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The view at left shows the cooling system monitor in operation while the above photo shows the radiator and cooling fan assembly that was added to the stock laser cutter. The air assist pump is behind the radiator in the background, while the water pump is in the water reservoir out of picture to the left (see photo on facing page). By Nicholas Vinen Arduino cooling system monitor for a laser cutter This unit is based on a small Arduino module and monitors the cooling system in a large laser cutter. It monitors the speed of the fans, the water flow and temperature and sounds an alarm in the event of a malfunction, so the operator can take action before any damage occurs. Although designed for a laser cutter, it would suit a number of similar applications. L ASER CUTTERS are now available at quite reasonable prices from China but in line with their modest prices, they do require quite a bit of work to get them up and running, in our experience. In our case, the supplied cooling system was quite rudimentary, consisting of nothing more than an aquarium pump and a couple of hoses. The instructions were to the effect that the pump should be submerged in a large bucket of water and arranged to deliver water to the laser 42  Silicon Chip tube which would then flow back into the bucket; not the engineered solution we would expect. Nor was the arrangement to exhaust toxic fumes from the cutter well sorted out, as it came with a very noisy centrifugal fan which actually leaked fumes, while the large cutter housing itself had multiple air leaks, all of which had to be sealed off. And there were other problems with the assembly which required attention. Fortunately, the laser cutter itself actually works very well. As for the rudimentary cooling system, a bucket of water obviously has a limited capacity to absorb heat and as the water gets hotter, the laser performance drops. So we decided to modify the system to incorporate a metal radiator with fan-forced air cooling to keep the laser tube operating at a reasonable temperature long-term, especially in the hotter months. We selected a copper-cored radiator designed for computer water cooling, siliconchip.com.au The water reservoir (clear container) and the radiator/fan assembly sit on a platform at the bottom of the laser cutter. Together with the pump, they keep the temperature of the water circulating through the laser tube to about 35°C. teamed with three 120mm brushless fans. However, we were concerned that if the pump failed, or its power cable somehow became disconnected or a hose leaked, there would be no obvious sign until the laser tube was destroyed. So we decided to include sensors to monitor the fans and coolant flow and provide a water temperature display. Cooling system upgrades The parts list shows the items we used to upgrade the cooling system, with the electronic parts listed separately. Besides the electronic components, pretty much every­ thing was purchased via the www.aliexpress. com website. Some would no doubt be available from plumbing supply stores or specialist computer stores but we liked the convenience of ordering them all in the one place. Most of these parts were used to plumb the radiator, which has British Standard Pipe (BSP) G1/4” female connection points, into the existing laser cutter cooling system which used 8mm ID silicone tubing pushed onto hose barbs. The T-fitting was attached to the inlet end of the radiator to allow the G1/8” threaded temperature sensor siliconchip.com.au to be screwed in (via an adaptor), to monitor the temperature of the water coming from the laser tube. The G1/2” flow sensor was connected to the radiator outlet via an elbow fitting and G1/4” to G1/2” adaptor. A flow sensor with G1/2” fittings was chosen as it was thought that this would provide less flow resistance than a G1/4” fitting flow sensor with much smaller internal passages. The electronics and fans run from 12V. The laser cutter has a 24V + 5V power supply, so we used the Mini­Switcher (Simple 1.2-20V 1.5A Switching Regulator, February 2012) to efficiently convert 24V to 12V. The photo below shows the Mini­ Switcher board glued into the laser cutter chassis with white silicone sealant. One grey figure-8 lead brings 24V power from the laser cutter supply and another routes the 12V output up through the chassis to the control box on top. Electronic module The control box is based on a tiny Arduino board (a “Pro Micro”). The circuit is shown in Fig.1, along with some