Category: Hacking/Making

A couple of months ago I posted about trying to get my Monoprice Maker Select Plus 3D printer replaced, or at least get a new main or breakout board for it. Ultimately they agreed to replace the whole printer. They don’t have any of the individual components to even repair the printer themselves. That is a shame since that means that otherwise perfectly good printers are sent back to the manufacturer (Wanhao) and never actually get repaired by Monoprice.

Monoprice’s Offer

Monoprice’s solution/agreement was that, yes the printer was poorly manufactured and that it is their fault that my printer does not work. However, because I installed firmware on it, they would no longer cover it under their normal warranty policy. I was welcome to send it back to them at my expense and they would replace it with a new machine.

There are two problems with that: at my expense and new machine. It would cost just over $70 to ship the printer back to them. I realize that if you are not interested in upgrading and modifying your own printer, $70 may seem like a good deal. However, I was probably going to replace all the logic parts on this printer in the future anyway. I like the design of the Maker Select Plus (though if you are doing this upgrade, the Maker Select v2 is the better choice at a cheaper price), but their motherboard and firmware are not the most friendly for hacking purposes. Since I already bought all the electronics to do the upgrade when they had originally convinced me that they would not consider replacement, I would rather move forward with that upgrade path.

The second problem I had with their offer is that they would completely replace the machine and not send me my old machine back. My machine is not perfect (print bed base is bent) but at least I know its quirks and have learned to work around them. I have also done some reversible mods, but I really don’t want to have to disassemble all of my LED and Z-axis upgrades and start over. I would rather have this same machine back.

Definite Main Board Problem

Up to the point of them agreeing to replace the machine, I wasn’t even certain which of the two boards was at fault on this printer. At first it seemed like it was the main board. Then I found a burned electrical trace on the small breakout board as well as a couple of bad solder joints. Since I decided that I would not have the machine replaced I launched into repairing the breakout board myself. I found that the printer still did not function properly after repair. It displayed the exact same symptoms. So the problem is definitely the main board which may have caused the breakout board to fail.

Installing RAMPS

Now I am in the process of installing a RAMPS board and getting it all wired up. (Here’s the board I bought. It seems the manufacturer/seller has some serious quality control issues. Spend more money for a better board if you are able to). Even though the original problem showed up 3 months ago, it took me a month to finally get Monoprice to answer emails and phone calls to come to the decision that I was going to keep it and not have it replaced. Then I began a busy time of work and travel that kept me from doing the upgrade. I am home for a few weeks and will get back to the RAMPS upgrade. I will document what I can here for others who want to convert their Maker Select Plus to an open source control board.

I have actually gotten far enough into the upgrade to be encouraged that this will work as well as I had hoped. I have been able to test most of the motors and sensors with the new board. I am now in the process of assembling the new wiring harness for the machine. I will probably break down the upgrade path into several blog posts. I hope it is a help to the next person who would like (or need) to do this conversion.

And for those who have the Maker Select v2 (or 2.1) or the Wanhao original version of the same thing, there is already a great tutorial on how to do the conversion. If you are looking for a base printer to convert, then the hardware on the $300 Monoprice v2 is almost identical to the $400 Plus (with the exception of the motherboard and control screen which get replaced in the conversion anyway). The Maker Select v2 is cheaper and easier to modify in this way.

I’ve had an issue with my 4-month old 3D printer. I have made heavy use of it and it has performed well…at least until it didn’t. It is a Monoprice Maker Select Plus printer. It is the Wanhao Duplicator i3 Plus that has been rebranded for Monoprice.

Thermistor Reporting Error

About a month ago (from when I am documenting this), my printer suddenly started reporting that the hotend temperature was 58° C no matter what the temperature actually was. It seemed likely that it was the thermistor itself since they seem to short out or go bad according to my reading. And they are so cheap that it is worth trying with a replacement.

I did not have a replacement yet, so I did some testing. The thermistor performed as expected when it was removed from the printer. Yet when the thermistor wasn’t even plugged in, the printer and OctoPi reported the hotend at 58°. Everything pointed to the main control board as being the problem.

