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Mini Projects #013 – by Tim Blythman SILICON CHIP Digital Spirit Level Here’s an easy project that’s really on the level! Using a digital accelerometer module and a bright LED display, it indicates its tilt in either degrees or percent. It’s powered via a USB cable (eg, from a USB battery bank). › Tilt angle display: -99° to +99° (1° resolution) › Gradient display: -99% to +99% (1% resolution; equivalent to -44.5° to +44.5°) › Power: 5V DC via micro-USB socket › Other features: an error message is shown if the Level is not aligned correctly A device like a spirit level is a handy tool for knowing whether things are level or not. It can also tell you how far something is from being level. For example, we recently had to install shelves on a sloping floor. We used a spirit level to adjust the height of each foot so that they were stable and round items wouldn’t roll off them. We thought a Duinotech Arduino Compatible 8×16 LED Matrix display (Jaycar XC3746) would make a great base for attaching a few other parts to build a Digital Spirit Level. It has mounting holes in the corners, so you attach this Level to a piece of equipment to check if it’s level or not (or screw it to a long piece of straight timber to make it more accurate). If you’re driving off-road, it’s important to know that your vehicle isn’t tilting beyond its abilities. You could mount this Level on the dash or near the rear-view mirror to make it easy to tell. Knowing that your caravan is parked on level ground will help you sleep at night, since you’re less likely to fall out of bed! In a vehicle, you could power it from a car phone charger, while if you want to make it portable, it can easily run off a USB battery bank. You can see a video of the Level in operation at siliconchip.au/Videos/Digital+Level Circuit details The Level is made from three modules and one pushbutton, wired Parts List – Digital Level (JMP013) 1 Leonardo Tiny main board [Jaycar XC4431] 1 I2C Tilt Sensor module [Jaycar XC3732] 1 16 × 8 LED Display module [Jaycar XC3746] 1 2-pin through-hole tactile pushbutton switch [Jaycar SP0611] 1 5cm length of double-sided foam tape [Jaycar NM2821] 1 micro-USB cable to suit Leonardo Tiny [Jaycar WC7724] 30cm of wire in various colours (display module wiring harness can be cut up if required) siliconchip.com.au Australia's electronics magazine together as shown in Fig.1. The Leonardo Tiny main board connects to a tilt sensor module, which incorporates an MMA8452Q three-axis accelerometer. By sensing the acceleration due to gravity, it can tell which way is down and thus how far from level the module is. The accelerometer is a digital IC that is controlled by and sends data over an I2C serial bus. An I2C bus requires two lines plus ground, so it connects to the SDA (serial data) and SCL (serial clock) pins of the Leonardo Tiny. There is also a tactile switch connected between the A1 pin and ground. The main board applies a pullup to the pin to sense when the button is pressed, which shorts that pin to ground. The LED matrix display module is also marked with SDA and SCL, but it doesn’t actually use the I2C protocol. Thus, we have connected it to different pins, which we can directly drive to produce its somewhat peculiar protocol. This sort of strategy is often called ‘bit-banging’, where I/O pins are driven manually high and low as needed to generate the required sequences. November 2024  63 Fig.1: follow this wiring diagram to connect the modules and switch. The SDA and SCL wires for the tilt sensor must be soldered to the underside of the Leonardo, while the remaining wires can be attached from above. In short, the AIP1640 chip in the LED module expects 8-bit bytes with their least significant bit first, while I2C uses 9-bit bytes (as it adds an acknowledgment bit) and sends them with their most significant bit first. The first byte that is expected by the AIP1640 chip is a command, while I2C devices expect to see an address first (allowing multiple devices to coexist on the same bus). Using the same pair of pins to communicate with both devices thus risks triggering unwanted actions, so we have kept them separate. Luckily, we had enough spare pins on the Leonardo Tiny to do that. Construction We’ve used the large back surface of the LED module as a convenient place to mount the other modules. It’s a bit fiddly to put together, but it makes for a tidy final package. Start by removing the header pins from the tilt sensor module, if it came with them fitted. We found it easiest to start by bending the pins straight. Apply heat to the underside of each pin and pull it upwards; it should slide right out of the