Improved K40 Operating Panel

K40 Operating Panel

Donate:

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.

For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Background

For some time I have wanted to:

• Have all the laser systems indicators to be in one place and up on the panel
• Add a Laser tube surface temp sensor
• Have a better looking power pot position meter.
• Try out a sensor mounted on the head to detect a fire

Everything up on the panel

On the panel above:

Upper left: Senses heat at the head and shuts down LPS on overtemp with an alarm

Upper Right: Senses coolant temp and shuts down LPS on overemp with an alarm

Lower Left: Laser temp. Measures temp at the surface of the tube

Lower right: A DVM that measures the voltage on the LPS "IN" pin. 

I got all the sensing meters cut into the upper part of the panel. The Power setting meters bezel had to be hand fabricated. I am satisfied that they are all in one place but I wish I could have all the meters look the same. That's the result of some meters being discontinued and other not having controllers.

Cutting out the panel

The Plan

Nibbling Away

Final Cutout

Sensor Locations

The water sensor is located in the bucket at the end of the output pipe.

The laser jacket sensor is tie wrapped to the laser housing

The cabinet sensor is mounted on the head.

Note I have no idea if this sensor and the controller will respond fast enough to prevent a fire but I figure something is better than nothing at all.

Power Control Meter

More work needed to make this pretty!

Wiring

The meters that require the machine to be shut down have relays wired in series with the laser interlock circuit. These meters have high low setpoins and have audible alarms. 

Parts List

Upper left: Temp Controller

Upper Right: Temp Controller (not available). Use one from above.

Lower Left: Thermometer

Lower right:  DVM

Enjoy & Comment

Don

Understanding the K40 Digital Control Panel???

K40 PowerLED Control Panel

Newer versions of the K40 sometimes ship with a digital control panel. This panel retains the main power switch but the Calibrate (potentiometer), Laser Switch, and Laser test buttons are replaced by push buttons and a controller PCB.

Warning: this vintage K40 control panel does not ship with a laser current meter. Therefore it is not possible to know the actual operating power the laser is running at a particular digital setting. It is important to monitor the actual running power of the tube during operation to maximize the tube's life.
All tubes will eventually fail and are generally considered consumable but their life can be optimized. Tube life is proportional to the running current* so setting the machine to run at the minimum current required for the job and staying under the tube's rating will optimize its life.

Some users have made the argument that although running the laser at higher currents may shorten the life of the tube it also shortens job time, so it's worth it.

Add a Laser Current Meter

I recommend adding a current meter to your machine if you do not have one. The meter will assist you in running your laser at a current that is consistent with optimizing its life consistent with your expectations.

Add an analog meter to your K40

Most manufactures specify their tubes reliability @ 1500-2000 operating hrs running a working current of 20-22 ma. Check your tube's specifications, especially if you have replaced the stock tube.

The longest life I have seen specified is:

• 3000-4500 @ working current of 10-13 ma
• 40W tube with lower current longer life specified.

* There are other factors such as shelf life and operating temperature that cause a laser tube to fail. 

Donate:

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.

For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Thanks to +Chris Hawkins for donating a panel for this exploration

Testing

A donated K40 PowerLED V3.0 was bench tested using a simple tester made from a USB adapter a few resistors, a voltmeter, and connectors. This tester provides 5V through a USB brick and listens to the IN and P pins of the panel.

This tester was connected to the panel and various tests were performed as described below.

Schematic

The schematic of the panel and the test board as it develops is here:

Interconnection with the Laser Power Supply (LPS)

You will note that this control panel connects both the P + & P- of the panel to the K+ signal on the LPS rather than the P signals on the LPS. Wow, now that's not confusing :(.

Also, note that nothing is connected to K- on the LPS and P+ & P- on the control panel are shorted together.

A LPS wired to a K40PowerLED Panel note the 4 white wires (from panel) and the black wires (from water sensor)

Operation:

The PowerLED [as best I can tell so far] utilizes an embedded processor to provide the functions of the panel. The main functions of the panel are to set the power level of the LPS, enable the laser to fire, and test fire the laser. The indicators and controls include:

• Laser power display
• Laser Switch
• Laser Test Switch
• Light Instruction
• 3X +/-Digit Controls: 10, 1,.1

Laser Power Display

Indicates the % of the power the LPS is set to. This display indicates the % of the LPS max power it is set to via the IN signals voltage on the interface. This display is operational as long as the Laser Switch is enabled.
The LPS power is controlled via an analog value of 0-5V on the IN pin of the LPS.

