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By Tim Blythman μDCC Decoder Accessory Decoder I2C Controller Destination Display Model Headboard Destination Display Background source: https://unsplash.com/photos/ train-tracks-with-trees-on-either-side-3TXv9NJZZTk Miniature electronics have come a long way and are now at the point that it is possible to create displays compact enough to fit into small (HO or N) scale models. This tiny display can be controlled by our microDCC (μDCC) Decoder, an infrared remote control, or a serial port. M ovement is a key aspect of giving realism to models; the motion of trains in a model railway is much of what makes them so engaging. Signals and points also add to an authentic nature. Much of this series has been devoted to adding movement to a DCC (digital command control) model railway. Lights and sound also add to engagement and don’t require moving parts. We noted in the microDCC Decoder article (May 2026 issue, siliconchip. au/Article/20239) that some modellers are now adding small displays to their trains. We showed an example of an LCD (liquid crystal display) fitted to one HO-scale model to emulate a headboard. This Model Headboard Destination Display project provides something similar. While this board can be used without the microDCC decoder, once the graphical data has been loaded onto the chip, with it you will be able to send DCC commands to the loco and have it update the display (eg, select a new destination). Otherwise, you siliconchip.com.au could use an IR remote control aimed at a receiver on the loco to perform the same task. Headboards and destination displays “Headboard” is a term originally used to describe a painted timber Features & Specifications 🛤 The 19 × 12mm PCB drives a tiny OLED panel 🛤 Serial input for control (eg, from our microDCC Decoder) 🛤 Infrared remote control 🛤 8kiB+ NFC EEPROM chip for display data 🛤 3.3V operation; 6mA typical draw at full brightness 🛤 Suits a variety of monochrome display panels and sizes 🛤 Display contents (graphics and animations) are configurable Australia's electronics magazine board placed at the front of a train to indicate its line or destination. Later, adjustable mechanisms using handpainted linen scrolls on rollers were used. Photo 1 shows an example of a scroll from an old Ballarat tram and a Geelong tram, showing how this appears in use. The translucent linen allows effective backlighting. Originally adjusted by hand, these mechanisms later received electronic controls and plastic screen-printed scrolls. Other variants include airport-­ style split-flap displays and flip-dot mechanisms. We created our own version of a flip-dot display, published in the April 2019 issue (siliconchip.au/ Article/11520). Many modern displays use LED matrices. This sort of display is what the Destination Display is intended to replicate. You might wonder about our claims that this unit will fit in an N-scale model, but we have found a tiny 0.32-inch (8.1mm) OLED (organic LED) display panel that is one of a few that can be used for this project. Photo 2 shows the Destination August 2026  51 Display fitted to the same N-scale chassis that we used for testing the DCC Decoder project. The OLED and PCB assembly has an outline that fits within the profile of an N-scale unit. The 8.1mm dimension is the active area; the OLED panel itself is about 10mm wide and 9mm tall, with the total assembly being about 20mm long. We expect that readers will find other uses for the Destination Display. Its size would suit other model railway applications, such as departure boards or even advertising signs. The Destination Display offers animations that include the scrolling motion that would be seen in a changing sign, and it has a mode that emulates the alternating screens of modern digital signs. The video at siliconchip.au/Videos/ Destination shows the Destination Display and a 0.32in OLED panel inside a 3D-printed N-scale model tram. The model is 22mm tall. OLED panels Fig.1: these diagrams show the mapping of the pixels in the displays; the mauve numbers 1-8 indicate the codes used to program the different display orientations. So, to arrange the 0.50in display in landscape with the FFC on the left, you would set the orientation to 2 and the x-value to 40 or higher to ensure the bitmaps are in the active area. 52 Silicon Chip We found several small panels that we have tested with nominal display sizes of 0.32in, 0.50in and 0.54in. Since they offer comprehensive data sheets, we sourced all these from www.buydisplay.com These OLED panels all use a similar controller to the SSD1306 that is found on the common 0.96in and 1.3in OLED modules. The controller types on our panels include the CH1115 and the SSD1315. Like the SSD1306, these display controllers feature a 128 × 64 pixel display memory, but for