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Flavio Spedalieri’s Arduino-based Coffee Grinder Timer Take your coffee grinder (or other motorised appliance) to the next level with a custom timer module, programmable presets and an LCD or OLED screen. G ood coffee grinders are expensive – even basic, manual models operated by a simple switch can cost over $500, and some well over $1000! You’d think that they’d throw in a timer for that much money, but there’s often a premium of several hundred dollars on models with timers. Having a programmable timer in a coffee grinder used for making espresso is a big advantage. Once you’ve determined the correct grind setting and time to make a good coffee, it will produce a consistent amount of grounds so that each cup is consistently good. Too many grounds will choke off the water flow, while too few will make weak coffee. You want minimal variation from cup to cup. It would be ideal to buy a grinder that does an excellent job of making the coffee grounds without spending siliconchip.com.au too much money, then add a timer if it lacks one. That’s what I did, and you can do the same. Why spend so much when you can get a coffee grinder at Kmart for $18? Because it won’t be ideal for making good-quality espresso. It won’t grind finely enough or consistently enough, won’t be adjustable enough, and will take quite a long time to produce enough grounds for one cup. It also won’t last very long. While this project is designed to add a timer to a coffee grinder, it could be used for just about any appliance that runs off the mains and can be switched using a solid-state relay. It could also be used to switch low-voltage AC or adapted to switch low-voltage DC. The circuit is simple, and the parts are inexpensive; with some work, you can upgrade just about any grinder with this programmable timer. In my case, I wanted to add a timer to a used Compak K6 grinder (a well-­ regarded unit) that was generously donated to me by Dean and Rose Kiner of Siboni’s Coffee in Pymble NSW. I had two main jobs to do. One was to design the electronics and create the software for the timer itself. The other was to figure out how to modify the grinder to nicely integrate the electronics. A timer should be easy to use and free from complexities, with a simple menu for making adjustments. I considered using a DIN-style timer; however, they can be difficult to use and require substantial clearance to fit, meaning it would have to be external to the grinder. So I decided to base it on an Arduino module, as I am familiar with that ecosystem. The first part of this article will concentrate on the timer module and its functions. It could be adapted to many other applications or even built as an external module, making it easy to add to use with any suitable appliance. It is incredibly handy for more precise measurement and dosing of the coffee grounds. Note that some timerless grinders have a ‘doser’ mechanism that catches the grounds and apportions them to suit the coffee machine. This has several disadvantages, including stale coffee getting stuck in the doser, especially since you have to keep it close to full for the doses to be accurate. If adding this timer to a grinder with a doser (as I did), it would be necessary to remove the doser and replace it 230V AC Mains Safety The entire timer module can be built, tested, and made functional without touching mains voltages. However, should you wish to interface the module to a solid-­state relay (SSR) for mains switching as described, please follow all the precautions described in this article for safely working with 230V AC mains. That includes using correctly rated parts and wiring, properly insulating all exposed conductors and avoiding touching any part of the circuit when the mains cord is plugged into an outlet. Australia's electronics magazine September 2023  57 Photo 1: the Arduino Pro Mini is basically a shrunk version of the Uno. It’s no longer officially made, but plenty of clones are still available. Photo 3: the three buttons that control the Timer all have integral LEDs. You could use three similar types of buttons if you want. with a chute that dispenses the ground coffee straight into a ‘portafilter’ basket or similar. an I2C serial interface, the addition of a ‘manual grind’ display, a rotary encoder for easier time setting, the reconfiguration (and reduction) of the buttons, adding visual feature through LED fades and flashes, plus an ‘offset mode’ and the ability to display the firmware version and disable the splash screen. I eventually added support for multiple display types, including OLEDs. Timer design I found some code online for a very basic two-preset timer to control an electrical appliance. A 16×2 character backlit LCD with a parallel interface was used as the display, with four control buttons (+/−, P1, P2 & manual) for control. It integrated with the appliance’s