Laser Switch

This alternate action PB enables and disables voltage to the IN signal and the Laser Power Display. When this switch is OFF the display is off (except for decimal points). When the display is off the IN pin to the LPS is reduced to zero volts. When this switch is ON the IN signal will be a voltage proportional to the % displayed on the Laser Power Display.

Laser Test Switch

When this PB is pushed the +P/-P signal is grounded for as long as the PB is held. The Laser Test Switch grounds the +P/-P irrespective of the state of the Laser Switch. When this PB is pushed the "Light Instruction" LED illuminates.

Digit Controls

There are 3 sets of digit controls with a + and - control for each. These pushbuttons (PB's) allows the setting of the respective digit in the Laser Power Display.

Testing Data

The following spreadsheet contains:

• A table of the IN voltage vs the digital % power setting taken during the test
• The calculated error between actual and calculated power values for % settings.
• A math model (equation) for the input-output function of the panel

Model: 

VoltsOnLPSIN = 2.4562 * (%PanelSetting^2) + (7.6189 * %PanelSetting) - .2686

R^2 = 99.69% (good fit!)

Plotted Test Data & Error Calculations

5vdc Power Supply Loading

This panel draws about .2 amps from the stock K40 supply. That's about 20% of the safe 5vdc capacity. Note that some new machines have an LPS with the fan missing. I have to believe that the stock LPS is running on its limit (1 amp w/o fan) with these vintage machines.

NEW! Go figure, the IN output is a PWM signal

After being prompted to dynamically look at the IN pin of the panel by +Lukas Bachschwell who showed us a scope trace of the signal I was surprised to see that these panels acutely drive the IN pin of the LPS with a PWM signal!!! Thanks, +Lukas Bachschwell

PWM signal on IN

As you can see in my test setup the power was set to 50% and the IN voltage read 2.9. The readings here are average since the signal is actually a PWM square wave. My cheap DVM read 2.9 (which we now know is an average) 

"IN" Scope readings

Vavg: 2.98VDC. 

Duty: 58.8 [*seems like an 8.8% error from panel settings to actual?]

Freq: 24.55kHZ

*it would be useful to test and plot PWM linearity, i.e. panel settings vs actual PWM DF.

Why is the "IN" pin driven with a PWM? 

Keeping in mind that the digital panel wants 

• Digital control of the power by switch settings
• Power value display

Since most embedded controllers have PWM capable outputs it's rational to use PWM rather than a D/A approach. The controller can manage the display, switches, and the power this way.

Can we connect our controllers PWM output to "IN" on the LPS

Yes. An open-drain could drive the IN pin on the LPS but in my assessment, it does not gain you anything that I can fathom and has downsides.

Should we use the "IN" pin vs the "L" pin for power control?

No. Although this is an ok way to control power locally between the panel and the LPS, connecting a controller to the IN pin is a bad idea because:

• We need manual control of the power for testing without a controller connected. 
• We need a manual offset adjustment. This allows us to avoid having to make job setting* changes to account for laser depletion. The laser wears over time and uses so the power setting for any given job will change over time.
• The IN pin is not optically isolated from the HV supply but the L pin is. Using the L pin is close to the same as driving the IN pin but it's optically isolated.

*the software that is sending GCODE

Using both the "IN" and "L" pins give us good local power control as well as isolated power control from an external controller. 

 Assessment:

The display and controls worked as expected. See the graph for data on accuracy and linearity errors.
I felt the .1 digit was a bit overkill for a Laser Engraver as I think there are many variables in the process that are much larger than a .1% laser power change. I did not plot the tenths.

The % settings vs actual output voltage were pretty linear. The error increased to its largest value (10.15%) exactly at 50%  and then decreased until it reached 100%. I suspect this is related to the type of D/A that the controller employs (actually it's likely because the IN signal is actually a PWM).
From a practical perspective, the linearity error doesn't really matter. What is important is whether the panel can provide a full range of adjustable power from 0-100%. In normal use the operator adjusts the power to suit a particular job noting the best setting and as the laser "wears" that setting will change anyway.

