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Using Electronic Modules with Tim Blythman Large OLED Panels The displays that we describe in this article are similar to other OLED screens we have reviewed and used previously, although they are larger. Since bigger is usually better, we thought we ought to try them out. O ften we have used this style of OLED panel in projects because they are compact, use little power and allow both text and graphics to be displayed. They also have very high contrast. The 0.49in OLED module that graced the Audio DDS Oscillator exemplifies this (September 2020; siliconchip.au/Article/14563). The Oscillator generates an audio signal and shows its frequency on the OLED screen, while running from a pair of AAA cells, all in a unit less than 75mm long. Since then, we have produced numerous projects using OLED displays, including several Tweezers-style test instruments. Jim Rowe previously looked at different OLED variants in the October 2023 (siliconchip.au/Article/15980) and November 2024 (siliconchip.au/ Article/17027) issues. These modules often integrate a Solomon Systech SSD1306 or Sino Wealth SH1106 controller IC. They take control inputs over an I2C bus and drive the display matrix accordingly. Some readers would like to use larger versions of these display modules in our projects to provide a larger and more legible display. However, we know that the larger displays use a different controller IC, so they are unfortunately not a direct replacement. So, this article will investigate these displays and their differences from similar, smaller displays. We’ll also look at how easy it is to substitute them for the smaller displays, and what software changes are needed. The SSD1309 IC The larger units we tested all use the Solomon Systech SSD1309 controller IC. We have seen comments to the effect that the registers in the SSD1309 match those of the SSD1306, so it sounded quite possible that using these modules would be straightforward. Some of these large displays using the SSD1309 have a seven-pin header and are configured to use an SPI interface. With these modules being bigger, there is more space for the longer header. However, we’ve stuck to those that include an I2C interface, similar to the smaller units, and those we purchased specify a display size between 1.54in and 2.42in, equivalent to 39mm and 61mm. The previous, smaller displays vary from 0.91in to 1.3in (23-33mm). Table 1 summarises the modules we purchased and tested. Like TVs and mobile phones, the display size is measured diagonally, from lower left to top right. We’ve included sources Module name Display size OLED_M154_4P (Photos 1 & 2) 1.54in (36mm) (some local), but in most cases, searching for the controller name “SSD1309” is the easiest way to find similar products on websites like eBay and AliExpress. We have previously used a version of the 2.42in display in the Hot Water System Solar Diverter project from the June & July 2025 issues (siliconchip. au/Series/440). We found a comparison of some Solomon Systech OLED driver ICs (siliconchip.au/link/ac7s) and noted a handful of differences between the SSD1306 and SSD1309. They both offer control of a monochrome 128×64 pixel panel with 256 steps of contrast control. For a monochrome OLED panel, contrast is effectively the same as brightness. The SSD1309 can sink more common (ie, row) drive current from the display (40mA maximum vs 15mA for the SSD1306). The SSD1309 can also operate with a higher voltage, but does not incorporate an internal charge pump like the SSD1306. OLEDs typically require a higher voltage to work than conventional LEDs, hence the need for such circuitry. Circuit details Let’s look at the circuit of one of the modules, the Waveshare 2.42inch Module size Source Current draw all pixels off/on (full brightness) 43 × 38mm eBay 156327080574 2mA/285mA Core Electronics CE09964 2mA/237mA 2.42OLED-IIC (Photos 3 & 4) 2.42in (61.5mm) 70 × 48mm Waveshare 2.42inch OLED 2.42in (61.5mm) 62 × 40mm module (Photos 5 & 6) Core Electronics WS-25742 8mA/290mA Table 1 – Modules tested (names are as printed on the modules) 62 Silicon Chip Australia's electronics magazine siliconchip.com.au OLED Display Module, shown in Fig.1. The other modules differ in their exact circuitry, but this example is representative of the features that are present in all. This is the module that was used in the Hot Water System Solar Diverter project. The driver IC is present in a so-called COG (chip on glass) package that is bonded to a thin sheet of glass along with the actual OLED matrix. The connections between the driver IC and the OLED matrix are made on the glass using traces of ITO (indium tin oxide), a conductive material that is also transparent. The connections between the module PCB and driver IC are via a 26-way flat flexible cable, which is also attached to the glass. The 26-way connector is labelled OLED1 in the circuit diagram. U1 is an RT9193 3.3V low dropout (LDO) regulator that provides the 3.3V rail needed by the controller. This part can work with up to 5.5V on its input, so this circuitry allows the module to work with 5V microcontrollers. U2 is an AP3012 1.5MHz switching boost regulator with an external diode for asynchronous