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Using Electronic Modules with Tim Blythman GM805 Barcode Reader We recently reviewed the Tiny QR Code Reader module and lamented that it did not support linear barcodes. We have since found a module that fills this gap and can do a lot more, including reading QR codes and other types of 2D codes. W e reviewed the Tiny QR Code Reader in the February 2026 issue (siliconchip.au/Article/19663) and it definitely lived up to its name. It was tiny (just 19 × 16mm) and had no trouble reading QR codes. Since linear (1D) barcodes have been around a lot longer, we wondered if that device could read other types of 1D and 2D codes, but it appears that it could only handle QR codes specifically. While QR codes are great at packing in lots of information, simple codes still abound; UPC (universal product code) and EAN (European article number) barcodes are still used on products in stores. There are many other types of linear codes that are used for other purposes, such as tracking numbers on parcels (Australia Post uses both linear and 2D codes extensively). We searched the usual online stores to see what features could be found in a barcode reader, especially one that would be easy to interface with and use, as well as being compact. We settled on a unit dubbed GM805 on AliExpress, mostly because it appeared to be well-documented. You can find it on sites like AliExpress or eBay by searching for “GM805”. It is made by the Hangzhou Grow Technology Company Ltd (www. growscanning.com). They also have several other scanners, including some with more consumer-oriented enclosures. The GM805 manual can be downloaded from siliconchip.au/ link/acbl 70 Silicon Chip The GM805 module The GM805 features UART (asynchronous serial) and USB interfaces, which are quite different from the I2C interface on the Tiny QR Code Reader. There are GM805-S and GM805-L variants that differ only in their specified reading distances. We tried the GM805-L, which is claimed to work between 7cm and 50cm, as it is the closer match of the two for the Tiny QR Code Reader. We paid around AU$45 for two units, including shipping. It measures 28 × 21 × 10mm, supplied with two six-way 1.27mm pitch pin headers and a six-way socket fitted. A matching plug with flying leads is also included. The socket breaks out 5V power connections and two lines each for the USB and UART interfaces. The UART interface uses a 3.3V logic level. One of the six-pin headers has the same pinout as the six-way socket, while the other is marked with signals for the LEDs, BEEP and trigger functions. Our photos show the module. It is supplied as an assembled PCB with two mounting holes in opposite corners. The front has two LEDs and a camera, while the rear has a processor and related components. There is also a piezo sounder at the rear. The shape and layout of the module make it quite easy to fit into custom project designs. Fig.1: this wiring connects the GM805 to one of our USB-C Serial Adaptors (June 2024; siliconchip.au/ Article/16291), which has the same pinout as some CP2102 adaptors. The Scanner takes a 5V supply but works with 3.3V logic levels. Note that the ground wire is white, not black! Australia's electronics magazine siliconchip.com.au Perhaps unsurprisingly, the main processor chip had its identifying features removed. It had a rectangular area laser-etched out of the back of it, with the pin 1 identifier barely visible. The manual is quite detailed and is scattered with QR codes. It turns out that the easiest way to configure the GM805 is by scanning codes! We wired up the UART pins to a USB-­serial converter and scanned the “Serial Output” code; immediately, the scanner was able to send codes over the serial port to a terminal application. Fig.1 shows the wiring for serial operation. It appeared to simply work with a default baud rate of 9600. This and other settings can be changed via the UART interface (or QR codes), although we did not need to use that option. The GM805 uses a white LED for illumination, which is automatically controlled. A blue LED flashes and the piezo sounder beeps when a code is detected. The white LED and sounder can be disabled with other QR codes; it’s also possible to force the white LED to be on at all times. USB interface The UART interface makes it trivial to interface with a microcontroller, but the GM805 also provides a USB interface; in fact, several of them. One of these is to emulate a keyboard, since this is one of the easiest ways to get data into a computer. Fig.2 shows the wiring we used to connect it to a USB-C breakout board for all the USB interfaces. Fig.3: compared to the Tiny QR Code Reader, the GM805-L has a generally wider and longer operating span, although it was not as good up close. If shortrange operation is needed, there is also the GM805-S variant. Some of the earlier instances of barcode scanners being used with computers used a so-called ‘keyboard wedge’ (KBW) arrangement, where a splitter cable ‘wedged’ the scanner into the PS/2 keyboard interface, and the scanned codes appeared as if keys were being typed on the keyboard. One of the GM805’s interfaces is as a USB keyboard; this is the HID-KBW mode noted in the manual. Many smartphones also allow the connection of a USB keyboard, so this could be used for data entry in a mobile system. It could even be used with one of the PicoMite (February 2025; siliconchip.au/Article/17729) variants that support a USB