During testing, I noticed that sometimes the % value would decrease when the + key was pressed and sometimes it did not recognize a keypress. More of a nuisance when setting the power but a safety issue if the Laser Switch behaves that way.

Safety

My biggest concern is how the laser is enabled. The embedded controller apparently reads the Laser Switch (the fact it is a momentary PB yet operates as an alternate action switch is the giveaway) and sends the set voltage to the LPS.
If the Laser Switch is alternated to the OFF position it puts 0V on the IN pin and this is the only way the laser is "turned off". Essentially the laser is enabled, just at 0 power. I guess that is not theoretically different than disabling the power with one of the other enable functions (K or P) but it just feels wrong to me. It's reducing the power NOT disabling the LPS.

Let's consider how this safety mechanism can fail:

1. A firmware bug does not turn off the IN voltage when the Laser Switch PB is alternated. Example: a bug turns off the display but leaves a voltage on "IN".
2. The firmware does not recognize an alternate push of the Laser Switch and does not turn off the IN voltage. The operator does not notice the display is ON and thinks the Laser Switch was pushed. I have noticed during testing that sometimes the +/- keys and the Laser Test Switch does not work. The switch seems to be intermittent or the firmware is missing the press. 
3. There is a failure on the control panel electronics that keeps the IN pin at a voltage.
4. Somehow a voltage gets on the "IN" pin from somewhere else in the machine's circuitry there is no secondary means of inhibiting a beam.
5. The display being ON or OFF is a confusing way to tell the operator the state of the "laser enabled" function. In most machines, the display turns on when the power turns on and stays on during operation. A specific indication that the laser is enabled is more appropriate. 
6. Example dangerous scenario: the laser is enabled and the operator pushes the Laser Enable button, the display turns off but the IN voltage is left at whatever value it was before. The operator thinks the panel being off means the machine is powered off. During troubleshooting inside the covers, the operator starts a job ...... the laser is now active.

I doubt that this kind of circuit strategy for making a laser safe would be considered "fail-safe" according to OSHA regulations.

1. Under the requirements of the ANSI Z 136 Standard, for embedded Class IIIB and Class IV lasers only, the interlocks are to be "fail-safe." This usually means that dual, redundant, electrical series-connected interlocks are associated with each removable panel.

Definition of a Fail-safe Interlock

An interlock where the failure of a single mechanical or electrical component of the interlock will cause the system to go into, or remain in, a safe mode.

Editorial Comments

Safety

I am not under any illusion that the K40 is SAFE as shipped although I do wonder what the FDA symbol on the K40PowerLED panel infers???? That said, I endeavor to follow OSHA and FDA recommendations whenever possible while doing conversions. This is to enhance my own safety and the safety of those mimicking my builds. To that end my machine has interlocks. These interlocks are not in series with any firmware and consist of nothing but wire, connectors, and mechanical switches. They all fail in the disabled mode...

For those using this panel; ensure that you install interlocks on all accessible covers using the P+ loop on the LPS. Put front and rear cover interlocks in series with the water-flow switch. 

Operation Improvement

The K40PowerLED panel would at first glance present itself as a high-tech implementation of K40 control. In my assessment, it does not provide much if any, advancement in the operation of the K40. In fact, the missing laser current meter makes an important operational measurement invisible to the user. Running overcurrent is the fasted way to shorten the life of a tube. Without a substantial improvement in functionality I am not willing to take the safety risk I think this panel may present.

The Good!

• You can see a digital display of the % of max power the laser power is set to.

The BAD!

• The buttons do not always respond or respond correctly
• The panel draws an additional 20% of the already loaded 5V supply
• No laser current meter leaves the operator blind to laser tube stress
• Less linear than a linear pot 

The UGLY

• Potential safety hazard in that the laser enables indication is confusing and the circuitry is not fail-safe.

Next steps

I do not think that further exploration into this panel will reveal more than the actual design that was used.

I am noodling if a safer, and more comprehensive control panel is wanted, needed, and cost-effective to improve the operability and safety of K40 conversions. Let me know your opinion in the comments..

Enjoy,

Comments and corrections expected;

Don

Enhanced K40 Temperature Monitoring

Updated K40 Temperature Sensing

I have one point of temperature monitoring  in my K40, water. I recently moved my K40 to the garage shop and decided to get rid of all the hacks and partially complete conversions. Temperature monitoring was one of those on the agenda to be completed. Mostly the temperature controller needed to be remounted but while I was at it I decided to add some more gauges .....

