#Inktober Project 2019 – Post 4
Electronics
I intend to replace the stock controller board with an Grbl_ESP32 version. Here is an picture of the existing controller.
Power Input
The power input to my board will be 5VDC. I will not need any power conversion on my PCB, because everything runs off 5V. Measurements suggest I will only need about 2A.
Stepper motors
The stepper motors are unipolar 5 wire motors. I have been testing with a ULN2003 (darlington array) board I got with some motors a while ago.
This worked fine, so I will be using the SMT version of the IC in my controller.
Pen Up/Down Solenoid Driver
A solenoid coil is used with a small magnet mounted to a bar that controls the position of the currently selected pen. Sending the current one way attracts the magnet and sending the current the other way repels it. That controls the up/down state of the pen. I thought a simple DC motor driver would be a good way to control it.
The solenoid runs at 5V and draws about 0.8A of current. I found a nice little motor driver at Pololu that works great. I use one pin to set the direction and the other is used for PWM. I can do an initial full current pull on the solenoid, then switch to a much lower hold current. This prevents overheating of the solenoid.
I decided it was easiest to just put a socket on my controller for the Pololu board, since I already bought a few of them for testing.
SD Card
One of my favorite features of Grbl_ESP32 is the SD card support. That, paired with the WebUI (Web User Interface) is a great way to run gcode. You can upload gcode via WiFi and simply click “play” in the WebUI.
I put a micro SD socket on the board that is accessible though one of the connector holes in the back of the chassis.
USB
The standard USB serial connection of Grbl_ESP32 will also be accessible through one of the connector holes in the chassis
ESP32 Controller PCB
The design is done. I just need to order some. China is on a national holiday, so that will add a few days to the delivery. Here is a screen shot of the design.
The PCB is way bigger than it needs to be. I wanted it to use the same mounting holes, have the same connector locations.
Here is a link to the schematic.