keyboard. Screen 1 shows an Android phone connected to the GM805. While simple and effective, the HIDKBW mode can be troublesome. If, for example, the wrong program has focus, the scanned codes can cause havoc (ask me how I know!). There is also a USB HID-POS mode, which is intended to communicate directly with POS (point of sale) software. HID-POS also allows bidirectional communication, including from the computer to the scanner. We tried some HID-POS test software to try to communicate with the GM805, but were not able to get it to work. The USB vendor ID (VID) for the GM805 is 0x002C, which we could not find in any VID lists. Its product ID (PID) changes depending on the mode; the HID-KBW mode uses PID 0x261A, while HID-POS mode uses 0x0300. The USB interface can also behave as a virtual USB-serial adaptor, which appears as PID 0x0302. This mode is activated by another QR code, and we found that this worked seamlessly with the TeraTerm terminal program. Working range The manual suggests a working range for the GM805-L of 7-50cm. As we found for the Tiny QR Code Reader, the usable range can depend on the printed size of the code. We tried numerous EAN-13 codes from typical supermarket products and could not read these from more than 25cm away. However, we were able to successfully read such codes from as close as 5cm. Fig.2: this shows the wiring we used for a USB-C socket breakout, including the 5.1kW CC resistors (required for a USB-C to USB-C connection at 5V). If you are using a USB-A or USB-B connector, the four wires would be connected as you might expect. The wire colours here match those found on the breakout leads that were supplied with the readers. Screen 1: the USB-KBW interface is even recognised by Android phones. Australia's electronics magazine August 2026  71 For a comparative test, we used the same printed 62mm QR codes that we used for the Tiny QR Code Reader article and also turned off the illumination LED. The results are shown in a similar fashion in Fig.3. For these specific QR codes, it appears that the GM805 has a wider view and longer range, although it does not do so well at short distances; not surprising for the longer-­ range variant. The spans correspond to wider viewing angles as well. As expected, the actual performance depends a lot on the size of the code being scanned and how it fits in the field of view, combined with the limitations of the focus and camera resolution. The camera sensor in the GM805 is quoted as 640×480 pixels. The GM805 (shown at actual size) is well laid out, with the camera and LEDs on one side and the connectors and remaining components on the rear. Note that the GM805 has at least two variants. The GM805-S (shown in the centre) has a slightly smaller reading distance of 5-30cm, versus the one we used with a reading distance of 7-50cm (-L model; right). The GM805 manual states a maximum operating current of 70mA. In practice, we found that was a typical value with the default settings and with neither LED lit. The white LED drew about 20mA when lit, and the blue LED about 10mA. So we suggest that you should budget at least 100mA for the module. stuck with the defaults, which seemed to work on all the common types of barcodes and QR codes we came across. There are also settings to add prefixes and suffixes to scanned codes, which could be handy if you need to automate an existing system. And of course, there is a code that can be used to reload the defaults. The default settings appeared to be capable of about three scans per second (of our test QR codes), but there are various timeouts, delays and sensitivity settings that can change that. Options Summary There are many options that can be selected by means of QR codes; we counted hundreds of configuration codes in the manual. Apart from the main modes noted earlier, it’s possible to set the reader to require triggering before producing a code; presumably, this is provided via the TRIG input pin. There are also settings to determine the fraction of the camera’s view that can be used for scanning. In other words, it’s possible to set a narrower field of view than noted above. The codes that are produced can be selected by symbology, and many code types have other specific settings. Thus, it is possible to only allow specific types, which might be helpful depending on your application. There is a setting to allow all codes, which would be good for experimenting with the GM805’s abilities. There is also a setting to allow no code types, which then allows just configuration codes to be read. If you needed to limit the reader’s output to just one code type, you could scan this ‘forbid all’ setting and then add just the codes you wanted to accept. We just The GM805 is a very versatile and flexible reader that can handle both QR codes and 1D/2D barcodes. It has numerous interfaces that allow it to easily connect to a microcontroller or a computer. Its mechanical design should also make it easy to incorporate into a larger project. Importantly, it was very easy to get working. The GM805’s scanning performance and versatility are easily better than the Tiny QR Code Reader. It has an inbuilt illumination LED and can be programmed in more ways than we could easily test. Still, the Tiny QR Code Reader is smaller, uses less power and defaults to a higher scan rate. With all this in mind, we would probably tend to favour the GM805 in a project unless size or power was a critical factor in the project’s design. Having