Introduction: E-dohicky the Electronic Version of Russ's Laser Power Meter Dohicky

Laser power tool.

e-dohicky is the electronic version of the dohicky from Russ SADLER. Russ animate the very good SarbarMultimedia youtube channel

Russ SADLER presents an easy and cheap accessory to measure the power of a laser in the 'RDWorks Learning Lab 53'

Here is a description of an electronic, version who automaticaly show the power after the exposure.


is the description of an electronic version which indicates automatically the power.

The procedure begins as described by Russ Sadler. It is necessary to begin by choosing an exposure time among 3 proposed by Russ, 10.25, 20.5 or 41 seconds with patterns supplied by Russ. It is then enough to push on the button start of the e-dohicky and to start the laser.

Russ created 3 patterns for 3 exposure times, 10.25, 20.5 and 41 seconds. You will choose the duration which corresponds to the power of your laser. More the laser is powerful shorter will be the exposure time. Before beginning a measure, it to tell is necessary in e-dohicky which will be the exposure time. It is simply made via the setup screen.

The e-doHICky is created with an Arduino pro mini so it's easy to create your own.

Bill material:

- 1 x Russ's dohicky

- 1 x very precise NTC MC65F103A( ) ( about 6€) or find 'MC65F103A' on Mouser, Digikey, or in your facvorite store.

- 1 x TL431B ( ) ( about 1.5€ )

or find 'TL431B' on Mouser, Digikey, or in your facvorite store.

- 1 x Arduino mini pro 3,3V or 5V ( or equivalent ) ( about 5€)

- 1 x Oled SSD1306 display (or equivalent ) ( about 5€)

- 1 x DS18B20 ( about 1€)

- 1 x step up booster 0.9V-5V->5V ( )

or ( )

or ( )

or ( )

( about 5€)

- 1 x buzzer ( ) or equivalent ( about 1€)

- 1 x transistor BSS138 or equivalent ( ) ( about 0.01€)

- 1 x resistor 100 R smd 1206 ( about 0.01€)

- 1 x resistor 10K smd 1206 ( about 0.01€)

- 1 x resistor 10K 0,1% smd 1206 ( about 0.2€)

- 3 x capacitor 0,1uF smd 1206 ( 3 x about 0.5€)

- 3 x capacitor 10uF smd C ( 6032-28 ) ( 3 x about 1.5€)

- some normal pins header

- 1 x switch about like this : ( )

OR ( ( about 0.5€ )

  • 1X Push button like this :

- 1 x PCB ( about 2€ ? ) The PCB is now available at EasyEda:

- 2 x Neodymium magnets ( ) ( 1.28€ )

IF Arduino 3,3V

- 1 x 3,3V regulator : AP2210N-3.3TRG1 or equivalent ( about 0.4€)

- 1 x capacitor 0,1uF smd 1206

- 1 x capacitor 10uF smd C ( 6032-28 )

OR directly that ( )

For 5V Arduino, do not populate the 3.3V regulator and shorting jump on PCB.

All the files can be downloaded below.

There is 4 resources type :

- C program for Arduino.

- Sketchup, stl and DXF files for case plastic laser cuting and some 3D pieces.

- PCB files. ( also available by EasyEda )

- Instructions, pictures and videos.

This project is open and it's possible to enhance it. It's the first version and all your idea are welcome :-)

It's easy to make simplified version.

I'm working on a version of the case with a simple mecanical switch cuted in acrylic. (A simple slide who separate the door with the magnets and the battery.)

Thank-you :-)

Step 1: Order the Pcb on EasyEda

The pcb is now public on EasyEda:

Or, make it yourself with the Eagle's .brd file attached.

Step 2: Assembling PCB

Put the right component at the right place in the right direction. I hope the pictures will help enough for that.

I'l try to put more details as soon as possible, depending of yours questions.

The connector of the SSD1306 have to be a few shortened ( about 2 mm) to fit in the case.

The DS18B20 is soldered by an about 3,5 cm 3 wires. It will be attached in the head like in the picture.