these small units, not all the pixels map to active elements. For example, the 0.32in panel’s matrix only has 60 × 32 pixels. So the Destination Display must be configurable to work with these limitations. Ample EEPROM memory in the microcontroller allows all manner of graphics and settings to be loaded and displayed. To give you an idea of the scale of these displays, their pixel pitch is about 0.12mm. That means a seven-­ pixel font will be displayed less than one millimetre in height. Fig.1 shows the different panels that we have tested and how their matrices are mapped to their internal memories. We will provide some sample display data sets, but understanding Fig.1 will be important if you wish to generate your own display data. Australia's electronics magazine Fig.1 also shows the main dimensions of the panels (to the nearest 0.1mm); there are detailed dimensional diagrams in the panel data sheets. The panel sizes, model numbers, data sheets and sources are: ● 0.32in panel: ER-OLED0.32-1W data sheet: siliconchip.au/link/acbu > siliconchip.au/link/acc0 ● 0.50in panel: ER-OLED0.50-1W data sheet: siliconchip.au/link/acbv > siliconchip.au/link/acc1 ● 0.54in panel: ER-OLED0.54-1W data sheet: siliconchip.au/link/acbw > siliconchip.au/link/acc2 The “W” suffix indicates that these panels have white light-emitting elements; this colour appears to be the only available variant for panels this small. Importantly, they also feature the same narrow 14-way FFC (flat flexible cable) connector, making them electrically equivalent. We tested some other panels with the same connector that were not compatible or did not work. This included some variants of the 14-way connector that use a different pad arrangement. That’s why we have chosen the three displays noted above. Circuit details For this project, we are using a bare OLED panel, which means that our circuit needs to provide the support circuitry that is typically seen on the modules that we have used for other projects. Fig.2 shows the circuit of the Destination Display. IC1 is an 8-bit PIC16F18115 microcontroller from the same family as the PIC16F18126 and PIC16F18146 that we have used in other projects from the DCC series. The ‘15’ suffix indicates that it is an 8-pin part with 1kiB of RAM and 14kiB of flash memory; this is the largest available memory option for 8-pin parts in this series. Pins 1, 4, 6, 7 & 8 connect to the ICSP programming header (CON1-CON5), which is also used as the main power and data interface during operation. IC1 receives power from CON2 and CON3 and expects serial data to be delivered to pin 7 via CON4. The header is simply a row of surface-­mounting pads, much the same as we have used for the Decoders in this series. The 10kW resistor pulls up pin 4 (MCLR) to allow normal operation. The 3.3V supply (pin 1 of IC1) is bypassed by 1μF and 10μF capacitors to ground (pin 8). Pins 2 and 3 of IC1 siliconchip.com.au are used for the I2C serial interface, so they have 4.7kW pullup resistors to 3.3V. That’s already most of IC1’s pins allocated! CON7 connects the remaining I/O pin on IC1 (pin 5) to a three-way pad header that also includes ground and power. An infrared receiver module can be connected here to allow IC1 to receive commands from a remote control. The pinout matches common IR receivers, so they can be soldered directly to the PCB. The I2C bus also connects to pins on 8-pin IC2; this is a chip from the ST25DV NFC family. These parts are effectively an EEPROM that can be read or written over an I2C bus or via NFC (near-field communication, such as with a device like a mobile phone). The Dynamic NFC Tag from July 2023 (siliconchip.au/Article/15860) demonstrates these features. Unlike the Dynamic NFC Tag, the Destination Display does not use NDEF (NFC Data Exchange Format). Since the data format is unique to this application, it is not important to mark the data with its type. Our prototypes used the ST25DV64KC, which has 8kiB of EEPROM, but we also think that the 2kiB ST25DV16KC part has enough storage to be practical. We’ll look at the memory requirements later. A pair of pads, CON9 and CON10, allow the connection of an external antenna for the NFC interface. We have designed a small, flexible antenna PCB that we tested on our prototypes. We also tested a small coil made from Photo 1: these destination scrolls, seen at the Ballarat Tramway Museum, demonstrate how a tall bitmap can be used to implement the Destination Display. Photo 2: when fitted in this fashion, the assembly is 20mm tall & 12mm wide. This is small enough to fit into the profile of an N-scale model and display a line or two of text at roof level. a length of enamelled copper wire (ECW). The I2C interface is used to read from the EEPROM in IC2 and also to communicate with the controller in the OLED panel connected at CON6. CON6 is