PCB adaptions for Mendel

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Revision as of 16:58, 24 May 2010 by Ethan (talk | contribs) (Added BOM for pin headers and screw terminals to aid in planning component orders)
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If you buy ready-assembled printed circuits for RepRap that will save you a lot of time. But the connectors they come with are for the MakerBot CupCake machine, not RepRap. This page tells you how to modify them. You will need a soldering iron, long-nosed pliers, forceps, and a small screwdriver. If you have one, a solder sucker will also be useful.


Total # of assemblies: 5

Name Qty/assembly Total Qty Type
Stepper Motor Driver v2.3 1 3
5.08mm-pitch 2-pin screw terminal 1 3
3.81mm-pitch 4-pin screw terminal 1 3
2.54mm-pitch 3-pin polarized header 1 3
Motherboard v1.2 1 1
78L33 TO-92 3.3V regulator 1 1
100uF (106K) Radial-pin Aluminum Electrolytic Capacitor 1 1
2.54mm-pitch 2-pin header - 2 pin 1 6
2.54mm-pitch 2-pin jumper 1 1
Extruder Controller v2.2 1 1
2.54mm-pitch 2-pin screw terminal 1 1
2.54mm-pitch 2-pin header - 2 pin 1 6

Replacing the connectors on the stepper driver boards

The RJ45 connectors are low-cost, as is the cabling for them. But they are not very neat. To replace them do the following.


Use a pair of forceps to pull the gold-plated connectors inside the RJ45 shell and push them up through the top. Then pull them out from the top and straighten them out.


Next desolder each connection separately, pulling it out with long-nosed pliers. The plastic shell will then be easy to remove.


This shows all modified connectors. The original is on the left; the modified is on the right. The two RJ45 connectors have been removed as above. The bottom one at A - the MIN connector - has been replaced by a 3-pin 2.54mm-pitch pin-strip connector. The RJ45 connector just above A - the MAX connector - has also been removed, but Mendel doesn't use this so you can leave it there if you like.

The power connector (at B) has been replaced with a two-way 5.08mm-pitch screw connector. The other two power connections are not needed. This allows the 12 volt power wires to be permanently attached to the board with the screws. The ground connection is on the left in the picture, and the +12v connection is on the right next to the capacitor. Removing the power connector is the only difficult operation that needs to be done on this board. The only way to do it is to clamp the board, put a small screwdriver under the connector at one end, desolder the connection (wait for the solder to melt fully) and lever the connector slightly away from the board. Hold it away while the solder freezes. Then move on to the next connection. By working back and forth between the connections in sequence you will eventually be able to remove the connector. Don't forget allowing the solder to freeze - this puts the next connection along under tension for the next step. Make sure the solder is fully-melted before you start levering, otherwise you may strip the copper from the PCB.

The stepping-motor connector (at C) has been removed and replaced by a 4-way 3.81mm-pitch screw connector. To remove the original connector place the board in a vice, clamping it so that the jaws just cover the letters A B C D on the board's silkscreen. Then desolder each pin separately and pull it out with long-nosed pliers. The plastic spacer will come away with the last pin.

You can just put the motor's wires straight in the screw connector without needing to put a corresponding connector on them. Do tin the ends of the motor's wires first, though.

Replacing the connectors on the Motherboard

First remove the RJ45 connectors at D (below) and to the left (see above in the stepper-motor control board section for how).


Now the tricky bit: removing the chunky power connector at C.

If you do this right, it takes time, but not a toll.

The trick is to remove the pins one by one. Grasp them firmly with forceps, apply a soldering iron to the back (get the right pin...), wait for the solder to melt right through, then pull the pin out.


When you're done solder in the link shown at the penultimate pair of holes on the right, a 3.3 volt regulator (78L33 - get the TO-92 packaged one) and a 100 μF capacitor just to the left of C. The regulator has its flat facing the bottom of the picture. The negative pole of the capacitor faces goes to the bottom of the picture too. The positive pole of the capacitor shares the same hole as the leftmost regulator pin.

Now the easy bits: clip away the chunky 30 ohm resistor at E. Make sure there is at least one connection to SDA and SCL at B (if the standard socket connectors are on the board those are fine). It is also useful to have a ground pin soldered in somewhere on the board. This can either be at B or one of the two pads labeled GND just under the ATmega644P microcontroller chip. Make sure there are two pins and a jumper at A.

Replace the RJ45 connectors you removed with 2.54mm pin headers as shown at D and to its left.


Finally on the back of the board solder a link from the fourth pin of the 6-pin USB<->serial connector to the corner pin of the ICSP connector as shown. This allows the entire board to be powered from the USB cable. Make sure the link doesn't short on any of the other connections. (Unlike me, you may care to put a short length of heat-shrink on it to insulate it...)

Replacing the connectors on the Extruder Controller


Here you just need to replace the RJ45 connector at A. Remove it using the technique in the stepper-motor controller section above, then solder in a 2.54mm screw connector for 12 volt power and a 2.54mm 2-pin header for RS485 comunications as shown. The +12v connection is on the right, ground is on the left.

Back to Circuit board construction.