rectification. Its output divider sets its output to 12.5V, based on a 1.25V reference voltage at the FB pin. This circuitry replaces the integrated charge pump circuit used by modules based on the SSD1306. The data sheet for the SSD1306 indicates that the charge pump circuit can only generate up to 7.5V, so an external circuit is needed to generate the higher voltage needed for the larger panel. U3 is a TXB0108 automatic bi-­ directional level converter IC that interfaces between different logic levels. It too can work at up to 5.5V on its ‘B’ side, so it is also suitable for 5V microcontrollers. The other modules do not include a level-converter IC, but are permanently configured to use I2C communications. Since I2C is an open-drain bus, a 5V microcontroller will usually have no problem communicating with a 3.3V driver IC, as long as a 3.3V supply is present. Thus, the level converter is primarily needed to allow the module to use the SPI bus. The two 4.7kW resistors provide the pullups needed for an I2C bus. They are also connected in SPI mode, but will simply be overridden by the external microcontroller actively driving siliconchip.com.au Fig.1: the regulator and boost circuitry (U1 and U2) in this circuit diagram for the Waveshare 2.42in module is common to the units we tested, although the others lack the level conversion (U3) chip, so are set up for I2C comms by default. those pins. The 910kW resistor shown connected to the Iref pin sets the display drive current. The driver IC has pins BS0, BS1 and BS2 to set its communication mode. BS0 is pulled low by a connection internal to the COG assembly, while BS2 is pulled low on the module PCB. By default, BS1 is also pulled low and thus the module is configured for operation with a 4-wire SPI bus. J1 and J2 are 0W resistor links that can be moved to change how they are set. Both the SSD1306 and SSD1309 controllers can be set for I2C, 3-wire SPI and 4-wire SPI, as well as two parallel bus types, although not all module types will make the necessary pins available. Most of the monochrome OLED modules we have seen are fixed to I2C mode, with the exception of this Waveshare unit. JP1 is changed to set BS1 high and enable I2C mode, while J2 bridges two pins together in I2C mode; these need to be separate in SPI mode but connected in I2C mode. A copy of the SSD1309 data sheet can be downloaded from www.hpinfotech.ro/ SSD1309.pdf Variants Here is a brief overview of the different modules. For consistency, we Photos 1 & 2: the fivepin header seen here seems to be common to 1.54in variants of this module. It’s not much bigger than the 1.3in modules, but it can draw more current and is bright. Source: www.ebay.com.au/ itm/156327080574 Australia's electronics magazine November 2025  63 Photos 3 & 4: the generic 2.42in version of this module has a four-pin header that matches the smaller modules, while the blackened bezel improves the appearance and robustness of the unit. The locations marked D1 and D2 are fitted with 0W resistors, as required for correct I2C operation. Source: https://core-electronics. com.au/large-oled-i2c-display-ssd1309.html tested those mainly with a white light output, although we did try some other colours. Some have options for blue, green and yellow. The first is the 1.54in variant, as seen in Photos 1 & 2. It is the most similar to the 0.96in and 1.3in modules, and comes closest to being a ‘drop-in’ replacement. It has a five-pin header instead of a four-pin type, but the four GND, Vcc, SCL and SDA pins are centred at the top of the module in the same fashion as the smaller modules. The fifth pin is marked as RES (reset), and was not fitted with a pin in the samples we received. There is a jumper resistor on the rear of the PCB that can be used to set the I2C slave address. The default is 0x78, with the other option marked as 0x7A. These are 8-bit addresses that correspond to 7-bit addresses of 0x3C or 0x3D, respectively. All units we tried were set to the 0x78 address that we typically use. The units that we purchased were supplied with plug-socket jumper wires, which would be well-suited to experimenting with an Arduino board fitted with header sockets, such as an Arduino Uno or similar full-sized board. 2.42in module The generic 2.42in module (Photos 3 & 4) also has the familiar four-pin header at the top of the display, as well as on the left hand-side, which gives some flexibility for wiring. Using the top headers, it too can be simply plugged into the place of one of the smaller modules and has a jumper resistor that can be used to set the I2C slave address. There is a broad border with plated mounting holes. This unit also has a metal bezel covering the OLED glass assembly. As well as giving the unit a more finished appearance, it has the benefit of protecting the fragile glass. With any of these OLED modules, including the smaller types previously reviewed, when we have seen the glass cracked or damaged, it has usually resulted in the display failing, with pixels not illuminating, so this is a handy addition. We also tested a few variants of this display, since we found some available in different colours (see Photo 7). These behaved much the same as Photo 7: the green version of the generic 