simply a row of pads on the PCB, and the OLED panels have an FFC (flat flexible cable) connector that is intended to be soldered directly to the PCB. The OLED panel consists of a controller chip and OLED matrix mounted to the panel glass using a so-called COG (chip on glass) construction. The connections are made with conductive traces of transparent indium tin oxide (ITO). The remaining circuitry is to support the controller chip for the display panel. Two of the 1μF capacitors are part of a charge pump circuit used to generate the voltages needed to drive the OLED matrix. Two of the 10μF capacitors store the voltages generated by the charge pump. The remaining capacitors bypass the 3.3V rail for the ICs and OLED panel. The third 4.7kW resistor pulls up the RESET pin of the controller to allow it to operate, while the 560kW resistor connected between the Iref pin and ground sets the OLED matrix drive current. The 3.3V supply and the I2C signals also connect via the FFC. Software Fig.2: the circuit is fairly straightforward, with most of the passives being needed for the OLED panel’s operation. siliconchip.com.au Australia's electronics magazine Apart from the firmware that runs on the microcontroller to manage the Destination Display, we have also written an application in the cross-­ platform Processing language. That means that you can use a Windows, Linux or macOS computer to generate data for the Destination Display. The program delivers data as a single file, which is simply copied to the EEPROM on IC2 using a suitable NFC-equipped device such as a mobile phone. Information about the program August 2026  53 can be found on page 56 (see “Destination Display Configuration for Processing”), while the file upload process is described later. Firmware The firmware on IC1 loads configuration data from IC2; this contains information about the display format and where the display data can be found on the EEPROM. The display data is simply a tall monochrome bitmap that is laid out in the fashion of the hanging scroll seen in Photo 1 and a display pointer sets a window so that only a small part of the bitmap is visible. IC1 then waits for commands from either the serial or IR interfaces. The command sets which specific item is to be displayed. The item has an index between 0 and 255, which corresponds to the byte received over the serial line. Being a single byte means there are no concerns with data framing or the like. The IR interface is programmed to respond to NEC codes addressed to device ID 0 or device ID 1. That means it should be easy to build a controller using basic hardware such as an Arduino board and IR transmitter. A data byte for device ID 0 is treated the same as a serial data byte and simply indicates the item index. Compact IR transmitters such as Jaycar’s XC3718 send compatible codes, although the data bytes do not have any obvious correspondence to the button markings (see Table 1). Signals addressed with device ID 1 are treated as increment, decrement, or zero commands and simply update the index. This command set has been chosen to allow a suitably programmed NFC IR Keyfob (February 2025; siliconchip.au/Article/17730) to control the Display. A data file to suit the Fob (to use device ID 1) is included in the software downloads for this project. The indexed item contains information about the graphics to be displayed and how it is to be updated. For example, one mode causes the display pointer to steadily increment or decrement until the desired item is reached; this emulates the behaviour of older scroll-type displays. There are several scroll rates that can be selected. Another mode causes the pointer to immediately jump to a specific display, while other modes allow animation, with the display alternating between two or three bitmaps, like a modern LED sign. There are three different speeds for the alternating options. A Destination Display can be programmed with any combination of these modes, since each individual item has a mode setting. Whenever the selected item is changed, the new index is saved into the internal EEPROM on IC1 so that the most recent display is shown if the power is cycled. Construction This project is on a tiny PCB (19 × 12mm, coded 09111252) fitted with very small parts, packed pretty tightly. We recommend patience and experience with surface-­m ounting components, as well as all the gear commonly used for manual SMD assembly. The PCB is 0.8mm thick and has numerous vias inside pads. This is not recommended for automated assembly, since the vias can draw away solder from the joint (although there are techniques to cap the vias to prevent issues). We found that this made the PCB quite thermally conductive, so we had to wait longer for the solder to solidify as we worked. We used a fairly wide-tipped (2mm) iron as we normally