Step 3: Assembling PCB Oled Polarity

For the SSD1306, there is two polarity type. The jumpers help you to
set the right polarity for your own SSD1306. Simply short the jump with a few solder.

Step 4: Assembling PCB If 5V Arduino or With an 3.3V Step-up Converter.

If you use a 5V Arduino, you dont need the 3.3V regulator. Then simply not populate the 3 components, and short the jump with solder. ( the good SSD1306 can work with 3,3V and 5V)

If you use a 3.3V step-up converter you dont need the 3.3V regulator. Then simply not populate the 3
components, and short the jump with solder. ( the good SSD1306 can work with 3,3V and 5V)

Step 5: Temperature Accuracy

There is one special operation:

I wanted to include a rather precise measure of the absolute temperature. To arrive there, I used a very good NTC probe and a TL431 as a reference of precise tension. It is not maybe essential, but if you can do the big things, you can do the little things as well. ( It's necesary for be better than the 0,3°C required for 10.25s exposure) Arduino is equipped with one ATmega328P which has a voltage reference entry for the ADC. In brief is on the pin 20. Unfortunately, this pin is not available on the connector of the Arduino mini pro. It's relatevoly esay to solder one wire on this pin. I prefered solder the wire on the capacitor near the pin 13 of the external connector. The wire need to be soldered on the PCB as show on the picture.

If you thing that it's not necessary to get an as good accuracy, you can forget the TL431 ( the 100R resistor and the two capacitors) and the wire. It's also necesary to remove two lignes in the program :

- at about line 12

#define VREF2495 2495

change to

#define VREF2495 3300 ( for 3.3V )


#define VREF2495 5000 ( for 5V )

- In the setup() function:

remove the

analogReference(EXTERNAL) ;

Step 6: Preparing 3D Printed Pieces

After removing the printing defects, adjust holes to 2.5mm

Step 7: Preparing 3D Printed Pieces

Make threads into all 2.5 holes previousely adjusted.

Step 8: Preparing the Dohicky's Nozzle. Insert the Nut

Step 9: Preparing the Dohicky's Nozzle. Reinforcement Ring

Step 10: Preparing the Dohicky's Nozzle.

Step 11: Preparing NTC

This is one delicate step ! ( take your time for do it )

Here is the NTC

Cut the two wires of the NTC at different length.

Get a few insulator silicon from a electric cable. One of about 5 cm ( AWG 22 ) and one of 8 mm ( AWG 18 )

Insert the cable's NTC into the 5 cm silicon.

Solder the NTC to an about 10 cm thin cable and isolated it with heat shrink tube.

Step 12: Assembling NTC in Dohicky

Put a few thermal paste on the NTC.
Insert the NTC deep down the dohicky.

Step 13: Assembling NTC in Dohicky (next)

Add a 8 mm * 2.5 mm ( AWG 18) silicon tube or equivalent soft before the screw then tight gently the screw.
The silicon (or soft thing) is for not break the NTC when tight then screw.

Step 14: Preparing the Dohicky's Nozzle.

Step 15: Preparing the Dohicky's Nozzle. Insert Dohicky

Insert the thin cables through the 3D printed 'dohicky' support.

Insert the dohicky in the 3D printed 'dohicky' support then tight the screw

Step 16: Preparing the Dohicky's Nozzle.

Tight gently the screw, just for keep the NTC's cable in place, only to avoid that the cable moves.

Step 17: Shorten SSD1306's Pines

Shorten the pins from about 3 mm.

Step 18: The Case

Here are the files for create the case.

The case is to lasercut in Acrylic 3mm. There is 3 pieces who need to be 3D printed.

I used 2 litle 2,9mm*7mm magnets for battery case. (

You can use differents magnets, but you need then to change the holes size.

The dore have to be glued. Take care about the orientation. The hole have to be by the bottom as shew in the picture.

Take car about the orientation of the magnet support, the hole have to be by the botton right.

I'l add steps for assembling all that.

I hope you have sketchup ( V8 or greater ) for watch all details.

Step 19: The Case : Glue the Door With Switch.