reviewed the GM805 module, let’s now investigate the properties of barcodes themselves. Power consumption 72 Silicon Chip Linear (1D) barcodes We covered QR codes in the previous article about the Tiny QR Code Australia's electronics magazine Reader module. Here, we’ll explain some of the history and technology of linear barcodes. Barcodes were inspired by the pattern of long and short pulses used in Morse code. The first barcode system was patented in the USA in 1952. During the 1960s, projects and standards were developed to use coloured barcodes to identify railway rolling stock, such as freight cars, but the system was abandoned because it was not reliable, depending on older technology such as valves and photomultiplier tubes. Advances in computer and laser technology set the scene for its widespread use for product identification in the 1970s. It is on supermarket products that barcodes ultimately succeeded. These are known as UPC (Universal Product Code) barcodes. Other places they are widely used include being printed on letters, parcels and tickets. Just about any situation where an item needs to be identified by a machine could potentially use a barcode. Structure The connection between Morse code and a barcode can be easily seen if you take a visual snippet of Morse code and stretch it out vertically, as in Fig.4. In practice, different encodings are used, since Morse code is intended to be interpreted by a human, while barcodes are designed to be machine readable. Fig.4 shows how the ‘stretching’ of the bars and spaces allows for better Fig.4: a simple barcode can be generated from a printed Morse code message, but most modern barcodes have features that make them better for machine reading. siliconchip.com.au tolerance in reading the barcode. The red lines show that the reader only needs to scan along a single line through the code. Even if that path is not exactly at right angles to the bars and spaces, the relative spacings of the various zones remain the same. The so-called quiet zone is an area with no features that allows the hardware to distinguish the start and end of a valid code from other noise. While the characters in Morse code have varying lengths, most barcodes use a fixed width per symbol. Early patents also suggested that a circular arrangement (looking somewhat like a bullseye) might be preferred. In hindsight, the need to accurately scan through the middle of the bullseye meant that this layout did not succeed (see US patent 2612994A). Symbologies As the QR code is just one type of 2D code, there are numerous types of linear barcodes using different symbologies or encodings. A typical encoding has a fixed width per character and also a fixed number of bars and spaces. This means that it is very easy for a reader to keep track of its position within the code; the code is self-clocking. QR codes use a masking step to try to achieve a balance between light and dark areas over their surface. Similarly, most barcodes are designed to have an equal amount of bar and space, since this provides the best chance for code recovery. The lack of a masking step makes barcodes simpler to decode. You can imagine that these factors severely limit the number of combinations that are valid within a given symbology. We’ll look at the EAN-13 (European Article Number) symbology, which is used for the 13-digit barcodes commonly found on products, including this magazine. So-called UPC-A is very similar. EAN-13 The 13 individual digits of an EAN13 barcode are encoded by a sequence of seven units of width, making up two bars and two spaces; this gives a total of 40 symbols. Twenty start with a bar and twenty start with a space, so there are really only 20 usable symbols, since they must all be the same type to be processed consecutively. EAN-13 encodes 12 of its digits using this scheme. It also adds a start marker, a centre marker and an end marker. On one side of the centre, the symbols start with a bar, and on the other, they start with a space. Since the 20 symbols are only used to encode the 10 digits, zero to nine, two groups of codes exist, and they can provide an extra layer of information and redundancy. Firstly, the codes can be used to determine whether the barcode is being read from right-to-left or left-toright. The choice of code groups in one half of the barcode is used to encode the thirteenth digit. You might also see that most barcodes have a human-readable version printed underneath. This allows the code to be manually entered if the scan fails for whatever reason. One of the thirteen digits is designated as a checksum; since this is also one of the printed numbers, both scanned and manually entered codes can be verified. Fig.5 shows a breakdown of a typical EAN-13 barcode. Other types Fig.5: the start, centre and end markers of a typical EAN-13 barcode. The red lines show how the scanner can use the centre marker to decode it even if the scan does not cover the entire barcode in one pass. Source: https://w.wiki/8WbT siliconchip.com.au You can see that a typical example of a modern barcode actually has numerous layers to store, encode and verify the information that is held. EAN-13 is just one example; there are other types that can have a variable length and can encode other data, such as ASCII text. Code 128 is one such type; there are many other types for differSC ent applications. Australia's electronics magazine Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 August 2026  73