of the plumbing details. Its job is to control and monitor the fan speed and also monitor the water flow. If the speed of any fan or the water flow rate drops below a predefined threshold (80% of nominal), red LED3 lights and a piezo transducer beeps. The Mini­Switcher power supply board was glued onto a shelf inside the laser cutter chassis using white silicone sealant. June 2016  43 The copper radiator, the three 120mm-diameter ball-bearing fans and the various brass plumbing accessories were all purchased from www.aliexpress.com The fans are all controlled by an Arduino module in the Cooling System Monitor. Warning yellow LED2 lights if the fan speed or water flow rate drop below 90% of the nominal rates, indicating a possible pending failure, blockage or perhaps pinched off water tube. Otherwise, if everything is OK, green LED1 lights to indicate that it is operating normally. The temperature display unit is powered from a 12V output on the control module (CON3) and sits on top of it. Circuit description MOD1 is an Arduino “Pro Micro” board based on the ATmega32U4. This is very similar to the LeoStick module from Freetronics that we reviewed in July 2012, and is available from Jaycar. The main difference is that the Leostick plugs into a USB port directly while the Pro Micro is a little smaller and has a MicroUSB socket instead. The Pro Micro comes in 3.3V and 5V versions; we used the 5V version. In this application, the USB connection is used only for initial programming so we decided it would be better to use the smaller Pro Micro. The software could be adapted to just about any Arduino board. Since the LeoStick uses the same processor, it would probably work without any changes but we haven’t tried it. MOD1 senses the position of fan speed control pot VR1 which is connected across the micro’s 5V supply. The voltage (0-5V) at its wiper is sensed 44  Silicon Chip by the Arduino’s A6 ADC input at pin 7. Depending on the voltage sensed, it produces a 50-100% duty cycle PWM waveform at output D10 (pin 13) which drives the gate of N-channel small signal Mosfet Q2. When Q2’s gate is driven high, it switches on and pulls Q1’s gate low. Q1 is a P-channel Mosfet so this switches on in turn, allowing current to flow from the 12V supply at CON1, through reverse polarity protection diode D1, polyswitch PTC1, Q1, inductor L1 and to the fans. PTC1 provides short-circuit protection; in the case of a short across the fan supply, it will rapidly heat up and its resistance then increases, limiting the maximum current to around 1A. When pin 13 of MOD1 goes low, Q1 switches off and the two parallel 470Ω 0.5W resistors pull up Q1’s gate to its source voltage, switching it off. This cuts off the current supply for L1, however its magnetic field is still initially charged and this causes current to flow from ground, through Schottky diode D2, inductor L1 and the fans. The 220µF output capacitor also provides current to the fans for the period that Q1 is off. These two phases are repeated as the PWM signal toggles and this forms a basic buck regulator. What this means is that the voltage across the fans varies smoothly as a function of the PWM duty cycle from pin 13 of MOD1. With VR1 at a minimum setting, the duty cy- cle is 50% (and the frequency is around 50kHz), giving around 6V across the fans, resulting in slow but steady operation. As VR1 is rotated clockwise, the duty cycle rises to 100%, increasing the voltage at the fans to the full supply, ie, around 11.4V. Each fan has a Hall effect sensor with an open-collector output and these are wired back individually to inputs D19D21 (pins 18-20) of MOD1. MOD1 has weak internal current sources enabled for these pins to pull them up, so they are held at 5V unless the fan sensor is pulling them low. MOD1 uses an internal 1-second timer to count the number of pulses per second on each of these inputs, with software debouncing to eliminate spikes that may be due to electrical noise picked up by the wires. Thus, it can sense the speed of each fan and sound an alarm if any of them drops too low. In this case, the duty cycle from pin 13 is automatically increased to 100% so that if one fan (or the wiring to it) fails, the others will run at full speed to provide adequate radiator cooling until the situation is rectified. The same method is used to check the output of the Hall effect sensor in the water flow meter, which is connected to input D2 (pin 5). Note that all four sensors are connected via 1kΩ series resistors. These are not strictly necessary