multi-switch, which was rewired to activate the timer (effectively giving it five buttons). I loaded this code to understand how the timer would work from an end-user/operator perspective. Still, I knew I would have to redesign the circuit and rewrite the code to suit my needs better. Some improvements I made include the ability to drive the LCD through Arduino software Besides being easy to use with a clear display, I decided the software should have a screen saver mode (where the screen is turned off after five minutes of inactivity) and the visual LED fades. The Arduino platform I ended up using is the Pro Mini board (Photo 1) with the usual ATmega328 microcontroller. One advantage of using the Pro Mini is that I could prototype the system using an Arduino Uno (Photo 2) and then transfer it quickly to the compatible Pro Mini later. I split the software up into nine source code files: 1. the main program 2. button press handling 3. display driving 4. rotary encoder sensing 5. utility functions 6. initialisation 7. LED driving 8. & 9. splash screens for the two OLED display options These files and the compiled HEX file are available for download from siliconchip.com.au/Shop/6/248 Button configuration Photo 2: the prototyping rig used to develop the software, based on a few small modules and jumper wires. 58 Silicon Chip I reduced the button requirement to three; one button to select between the two presets, one to trigger the selected preset and one for manual grinding. The rotary encoder is used to set the Australia's electronics magazine times and has a fourth integrated button to access the menu. Photo 3 shows how I mounted the three buttons, and you can see the rotary encoder above them. However, the code also has the option to have two different trigger buttons, one which triggers preset 1 and one which triggers preset 2. Editor’s note: that is how the grinder at our office works, as it makes it convenient to select between single- and double-shot espresso. Display options As mentioned earlier, the original concept used a 16×2 character LCD. However, I realised that a smaller screen would be needed to fit within a limited space inside the grinder. I therefore modified the software to support a 128×64 pixel OLED display with an SSD1306 controller using the U8G2 Display Library – see Photo 4. After testing several OLED screens, I arrived at the Digole Digital Solutions DS12864OLED-2W white-onblack OLED (Photo 5). As driving it is different from the generic SSD1306 screens, there are two different versions of the firmware to handle both types of 128×64 OLED screen. Table 1 shows the various software versions I have developed that are available to download. The Digole screen (www.digole. com) is a graphic type with a fast update response and only needs a small library to drive it. It does need fonts to be loaded into the four user font addresses. The more common 128×64 graphic OLEDs using an SSD1306 or SH1106 controller can also be used, but they have a slightly slower display response. For these, the I2C communication speed may be improved by adding the function call “u8g2.setBusClock(600000);” in the initialisation code. If using the Newhaven character OLED, the display has a reset pin which can either be driven from the Arduino or connected to an RC circuit to pull it low for about 40ms during power-up. It uses the US2066 chipset; however, the I 2 C Display library is used (www.dcity.org/portfolio/ i2c-display-library/). This requires the following code changes to function correctly. Inside the function I2cChar­ Display::oledBegin(), where the siliconchip.com.au Photo 4: the graphic OLED screen (left) is much more compact than the alphanumeric version (right). Photo 5: the selected OLED screen fits neatly behind the new custom-made front panel, painted black. following two lines are found, change 0x00 on the second line to 0x10: // Set SEG Pins Hardware Configuration sendCommand(0xDA); // Enable SEG Left, Seq SEG pin config sendCommand(0x00); The 16×2 character LCD with I2C interface is the simplest display from the software point of view, but it is much larger than the other options, and isn’t capable of displaying graphics. Circuit details The resulting circuit is shown in Fig.1. The Arduino Pro Mini, OLED/ LCD screen and rotary encoder modules are powered by 5V DC from the switch-mode power supply. The Arduino updates the screen using a two-wire I2C serial bus, via its A4 (SDA) and A5 (SCL) pins. Internal pull-up currents are enabled on digital input pins D5, D7 & D8 to detect when pushbuttons S1-S3 are pressed. The integral LEDs in those buttons are driven by digital outputs D10, D11 & D9. Two of these (D10 & D11) have series current-limiting resistors to set the LED currents to around 9mA, while the third does not because the switch includes a series resistor for its LED. While the resistor integrated into switch S3/LED3 is designed