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Saturday, May 21, 2016

Bluetooth Connected Turbidity Meter

Hold handle and lower sensor into water without overflowing  into the coupler


I needed turbidity values for a project I was working on so I decided to make an instrument that I could use universally.


The meter consists of:


The sensor waterproof housing and base

Sensor mounted to base which is glued to coupler

Electronics acrylic covering and wiring

The handle

The photos shows the approach which was to house the sensor down in a waterproof cylinder that is lowered into the water. The acrylic handle houses the electronics. 
  • A PVC coupler is the housing.
  • A circular acrylic base was cut and is glued to the bottom of the coupler with "Plumbers Goop (PG)" (my favorite glue :)).
  • The base has hole drilled that fits the sensor and the sensor has an Oring fitted and then is screwed with sheet metal screws to the base. The screws are sealed with PG as well.
  • The base is glued to a 90 degree acrylic bracket with acrylic cement.
  • The housing is glued to the bracket with PG.
  • The bracket is fitted with an acrylic cover to provide a handle and some protection for the electronics.
  • The acrylic peices were bent on my "acrylic bender".


The analog output of the turbidity sensor board is connected to the Feathers A0 analog input pin.
Power to the turbidity sensor board is provided by the VBUS power on the Feather.


I used the code that Adafruit provided on the tutorial site using the blueart_cmdmode sketch.

Phone app

I used the Adafruit Bluefruit LE Connect mobile application.

Assy and test

I simply followed the Adafruit tutorial for reading analog values using the mobile app and had no problems getting a continuous reading to my phone from the turbidity sensor.
Make sure that you have the switch on the sensor interface board in the analog position.
Maker Don

Tuesday, May 17, 2016

Laser Power Meter


After your first mirror alignment on your K40 you realize how nice it would be to measure the optical power and have a reference for when things stop working. 
A store bought power meter is more than 1/2 the price of your K40. Here is an example Laser power meter that is employed by many K40 owners to measure absolute power. 
I wondered if I could construct a power meter that would be:
  • Lower cost
  • Fit in front of mirrors
  • Digital readout
  • Low power
  • Anti-reflective
After some research I stumbled across a Peltier module and was thinking about using this technology to build a cooling system for my K40.


Today I tried an experiment with a Peltier module connected to a voltmeter and exposed it to a K40 laser pulse. Peltier modules are typically used to convert electric power to heat/cold. Inversely when heated a Peltier module will output a voltage. 

Minor burn on the surface where laser impacted (just below mid line on left)
In the video below the Peltier module is on the left with a sticky note on it. Watch as the laser burns through the note and then notice that the voltmeter quickly raised to .05 VDC. It then slowly tapers back to 0 as the heat in the module dissipates.
It seems feasible that a relative and proportional laser power reading is possible.

Approach to power measurement

I suspect that each Peltier module would have a different voltage vs power characteristic. Therefore it would be difficult to get actual power readings unless each Peltier module was calibrated using a known power meter and source. The cost of calibration defeats the purpose for someone that wants an occasional use low cost meter.
The concept could be to make relative power measurements once the K40 is set up. These measurements would be made before and after each mirror and logged as relative values to be used as a reference if performance drops.
It can also be used to measure relative performance at different machine settings. Example: measure relative power at a specific laser current setting.

Use-case for Peltier Laser Power Meter (PLPM):

  • Align the K40 for the best power output
  • Take and record measurements at each mirror with the PLPM then compare with reference values 


Peltier module connected to stand alone controller with buttons and display
  • Reference mode: stores pre-mirror values 
  • Troubleshooting mode: take measurement from a specific pre-mirror and compare to reference
  • Bluetooth interface
  • A bracket that would allow the PLPM to interpose the optical path between mirrors

Next steps:

Decide if this project is worth pursuing? Leave a comment with your opinion.

Maker Don

Saturday, May 14, 2016

Stand alone K40 Zaxis Table & Controller Build


One of the first hacks most K40 makers undertake is some form of table that acts as a base for cutting material. The idea is to have a surface that will support the piece being cut while not catching fire allowing the piece to fall free of the cut. The new K40 user quickly discovers that the distance between the output lens and the piece being cut is a critical setting for getting a good cut. That means that the table must be movable or the piece being cut needs to be shimmed to the correct distance. 


Please consider donating (button to the right of this post).

