QRCode

A simple library for generating QR codes in C, optimized for processing and memory constrained systems.

Features:

• Stack-based (no heap necessary; but you can use heap if you want)
• Low-memory foot print (relatively)
• Compile-time stripping of unecessary logic and constants
• MIT License; do with this as you please

Installing

To install this library, download and save it to your Arduino libraries directory.

Rename the directory to QRCode (if downloaded from GitHub, the filename may be qrcode-master; library names may not contain the hyphen, so it must be renamed)

API

Generate a QR Code

// The structure to manage the QR code
QRCode qrcode;

// Allocate a chunk of memory to store the QR code
uint8_t qrcodeBytes[qrcode_getBufferSize()];

qrcode_initText(&qrcode, qrcodeBytes, 3, ECC_LOW, "HELLO WORLD");

Draw a QR Code

How a QR code is used will vary greatly from project to project. For example:

• Display on an OLED screen (128x64 nicely supports 2 side-by-side version 3 QR codes)
• Print as a bitmap on a thermal printer
• Store as a BMP (or with a some extra work, possibly a PNG) on an SD card

The following example prints a QR code to the Serial Monitor (it likely will not be scannable, but is just for demonstration purposes).

for (uint8 y = 0; y < qrcode.size; y++) {
    for (uint8 x = 0; x < qrcode.size; x++) {
        if (qrcode_getModule(&qrcode, x, y) {
            Serial.print("**");
        } else {
            Serial.print("  ");
        }
    }
    Serial.print("\n");
}

What is Version, Error Correction and Mode?

A QR code is composed of many little squares, called modules, which represent encoded data, with additional error correction (allowing partially damaged QR codes to still be read).

The version of a QR code is a number between 1 and 40 (inclusive), which indicates the size of the QR code. The width and height of a QR code are always equal (it is square) and are equal to 4 * version + 17.

The level of error correction is a number between 0 and 3 (inclusive), or can be one of the symbolic names ECC_LOW, ECC_MEDIUM, ECC_QUARTILE and ECC_HIGH. Higher levels of error correction sacrifice data capacity, but allow a larger portion of the QR code to be damaged or unreadable.

The mode of a QR code is determined by the data being encoded. Each mode is encoded internally using a compact representation, so lower modes can contain more data.

• NUMERIC: numbers (0-9)
• ALPHANUMERIC: uppercase letters (A-Z), numbers (0-9), the space ( ), dollar sign ($), percent sign (%), asterisk (*), plus (+), minus (-), decimal point (.), slash (/) and colon (:).
• BYTE: any character

