Ok, embarrassingly simple question...but so confused

Ok, I am pretty familiar with all things electronics but I am having a very odd issue that I need to correct before I go officially nuts(I must be missing something. Little background, I have the maslow motor shield from the maslow store. Being I had everything else except the motors, the goal was to build the Marlow CNC as close as the motors I could source would allow.

Now, please tell me the pinout of the shield motor connecter for motor1. I need to know what each pin does. Yes, I am very aware of the schematic and have reviewed all that info but something very odd is occurring. I made motor cables and could not get the motors to run at all. So after hours of mind numbing troubleshooting I was done for the day but had a thought about possible wrong cable construction…I do not know why I checked but the test motors script put out the signal I was looking for on totally wrong pins. So briefly tried and succeded to attach motors to what seem like the wrong pins and they worked well. Will test more after work but need to clarify the pin outout from the shield at the motor connector.


Starting with P1&2, the names M+ and M- are confusing :slight_smile:. M+ and M- carry the 12 volts that run the motor. The motor control chip can turn the motor in either direction by changing which one has 12V and which one has 0V. The motor control chip changes the speed by turning the 12V signal on and off rapidly. For more on this, research Pulse Width Modulation. Those are the only pins which are involved with making the motor turn. All the current used by the motor passes through these two pins.
P3-6 deal with the quadrature encoder used to detect the rotation of the motor shaft. The 5V and GND are what you expect. Note that this GND is not used by the motor. Pins5&6 are the encoder signal which is read by the Mega as interrupts with each pulse edge on each line.
If you’ve got an oscilloscope or a multimeter that has a PWM function, you can see what’s going on with the motor using the ‘test_electronics_firmware’ sketch found in the Firmware release. It uses analogWrite() statements to set motor speed, and also changes motor direction. (If using a scope connected across both M pins, think about using it in battery mode or with a ground buster - don’t want to ground a motor lead through the scope…)

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Thanks for confirming why this is strange and sorry to make you go through al that as I am pretty well versed in PWM and such…but get this …nothing was working, no motors moving…did not yet go pin by pin but did map all to source files today. Anyway, I plugged (I realize if it were in the 5 volt it could pull too many amps)…m+ and m- into the p5 and p6…which I thought were only encoder outputs…and when test is run I get full speed one direction and then full speed reverse. Hoping I just made some stupid omission but this makes no sense. Literally upside down of how it shows on schematic. I do not think the encoder lines would put full power out and then reverse with test. I feel like an idiot here…no clue why that works. If time tonight I will check the pins and attach the rest …plus it was working better with GC than it had all night. Actually stayed connected…which when plugged in pin1 and pin 2 it would disconnect. Really, I am not new lol…but because I only have little time to work on this here and there easy to make mistakes. But this makes no sense at least per the schematics. Tonight will trace all the mega pins per firmware and see what is going on.
Thanks again for verifying that this is crazy.

That sounds like a pin out issue. The test should put full speed forward and then reverse on the motor pins. If the onboard 5v and GND to power the encoder were shorted (through the encoder) the Arduino will shut down to protect itself.

Probably the easiest way to tell what’s going on is to follow the traces. The ±12V pins will go to the H-Bridge while the encoder pins will go to the Arduino

It might be worth checking to make sure the encoder pins are working OK, because if they are shorted to 12v bad things will happen to them


Thank you so much for clarifying that by using the labels. I was using the schematic as a reference and took it too literal. The motor plugs are upside down to what you showed on that. I hooked up the motors I finally just bought (starts to drive you crazy trying to source and hit as many of the stats as you can…always seem good except one no go spec lol.) …and being just ready to experiment with something I got very small but powerful motors. Hopefully the 14,000 ppr will be handled but they are not able to be used in a full size maslow.

Again, thank you so much. I was so sure of orientation …not new at this (believe it or not) but also because I had not traced all the lines yet. Been a project that I have to do whenever I have 30 mins here or there. Keep up the great work! If I find more full-size motors I will make sure to remain active as I have been playing around with the sled and plotter style set up for the Marlow since I started trying to source the only part I did not have…have…the motors 6 months ago.

You really are responsible for something great here and I wish you the best!


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So why are the pins upside down on the schematic? I haven’t got to the testing stage yet but I would have done the same thing as thuber! are the aux ports upside down too?

The layout of the parts on the schematic doesn’t really have any bearing on the PCB layout. On the schematic the parts are grouped by function (H-bridges together, Arduino pins together, LEDs together) and the pins on the components are generally inputs on the left, outputs on the right. The actual pinouts of the chips need to be referenced to the board layout.

It seems like more than one person has been confused, so if someone want’s to organize it in a way that everyone thinks makes more sense, I’m happy to merge the changes

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I don’t have the board, but silkscreen a “1” next to pin 1. There might not be room, but silkscreen the pin names next to them. Single row makes that a lot easier


I fell victim to the not true reference of component layout also.

I’m just about ready to start assembling my open source Maslow. Was thinking last night before I fell asleep, "man I wish I could locate an accurate diagram for all connections. It would make this easier. "

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I’d advise that one never assume that the connector orientation on a schematic reflects the same on the PCB. Get used to cross-checking on the PCB,it’s a good practice and will help you get familiar with the layout on the board. There is much to be learned from tracing signals on an unfamiliar board.
That said, a mark indicating the orientation of components and connectors is a standard convention. I’ll add the Pin1 marks for the connectors to the PCB layout.


Hey Bar et al…
I did realize that the schematic was not a exact part layout but functional diagram. Like I said I just had very little time and when some parts came I did what I usually do not do and just hooked it up. Totally my fault because I knew the schematic was functional groups but had it in my mind and was not careful. 100% on me.

Anyway, for anybody that was careless as I and if the reverse caused damage to the encoders in any way (encoders are something I have never built with before), they are very easy to fix. I blew one of the hall sensors, which are the same on all of that same style pretty much. Tested a fix via a sensor I pulled out of old throttle. Then got 10 of them for 6 bucks and back up and running. Plus so far my high ppr of 14,000 plus, no problems yet…but not yet complete build. Would love to know of any sources for the common (with motor) pcb 2 hall sensor encoder though because would make sourcing the motor so much easier. They seem next to impossible to source from the common places I have checked.

Thanks again for the clarification Bar!

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