It was a Sunday afternoon and Monoprice support was not open. So, it seemed reasonable to contact them via email. After waiting a couple of days with no response, I tried contacting them via chat. The chat sessions kept timing out. Presumably because there was no one available to help at that time.

Carlos from Monoprice finally got back with me by email on Thursday (4 days after my support request). He asked for more information and what exactly I had done to test for the problem. When he replied again on Friday it was agreed that the problem seemed to be the mother board. I would have to send in the whole printer for replacement and not just the board.

Well, in the mean time of waiting for support that I thought would never come, I reflashed the board to the Wanhao firmware (Monoprice has not released a firmware to the public even though theirs has had a typo in it since the printer first released). Even with the Wanhao firmware the symptoms were exactly the same. And, as a result of reflashing my board, I voided my warranty. So on Friday of that week, Carlos said that I could not get the board replaced under warranty. On top of that, Monoprice did not even have boards available they could sell me. They suggested that if I wanted to get a new board to buy it directly from Wanhao.

RAMPS Upgrade

I started down the path to upgrade to a RAMPS control board. Ultimately that is where I will probably go with this printer. But for the moment, while making the conversion to RAMPS, I found a definite hardware issue that I thought Monoprice would like to know about.

Monoprice Support

I started a new support request email. This time on a Saturday because that is when I discovered the problem. They don’t have phone support on the weekends. After sending the support request I got a message saying that Monoprice support would get back with me within 1 business day.

On Thursday of the same week (today) I tried Monoprice support chat again. Between the last attempts and the attempts today, I probably tried to use their chat 6 or 8 times. Each time the session timed out without an explanation. I assume that it is because no one was available to help.

I called and was put on hold for only 7 minutes. For which I was very thankful. Israel answered and I started off by telling him that I was trying to follow up on an email support request. I gave him the ticket number and he was able to find my email. He apologized for their support being slow but that they were very busy. “Then,” I said to him, “don’t tell me that you will get back with me within 1 business day.” He agreed that something should be done about the message. What would be better, in my opinion, is to hire enough qualified people who could help them stay caught up.

Cold Solder Joint

While I don’t have much hope that Monoprice will replace the broken part on my printer, I did still want to do the responsible thing and let them know they had a problem. I believe my printer failed because of a manufacturer defect and I wanted to send them pictures of what was happening. That was the nature of my second request for support. Of course, I hope they do replace the bad part, but I have been in the warranty-voiding business for approximately 37 years. So I am used to it. In fact, this may be the first time that I have approached a company about warranty work. I usually try to fix it myself if it is something worth keeping.

What I discovered were some poor solder connections. As you can see in the picture, there are at least 2 bad solder joints. One of the bad solder jobs is on the thermistor connector. No surprise. I have confirmed that there is no electrical conductivity from that pin to the ribbon cable connecting plug.

You also see that the connector is red. It is the only connector on the breakout board that is not white. I wonder if other Monoprice/Wanhao boards are like this?

Burnt Trace

On the top side of the board there is a burned electrical trace. You can see in the picture below that there is an enamel coating on the board. But one trace, which happens to be for the thermistor that is not working, is burnt.

What will Monoprice Do?

Again, I contacted Monoprice today to let them know about the problem and to see if they would at least replace that small breakout board. This board, by the way, is behind the print head and is only about 1.25 by 1.75 inches in size.

Israel said that I could send my pictures to him and he would pass them along to the next person. He also told me that the breakout board was not in stock at this time, but that I could call back on Monday and see if they had a projected date of getting more stock.

I dutifully sent my pictures to Israel today at the email address he provided. It is now 8 hours later and I have not heard back from him. A simple “thanks for the pictures” would have been nice.

We’ll see what happens.

Here is how to give speed control to a regular 12V computer fan using an Arduino and PWM (pulse width modulation). This will work for other motors as well.

This is not intended to be a deep tutorial on the subject, but if you need more information you can check out the various links provided. This is mainly a quick write-up to show a friend how to do speed control on a fan that will eventually be hooked to a temperature sensor so that the fan can regulate the temperature inside an enclosed box.