Here is the steps for glue the door.

take care about the orientation of the pieces.

Take care to not put to much glue on the last pieces. the 'switch' set must keep moving along the slot.

Step 20: The Case : Electric Wire With Magnet.

The 'switch' must be well able to pass above the magnet.

Step 21: The Case: General View

Take care to the legs

Step 22: The Case: Battery Older

First, check the right orientations of the 3 pieces.

Step 23: The Case: Battery Older Fix Magnet and Wire.

Tighten the magnet and the red electric wire.

Step 24: The Case: Fix Magnet and Wire to the Door.

Tighten the magnet and the black electric wire.

Step 25: The Case : Full Assembling

- Weld the red wire in the + to the PCB and the black wire in the ground, depending on the type of your power converter.

- Connect the douhicky's NTC and the DS18B20

- Then assemble the case

Step 26: Program for the Arduino

The sketch use a some standards librarys. There is one special for the SSD1306. I dont use the frequent one because the one I use is faster. This library is the one from Alexey Dynda.

After added the SSD1306's Alexey Dynda library, you can upload the sketch to the Arduino.

This project is not for dummies then I assume that you know how to load a sketch in an Arduino mini pro.

The sketch can work with others Arduino, then you can use it with an Arduino Uno.

Step 27: User Guide

The e-dohicky can be in 3 differents mode.

- Idle mode

- Run mode

- Setup mode

There is only one button and you can make operations with 'normal push' or 'long push'. A long push is 1 second long.

After power up, the e-dohicky is in 'idle mode'.

- In this mode you can read the dohicky's temperature, the room's temperatur and the actual exposition's time.

It's important to set the right 'exposition's time' according to the exposition time set in the Russ's patern, 10.25, 20.5 or 41 secondes.

Before start a mesure, check if the 'exposition's time' is correctly set.

Set the right 'exposition's time':

- The e-dohicky have to be in 'idle mode'. ( if not, 'long press' for back to 'idle mode' )

- make a 'long press'.

- then 'normal press' for loop until you chose the right time.

- When you see the right time, make a 'long press'.

- The e-dohicky save your choice and back to the 'idle mode'

In 'idle mode' the e-dohicky compare the dohicky's temperature and the room's temperatur.

The difference between both can not be more than 3 or 4 degrees. If the diffference is bigger, then an alert message is displayed and it's impossible to start a mesure.

When all is right, you can start a mesure.

Make a mesure :

- You normaly need to load the right Russ's patern in your laser machine.

- You can then start a mesure by press the e-dohicky's button and start the laser machine.

- Keep the dohicky in the laser according with the Russ video explanations.

When the laser is stoping the exposition, the e-dohicky is automatically waiting the end of the raising of temperature, then make a beep and show the measured power in Watts. This can take some seconds ( about 5 to 10 or more depending of the conditions )

After reading the power, you can back to the 'idle mode' with a 'long press'.

At this time, the e-dohicky will probably show an alert fot the dohicky temperature is to high.

You have then to get cold the dohicky as explained in Russ' video :-)

After that, the e-dohicky is ready for the next mesure.

- If you have to stop a mesure run, simply 'long press', then the e-dohicky go back to 'idle mode'.

Special alert:

There is a special alert if the dohicky's temperature is growing to 70°C or more. In this case, you have to power off the e-dohicky and get cold the dohicky to a 'normal' temperature.

Step 28: Take Care About the Electrice Spikes

My machine is rather badly assembled and the high-voltage cable passes along the tube. It entraine a dispersal of the high-voltage spikes at the ignition of the tube. The e-dohicky is an electronic device and he can be perturbed by it. I noticed that the e-dohicky sometimes makes a reset when I measure the power at the exit of the tube. The problem does not arise when I measure the power on the other side, nearthe mobile head. There are several manners to mitigate this problem. One manners is to armor the high-voltage cable. We can either, make cross the cable by the inside of the machine, or it armor with a piece of sheet of aluminum linked with the ground of the machine, an other way is to link the dohicky with the ground of the machine.