to allow it to operate from 12V, it isn’t too much dimmer when driven from 5V. The LED in the solid-state relay is driven directly from the D12 digital output. It has an integral 1.5kW resistor and supports a control voltage range of 4-32V DC. As it only draws less than 4mA at 5V, the Arduino output can easily drive it. The SSR’s outputs are connected in series with the mains supply to the grinder motor, so it switches the motor on while the D12 output is high. The rotary encoder I used is mounted on a small PCB, which includes three pull-up resistors for the two encoder contacts and the integral switch. Pins 1 & 2 are for ground and the power supply that drives the pull-ups, while the remaining three pins are for the encoder and switch contacts. These go to digital inputs D2-D3 and D4 on the Arduino, respectively. They are debounced and decoded in software. Fig.1: the Timer circuit is straightforward, with the Arduino module controlling all functions and updating the display over a two-wire I2C serial bus. It controls the SSR that switches the grinder motor via a digital output and uses three buttons (with integrated LEDs) and a rotary encoder for user input. siliconchip.com.au Australia's electronics magazine September 2023  59 If you want to use a different rotary encoder than I did, refer to “Encoder Setup” in the main code file to adjust its behaviour. While there are no doubt various SSRs that could be used in this application, I chose a high-quality unit, with much higher voltage and current ratings than necessary, for a long life. My grinder motor is rated at 245W (1.02A) <at> 240V AC. You should check yours against the ratings of your selected SSR; the one I specified should suit most grinders. The operation and functions of the Timer are listed below: #1 Splash Screen As a departure from traditional nomenclature, I adopted a more generic “PRESET 1” and “PRESET 2”. By default, the firmware uses single button control as fewer holes needed to be drilled in the grinder. In this case, pressing the Select button toggles between the two presets. The Run button illumination will Flash once when Preset 1 is selected and twice when Preset 2 is selected. The firmware also supports two buttons, one for Preset 1 and a second for Preset 2. Pressing the associated button will change the preset program accordingly. This second switch can be connected to pin D6 of the Arduino Pro Mini and then to Ground. #4 Program Mode Photo 6: the grinder I started with; it had seen a lot of use. Note the large doser assembly attached to the front and the original, tall hopper on top. If “Display Start” is enabled, the splash screen will be displayed on power-up for four seconds (see above and Screen 1). The displayed message is preconfigured in the initialisation file. If “Display Start” is disabled, it will instead immediately display the default Preset 1 (Idle Mode). The Run button illumination increases from off to bright as it enters idle mode. #2 Idle Mode Pressing the encoder button/knob (Program) enters the program mode for the currently displayed preset. The Run button illumination extinguishes in program mode. The display changes to show “PROG <> PRESET”. Turning the encoder knob will change the preset time. Pressing the encoder button will return to the current preset (Idle Mode) and will save the time if it was changed. The Run button will flash four times on exit. #5 Offset Mode Screen 1: an example of the splash screen displayed on the OLED module. Screen 2: the Firmware Version Display screen on the OLED module. 60 Silicon Chip Following power-up, the timer defaults to Preset 1 with the displayed time loaded from EEPROM. The Run button continuously cycles between dim and bright every three seconds. #3 Switching Preset Program The firmware has two preset times, inspired by commercial timed grinders that usually have ‘single cup’ and ‘double cup’ options. The ‘double cup’ grind is not necessarily twice the time of the ‘single cup’, as single and double espresso filters usually hold 7-10 grams and 16-18 grams of coffee, respectively. That, and the way roasted coffee beans vary, mean the times both need to be adjustable. Australia's electronics magazine Offset mode allows for ‘on-the-fly’ preset time adjustment throughout the day without changing the saved preset time. This lets you experiment with the amount of coffee without changing the stored presets. Rotating the encoder dial/knob in Idle Mode automatically enters Offset Mode. When the displayed time is lower than the preset, the LCD will show “<OFFSET”, and when higher, it shows “OFFSET>”. If you turn the encoder to return to the preset value, the display will return to “PRESET”. While in Offset Mode, pressing the encoder (Program) button will enter Program Mode and clicking again (to exit) will update the stored preset value in EEPROM with the new siliconchip.com.au value. The Run button will flash four