when interfacing to devices with open-collector outputs but it protects MOD1 in case of an accidental short of one of the sensor wires to a higher siliconchip.com.au A λ A λ PB1 3x 220Ω 12 11 10 9 8 7 6 5 MOSI/D16 MISO/D14 SCLK/D15 A0/D18 A1/D19 A2/D20 A3/D21 RST GND 3 GND 4 GND 23 D9/A9/PWM PWM/A10/D10 D8/A8 D7 D6/A7/PWM D5/PWM D4/A6 Vcc MOD1 Pro Micro (Arduino) RAW D3/SCL/PWM D2/SDA D0/RXI D1/TXO 21 13 14 15 16 17 18 19 20 22 A K S1 SET NOMINAL STATE 3x 1k D2 1N5819 Q2 2N7000 220 µF 16V LASER CUTTER COOLING SYSTEM MONITOR VR1 10k 1k 2 1 24 470Ω A CON3 + + LCD TEMPERATURE DISPLAY MINI SWITCHER SET FOR 12V OUTPUT CON4 FAN CONNECTOR 12V DC OUTPUT CON2 12V DC INPUT L1 100 µH 220 µF 3A 16V Q1 IRF9540 PTC1 RXEF110K 22Ω K D1 1N4004 – + K + – HALL EFFECT FLOW RATE SENSOR – + + TO LASER CUTTER 24V POWER SUPPLY – D3-D5 3 × 1N4004 COPPER RADIATOR + Fig.1: complete circuit diagram for the cooling system monitor. It’s based around “Pro Micro” Arduino module MOD1 and monitors the speed of three fans plus the water flow rate. Radiator input water temperature is displayed on an LCD while fan speed is controlled with a simple switchmode circuit comprising Mosfet Q1, Schottky diode D2 and inductor L1. SC 20 1 6 λ CON1 GND K LED1 K LED2 K LED3 A + SIGNAL TO FLOW SENSOR 470Ω θ siliconchip.com.au June 2016  45 θ WATER TEMPERATURE SENSOR CO 2 LASER TUBE COOLING WATER RESERVOIR WITH SUBMERGED AQUARIUM PUMP & FILTER 230VAC MAINS A Below: all the parts, including the Arduino module) were mounted on a small piece of phenolic proto-typing board. Above: this close-up view shows the flow sensor. It’s connected to the sensor circuit via a 3-wire cable (two for the supply and one for signal). voltage source (eg, 12V or 24V) or in the case of static discharge. The three status LEDs are driven from outputs D5-D7 (pins 8-10) with 220Ω current-limiting resistors, setting the LED current at around 12mA each. We used high-brightness LEDs with diffused lenses and wide viewing angles so they are highly visible. The piezo transducer is driven from paralleled outputs D8 & D9 (pins 11 & 12) so that the micro can provide sufficient current for it. It’s pulsed with a 25% duty cycle at 2Hz whenever the red LED is lit (ie, if any sensor indicates a rate less than 80% of nominal). Nominal rates are set using pushbutton S1 which is accessible via a hole in the front of the unit, with a small screwdriver. Like the Hall effect sensor inputs, D18 (pin 17) has a weak pull-up current enabled so that the unit can detect when the button is pressed. When this happens, the current readings for all four sensors are stored in EEPROM, as the nominal readings. The warning and alarm levels are then based on these readings. Since EEPROM is nonvolatile, they are retained even when power is lost. ed brass temperature sensor which connects to an LCD panel, the pair available for around $10, again from AliExpress (see parts list). There are various different-sized threads available and we asked for the “10mm” type which is actually BSP G1/8” (nominal outer thread diameter 9.728mm). Note that BSP sizes indicate the diameter of pipe a given thread is designed for, not the thread diameter itself. Happily, the two-conductor sensor wire provided was long enough to route it from the radiator input pipe, through the laser cutter and up to the control box. The only connection between the temperature monitor and the control box itself is the 12V power. As shown in the accompanying photos, the display shows the temperature in degrees Celsius with a 0.1°C resolution, along with a digital “needle” pointing to a temperature scale. It is easy to read, although if your head is above or below the eye-line of the display it looks a bit washed out. a MicroUSB cable before MOD1 was plugged into this board. The accompanying photo shows the basic layout of the parts on the board; note that some of the smaller passive components (eg, resistors) were mounted under MOD1 to save space. Basically, we cut a piece of board 22 x 14 holes wide, soldered the two female headers for MOD1 in place about one third of the way across the board, then proceeded to solder resistors with their leads directly adjacent to the pins on MOD1 to which they had to be connected. We then bridged the leads to the pins using solder. We then fitted the connectors to the far end of the board and the switchmode regulator components in between, with the pushbutton, LEDs and piezo at the opposite end, which would become the front of the unit. Where possible, component leads were bent over and soldered