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Constructing a 3D Printer [Prusa I3]

SECTION 5 - Electronics - Page 2

Section 1 - Wooden frame : part 1 - part 2 - part 3
Section 2 - Y Axis : part 1 - part 2 - part 3
Section 3 - X-Z axis : part 1 - part 2
Section 4 - Extruder : part 1 - part 2 - part 3
Section 5 - Electronics : part 1 - [[ part 2 ]] - part 3
Section 6 - Coarse Calibration & Software : part 1 - part 2 - part 3
Section 7 - Fine Calibration & Software : part 1 - part 2 - part 3
Section 8 - Extras : part 1 - part 2 - part 3
Section 9 - Maintenance & Modding : part 1 - part 2


We need to prepare our Ramps 1.4
electronics prusa i3

Solder the diode like the photos below.
Please notice the polarity.
electronics prusa i3

electronics prusa i3



Unbox your four StepStick A4988 drivers.
electronics prusa i3

Solder carefully all the pin legs of the A4988 drivers.
electronics prusa i3

Measure the resistor Rs.
Unfortunately not all the A4988 drivers have the same Rs resistor.
We need to find this value in order to limit our maximum current.
We must not exceed 1.7 A for our 42BYGHW811 motors.
We must not exceed 1.5A for our 42BYGHW609 motors.
We must not exceed 1A for our 42BYGHW804 motors.

Try to find out your correct type of stepper motor driver that you use.
For the pololu we have Rs=0.05 Ohm (labeled with "R050") FIND RESISTANCE pololu

Ebay blue stepstick. Rs=0.1 (labeled with "R100") FIND RESISTANCE

Older reprapworld stepstick Rs=0.2 Ohm (labeled with "R200")
Be aware that these stepsticks have a 1A max output current.
If you have these kind of stepsticks you should use 42BYGHW804 motors (max 1.2A) instead of 42BYGHW811(max 2.5A).
FIND RESISTANCE

A better and more secure way to find Rs is to measure the two Rs resistors with a precise multimeter into the Ohm range.
I am going to use a UT61E multimeter.
We need a multimeter capable to "detect" two digits after the decimal point.
In order to do this measurement you need to attach the two leads and press the relative button (Δ). Be sure you get relatively 0 ohms. This way you set the relative resistance of the multimeter leads to zero.
If you get 0.01 Ohm for example retry by pressing the relative button (Δ) again.

electronics prusa i3

Below is the measurement of the ebay stepstick Rs=0.1 Ohm
electronics prusa i3

Place the heatsinks to the drivers. Do not ignore this step.
Pay attention to not shortcircuit some pins with the heatsink
electronics prusa i3

electronics prusa i3

Make sure that all three jumpers need to be placed under each stepper driver. (red yellow blue in the photo above). We setting 1/16 micro stepping by installing all jumpers under the drivers. Place the four drivers at Ramps.
Notice the polarity.
electronics prusa i3

Place a heatsink to the mosfet Q3.
Notice that the Q3 is the MOSFET used for the heatbed
The assembly order is :
Screw head / Insulation Bushing / Mosfet Hole / Insulation Film / Heatsink TO-220
Please do not ignore the insulation bushing & film.
Take a look at the picture below :
electronics prusa i3

Clip Ramps board over the arduino mega board.
electronics prusa i3

Now we have to do all the cabling.


Find your cables.
x3 for the endstops
x4 for the motors [X,Y,Z,Extruder]
x2 for the thermistors [Extruder,heatbed]
x2 [one parallel pair] for the heatbed 60cm up to 1 meter long

electronics prusa i3

electronics prusa i3

The schematic :
electronics prusa i3

Plugging the cables :
electronics prusa i3

electronics prusa i3

Connect the heatbed with ramps by doing these steps :
Free the heatbed from the tray by unscrewing the bolts.
Parallelize the two pair cables and make one thicker pair 60cm - 1 meter long.
Connect to the D8 (-) slot the negative pair and into the D8 (+) the positive pair like the photo below
connecting the heatbed

If you have the MK2a 12V heatbed (older version) solder the positive and negative pairs into the pads like the photo below:
electronics prusa i3
Update : it is way better to make these solder joints at the bottom face of the heat bed and not from the top as shown at the picture.

If you have the MK2b version (dual power new version) then you should solder the wires like the picture below.
Notice that we use the 12V configuration so we have to short pins 2 and 3.
We solder the cables at the bottom face of the plate.
soldering heatbed with 12V configuration

Now it is time to connect the thermistor into the heatbed.
Separate the two legs of the thermistor EPCOS B57560G104F or ATC Semitec 104-GT2 and isolate each leg with kapton tape.
thermistor of heatbed

Pass the thermistor throught the hole then bent it and keep it stable using kapton tape.
Make sure that the head of the sensor is at the bottom face of the heatbed.
thermistor of heatbed
thermistor of heatbed
thermistor of heatbed
Twist and solder the sensor cables. Do not forget to isolate them using heatshrink tubings. cabling of the heatbed

Use zip ties in order to fix all cables like the pictures below :
cable managment of heatbed
cable managment of heatbed


Plug carefully all your wires into ramps like the two photos below : electronics prusa i3

electronics prusa i3

Do not forget to solder the motor cables with the ramps cables. Pay attention soldering the same color cables.
Take a look at the photos below :
soldering x motor cable
soldering y motor cable
soldering z motor cable
soldering extruder motor cable

Notice : into the T0 you have to plug the extruder thermistor and into T1 the heatbed thermistor. Thermistors does not have a polarity.

In the next part we will finalize the electronics section.



Section 1 - Wooden frame : part 1 - part 2 - part 3
Section 2 - Y Axis : part 1 - part 2 - part 3
Section 3 - X-Z axis : part 1 - part 2
Section 4 - Extruder : part 1 - part 2 - part 3
Section 5 - Electronics : part 1 - [[ part 2 ]] - part 3
Section 6 - Coarse Calibration & Software : part 1 - part 2 - part 3
Section 7 - Fine Calibration & Software : part 1 - part 2 - part 3
Section 8 - Extras : part 1 - part 2 - part 3
Section 9 - Maintenance & Modding : part 1 - part 2



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