Your donations help fund additional research, tools and parts that I will return to the community as information and how-to's. 

The Honeycomb

The most often first attempt is to procure some honeycomb material from local home improvement stores or to buy a honeycomb platform made for the K40.
I bought one of these and added an adjustable wood platform underneath it so that I could adjust it from above by rotating the 4 bolts. Yup you have 4 adjustments each time you use this and then you need to re-level:

Very crude but it worked to get started.

Motorized Z axis

One quickly realizes that having a motorized system for lifting the piece into cutting focus is a good thing to have. Especially since by this time I realized that I would be replacing my stock controller with a better DSP. Short story is that the tool chain for cutting parts with the stock K40 SUCKS. Therefore it made sense to get a motorized system that I could eventually control from the new DSP. I even think that "Auto Focus" is in the cards. I imagined having the design file adjust the table to the correct height automagically....

Light Objects Z axis table

I investigated building my own table and also studied the LO Z Axis table:

I decided that I could not easily build a better one at a lower cost. I wanted to get on with using and learning about cutting on my K40 so I bought the LO table vs playing mechanical engineer.
Z table assembly manual (seriously :( ...)
Limit switch mechanical parts zip. (there are also some parts in here to support LO approach to the control panel)
My goal going in was to make the entire Z axis table modular. All the electronics, limit switches and controls needed to be part of the table and plug into the 24 VDC supply. 
When I get my new DSP I plan to remove the stepper controller and connect the stepper driver to the new DSP.
After reviewing the above LO design I decided to use the LO limit switch part but make my own panel and mounting electronics.

Z axis controller

Here is a place that I figured I would add a lot of value and have some fun coding and building a controller. I actually did build one....... from a Trinket and motor driver from Adafruit.

After a few days of coding my new hardware build .....  I found out I needed a higher power stepper driver than the Adafruit driver could safely handle.
I investigated what LO had and selected a 2A stepper driver. As I was clicking through the LO site I discovered that they had a $20 controller that they sold to drive the table along with the driver. I needed the stepper driver anyway for the new DSP and the store bought controller would again save me time. I put my shop made controller on the shelf and ordered the parts: 24 VDC PS, stepper driver, stepper controller. They arrived and after assembling the table I was ready to wire it all up .....
The parts list:

The LO Z axis build

This was a simple build, just wire it up! Why are the simplest things the the hardest to do. 

Control Panel

The control panel was a challenge because there isn't much room to mount switches on the table and still be able to get to it when installed. I came up with a way to use a single momentary switch which reduced the control panel size.
There is no place to mount the panel so I bent a piece of acrylic and double back taped it to the stepper. 

This puts the control switch in the right back rear of the machine behind and below the gantry. A little inconvenient but I don't adjust the table that much and I gain the modularity that I want. This acrylic is .093 from HD.

Limit switch bracket

I cut the limit switch bracket from .20 acrylic per the LO design in the ZIP (link).
The first time I torqued on the bracket the top tab broke so I ended up modifying it and tie-ing it to one of the posts with a piece glued in at right angles to the bracket. This added piece just has a through hole that captures the post. I had to take the top of the table off to assemble it.

Limit Switches

These limit switches worked for me but you can also get them from LO. 


The controller doesn't have good documentation, after all this is a K40 adventure and nothing has a map. I did some research and turned up these sketchy links. 
LO provided documentation (I did not use this and in fact did not work)

After wiring it all up I visited controller hell. Nothing worked. God am I glad I made this modular!
I got help from the LO forum. You can see the dialog here if you can get into this forum Troubleshooting the Z table controller.
I never got a set of documents that matched how the switch settings and inputs to the controller actually worked so I moved the table to my bench and started oscilloscope-ing it out. I concluded that the problem was that the controller was not outputting PUL to the stepper driver. Probably cause I had the up/down switch wiring wrong .... and I did. None of the schematics I found worked.
I found that IN3 and IN4 are the DOWN/UP functions respectively and the IN1 & IN2 are the UP/DOWN limit switches respectively. They are all low (gnd) true. I started to draw a truth table for all 4 inputs and both switch positions on the controller and decided that was not productive since I am going to remove this controller eventually.

Optional Speed Control Pot

Various drawings show a 10K speed control pot with the wiper and one end connected across the controller pins SPD and GND. This pot is optional if you want a remotely wired speed control. I did not find it necessary to adjust the speed. If the pot is not installed the on-board pot sets the speed. 