directly to the pad for the component they connect to. Where this wasn’t possible, we ran point-to-point wiring on the underside of the board, primarily with Kynar (wire-wrap wire). The board was then powered up, programmed and tested. Building it All the components were fitted to a piece of phenolic prototyping board (with copper donuts, not tracks), with a pair of female headers to connect to MOD1 (which came with male headers). The program was loaded using Temperature display Rather than building a temperature display, we used an automotive thread- Custom case We used the laser cutter to make a Table 1: Resistor Colour Codes o o o o o No.   4   2   3   1 46  Silicon Chip Value 1kΩ 470Ω 5% 220Ω 22Ω 4-Band Code (1%) brown black red brown yellow violet brown gold red red brown brown red red black brown 5-Band Code (1%) brown black black brown brown not applicable red red black black brown red red black gold brown siliconchip.com.au small custom case, with holes in the front for the LEDs, access to S1 and to allow the piezo transducer to be audible. There’s also a hole in the side for VR1’s shaft and four small holes at the rear for the power input lead, power lead to the temperature display, fan power/sensing cable and water-flow meter cable. The leads were fed through the holes in the case and the case glued around the board. If we ever need to get it out, we will have to destroy the case but, of course, as long as we keep the files, we can always cut a new one. Software Because the software has a simple, dedicated task, hardware counters and interrupts are not used. Instead, Timer3 is set up to provide a 1-second timebase and the main loop debounces the four frequency inputs at pins D2, D19, D20 & D21 and then counts the number of pulses received at each input per 1-second timer period. These are compared to reference numbers stored in EEPROM and the appropriate LED is lit depending on whether any of these are below 90% of the nominal value (or 80% for the red LED). If S1 is pressed, the counter values from the last period are stored in those EEPROM values as the future nominal values and the EEPROM is read at power-on and loaded into RAM for comparison. Each time through the main loop, the analogRead() function is used to determine the voltage at analog input pin A6 and hardware Timer1 is used to produce a PWM signal at output pin D10 which is proportional to this. The software, being quite straightforward, is quite easy to read. For more details, download the “sketch” and examine the .ino file. We used two Arduino extension modules, “TimerOne” and “Timer­Three”, to make setting up and using the hardware timers easier. The Arduino sketch can be downloaded from the SILICON CHIP website (free for subscribers). You’ll find it in the June 2016 “Shop” section. Installation, set-up & use Once the radiator assembly had been built and all the plumbing done, the most difficult remaining task was routing the wiring under and through the internals of the laser-cutter to emerge near the control panel at upper right. We used a variety of methods to string siliconchip.com.au The Cooling System Monitor sits on top of the laser cutter, just behind the control panel. It’s connected to temperature and flow-rate sensors that are fitted to the radiator and sounds a piezo transducer if a problem is detected. Right: a side-on view of the completed unit. The cables run to the water temperature and flow sensors and to the power supply. The temperature sensor display sits on top of the monitor case and is a standard automotive unit (see parts list). the wires and keep them neat, including P-clamps attached to screws protruding from the bottom of the unit, adhesive wire clips, cable ties, heatshrink tubing and even clamping the wires with the various flip-down panels on the unit itself. We ran a 5-way ribbon cable from the fans to the control box for 12V fan power and speed monitoring, plus a 3-wire ribbon cable for the water flow sensor and a 2-wire lead for the temperature sensor. The only extra wiring required was the aforementioned 12V power supply wiring from the laser cutter internals to the control box. To extend the short 3-way cable supplied with the flow sensor, we simply soldered a 3-way ribbon cable onto the end of a standard 3-pin header, plugged this into the locking plug from the sensor (which also has 2.54mm pin June 2016  47 Parts List Radiator & plumbing Note: item codes are for AliExpress, although some may no longer be valid 1 360x120mm U-flow copper radiator with G1/4” inlet, outlet