Donate:

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.

For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

More Temperature Monitoring

I already had a sensor in the water bucket connected to a controller that I had mounted lazily on the frame of the K40's kart.

This controller will alarm at an over temperature and since its relay is in the K40's interlock circuit it will shut off the laser.

This is the controller.  If its no longer available check for other similar ones. It needs to have an alarm function that opens the interlock when the temp setpoint it exceeded.

Gauge Mounting

The current controller/gauges were mounted on the upper part of the K40 control panel. It would have been nice if all these gauges were the same type. Then again their difference in appearance makes their varying purpose more obvious. In any case I went with function and cost over aesthetics.

One of my next projects will be to engrave acrylic labels for these. In the mean time their functions are:

• Upper left: Cabinet temp
• Upper right: Coolant temp
• Lower left: Laser tube temp
• Lower right: Laser power level

Gauge Installation

After removing the current control panel and then the hinged cover I used my nibbler to cut the holes for the new gauges. That nibbler is a must have "maker" tool!

Cabinet Temperature

This sensor is more of an experiment than anything. The sensor is located on the gantry near the air assist nozzle and is wired into the K40 interlock circuit. Its purpose it to sense a fire in the cabinet and turn the laser off. I have no way of testing or proving if this will work but I figured considering the damage a fire can do it was worth the effort and money! The idea is that a fire will melt the sensor and open the circuit. The controller will alarm if the sensor is disconnected and open the interlock circuit..... I hope.

I can imagine many cases where this may not work:

• The head is not near the fire
• The sensor shorts from the fire
• The cabinet self destructs before the sensor sees it

I used this 2 stage controller which is overkill but can be used if I ever build in a water cooler. 

I plan to set this alarm on this sensor to the lowest practical operating temperature I can.

Laser Tube Temperature

A sensor was tie wrapped to the laser tube's glass and routed to the gauge. This sensor monitors only and is not wired into the K40 interlock circuit. I hope to learn more about the temperature in the lasers cabinet and eventually plan to add air to that cavity. This gauge required a spacer since the panel sheet metal was to thin for the mounting tabs to firmly hold the meter in place.

As an FYI you can see the new water sensor and air assist connections at the bottom of the photo.

Laser Power Meter

The last meter in this set is the digital voltmeter that is connected to the LPS's control pot. I had to add a frame and filter to the naked small digital voltmeter so that it had a better mounting, is more readable and somewhat nicer looking.

I added gel filter material between the display and the face plate to get the display to be more readable.

Old Power Setting Meter ... dangling

Mounting and Wiring

Meter mounting. Note the adapters on the upper meters.

Enjoy, comments and suggestions expected :)

Don

K40 GLCD Control Panel Housing

My K40-S conversion includes a GLCD and its adapter. After looking at multiple 3D printed enclosures I decided to design one that I could make from 1/4 MDF using my manual mill. I find making one of something is still faster on my mini-mill than traversing the entire tool chain to get to my laser cutter or CNC router :).

More information on the GLDC and its install with Smoothie is here:
http://donsthings.blogspot.com/2016/06/k40s-graphics-display.html

Donate:

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.

For other information on the K40-S build use the  K40-S BUILD INDEX with schematics. 

The design

I did the design in SU and it is posted here:

The design layers a top, bottom and 3 frame components.
I CA glued the frame components to the top, they act as spacers allowing the electronics to be sandwiched between the top and bottom plates.

1. The parts were made using 1/4 MDF milled by hand then sanded and painted. Note that clearance had to be milled for the connector pins and the back light which protrudes to the side of the LCD. These features are incorporated in the CAD model.
2. The panel sandwich uses 2x #4 screws for the top 2 holes and 2x #4 all-thread cut to size with acorn nuts for the bottom 2 screws. #4 nuts are used on all 4 screws.
3. The top two screws are counter sunk into the top surface with a nut on the back holding the assy. together.
4. The bottom 2 screws are longer and go all the way through the assy. and into the controller box. These screws hold the panel to the controller box. The panel ends up sitting at an angle since the top two screws nuts are on top of the mounting surface and the bottom 2 screws are under the mounting surface.