recommend for most SMD work. But since the PCB holds heat well, a fine tip may be better in this case, especially to get between the components to avoid forming solder bridges. We did create a couple of accidental bridges, even between the passives, so keep an eye out for that. We have managed to place all the SMD components on one side of the PCB (see the Fig.3 overlay diagram). Here’s how we worked through our prototypes. We started by applying flux to all the pads on the component side. Start with the two ICs, which have their pin 1s at opposite ends. We found that the Microchip part had a dimple, but the ST parts have a less-obvious bevelled edge. Refer to our photos to check the part markings to confirm their orientations. These are the only polarised parts (apart from the OLED panel). Parts List – Model Headboard Destination Display Fig.3: we have kept the components on one side of the PCB. Observe this overlay diagram carefully, since there is no room for silkscreen component designators. This diagram is shown at 400% actual size, and the PCB is shown at actual size in the parts list 1 0.8mm-thick, 19 × 12mm double-sided black PCB coded 09111252 1 OLED panel with a 14-way solderable FFC connector [Buy Display ER-OLED0.32-1W, ER-OLED0.50-1W or ER-OLED0.54-1W; see text] 1 PIC16F18115-I/SN micro programmed with 0911125D.HEX, SOIC-8 (IC1) 1 ST25DV16KC or ST25DV64KC NFC tag chip, SOIC-8 (IC2) 1 antenna to suit IC2 (flexible PCB coded 06101233 or made from 1m of enamelled copper wire) 3 10μF 50V X5R SMD M2012/0805-size MLCC capacitors 3 1μF 50V X5R SMD M2012/0805-size MLCC capacitors 1 560kW ±1% ⅛W SMD M2012/0805-size resistor 1 10kW ±1% ⅛W SMD M2012/0805-size resistor 3 4.7kW ±1% ⅛W SMD M2012/0805-size resistors 1 3.3V-compatible infrared receiver module (optional) [Vishay TSOP33436] 54 Australia's electronics magazine Silicon Chip siliconchip.com.au With the OLED panel fitted, flat against the back of the PCB, the unit is only 20mm tall, 12mm wide and about 4mm thick (shown at twice actual size). We preferred the hand-wound coil antenna to easily communicate with the NFC chip. The narrow neck between the PCB and OLED panel is flexible, which should help with trying to fit the assembly into a small model. In comparison, the flexible PCB antenna is simple to use but not as sensitive as the coil antenna. Subjectively, we thought that 0.54in panels were not as bright as the others. Next, fit the three 10μF capacitors, paying close attention to Fig.3, since there is no room for markings on the PCB silkscreen. Follow with the three 1μF capacitors. Despite the resistors being thinner, we found that it was easier to solder these last, since their profile seems to capture the solder better; you can confirm their locations against the photo. Use a solvent to clean away the flux residue and allow the board to dry. Each of the OLED panels can be fitted in one of two orientations, as seen in the photos above, so be aware of this when planning how you will use the Destination Display. Just make sure the pin 1 markers align. We found soldering the panels to be quite easy; the 0.62mm pitch is comparable to that of SSOP (small shrink outline package) IC leads. If possible, set the FFC back from the edge of the PCB so you can visually confirm the alignment of the FFC traces with those on the PCB. Clean up the joints with additional flux if necessary and check again for bridges before proceeding. Loading the firmware If you need to load the firmware onto the microcontroller (which shouldn’t be necessary if you have purchased the chip from the Silicon Chip Online Shop or as part of a kit), we recommend soldering a standard five-way pin header to the five pads in a row. The pads are placed at slightly less than 2.54mm/0.1-inch, but close enough that this is doable. This header should then plug directly into the socket header of a programmer like a Snap or PICkit. Be sure to align the pins marked with a chevron (>) on the Display and programmer. You’ll need to find a way to provide 3.3V power to the chip if the programmer isn’t able to do so. Table 1: Jaycar XC3718 IR Remote Control codes Button Code 100+ 25 (0x19) CH- 69 (0x45) 200+ 13 (0x0D) CH 70 (0x46) 1 12 (0x0C) CH+ 71 (0x47) 2 24 (0x18) PREV 68 (0x44) 3 94 (0x5E) NEXT 64 (0x40) 4 8 (0x08) PLAY/PAUSE 67 (0x43) 5 28 (0x1C) VOL- 7 (0x07) 6 90 (0x5A) VOL+ 21 (0x15) 7 66 (0x42) EQ 9 (0x09) 8 82 (0x52) 0 22 (0x16) 9 74 (0x4A) siliconchip.com.au Australia's electronics magazine You can use the other pads marked “3” and “G” to apply power if this is easier. Program and verify the chip. You should see some activity on the panel; a test pattern of stripes is shown for half a second if the EEPROM is blank or its contents are invalid. Disconnect the programmer when finished. Antenna options The RFID Antenna flat flex PCB (coded 06101233) can be