Items Needed

• Arduino (can be done with a Raspberry Pi using Python)
• TIP122 (or adjusted for just about any Darlington transistor)
• 1N4001 diode
• 12V computer fan
• 12V power supply
• 270Ω resistor

The above items are not special or magical. If you don’t have a TIP122 transistor, you can probably make this work with just about any large transistor or MOSFET (large as in handling power as opposed to just physical size, though they often correspond). The same applies for the diode: as long as it is sufficiently large, it will probably work. The resistor size was chosen simply based on it being the one closest to my Arduino when I started the project.

Hookup

I leaned heavily on an Instructables article for getting my wiring set up. Certainly check out his article for more details about the wiring if you need more than a schematic to figure this out.

Or, an even more detailed description of what we are doing (at least on a partial level) is the Adafruit article on motor control. They have lots of pictures and a great explanation. But what their article is lacking is how to power a motor that needs much more voltage than what the Arduino can provide. That is why you are reading this article.

Here is my schematic of the build.

The Build Logic

I find it helps to try to understand what is happening in the electrical path so that I can complete the build and adjust the hardware or the code. Let me try to logically walk you through what is happening. Check out the video below for a rough verbal description.

The two connections to the Arduino are ground and digital pin 9 which is what sends the PWM signal to the transistor. PWM signal goes out of the Arduino into a resistor. I’m not entirely sure how much resistance is needed for this build. It works with no resistor and I have seen builds that call for up to a 2.2 kΩ. I don’t know that the resistor value is super critical, but you should probably include one.

So far we have PWM → resistor.

Now you go from the resistor to the base of the Darlington transistor. I am using a TIP122 because that is what I had handy. This should work identically with a TIP120 (and probably dozens of other transistors).

When the base of the transistor gets power from the PWM signal, it will allow power to pass through from the collector to the emitter. Check out Adafruit’s explanation of transistors for more details.

When the signal on the base pin triggers the collector/emitter connection, the transistor begins passing 12V from the power supply to the fan. The signal on the base is making the transistor act like a switch to turn on and off the collector/emitter connection.

Therefore, we kinda have 2 separate halves to this project:

• The low power side (Arduino side) is PWM → resistor → base → emitter → ground.
• The high power side is 12V positive → fan positive → through the motor → fan negative → collector → emitter → ground.

Between the collector and emitter we also insert a diode. This prevents the spinning of the fan (or DC motor) from pushing power back through the transistor and blowing up the Arduino. A DC motor (which a fan is) generates electricity when spinning but does not have outside power pushing it. So when the Arduino stops sending a signal to the fan the fan will spin down and in the process create a small DC voltage. In this case it is probably not enough to matter, but it is a good habit to put a diode in place to stop the newly created voltage from traveling backwards into the Arduino. As you probably know, a diode only allows the electricity to travel one direction. We want power to travel from the Arduino to the fan but not the other direction.

Both the ground coming from the Arduino and the ground of the 12V power supply need to be tied together. You should have only 1 ground in a circuit even if you have multiple power supplies and voltages.

In my video below you also see an LED and another resistor. This is just an indicator that power is being supplied. The second resistor is 100 kΩ. Also carefully chosen because of its proximity to my workspace.

Note that the code in the video turns the fan/LED full on and full off. However, the code I provide here is full on and only about 40% off. Being able to adjust the speed of the fan using PWM is what this project is about. Therefore you can adjust the provided code to run the fan at any speed you would like.

Code

int TIP120pin = 9; // PWM signal out to transistor on pin 9

void setup()
{
  pinMode(TIP120pin, OUTPUT);
}

void loop()
{
  analogWrite(TIP120pin, 255); // Run full speed (255) 
    delay(3000);               // for 3 seconds
  analogWrite(TIP120pin, 100); // Run at approximately 40% speed
    delay(6000);               // for 6 seconds
}

This sets pin 9 as the control pin. Then makes its pinMode to be an output. The loop turns on pin 9 at 100% speed (255) for 3 seconds and then drops to 40% speed (100) for 6 seconds.

And that’s it!

The ultimate project is to control the fan based on temperature. Getting temperature values from a digital or analog temperature sensor on an Arduino is fairly simple. It then becomes a matter of telling the fan PWM to raise or lower the speed based on the temperature.