The Panel Components

Enjoy and comment
Maker Don

Adding an Analog Milliamp Meter to a K40

Instructions for Adding an Analog Meter to a K40

Some vintages of K40's now have digital meters and pots. Some users find then sufficient and convenient others have found that having more information about the position of the pot and an analog representation of the laser tubes current to be advantageous.  

While you are adding this meter to your K40 you may also consider adding a high resolution pot and/or a pot position indicator: 

• Instruction for installing a pot and/or a pot position indicator 
• https://donsthings.blogspot.com/2019/02/replacing-k40s-digital-panel-with.html

Thanks, to +Bob Buechler for testing out these instructions, doing the drawings and reporting on the results in this post.

Donate:

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.

For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Installing the Analog Meter

Summary of the installation.

The analog meter is going to be installed in series with the wire that routes from the lasers cathode to the -L connection on the Laser Power Supply (LPS). 

[the -L connection is the leftmost pin on the leftmost connector on most LPS's]

Here is a simplified wiring drawing of the installation, courtesy of +Bob Buechler:

Before

Installation

You will need the following materials

• New Meter Note: this meter is larger than used in the stock K40
• Wire, as needed for your installation
• Heat shrink tubing, as needed for your installation
• Ring tongues, as needed for the meter you choose
• Terminal Pin  and crimper

You will need the following tools:

• Wire cutters
• Soldering iron & or crimp-er to match the terminals you are using
• Pliers or small wrench for tightening the meter nuts

Meter Mechanical Installation

• Pick an appropriate place to install your meter, cut hole(s) as needed and install

Meter Wiring

1. 1. Pre-check:
1.  Verify that with the "Laser Switch" enabled, when you push the test function the laser fires.
2. Power down and unplug the mains from your machine
2. Find the wire that connects to the cathode (the end the laser light comes out of) end of the laser tube. Often its a black or green wire. 
3. Trace that wire to its other end which should be connected to ground (L-) at the LPS. Note: never not ground the cathode or the (-) side of the meter directly to the frame. The lasers current must return to the LPS itself on pin -L. 
4. Find the lasers ground port on the LPS. Its usually called L-, its the leftmost connection on the leftmost connector. Do not confuse this with the L that is on the rightmost connector with the DC voltages.

   

   L- on LPS with all green connectors

   
   

   

   L- on LPS with green and white connectors

5. Remove the existing wire from L- and verify with an ohmmeter that that the LPS pin (L-) is connected to the FG pin on the LPS and that both of those pins (L- & FG) are connected to the frame of the machine. There should be close to 0 resistance to ground (frame) on these pins. Note: this is a good time to test that there is 0 ohms to GND at the frame pin on the mains connector.
6. We want to reroute the existing wiring (that went from the tubes cathode to the LPS) to the (+) side of the meter. Do such by pulling the L- end of the wire that connects to LPS out of the harness enough to reroute it to the + side of the newly installed meters terminals. Note: Unless absolutely necessary do NOT disconnect the wire from the cathode as that is difficult to replace. When this step is finished the wire that previously was routed from the lasers cathode to the L- is now rerouted to the + side of the meter.
7. Connect the wire of step #6 to the meters + terminal with an appropriate terminating terminal. Usually the meter has threaded studs with nuts and washers. I recommend using a ring tongue terminal soldered to the wire. See parts list above.
8. It is common for the meters terminals not to be marked. If not marked start by connecting this wire to the left terminal of the meter (looking from the back), its a guess!
9. Get a new piece of wire that is long enough to route back to the LPS (L-) pin from the (-) of the meter. 
1. Use the same size or larger wire (yes it matters) and the same color if possible (colors do not matter but will be easier to trace later). 
2. Connect this wire from the meters (-) terminal to the L- of the LPS.  
3. Terminate the meter end with a ring tongue like step #7. For the LPS end use a crimped pin of the correct wire size. If you do not have the ability to crimp a pin at least strip back and tin the wire with solder. Insert the wire into the L- terminal and tighten securely.
10. After insuring that you have not shorted anything with shards of wire etc prepare to return power to the machine. As a rule I vacuum my machine in the area I have been working with a crevice tool. Be careful not to create a static charge.
11. Return power to the machine with your hand on the switch in case of smoke. No smoke? Then proceed.
12. Turn the power adjustment pot (or digital control) to about 1/3 or less of its range. In case the meter is in backward we do not want to stress it. 
13. To test the meter enable the laser [Laser Switch] and then push the [Laser Switch] while watching for movement in the meters needle. The meter should read the lasers current and you are done.
14. If no movement is noticeable on the meter these things could be wrong:
1. An error in the wiring, recheck using the steps above.
2. The meter is in backward. Swap the wires on the back of the meter and return to step 10.
3. The laser is not firing, check to see if the tube ionizes?
4. If you cannot get it to work post a picture of all of the above connections and wiring with my G+ address +Don Kleinschnitz in the Laser Engraving 