and centre tap (item# 1956079016) 3 Sunon KD1212PTB3-6A 12V 1.9W double ball bearing 120mm fans (item# 2022379891) 3 120mm fan vibration-damping silicone gaskets (item# 32224342946) 3 120mm clip-on plastic fan grilles (Rockby Electronics code 39067) 1 automotive temperature sensor with LCD display, mounting bracket and G1/8” threaded sensor (item# 32450099507, “10mm” sensor) 1 G1/4” end cap, to block centre tap port in radiator (item# 32264189117 [pack of two]) 1 G1/2” 1-30L/min Hall effect flow sensor (item# 32605214366) 1 G1/2” female-female copper/ brass adaptor (item# 32345278486 [#3]) 1 G1/4” male-female-female brass tee fitting (item# 1902581471 [pack of three]) 1 G1/4” male to G1/8” female brass adaptor (item# 1926696115 [pack of five]) 1 G1/4” male to G1/4” female brass elbow adaptor (item# 1922705891) 1 G1/4” male to G1/2” female brass adaptor (item# 1876999872 [pack of two]) spacing) and used a heatshrink tubing sleeve to hold the assembly together. Similarly, three polarised headers soldered onto a small piece of phenolic prototyping board were used to connect the 5-way ribbon cable to the three fan power speed-sense cables. Having completed the wiring, all we had to do was switch the laser cutter on and press S1. Green LED1 lit up. We then unplugged power to the water pump and checked that red LED3 lit instead and that PB1 beeped constantly. Plugging water pump power back in silenced the alarm. Similarly, turning down the fan speed triggers the alarm (and automatically sets the fans to run at maximum speed). 48  Silicon Chip 1 G1/4” male to 8mm hose barb brass adaptor (item# 1924530597 [pack of two]) 1 G1/2” male to 8mm hose barb brass adaptor (item# 1924378817 [pack of two]) 1 2m length 8mm ID 12mm OD food grade silicone tubing (item# 32410550179) 8 M4 x 40mm machine screws 4 M4 x 45mm machine screws 12 M4 nuts 6 small L-shaped brackets (from Bunnings) 1 electronics module (see below) 1 “Mini Switcher” step-down module (see February 2012 issue; Jaycar KC5508, Altronics K6340) 1 small piece protoboard 3 3-pin polarised headers 1 3-pin header Miscellaneous Teflon tape, various cable ties, P-clamps, adhesive clips and short lengths of heatshrink tubing Electronics module 1 small protoboard (with copper “donuts”) 1 set of laser-cut case pieces 1 small tube acrylic glue 1 200mm length thin double-sided tape 1 5V Pro Micro-clone Arduino module (MOD1; Ali Express item# 32284746884) 1 10kΩ linear 9mm potentiometer (VR1) We decided to run the fans near maximum speed, with potentiometer VR1 almost fully clockwise, as the noise is drowned out by other components of the system and this provides the best cooling. To reduce fan speed, it’s necessary to initially do so in stages, pressing switch S1 as you go, to prevent the alarm from triggering and forcing them to maximum speed. Once the nominal fan speed has been reduced, VR1 can then be used to adjust the speed up and down as you would expect, as long as it is not set below the nominal level. Conclusion Fitting the new cooling system re- 1 3-way polarised pin header & plug (CON1) 2 2-way mini terminal blocks (CON2,CON3) 1 5-way right-angle polarised pin header & plug (CON4) 1 mini 12V sealed piezo transducer (PB1) (Jaycar AB3459, Altronics S6105) 1 right-angle tactile pushbutton (S1) 1 1.1A hold, 2.2A trip polyswitch (PTC1) (eg, RXEF110K) 1 100µH 3A powdered-iron core toroidal inductor (L1) 1 2m length rainbow cable 1 2m length light-duty figure-8 wire 2 12-pin female headers (for MOD1) Semiconductors 1 IRF9540 P-channel Mosfet (Q1) 1 2N7000 N-channel small signal Mosfet (Q2) 1 5mm high-brightness diffused green LED (LED1) 1 5mm high-brightness diffused yellow LED (LED2) 1 5mm high-brightness diffused red LED (LED3) 4 1N4004 1A diodes (D1, D3-D5) 1 1N5819 1A Schottky diode (D2) Capacitors 2 220µF 16V low-ESR electrolytic Resistors (0.25W 1% unless specified) 4 1kΩ 2 470Ω 0.5W 5% 3 220Ω 1 22Ω ally transformed the laser cutter. With the original cooling system, we had to wait for around an hour between cutting large panels to let the water cool down and we got inconsistent results, with cuts made later in each run not necessarily going all the way through the material. Now the laser cutter can run continuously all day with barely more than a 10°C rise in water temperature and with perfectly consistent cut depth. Importantly, we now have peace of mind since we will be immediately alerted to any serious problem which may occur with the laser cooling system and we can check the water temperature at a glance. SC siliconchip.com.au