times on exit. Note that for the V2.65 firmware (single button configuration), once Offset Mode has been activated, when returning to normal Idle Mode, the Preset button must be pressed twice to change the preset. #6 Grinder Activation Pressing the Run button runs the grinder for the currently selected preset time. The Run button illumination will extinguish when the grinder is operating, during which time a countdown is shown on the screen. When it finishes, the display returns to idle mode and the Run button will re-­ illuminate. #7 Manual Grind/Purge A manual grind/purge button is an important feature of any grinder. Pressing and holding the Manual button causes the grinder to run while the button is held down. The display shows “MANUAL GRIND” during this time while the Run button cycle-flashes. #8 Enable/Disable Splash Screen To enable or disable the splash screen, press and hold the Select button (or P1 if you’re running the dual preset button firmware) for four seconds. The Run button will flash at 1Hz. Release once the display shown above appears. Again, on this screen, hold that button for four seconds to save the change. The Run button will flash four times on saving the change to EEPROM and returning to the Idle screen. The Splash Screen is toggled on or off each time you go through this procedure. #9 Firmware Version Display Press and hold the rotary encoder siliconchip.com.au Table 1 – software versions Name Screen Preset buttons HEX file? 1B_128x64OLED 128×64 graphic OLED (SSD1306) 1 Yes 2B_128x64OLED 128×64 graphic OLED (SSD1306) 2 No 1B_DS12864OLED 128×64 Digole DS12864OLED-2W OLED 1 Yes 1B_NW1602OLED 16×2 character Newhaven NHD-0216AW-IB3 OLED 1 No 1B_1602LCD 16×2 character LCD 1 No 2B_1602LCD 16×2 character LCD 2 No (Program) button until the Run button begins flashing, then release it. The firmware information will be displayed for four seconds before returning to Idle Mode (also see Screen 2). The Run button flashes once on exit. Note that most of the screengrabs shown are for the 16×2 alphanumeric displays. As seen in Screens 1 & 2, the OLED has a more square aspect. In most cases, it shows the same information as the LCD screens, just reformatted to better fit the OLED. Grinder conversion The coffee grinder to which I added this timer was an old Compak K6 that I refurbished and modified at the same time. Photo 6 shows it in its original state. As it was ‘well-loved’, I completely stripped the grinder (Photo 7), cleaned everything and sandblasted the housing (Photo 8). Converting it to be doserless required the removal of the old dosing chamber, re-engineering the outlet port and mounting a spout or cone. A Rancilio Rocky doserless grinder spout (which Dean also provided) was my first choice (see Photo 9). I also considered retrofitting a dose cone from a Mazzer Mini but decided against it as they are expensive (over $250). Also, it would have been too tall, pushing the placement of the portafilter holder much lower than where the display is positioned. You might notice that I reduced the size of the hopper, something that was not required but that I decided to do. I accomplished this by marking, hand-cutting and sanding the hopper. A felt strip on the inside edge of the hopper lid made for a snug fit. One of the main challenges was Australia's electronics magazine Photo 7: the cut-down hopper and the curved front panel with the doser removed. That made attaching the new chute and display challenging. Photo 8: the stripped chassis after sandblasting. Note how I have ground away some of the metal around the opening at the top so the new flatflanged chute can be fitted. September 2023  61 Photo 9: after reshaping the orifice, the chute (designed for a different type of grinder) fits nicely. Photo 10: this handmade timber piece covered up the gap left by removing the doser. modifying the existing casing, which had a curved section where the outlet port is, to mount the spout with its flat mating flange. This required modification to both the case and the original plastic coffee outlet adaptor. If you can modify a grinder that has a flat front face, that will make everything a lot easier! To pay homage to Siboni’s Coffee and one of my favourite blends, “Romeo”, I programmed the “Romeo” graphic to appear on the splash screen, as seen in Photo 5 and Screen 1. With the timer ready, I started cutting and drilling holes in the grinder case for the switches, screen, and mounting point for the portafilter fork. I used the portafilter holder from a Mazzer Mini grinder. Depending on the design of your grinder, its motor might be switched by a manual switch or a relay. In my case, it was a 16A mechanical relay. I simply removed this and connected the SSR in its place. I securely mounted the SSR and switch-mode power supply inside the grinder case and wired up the switchmode supply to the incoming mains (after the power switch). One question