Daily Archives: 2014-11-18

CNC – Update 4: Limits & homing

I have been playing with the CNC machine and all too often I’ve accidentally hit both X and Y extreme limits of travel. I don’t know if there is any damage being done but felt I should do something about it.  The controller software has a panel in the setting menu for both positive and negative limit switches for all three axis so I needed to find the associated hardware connections. The company I bought the machine from claimed not to have hardware schematics for the CNC controller or the USB interface. However, I did receive an image of the CNC Driver Board board indicating where limit switches may connect (top left).

CNC Drive Board

CNC Drive Board

Through trial and error, I found that the model of my controller only provides one input per axis for a limit switch. This means that in the X and Y axes, a limit switch only works when the unit is traveling in a positive direction (i.e. towards the back and right edge). For the Z-axis, the limit switch only works when the spindle moving downwards.  In normal operation the limit switch input is open circuit. If and when the machine moves to a limit, the switch shorts the input to GND and this stops the movement immediately.

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Nano with CH340G USB chip driver

For those of you familiar with buying Arduino-related products on eBay, you probably would have seen a slew of cheap Arduino Nano boards (specifically the V3.0 ATmega328 16M 5V) being sold ($4 vs. $7.50).

So, what’s the catch?

Well, instead of the more common FTDI (FT232) chip, these modules include a CH340G USB interface chip, which is apparently much cheaper. Now, while the FT232, and specifically the FT232R, can throw driver errors (see this post for discussion), the CH340G requires a specific driver. I found the driver online although there were only Chinese instructions. However, installation is very straight-forward (on a Windows 7 (64 bit) machine, at least.

HERE’S MY DISCLAIMER…

I cannot attest to the quality of the download files. I have tried it, successfully run a Microsoft Security Essentials scan and it does not trigger any issues with virus protection. Please proceed at your own risk!

Click here for the driver software

Before connecting the Nano to your USB port:

  1. Download the “ch341ser,exe” file and run it.The software extracts about 8 files.
  2. The software asks whether it can install the CH341SER.INF driver for the CH340 chip (Version 11/04/2011, 3.3.2011.11). Click INSTALL
  3. A Windows message asks whether the driver has installed correctly. Click YES.
  4. Connect your Nano.
  5. From Control Panel, open Device Manager and Ports. If installed correctly you should see an entry “USB-SERIAL CH340 (COMXX)

That’s it… Cheap Nanos for all!