soldered directly to the main PCB. It worked fine during our testing, but we found that the handmade wire loop antenna was more forgiving. Since it would also be easier to form into a specific shape to be fitted inside an item of model rolling stock, we prefer it. We started with just over 1m of 0.25mm diameter enamelled copper wire. The diameter is not critical, but much finer would be finicky to handle. Wind five turns around a former with a 5cm diameter (we used an isopropyl alcohol spray bottle) and gently twist the trailing leads together. Use some tape or glue to secure the turns against each other; we used short pieces of Kapton tape, as you can see from the photos. Remove the coil from the former, trim the trailing ends to the same lengths and tin their ends to remove the enamel coating. Solder to the antenna pads on the main PCB. Wiring Fig.4 shows the wiring needed for a comprehensive installation, including a microDCC Decoder and IR receiver. For clarity, we have not shown the OLED panel. The microDCC Decoder provides the 3.3V supply and a serial signal, while the IR receiver takes its 3.3V supply from the Destination Display board and sends its data back via the pin labelled IR. August 2026  55 Fig.4: you may not need all the parts shown here; as long as you can supply 3.3V power and ground and one of the control signals, the Destination Display will be fully operational. We soldered the receiver directly to the PCB for our testing and had no problems receiving signals. Some IR receiver data sheets recommend extra components for power supply filtering, so you should consider that in the case of longer wiring runs. If you plan to use only the serial input, the IR receiver can be left off. Alternatively, if you only wish to use the IR receiver, the serial connection can be left off, and you can supply 3.3V power into either 3.3V pad and similar for the ground connection. If you wish to use the Destination Display as a fixed sign, only power needs to be applied. The Display will use index zero initially. The antenna is only needed to upload data to the EEPROM and it can be removed after uploading if it would be awkward to leave it in place. We made a few antennas and moved them around to test the different OLED sizes that we had attached to our prototype PCBs. We did most of our testing with a USB-to-serial adaptor. That would be ideal for a fixed application, such as an advertising sign or station departure board. A suitably programmed microcontroller could even be used to coordinate several different signs, such as the 56 Silicon Chip multiple departure screens at a model railway station. We have not tested this, but it should also be possible to connect multiple Displays to the same serial and IR sources, since they are simply inputs to the Display. Remember that the microDCC Decoder has limited capacity on its 3.3V regulator, so check that the load is suitable if connecting multiple Displays to a single Decoder. Naturally, any power supply used must be stable for proper operation. The default data should also result in an image on the 0.50in and 0.54in displays. We don’t think it will be usable (for a model) with these displays, but should give you confidence that the hardware is working as expected. If you want to just load our sample datasets onto the NFC chip then you can skip these next few sections and go straight to the heading labelled “NFC chip” overleaf. Defaults We used the Processing language to create the configuration programming sketch. The Processing IDE (preferably version 4.4.7 or later) can be downloaded from their website, see: https:// processing.org The sketch presents as a windowed application with buttons, text fields and the like. Processing does not provide these graphical user interface (GUI) features, so we have had to create them from scratch. There is no image editing and only very basic text editing capabilities, so we recommend using other programs to do this. You might find edge cases in the sketch that will cause it to crash, but it should be well-­behaved with sensible inputs. The internet is a wonderful thing, and on it we found a list of Australian railway station names that are duplicated (or triplicated) in different states. We have used this list as the basis for our default demo. The list is shown in Screen 1. The flash memory of IC1 is loaded with these default graphics that are used if the EEPROM does not carry valid data. It is designed to be usable on the 0.32in panel, and should respond to commands on the serial line or from the recommended remote controls. The data corresponds to the DEFAULT 0.32in.bin file in the software downloads, so you can view and edit this data. Australia's electronics magazine Destination Display Configuration for Processing siliconchip.com.au Open the sketch file (Destination_ Config.PDE) and