was how to fill in the original gap at the top of the grinder, where the doser used to attach, and how to tidy up the front face. For the top of the grinder, I wanted to use a piece of timber as it would add a ‘warm tone’ to the project. I cut three sections of Tasmanian Oak, glued them together, then sanded and contoured the piece (Photo 10). Two Neodymium magnets secure it to the body and allow for its removal if the front needs to be disassembled, eg, to remove the spout for servicing. I gave the timber piece several coats of walnut stain before two coats of Scandinavian Oil and final coats of beeswax. I also needed to produce a new front face to attach the spout, portafilter holder and timer display. I first mocked up the plate for the front face with card (Photo 11), then 3mm ply, and eventually translated it to 1.2mm-thick aluminium (see Photo 12). I hand-cut the aluminium stock (using a nibbling tool) and finished it by hand. I conducted a final fitment test before painting it (Photo 14). I added an indentation above the portafilter holder to position the filter directly under the spout. As a bonus, it can aid in holding the filter in place during grinding (shown in Photo 14). With the grinder housing completed, all holes cut, drilled & tapped, fitment tested and the timber in-fill finished, it was time to sandblast the case and prepare for final painting. I gave the case five coats of black satin paint with a final sandy texture finish, sealed with a clear topcoat. As you will see from Photo 16, I opted to mount all the new controls along the side of the base, as there was plenty of room, except for the rotary encoder, which is mounted above the Photo 12: the metal face plate was made from 1.2mm-thick aluminium and painted to match the body. Photo 13: the OLED screen fits nicely near the base. The new front panel will cover its mounting screws. Aesthetic details Photo 11: I cut and folded this card to figure out how to shape the new metal front panel. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au buttons on the side of the main body. Wiring it up As I had already installed the switch-mode supply and SSR, as mentioned earlier, all that was left was to wire the Arduino and other modules as per the circuit diagram (Fig.1). Given the simplicity, I mostly used point-to-point wiring to connect the components to the Arduino. You can see how it all (just) fits inside the grinder base in Photo 15. If your grinder does not already have a relay to control the motor, you will need to cut one of the wires going to it and connect the two ends across the SSR’s mains terminals. The power supply and SSR both need to be solidly anchored to the case. Use mains-rated wire for the new connections to the switch-mode power supply and fully insulate all new or modified mains connections. Cable tie the Active and Neutral wires to the switch-mode supply together at both ends. Also, cable tie the mains wires to the SSR together if possible. I haven’t gone into great detail about how I modified my grinder because most of the steps will depend heavily on the specifics of your grinder. Still, if you want to see exactly how I did it, you can see all the details on my website at www.nightlase.com. au/?pg=coffee The lead photo and Photo 16 shows the final result with the grinder up SC and running! Photo 14: a bracket and a detent in the front panel hold the portafilter in place during grinding. siliconchip.com.au Parts List – Timer for coffee grinders 1 Arduino Pro Mini (MOD1) [Core Electronics 018-MINI-05] 1 230V AC to 5V DC 1A enclosed switch-mode power supply [Jaycar MP3295] 1 USB/serial adaptor (to program MOD1) 1 Digole DS12864OLED-2W or SSD1306/SH1106-based 128×64 pixel graphic OLED (MOD2) 1 25A 480V AC solid-state relay (SSR) [Kyotto KD40C25AX] 1 chassis-mount momentary pushbutton with integral white LED (S1/LED1) [Core Electronics ADA1479] 1 chassis-mount momentary pushbutton with integral red LED (S2/LED2) [Core Electronics ADA1439] 1 chassis-mount momentary pushbutton with integral green LED and current-limiting resistor (S3/LED3) [Jaycar SP0804] 1 five-pin rotary encoder module with integral pushbutton plus knob (RE1) [www.aliexpress.com/item/32790788377.html] 2 220W ¼W resistors various lengths of mains-rated wiring, heatshrink tubing, cable ties etc various screws, nuts and other mounting hardware Photo 15: this photo inside the grinder base shows the added 5V power supply (upper left), SSR (bottom middle, under Presspahn insulation), buttons and some of the new wiring. Cable ties were used extensively to prevent wires from floating around in case they came loose, and all mains connections were fully insulated. Photo 16: the finished grinder conversion, with the OLED screen, buttons and rotary encoder visible towards the bottom. Compare this to the original (shown in Photo 6) to see the transformation. Australia's electronics magazine September 2023  63