2.42in module is a striking colour that brings back memories of monochrome computer terminals from many years ago. It is a comfortable fit for the existing GPS Speedometer PCB. the display listed in Table 1, although they did need to have their D1 and D2 diodes replaced by 0W resistors, as seen in Photo 4. It appears that these diodes are provided to protect the display controller from incorrect voltages on the SDA and SCL lines. This should not be a concern if the correct (as required for I2C) open-drain outputs are used, even if the connected microcontroller operates at a different logic level. Without replacing at least diode D2 (on SDA), the display may not work, since the diode blocks the display controller’s acknowledgement of the microcontroller’s commands. Waveshare module The Waveshare module (Photos 5 & 6) has the same display dimensions as the generic part, but is more compact. The underlying PCB is barely larger than the glass assembly, and the unit is fitted with M2.5 standoffs soldered to the rear of the PCB instead of having plated holes. As noted earlier, this module can be set to work with either I2C or SPI. As well as a 0.1in (2.54mm) pitch header, there is a JST header on the board, and the module is supplied with a seven-way JST-to-socket jumper wire (‘DuPont connector’) breakout cable. The 0.1in header is mounted parallel to the PCB, unlike the other modules. Thus, this module is not really a drop-in replacement for the smaller OLED modules. There is no jumper resistor to set the I2C slave address, but it can be set with one of the other pins. The SSD1309 data sheet indicates that the DC pin is used to set the optional bit of the slave address, so it is simply necessary to tie this to either Vcc or ground. For our tests, we configured the module to use I2C mode and connected DC to ground, resulting in this module responding to address 0x78 as expected. Testing We started testing the generic 2.42in module, since we are accustomed to using these modules with an I2C bus. To test the claim that the registers in the SSD1309 match those of the Photos 5 & 6: the Waveshare 2.42in module has an SPI interface by default, but can be configured for I2C by moving two resistors. It is compact, but does not have a header that matches those commonly found on the smaller displays. Source: https://coreelectronics.com.au/242inch-oled-display-module-128x64px.html 64 Silicon Chip Australia's electronics magazine siliconchip.com.au SSD1306, we plugged one of the larger modules into the four-way header on one of our Coin Cell Emulator prototypes. Fortunately, all these modules use the same GND, Vcc, SCL, SDA pin order, although we have seen a handful that swap GND and Vcc! In a pleasant surprise, the display powered up and showed the expected display for the Coin Cell Emulator. This also means that the default I2C address is the same as for the smaller modules. A thorough inspection of the respective data sheets revealed a few registers that do behave differently, but it appears that the registers that we have used for much of our software are in fact identical, with the exception of the charge pump register, which is not present on the SSD1309. The data sheet notes that registers that are not present should not be written to, so the software does not strictly follow the constraints of the data sheet. However, the same code seems to work fine. It would not be difficult to make the necessary changes to fully comply with the data sheet. In all of our tests, we did not note any problems using software written for the SSD1306 with the SSD1309 controller. We also had an enquiry about fitting a larger display to the GPS FineSaver project from June 2019 (siliconchip. au/Article/11673). We had produced a simplified version of this in the July 2025 Circuit Notebook column as the GPS Speedometer (siliconchip.au/Article/18523). This version used a larger font to slightly increase the size of the displayed figures. So we also tried plugging these modules into the simplified PCB for the GPS Speedometer and found that both the 1.54in and 2.42in versions worked without changes to the software. Although we haven’t performed any long-term testing with this arrangement, we think this might be worth trying if you need a larger display for your GPS Speedometer. Photo 7 shows it with a 2.42in display fitted. Comments Versatile One thing that we noticed with the generic 2.42in module was that the switch-mode circuitry gave off an audible squeal, which became louder as more pixels were lit up and the load increased. It was clearly audible when all pixels were at full brightness, but was not as noticeable during more typical displays such as text, where a lesser fraction of the pixels were lit. This display also showed some artefacts, which appeared to be related to matrix scanning. For example, if a row of pixels was lit up, they appeared dimmer than adjacent pixels in rows that were not fully lit. In other words, the drive current seemed to be inconsistent; perhaps another shortcoming of the switchmode circuitry. We didn’t notice those sorts of effects with the other two displays. The current draw values shown in Table 1 tend to back this up and, not surprisingly, the 1.54in module looks more