The wiring

Notes on wiring: make sure to check your stepper the wire colors may not be the same as mine. You can find the winding pairs by measuring with an ohn meter looking for continuity between pairs of wires.

The end result is the following schematic: K40 Z axis table schematic @ SchemIT

K40 lift table schematic

Done and Done

So now I have Zaxis control and I am one step closer to my dream of auto-focus. That's another post ......another day.

Here is the final product:
Modular lift table

Installed in machine switch upper right

Access to the switch

Using the table

This is how I hold the parts during cutting:
Studs with threads added.

Studs mounted in a matrix

Studs used above are here!

On to the next hack

If your going to add a LO Zaxis table I hope this build log helps ease the pain and minimizes your research.

Other lift table designs

Here is an impressive and simple design with off the shelf parts. I may have gone this route if it was available when I bought the table.

Maker Don

Sunday, May 8, 2016

Breadboarding Station

I do a lot of electronics bread boarding and up to now, just like most Makers, have everything flaked out on my bench. For some time I have been wanting to get things more organized making it easier to hack out my embedded controller ideas.
I wanted a work space that includes:

  • Power (5, 9, 12, 24 vdc)
  • Integrated oscilloscope and logic analyzer 
  • Control panel switches pre-wired as input and at lease one LED as output
  • A main power switch
  • Space for an Arduino

Finally, this weekend I set aside time to build my dream breadboard workstation


Although I have a nice oscilloscope I found this really impressive miniature oscilloscope that also has a 8 channel logic analyzer function.

Xprotolab Plain

I imagined that I could integrate this scope with a bread boarding station. I got one at:

The oscilloscope is mounted to a right angle acrylic bracket with a set of probes. Well not probes rather these test clips:

The the Oscilloscope is mounted on a acrylic angle bracket that is screwed to the underside of the base. The clip wiring it restrained to that bracket. Slots were milled in the acrylic to accommodate connecting the clip wiring. The entire bracketed scope can be removed if I want to use it in another location.
This wiring schema keeps the scopes probes short and above the breadboard and out of the way.

Tablet Application

The scope connects to my tablet using this software and an OTG cable:

   Oscilloscope Pro- screenshot

You can find a variety of OTG cables on amazon.
The tablet is held with a 2 x 4 that has a 10 degree slot cut in it to the size of the tablets thickness.

Note: I also like to use other tablet based test equipment so this setup affords me access to spectrum analysis, function generator etc.

Mechanical packaging: 

I don't have drawings for the mechanical parts because I designed them on the fly as the build evolved.
The based frame is made from some solid surface (SS) left over from the new kitchen. SS is easy to cut and it can be conveniently tapped eliminating lots of fasteners.
The control panel is fabricated from acrylic sheet (Home Depot) and bent using a shop-made hot wire acrylic bender. "Google" "Bending Acrylic" if you want to build one.

Electrical parts:

The base bread boards is made from 4 of these:

Four is probably more than I need but I like to prototype stuff and leave it set up until I have converted it to whatever the operation format is going to be, usually a one-of-a-kind soldered breadboard.


The best power setup i found is to use mini/micro USB for 5vdc and 2.1mm jacks for all other DC. All my power supplied have been fitted with these male and female jacks using these adapters:

The 3 rear power jacks are for other voltages than 5vdc such as 9vdc, 12vdc and 24 vdc. They are wired though the main power switch and color coded wires are brought to the upper left of the breadboard for distribution.
These jacks are:  5.5mm x 2.1mm Power Jack Socket Female Panel Mount Connectors from here:

The 5vdc is supplied by a micro USB connector breakout board. I like to use 5vdc bricks for my logic power. I think the breakout board came from Sparkfun.

All the power is routed through the main power switch ( a 4 pole double throw I found in my stash) for those moments when you smell smoke and want to cut all the power.

Control Panel:

I have struggled for some time with making it easy to add switches into a prototype and then I landed on simply jerking a panel from a old DVD player. This was mounted on the base, it includes 3 buttons and one LED that are wired down to the breadboard on a .1 inch connector strip.

Can't live without an Arduino:

A "biggie" Arduino is mounted on the lower left for those times when I need more compatibility or shield capability, "Arduino" style.

Final configuration