## Introduction: K40 Laser Cooling Guard Tutorial

The K40 Laser Cooling Guard is a device that senses flow rate and temperature of the K40 Co2 Laser´s cooling liquid. In case the flow rate drops under a certain amount, the Cooling Guard cuts the Laser switch preventing the lasertube from overheating. It also gives you indication about how much fluid is passing the tube per minute and at what temperature.

## Step 1: What Do We Need

1 Arduino Nano

1 1602 LCD Display (16x2rows)

1 Flow Rate Sensor / 3/4" Hall Effect Liquid Water Flow Sensor

1 Relay Board / 5v KF-301

1 10k Thermistor

1 10k resistor

2 1k resistors

https://bit.ly/34N6dXH

Also i made an Amazon shopping list with all the components:

https://amzn.to/3dgVLeT

## Step 2: The Schematic

The Schematic is straight forward, i would however recommand to not use pin D0 as this is used by the Arduino for serial interfacing. You can easily use another free pin. Only thing to do is changing "0" to the port you connect the relay board to in the code.

## Step 4: Thermistor

For the thermistor we need to build a voltage divider, therefore we hook up the 10k restistor in paralell between ground and the thermistor. A thermistor basicly is a resistor that changes resistance by temperature.

To get a reading in deg. f or c we need to know what values this thermistor gives us at 100 deg. c and 0 deg c.

I measured this and brought the results into my Arduino code. With some math it now calculates and displays the temperature. Important is that you use a 10k resistor as the values for 100 deg. c are differend than on a 100k thermistor. As we are later using this device to get an idea of how warm the cooling liquid gets, i suggest to go with the pre-entered resistance values. In that case you don´t have to change anything.

The thermistor does not have any polarity.

## Step 5: The 1602 LCD Display

As i am not using a serial interface for the LCD i hook it up directly to the Arduino. I used the two 1k resistors between ground and V0 to regulate the contrast of the display. However it is recommanded to use a potentiometer for an adjustable contrast level. As those corrode over time i went with a fixed resistance value.

Else we need to connect all the wires as shown in the diagram

## Step 6: The Flow Sensor

A Flow Hall Effect Sensor is basicly a pulse generator. In a piece of pipe or a watertight housing there is a rotor that rotates when liquid passes thru. On the edge of the rotor are little magnets that induct engery to a recieving coil.

These pulses then can be counted by an Arduino for ex..

With a bit of math and code we can now translate these pulses to Liters per Minute.

The Flow Sensor needs 5v to operate and has a third yellow wire for the signal that hooks up to the D2 port of our Arduino Nano.

The Flow Sensor i use (in the Amazon shopping list) has a minimum reading of 2L/min what is quite limit for the K40 Laser as for my setup the cooling "broth" runs thru a radiator, the laser tube and an analog flow rate meter using 8mm hoses. Even i use a quite powerful pump there is only 1,5L/min coming out on the end. I had some issues in the beginning as the flow sensor did not show anything at all.... I ended up mounting the sensor vertically to the reservoir to have enough flow rate for the sensor to encode... In conclusion i would recommand of using another flow rate sensor that is more precise... you find them on ebay from china for arround 6 bucks..

## Step 7: The Relay Board

A Relay is a electromechanical switch. When the Arduino sends a signal (+5v) to the relay board the relay closes. This is a double acting relay, you first solder ground to ground, secondly you can rather solder to the open side or closed side of the relay. What means when the relay gets no signal from the Arduino it remains open (light is Off), solder it to the other side and it is closed (light is On) when no signal is recieved from the Arduino board. In our case we want the relay to be Off (open circuit) when no signal is recieved.

To be sure, use your Multimeter and measure the pins of the board.

A red LED indicates that the board does not recieve any signal from the Arduino. Red and Green means there is signal and the Relay is switching.

## Step 8: The Code

Now here is what this system does:

It reads the flow sensor and thermistor.

As long the flow rate is over 0,5L/min the arduino kepps the relay closed what means the laser tube may operate.

If the flow rate drops due to a pump error or you simply forgot to turn it on, the relay opens and the laser will be turned off automaticly.

You could go ahead and add code to set a limit temperature the laser should turn off too... thats up to you.

In this setup for now the display only shows the temperature without having any influence on the relay.

You can also weak settings in the code, i added discriptions beside the values so you know what it is.

For instance you can swap deg. C to deg. F by simply swapping two letters (described in the code file).

## Step 9: The Console

Here is the file for the housing of our build using the PCB i had designed (step below)

I added the PCB as a size reference in these files that has to be deleted before cutting it with a Laser Cutter.

The Parts are layed out in a way you can first engrave the Logo and name, then stop the machine when it got thru this and cut it out.

The file is made for 4mm plywood or acryllics!

## Step 10: The PCB

As you see in the video, i had some issues and failures on my first PCB Layout... However i corrected them an uploaded this file here. You can simply upload this zip file to any PCB Manufacturers webpage and order it.

Please do check the file by yourself before ordering it! I am not responsable in case there is a failure or issue with the layout!

## Step 11: Setting It Up

Last step is to set up the K40 Laser Cooling Guard.

The relay contact needs to be spliced in series between the laser switch of the K40 Laser machine. Therefore you can rather solder it between the switch itself that is situated on the instrument hatch of the machine or you could hook it up directly at the power supply. In my case there are two pink cables going to the switch from my power supply, so i disconnected one and spliced the circuit in between (in serie) using a Wago cable clamp.

I decided to hook up the flow meter as last part of the chain right before the liquid flows back into the reservoir.

In my case as i already had an analog flow meter i had ordered a thermistor with a metal plug that screws right into it. Else you could simply dip the thermistor into to reservoir. Make sure it is situated next to the outlet to get a more acurate reading.

Make sure you disconnect your Laser from the Mains before even opening the hatch!