plastic shroud. Use some solder-wicking braid (with a bit of extra flux, if you have some) to remove any stray blobs or lumps of solder. For wiring, we used some coloured solid-core wire we had on hand, but the LED module also comes with a harness we do not need, so you could scavenge some wire from that. Solder the tactile switch between the GND (−) pad and the A1 pad of the Tiny. Trim any excess lead length so they do not protrude below the bottom of the PCB. Then solder some insulated wires to the SDA and SCL pins on the underside of the Leonardo Tiny. These are the white (SCL) and light blue (SDA) wires in our photos. Attach the Leonardo Tiny and tilt sensor to the back of the LED Module using some lengths of double-sided tape, being sure to keep the tilt sensor’s edge parallel to the LED Module’s edge. We placed them in the corners of the module, but you might like to move them down slightly to make the top mounting holes more accessible. Be sure to use foam-backed tape so there is no chance of the boards shorting together where they touch, particularly the wires on the back of the Leonardo Tiny. Solder the other ends of the white (SCL) and light blue (SDA) wires to the corresponding pads on the tilt sensor. Next, run the red wires seen in the photo. They connect the Leonardo Tiny + pad to the Vcc pad on both modules. Similarly, the black wire in the photos connects the Leonardo Tiny – pad to GND on both modules. Now solder a wire (yellow in our photos) from D11 on the Leonardo Tiny to SCL on the LED module. A dark blue wire then goes from D10 on the Leonardo Tiny to SDA on the LED module. Software The software is simple enough. A library is used to communicate with the tilt sensor and gather data from it. It is processed to display a reading in degrees, or a percentage gradient, on the LED module. When the pushbutton is pressed, the display blanks and changes modes. The software is compiled and uploaded using the Arduino IDE, We found it best to lay it out in this fashion, with the switch and the white and light blue wires attached to the Leonardo Tiny before it is stuck to the LED Module. The remaining wires can then be soldered to complete the circuit. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P The display will show a percent symbol when a gradient is being shown. A 100% gradient is the same as a 45° angle. An arrow is shown to the left of the numerical display to show whether the slope is upwards or downwards. It is not shown when the displayed value is 0° or 0%. which can be downloaded from www. arduino.cc/en/software You will also need the SparkFun MMA8452Q library, which can be installed by searching for “SparkFun MMA8452Q” in the IDE’s Library Manager. We’ve also included a copy of version 1.4.0 of the library in the software downloads (siliconchip.au/ Shop/6/462). The library file for the LED module (XC3746.h) is included in the sketch folder. You can use this for your own projects by simply copying it to another sketch folder. Connect the Leonardo Tiny to your computer using a USB cable, then choose the Leonardo board profile in the IDE and set its serial port. After that, you can upload the sketch. The LED module should light up with a splash screen and then display an angle in degrees. If you want to change the default startup mode to percentage gradient, change the code to initialise the dispMode variable as ‘true’ instead of ‘false’ and reupload the sketch. If you see the message ERR flashing on the LED display, the sketch cannot communicate with the tilt sensor. Pressing the tactile switch (attached siliconchip.com.au to A1) when the message is flashing should reset the Leonardo Tiny so that it tries again. If the ERR message is shown but not flashing, ensure the Level is strictly vertical. If that is not the case, errors can creep into the calculations, so the Level presents a warning instead of producing erroneous values. During regular use, pressing the button will cause the display mode to change between degrees and gradient. The up or down arrow indicates whether the left-hand end of the Level is higher or lower than the right. Completion Place the Level on a horizontal surface and carefully adjust the tilt sensor until the Level reads 0°. If you like, cut a piece of card the same size as the LED module and use double-sided tape to stick it to the back of the Level. Remember to cut out a hole for the switch. You could also use some tape to stick the Level to a vehicle or a length of straight timber. Be sure the vehicle or timber is level and place the Level so it reads 0° or 0% before securing it. SC Australia's electronics magazine Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. November 2024  65