click the Play button at the top of the window to run the program; this will open in a new window. The File Menu also has an option to export a standalone application, which will only work on the same operating system on which it is created. Screen 1 shows this window in use. There are three main steps. Firstly, the image data on the left is created or loaded. Secondly, the individual index items are created based on the image. Finally, the data is generated and exported to a file. Image data You can load image data via a file (eg, PNG, GIF or JPEG formats). The image is converted to monochrome using a threshold (“thresh.” text box) between 0 and 1. A lower value will result in more white pixels, and a higher value more black pixels. The image width is cropped at 128 pixels and the “w” and “h” fields are set based on the image. If you need to adjust the threshold, click on the number box and enter a new value, then reload the image using the “Load image” button. If the image is taller than the window, you can scroll up and down using the up and down arrows at top left. Alternatively, you can enter text in the box under “Load text”. This is a simple multi-line field, so you can’t move around within the field using The prototype being controlled by a μDCC decoder on a loco chassis. siliconchip.com.au the arrow keys; the text can only be edited at the end. You can use Backspace to remove the last character and paste from the clipboard with Ctrl-V. Delete all text with the Delete key. Use the “Load text” button to generate an image from the text in this field. This step responds to the threshold field as well as the “w”, “y pitch” and “cond.” fields. The “w” field sets the width (in pixels) of the generated graphics, while the height depends on the number of lines of text and the “y pitch” value. The “cond.” (condensed) field can be used to narrow the text if it is too wide. For example, the data generated in the adjacent screen uses the value of 0.7. You can use a value larger than 1 to expand the text if desired. The “Save img” button can be used to export this image to a PNG file; there is no prompt for a filename – it is simply saved in the sketch folder with a name based on the current timestamp. Index items The “Create fixed” buttons will do most of the work of generating the single-­screen index items. Press “CLEAR ALL” if necessary to clear any existing entries. If you want the indices to start at a specific value, you can enter this in the “index” field. You should also set the “type” field to suit the scroll rate (or FIXED for non-­scrolling items), or click the button below it to view the options. Any animated or multi-screen items need to refer back to a single-screen item, so these items will need to be generated anyway. You should see the sample views at right populate when the “Create fixed” button is pressed, and you can scroll up and down through these with the “UP” and “DOWN” buttons. Dual-screen items can then be generated by setting the index, type and index 1 and index 2 values before pressing “Create #”. The index 1 and index 2 values can be entered manually or loaded by pressing the “<1” or “<2” buttons next to the desired images. For example, to generate an animation showing “ADELAIDE AIRPORT” over two screens, click the “1X MED” button until it shows one of the 2X types, then click “<1” next to “ADELAIDE” and “<2” next to “AIRPORT” at right. Finally, click “Create #31” to generate the item, which can be previewed by scrolling down the list at right. Triple screen items are created in a similar fashion by choosing one of the 3X types and ensuring that all three pointers are loaded correctly. Note that triple items can only use an index up to 31, since there are only 16 bits available for indexing. The index will increment after each item is created, so it is not hard to create several similar items. Screen 1: the Silicon Chip Destination Display Configuration sketch provides an easy way to generate the data file necessary to create custom displays and can mix and match different styles of animation. Australia's electronics magazine August 2026  57 Silicon Chip PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). Exporting Check that values such as the x, y, w, h, rotation (from Fig.1) and “bright.” (brightness from 0 to 255) values are correct. The scale values are ignored by the current version of the software, while the x bytes and pointer values are updated automatically. It’s easy to change any header data later using the ST25 NFC Tap app. Press “UPDATE DATA” to generate the dataset. The file size will be reported at the bottom of the column, so you can check that it will fit in IC2’s EEPROM. If all is well, press “SAVE DATA”, which will create a BIN file named for the current timestamp in the sketch directory. You can now transfer the