to PIn6 = -____ ?
Pin11 to Pin14 =____ ?
3- Wiring Motor wires (from chip to motor) replaced ?
4- Code Posted ? (probably not S/W issue)
I'm sorry what I meant to say was that the bottom LEFT pin of the H-bridge was connected to arduino 5v output pin. This bottom left pin is pin 8 of the h-bridge which is indeed the power supply for both motors. I do not have complete knowledge of schematics and proper symbols (I am a high school AP physics student) so I did not draw one because I feared it would be incorrect and waste your time. I don't need to swap the motors because I have measure the voltages of the outputs with a voltmeter and they show the same problem every time. I do have a second h-bridge and did try that one out in this configuration as a way of troubleshooting, but I had the exact same result. Once again the original configuration (the power supply that powered the h-bridge itself as well as the motors came from the 5v arduino pin) worked fine. This tells me it is definitely not a coding error (I also checked all my code again). As soon as I introduced a 12v power supply to the motors through the h-bridge (pin 8 of the h-bridge) I started having this problem. I had checked online prior to doing this that the h-bridge I owned could handle voltage up to about 36 volts. I don't see where I went wrong. Thank you for your help.
Think about what you just said.
If one motor does not work on reverse and replacing the chip doesn't fix the problem, what does that tell you ? ( assuming you already replaced the motor wires and and moved the chip to a different location on the breadboard..
If you swapped chips then the only other cause has to be the motors. If you are a H.S. student then you need to psy attention yo mg last post. Measuring the motor voltage doesn't tell you anything. You need to swap the mohofs but before you do that you need to remove them and measure their motor resistance. You asked for help . Either follows instructions to the letter or post somewhere else or find the problem yourself. Label the motors with a marker pen so as not to get them mixed up.
Post their winding resistance.
raschemmel:
Think about what you just said.
If one motor does not work on reverse and replacing the chip doesn't fix the problem, what does that tell you ? ( assuming you already replaced the motor wires and and moved the chip to a different location on the breadboard..
If you swapped chips then the only other cause has to be the motors. If you are a H.S. student then you need to psy attention yo mg last post. Measuring the motor voltage doesn't tell you anything. You need to swap the mohofs but before you do that you need to remove them and measure their motor resistance. You asked for help . Either follows instructions to the letter or post somewhere else or find the problem yourself. Label the motors with a marker pen so as not to get them mixed up.
Post their winding resistance.
It's not the motors. They work fine in both directions. It's something else trust me this much I know. I can see it on the voltmeter! 12v out of the wires that hook up to the motors when running them both forward but only 12v out for one set of wires in reverse while the other set of wires is at .9v. I am 100% sure it is something other than the motors so unless you have a different suggestion I will look somewhere else
Remove the motors and measure the voltage with no load.
Bread boards aren't really designed to run motors for any prolonged period of time, there is a good chance that there is a burned up a wire or a trace on the board.
If your voltage is good, put a DIFFERENT motor on. If the voltage is bad, move to a different spot on the bread board and change all the VCC and output wiring. If the voltage is still bad, then you are wiring something incorrectly or have a bad chip (or two). Did you apply the 12v to both chips at the same time? Do you have a new, never used L293D to troubleshoot with?
If your voltage is good and you put a different motor on with the same result, move the chip and replace the wiring.
This is troubleshooting, break the circuit into sections, we know the motor isn't working, remove it, does the circuit work now with no motor? Maybe the previous answers were a bit curt, but all the relevant information was put out there.
lmarklar:
Remove the motors and measure the voltage with no load.
Bread boards aren't really designed to run motors for any prolonged period of time, there is a good chance that there is a burned up a wire or a trace on the board.
If your voltage is good, put a DIFFERENT motor on. If the voltage is bad, move to a different spot on the bread board and change all the VCC and output wiring. If the voltage is still bad, then you are wiring something incorrectly or have a bad chip (or two). Did you apply the 12v to both chips at the same time? Do you have a new, never used L293D to troubleshoot with?
If your voltage is good and you put a different motor on with the same result, move the chip and replace the wiring.
This is troubleshooting, break the circuit into sections, we know the motor isn't working, remove it, does the circuit work now with no motor? Maybe the previous answers were a bit curt, but all the relevant information was put out there.
Thank you for your response. What I have been trying to say I have been doing this whole time is what you have told me which is to measure the voltage of the wires without the motors on them (ie no load). I did not think to move the setup to a different part of the breadboard though. Thank you for your time.
If you reread this thread from start to finish, you (maybe not you, but anyone with electronics experience)
can come to only one conclusion: the circuit is mis-wired. (despite your insistance that it is not).
If you remove the motors and measure the voltage across the pins, and see -0.9V on one of the outputs
then you have eliminated the motors as the cause. If you then remove the chip and install another and see the same thing, then you have eliminated the chip as the cause. The only factor left is the wiring. Can you see how anything else could be true (asssuming your miswire did not damage the second chip, and assuming the results are the same after moving the chip to a different breadboard location).
Post a photo taken from one ft directly dead center above breadboard
I do not have complete knowledge of schematics and proper symbols (I am a high school AP physics student) so I did not draw one because I feared it would be incorrect and waste your time.
Can a H.S. Applied Physics student draw boxes with pin numbers and alphabetical pin function labels ?
FYI, the motor is a circle, the arduino and L293 are rectangles.