Data Capacities

Version	Size	Error Correction	Mode
			Numeric	Alphanumeric	Byte
1	21 x 21	LOW	41	25	17
		MEDIUM	34	20	14
		QUARTILE	27	16	11
		HIGH	17	10	7
2	25 x 25	LOW	77	47	32
		MEDIUM	63	38	26
		QUARTILE	48	29	20
		HIGH	34	20	14
3	29 x 29	LOW	127	77	53
		MEDIUM	101	61	42
		QUARTILE	77	47	32
		HIGH	58	35	24
4	33 x 33	LOW	187	114	78
		MEDIUM	149	90	62
		QUARTILE	111	67	46
		HIGH	82	50	34
5	37 x 37	LOW	255	154	106
		MEDIUM	202	122	84
		QUARTILE	144	87	60
		HIGH	106	64	44
6	41 x 41	LOW	322	195	134
		MEDIUM	255	154	106
		QUARTILE	178	108	74
		HIGH	139	84	58
7	45 x 45	LOW	370	224	154
		MEDIUM	293	178	122
		QUARTILE	207	125	86
		HIGH	154	93	64
8	49 x 49	LOW	461	279	192
		MEDIUM	365	221	152
		QUARTILE	259	157	108
		HIGH	202	122	84
9	53 x 53	LOW	552	335	230
		MEDIUM	432	262	180
		QUARTILE	312	189	130
		HIGH	235	143	98
10	57 x 57	LOW	652	395	271
		MEDIUM	513	311	213
		QUARTILE	364	221	151
		HIGH	288	174	119
11	61 x 61	LOW	772	468	321
		MEDIUM	604	366	251
		QUARTILE	427	259	177
		HIGH	331	200	137
12	65 x 65	LOW	883	535	367
		MEDIUM	691	419	287
		QUARTILE	489	296	203
		HIGH	374	227	155
13	69 x 69	LOW	1022	619	425
		MEDIUM	796	483	331
		QUARTILE	580	352	241
		HIGH	427	259	177
14	73 x 73	LOW	1101	667	458
		MEDIUM	871	528	362
		QUARTILE	621	376	258
		HIGH	468	283	194
15	77 x 77	LOW	1250	758	520
		MEDIUM	991	600	412
		QUARTILE	703	426	292
		HIGH	530	321	220
16	81 x 81	LOW	1408	854	586
		MEDIUM	1082	656	450
		QUARTILE	775	470	322
		HIGH	602	365	250
17	85 x 85	LOW	1548	938	644
		MEDIUM	1212	734	504
		QUARTILE	876	531	364
		HIGH	674	408	280
18	89 x 89	LOW	1725	1046	718
		MEDIUM	1346	816	560
		QUARTILE	948	574	394
		HIGH	746	452	310
19	93 x 93	LOW	1903	1153	792
		MEDIUM	1500	909	624
		QUARTILE	1063	644	442
		HIGH	813	493	338
20	97 x 97	LOW	2061	1249	858
		MEDIUM	1600	970	666
		QUARTILE	1159	702	482
		HIGH	919	557	382
21	101 x 101	LOW	2232	1352	929
		MEDIUM	1708	1035	711
		QUARTILE	1224	742	509
		HIGH	969	587	403
22	105 x 105	LOW	2409	1460	1003
		MEDIUM	1872	1134	779
		QUARTILE	1358	823	565
		HIGH	1056	640	439
23	109 x 109	LOW	2620	1588	1091
		MEDIUM	2059	1248	857
		QUARTILE	1468	890	611
		HIGH	1108	672	461
24	113 x 113	LOW	2812	1704	1171
		MEDIUM	2188	1326	911
		QUARTILE	1588	963	661
		HIGH	1228	744	511
25	117 x 117	LOW	3057	1853	1273
		MEDIUM	2395	1451	997
		QUARTILE	1718	1041	715
		HIGH	1286	779	535
26	121 x 121	LOW	3283	1990	1367
		MEDIUM	2544	1542	1059
		QUARTILE	1804	1094	751
		HIGH	1425	864	593
27	125 x 125	LOW	3517	2132	1465
		MEDIUM	2701	1637	1125
		QUARTILE	1933	1172	805
		HIGH	1501	910	625
28	129 x 129	LOW	3669	2223	1528
		MEDIUM	2857	1732	1190
		QUARTILE	2085	1263	868
		HIGH	1581	958	658
29	133 x 133	LOW	3909	2369	1628
		MEDIUM	3035	1839	1264
		QUARTILE	2181	1322	908
		HIGH	1677	1016	698
30	137 x 137	LOW	4158	2520	1732
		MEDIUM	3289	1994	1370
		QUARTILE	2358	1429	982
		HIGH	1782	1080	742
31	141 x 141	LOW	4417	2677	1840
		MEDIUM	3486	2113	1452
		QUARTILE	2473	1499	1030
		HIGH	1897	1150	790
32	145 x 145	LOW	4686	2840	1952
		MEDIUM	3693	2238	1538
		QUARTILE	2670	1618	1112
		HIGH	2022	1226	842
33	149 x 149	LOW	4965	3009	2068
		MEDIUM	3909	2369	1628
		QUARTILE	2805	1700	1168
		HIGH	2157	1307	898
34	153 x 153	LOW	5253	3183	2188
		MEDIUM	4134	2506	1722
		QUARTILE	2949	1787	1228
		HIGH	2301	1394	958
35	157 x 157	LOW	5529	3351	2303
		MEDIUM	4343	2632	1809
		QUARTILE	3081	1867	1283
		HIGH	2361	1431	983
36	161 x 161	LOW	5836	3537	2431
		MEDIUM	4588	2780	1911
		QUARTILE	3244	1966	1351
		HIGH	2524	1530	1051
37	165 x 165	LOW	6153	3729	2563
		MEDIUM	4775	2894	1989
		QUARTILE	3417	2071	1423
		HIGH	2625	1591	1093
38	169 x 169	LOW	6479	3927	2699
		MEDIUM	5039	3054	2099
		QUARTILE	3599	2181	1499
		HIGH	2735	1658	1139
39	173 x 173	LOW	6743	4087	2809
		MEDIUM	5313	3220	2213
		QUARTILE	3791	2298	1579
		HIGH	2927	1774	1219
40	177 x 177	LOW	7089	4296	2953
		MEDIUM	5596	3391	2331
		QUARTILE	3993	2420	1663
		HIGH	3057	1852	1273

Special Thanks

A HUGE thank you to Project Nayuki for the QR code C++ library which was critical in development of this library.

License

MIT License.