This was my first try at making these kind of videos. I had no idea what i was doing…
The Geeetech Melzi is probably the cheapest RepRap controller board right now. But is it any good?
Watch me awkwardly stare past the camera as i use my cheesiest voice to read out the pros and cons of this board.
Just two years ago, a complete set RepRap electronics would cost upwards of 200 bucks. Now, this board has all features and cost me just 40 bucks. Is that too good to be true?
I’m Tom, and this is my review of the geeetech Melzi.
Now, the Melzi board is a RepRap control board that was designed to be cheap to manufacture and should enable as many users as possible to take up 3D printing. It’s based on the well-known Sanguinololu, which itself was already a low-budget board. The Melzi expands on that by including more features, like a high-power fan output and a microSD slot. Of course, it also has the basic set of features like four A4988 stepper drivers, two more mosfet outputs for a hotend and a heated bed as well as three endstop and two thermistor inputs.
Geetech aren’t the only ones manufacturing this board, but they were by far the cheapest. They sell it for 40€ on ebay and for about 60€ on their online shop, which is about in line with what other vendors charge. It came in this pretty large box, wrapped in bubble wrap and in an antistatic bag. Surprisingly, they still managed to choose a box that was actually too small for the board, and i doubt it would have survied if the box got smashed in any way.
The board itself doesn’t look too shabby at first sight – i’ve definitely seen worse. The SMD soldering job is top-notch, but there are some areas with flux residue on the front and the back. It’s easy enough to wash this off with alcohol, but it’s still a fairly sticky annoyance. The through-hole soldering job is fairly good as well, as these are typically hand-soldered. They managed to smear a bit of solder down here, which is pretty close to causing a short, but still doesn’t.
Now, what i did notice were two broken connectors. This one is missing its latching tongue, which secures the matching connector in place, and this one is missing another tongue, which should be there to protect bare braided wire. The missing pieces were non in the antistatic bag, so i guess it was already broken when they shipped it out. Again, these two missing pieces aren’t a huge deal, but they’re another small annoyance.
Now, what is going to be a huge annoyance are the type of mosfets they chose to use. They are ME10N06 types, manufactured by Matsuki. Now, these mosfets are about the worst type they could use. In fact, the manufacturer of these mosfets apparently had a hard time making ones that were this bad, so the only ones they’re still selling are a couple ranks up. They are 60V, 13A types, but because they have such a high DC resistance, you can only load them with about 3 amps before they burn up. A heated bed typically draws 12 or 13 amps, so running one directly from this board is out of the question. I guess you’ll be fine with a solid state relay added on, but on the other hand, they could have just used a better mosfet and made it work like it is supposed to.
The Geeetech guys obviously don’t pay much attention to detail, which should be clear by now. So as expected, they copied the flaw in the schematics where the thermistor inputs have a 10k pullup resistor. RepRap standard is 4.7k, which gives a better resolution at high temperatures and also means that the firmware’s thermistor tables are interchangeable between boards. With the 10k resistor in there, you’ll either have to compile your own tables or simply swap out the resistor for a 4.7k one to get correct readings at all.
Basic functionality, is all there, though. I tested all three mosfets with a 40W heater cartridge and they’re all working just fine with a small load like that. The stepper drives work nicely as well, and they should even be able to pump out a bit more current than the typical pololu driver boards since the Melzi provides more area for cooling. In fact, since the bottom of the board has no obstructions around the drivers, you can just glue a heatsink or aluminum slab to the bottom and cool them that way, which is the preferred way anyways. The pots were initially set to 2A, but you need to setup the drivers for your individual motors anyways. They use 50 milliohm sense resistors, which is the same value as genuine Pololu boards.
The board came with a standard Arduino bootloader installed, so uploading firmware is farily painless once you figure out that the chip isn’t an ATMEGA 1284p, which the RepRap wiki provides Arduino hardware files for. It’s actually the smaller 644p, the same chip as the Sanguinololu, so you have to use the sanguino files to be able to upload to it. One more specialty about the Melti in general is that it has a green status LED, which. by default, does nothing at all. You have to trigger it manually by sending an M42 without the P argument for pin, so you can just send M42 S255 to turn it on and M42S0 to turn it off. Not particularly useful in any way, but, hey, it’s a feature.
So, would i recommend this board to other users? Not at all. The wrong choice of thermistor pullup and the super-shitty mosfets make the board unusable for anyone who isn’t an expert user, and we really don’t need yet another brick in the road when building a 3D printer.
Would i personally buy it again? Probably. Swapping in proper pullups is a quick job when you have the right tools at hand, and even the mosfets aren’t bothering me much. I’ll be expanding the board for dual extruders, so i’ll just use the onboard ones for the hotends and power the bed through a beefy external mosfet.
But then again, if you know what you’re doing, you can fix about anything. Geeetech really could have done a better job with this board at minimum effort.
So that concludes my first RepRap video, if you like what i’m doing, give this video a thumbs up and subscribe to this channel. I have a lot of subjects lined for my next videos, so let me know in the comments what you’d like to see next.
I’m Tom, thanks for watching.
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