file to your NFC device (such as an Android mobile phone with the ST25 NFC Tap app) to program the EEPROM chip on the Destination Display using the instructions in the main article. EEPROM capacity If you do wish to view or modify the exported file on your computer, we suggest using the HxD hex editor, which can be downloaded from https://mh-nexus.de/en/hxd Since the data is a monochrome, uncompressed bitmap, a byte of data can hold eight pixels. Our sample file is 3776 bytes, of which the headers are 192 bytes and the image EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 data is 3584 bytes, corresponding to a bitmap of 56 pixels by 512 pixels. This effectively contains 32 unique screens that each measure 56 × 16 pixels. The 0.50in panel has the most pixels, with 4224 pixels, requiring 528 bytes. The 8kiB ST25DV64KC can store 15 full-sized images to suit the 0.50in panel, with room to spare for 64 index items and the header. NFC chip To program the NFC chip, we strongly recommend ensuring the Destination Display is powered off, since the NFC chip cannot handle the EEPROM being accessed via both channels (I2C and NFC) at the same time. This will also ensure that the EEPROM data is properly reloaded after changes have been made. We used the ST25 NFC Tap mobile app on an Android device (siliconchip. au/link/ac38). There is also a version on the Apple App Store (siliconchip. au/link/ac39) but we have not tested it. Presumably, it works identically. We have created several data files so that you can perform this step without using the configuration program. These files are in the software download package (siliconchip.au/ Shop/6/3629). Although they may be suited to a specific display type, the ST25 NFC Tap App allows individual bytes to be edited, so parameters like the display orientation and size can be adjusted easily to suit different panels. One file has small bitmaps of the numbers from 000 to 255 with matching indexes, so this can be used to make a simple test that your control signals are working correctly. This is JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 JANUARY 2020 – DECEMBER 2024 OR PAY $650 FOR THEM ALL (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS 58 Silicon Chip Only three wires are required for the Destination Display: GND, 3.3V and the serial line for control. The μDCC decoder can supply enough current to run the Display. You can also use a USB/serial adaptor to control fixed Displays. Australia's electronics magazine siliconchip.com.au EEPROM data format While many of the details of the data format are not critical to use the Destination Display, some are worth knowing so you can tweak the data files to suit different displays or even to suit specific installations. For example, we envision that some uses of the Display will involve placing it behind a window cut out of a model so that only a small part of the Display is visible. Being able to make small adjustments to the location of the graphics within that window is handy and straightforward. The data file starts with a block of 16 bytes. After this, there are several four-byte index items, followed by the bitmap data. Organising the data in blocks of four bytes makes it easier to navigate in the ST25 NFC Tap App, since it displays the data in four-byte rows. The adjacent screen grab shows the start of a simple data file with four index items. The table directly below summarises the data structures. The first four bytes are simply a file type check, used to confirm that the EEPROM has been correctly loaded. The x and y fields determine the position of the top-left corner of the where the graphics are displayed. The w and h fields determine the extent of the area in which the graphics are displayed, while the orientation field is the value noted in Fig.1, where it indicates the corner that would be at upper left. The x-bytes field after that is used to know how many bytes of data to read for each row of pixels to be displayed. The y-pitch field is not used, although it should match the h field. Brightness is simply a raw value (0-255) that is written to the OLED controller’s brightness (or contrast) register. The bitmap pointer field holds the absolute address of the start of the bitmap data. It is a little-endian value (LE, the least significant byte is first), so the bytes “20 00” in the adjacent screen grab are read as the value 0x0020 or decimal 32. The first three index items (starting at addresses 16, 20 and 24) are single-screen types and will be activated with commands 0, 1 and 2 respectively (values in the first byte of each row). Their pointer fields (0x0000, 0x0010 and 0x0020) are offsets from the bitmap pointer field, so their bitmap data will be at decimal addresses 32, 48 and 64 respectively. The fourth index item (at address 28) responds to command 3 and is type 