Links on G+

https://plus.google.com/+BobBuechler/posts/cggqu9Rjh85

"Ideally you want to cut the wire in a way that the meter can physically be placed in series with it leaving the cathode and the LPS end terminations alone. Just putting ring tongues where you cut it to connect the the meter. i.e The meter is placed in series with the current wire.

If the wire is not long enough cut the cathode wire long enough to reach the meter and put a ring tongue on it and connect it to + of the meter. Get another wire that is long enough to reach the LPS and put a ring tongue on it connected to the - side of the meter. Put a pin terminal on the LPS end.

Don't have a pin terminal and crimp-er? Alternatively tin the wire with a liberal amount of solder and insert and screw that into the LPS terminal.

If you want to keep the pin terminal you can splice it and a section of wire to a longer piece just insure you solder properly and cover it with shrink wrap."

Soldering Ring Tongues

I solder these type terminals because I have had problems with crimps corroding and/or vibrating loose. Theory is that if you crimp correctly this will not happen however soldering insures it does not.

Prepare the wire:

Strip the wire back far enough so that the bare end inserts fully into the barrel to its end

Heat-shrink:

Cut and slide over the wire a piece of heat-shrink that will cover the barrel of the terminal after soldering. The plastic cover may or may not come off or loose from heating. Most of the time I remove the plastic before starting.

Solder

Put the ring tongue on a heat restive surface or in a clamp. I lay mine flat on a piece of 600 grit sandpaper (the surface is heat resistant). Insert the wire through the barrel. Press with the iron on the ring tongue side of the terminal and heat while applying solder until the barrel of the terminal fills up. Depending on the size it may take a fair amount of heat. Don't put so much solder on it that it flows around the ring as that will impede attaching it to screws.

Finish

Clean flux from the terminal and slide the heat shrink up over the barrel and shrink it over the plastic if its still there. Sometimes the plastic falls off or needs to be cut off.

Some say this is overkill because its a pain to do but I have never had one fail over years of use.

Enjoy and comment!

Don

K40-S Control Panels

Status is: IN DESIGN

There are two panels in the K40-S build configuration.

The rationale for using two panels is in the index 

http://donsthings.blogspot.com/2016/11/the-k40-total-conversion.html

For other information on the K40-S build use the  K40-S BUILD INDEX with schematic

Donate:

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 

The K40-S operations panel

The operations panel for the K40-S provides laser, temperature and power control functions. 

It is designed as a drop in replacement for the stock panel. 

Mapping K40-S functions to stock panel:

Power: uses stock switch

Fire: same switch as "Test Switch"

Enable: same switch as "Laser Switch"

Meter: same as stock current meter

Current preset: digital meter added with "Current Regulation"  pot below it.

Water Temperature: added digital metering (see schematics for part #)

Armed: The "Armed" light is part of the interlock circuit and illuminates if the "Enable" button is asserted and all the interlocks are closed.

Mechanical Design

The mechanical design is here: 

https://3dwarehouse.sketchup.com/model.html?id=1aafe451-6c19-4af0-b7e5-8f06dec84516

1-1 cardboard model installed to test fit

Figured I would add a logo while I am at it! Will be printed on sticky back something

Digital Relative Laser Power Setting 

This digital meter give you a digital value for the pots position. I makes is easier to read the posts position and reset it to the same position. Its called "Current Preset" in the above design.

A three wire digital voltmeter is necessary.

https://www.amazon.com/gp/product/B00C58QIOM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Here is how to connect it:

Add A New Pot For Finer Control

This pot is a replacement for the stock one and provides improved resolution and linearity.

https://www.amazon.com/gp/product/B00VG93UD8/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1


Enjoy and comment,

Maker Don