intense, since it draws similar current but has a smaller display area. The lower current draw of the generic 2.42in module suggests its output is sagging under load, and Battery Checker This tool lets you check the condition of most common batteries, such as Li-ion, LiPo, SLA, 9V batteries, AA, AAA, C & D cells; the list goes on. It’s simple to use – just connect the battery to the terminals and its details will be displayed on the OLED readout. Versatile Battery Checker Complete Kit (SC7465, $65+post) Includes all parts and the case required to build the Versatile Battery Checker, except the optional programming header, batteries and glue See the article in the May 2025 issue for more details: siliconchip.au/Article/18121 siliconchip.com.au Australia's electronics magazine November 2025  65 it does look distinctly dimmer when all pixels are lit. Photo 7 shows a green variant fitted to the GPS Speedometer PCB. The pixel dimming effect is most pronounced in views like this, where there are distinct horizontal elements. It is barely noticeable when the usual numeric display is showing. You might recall that some of our other projects using smaller OLED modules have a current draw of around 5-10mA, which is low enough to run from a coin cell. While the values given in Table 1 are with all pixels lit, we don’t think these large displays will be suitable for use with coin cells. The displays are at a size where the pixels are quite noticeable, around 0.3mm to 0.4mm across. Indeed, even the black borders between the pixels are apparent from a normal reading distance. It’s perhaps reminiscent of a vacuum fluorescent display (VFD), so might be handy if you are looking to create a retro appearance. Code examples We took the opportunity to write some code to test the modules. The latest versions of the Picomite BASIC software natively support I2C OLED panels, so it was easy to use a Pico for our tests. The Pico can also be programmed using the Arduino IDE. All of our examples (both Picomite BASIC and Arduino) use the same wiring diagram shown in Fig.2. We used the PicoMiteRP2040V6.00.03.UF2 variant of the firmware, although it should work with any version that supports an external display panel (ie, all but the HDMI or VGA capable versions). These two OPTIONs set up the display panel: OPTION SYSTEM I2C GP0,GP1 OPTION LCDPANEL SSD1306I2C,LANDSCAPE The OLED_DEMO.BAS file runs through a few demonstrations, including text in a variety of fonts and some shapes. It also shows a spinning cube, making use of the 3D engine that is included with Picomite BASIC. You can also try loading the OLED_ DEMO.uf2 directly onto a Pico. We were able to test the current draw by using the CLS 0 and CLS 1 commands to turn all pixels off or on once the display was configured. Arduino For the Arduino IDE, we used version 2.35.30 of the u8g2 library (https:// Fig.2: this wiring diagram can be used for either a Pico or Pico 2 microcontroller, although we only tested a Pico with our code examples. Other boards based on RP2xxx processors should also work when GP0 is connected to SDA and GP1 to SCL. 66 Silicon Chip Australia's electronics magazine github.com/olikraus/u8g2). It can also be installed by searching for “u8g2” in the Library Manager. The sketch we have written is based on the GraphicsTest.ino demo example from the u8g2 library. It shows a different set of animations. We have included the requisite constructor for an SSD1309 controller connected to I2C0 on pins 0 and 1, using the same wiring as the Pico­ mite example. The demo code shows several different drawing, text and animation examples. The sketch, library and a compiled UF2 file can be found in the Arduino folder of the software downloads (siliconchip.com.au/Shop/6/3563). Summary While there is a lot of similarity with smaller OLED modules, these larger parts have a few subtle differences from the smaller OLED modules that mean that they may not be a drop-in replacement. Their larger size means a higher current draw, so they will not be suitable for many battery-powered applications. In cases where power is not an issue, they could work well. The GPS FineSaver is a good example, where the car’s accessory socket can provide ample power and the larger display will be useful, although the higher current draw might be troublesome for the linear regulator on that project. Thus, we suggest using the 5V USB power input. Their larger size may make them more delicate and susceptible to damage. It is a pity that the generic 2.42in module seems to have inferior power circuitry, since the metal bezel protecting the glass looks to be a useful and elegant addition. Some models may need minor modifications to work correctly. The 2.42in versions of the OLED are almost as large as some LCD touch panel modules; we have used 2.8in versions of these LCD panels in numerous projects. The LCD panels typically have a touch sensor and 16-bit colour, so are quite a bit more versatile. Searching for the controller name (SSD1309) at online sellers seems to be the best way to find these and similar modules; the sources of the modules we tested can also be found in Table 1. Note that there are also some SPI versions of SSD1309-based display SC modules available. siliconchip.com.au