6, meaning there are two displays and they update every second. The pointers refer to item 0 and item 1. So it will alternate between displaying bitmap data from address 32 and address 48. The table at lower right shows the meaning of the other item types. Editing We mostly found ourselves changing the x, y and orientation fields to quickly modify a file to suit different displays. There would be little need to change the other parameters, although it’s easy enough to change the brightness if this is needed. Note from Fig.1 that the 0.32in panel uses different orientation values. This also encodes information to ensure that the data is ordered correctly for display. Values other than 1-8 are not valid and the display will not show any output if this is not observed. Data Format – 16-byte header You don’t need to know about the data format to use the Processing sketch, but it can help to understand how to make changes if things aren’t working as expected. Value Type description 0 (0x00) Null, used to mark an entry as invalid. 1 (0x01) Single display, slow scroll (7 lines/sec) 2 (0x02) Single display, scroll (10 lines/sec) 3 (0x03) Single display, fast scroll (20 lines/sec) 0x44 ‘D’ 0x45 ‘E’ 0x53 ‘S’ 0x54 ‘T’ 8-bit x-field 8-bit y-field 8-bit w-field 8-bit h-field 0x01 (unused) 0x01 (unused) 8-bit orientation 8-bit x-bytes field 4 (0x04) Single display, fixed 8-bit y-pitch field 8-bit brightness 16-bit (LE) bitmap pointer field 5 (0x05) Two displays alternating every 500ms 16-bit (LE) pointer field 6 (0x06) Two displays alternating every 1s 7 (0x07) Two displays alternating every 2s 8 (0x08) Three displays alternating every 500ms 9 (0x09) Three displays alternating every 1s 10 (0x0A) Three displays alternating every 2s One 4-byte single-screen item 8-bit entry 0x01-0x04 type One 4-byte double-screen item 8-bit entry 0x05-0x07 type 8-bit entry index 8-bit entry index One 4-byte triple-screen item 8-bit entry 0x08-0x0A type Three 5-bit entry indices padded with a leading zero. [0cccccbb bbbaaaaa] Bitmap data Each visible row of bitmap data consists of x-bytes count of bytes, with the left-most pixel being the MSB of the first byte. There should be h rows of bitmap data. siliconchip.com.au Australia's electronics magazine August 2026  59 Screen 2: choose the Memory tab from the main page of the ST25 NFC Tap app and use “Fill memory from file” to upload a data file. Screen 3: select the source file, ensure that the destination offset is zero and tap OK. It may take up to 10 seconds for the memory view to appear, confirming that the write has completed. Screen 4: the Read memory option allows the EEPROM on IC2 to be edited directly. Note that the displayed memory contents are in hexadecimal. the “256 Entries.bin” file. The screen seen in Photo 2 is one of these bitmaps. Open the ST25 NFC Tap App and place the device over the antenna. When the tag is detected, switch to the MEMORY tab (Screen 2) and select “Fill memory from file”. Select the source file and ensure that the Destination offset is zero. Press OK to transfer the file. This might take up to ten seconds, so wait until it completes and the memory contents are shown as in Screen 3. At this point, you can power up the Destination Display and see that it shows the screen that would be expected from index item zero. If you need to tweak the parameters, power off the Display and rescan the antenna with the App. From the MEMORY tab, choose the Read memory window. Press OK to perform a read and then hold your finger on a memory location to edit it; a row of four memory locations will pop up as seen in Screen 4. You can edit the values and then press Write bytes. The values are in hexadecimal, although they do not have a leading base marker like 0x or &H. The EEPROM data format panel has more detail about specific values that you might want to change. DCC PROJECT KITS DCC Destination Display (SC7697, $22.50) includes everything in the parts list, except for the screen (see below). The kit includes 1m of enamelled copper wire for the antenna 0.32in OLED Screen (SC7698, $5.00) 0.50in OLED Screen (SC7699, $6.50) 60 Silicon Chip Australia's electronics magazine Other uses While we intended this design to be used in model railways and the like, we think it could be useful anywhere that a small, simple display is needed. It can interface directly with a 3.3V device and only needs one signal wire. With the right bitmaps loaded, it could be used in much the same way as single-digit devices like Nixie tubes, although the control interface is quite different. Any device that needs a small status display could do so with an appropriately programmed Destination Display, providing dozens of different outputs (or more). These could include numbers, text, images, or anything else that can be encoded in SC a small bitmap. siliconchip.com.au