ATmega8 SHT71 Temperature Humidity and Dew point example

ATmega8 SHT71 Temperature Humidity and Dew point examplehttp://www.electronics-base.com/projects/complete-projects/152-atmega8-sht71-temperature-humidity-and-dew-point-example\Published on Monday, 19 March 2012 20:54|Written by Super User| Hits: 4918

In this article is provided 100% tested and working C code for AVR readout of SHT71 Temperature, Humidity and Dew point. Code itself is well commented and is easy to understand if combined withSHT71 Humidity and Temperature Sensor IC article.DATA pin is connected to Port C pin 0.SCK pin is connected to Port C pin 1.Pull-up resistor must be placed on DATA pin. Pull-up resistor of 10k to +5V is used in this example.Be careful that if you use Port C for other things lines that change its direction will change it. For example?1DDRC = 0b00000011; //

If this is the case just change only bits for selected pins for DATA and SCK.Complete project written in Codevision AVR C compiler written for ATmega8 can be downloaded from this link. Complete code is provided below this text and video showing demonstration of this code in action can be found at the bottom of this page. Data is read from serial port by com port terminal - development tool.?1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369/*****************************************************Complete example with more comments and further support can be found at www.Electronics-Base.com under complete projects sectionDate : 3/19/2012Author : www.Electronics-Base.comChip type : ATmega8Program type : ApplicationAVR Core Clock frequency: 8.000000 MHzMemory model : SmallExternal RAM size : 0Data Stack size : 256www.Electronics-Base.com*****************************************************/#include // Standard Input/Output functions#include //must be included to use delay functions#include //must be included to use itoa ftoa functions#include //must be included to use log10 functions#include

typedef union{ unsigned int i;float f;} value;enum {TEMP,HUMI};#define DATA_OUT PORTC.0#define DATA_IN PINC.0#define SCK PORTC.1 #define noACK 0#define ACK 1 //adr command r/w#define STATUS_REG_W 0x06 //000 0011 0#define STATUS_REG_R 0x07 //000 0011 1#define MEASURE_TEMP 0x03 //000 0001 1#define MEASURE_HUMI 0x05 //000 0010 1#define RESET 0x1e //000 1111 0// Declare your global variables hereunsigned int tempervalue[2]={0,0};/***********************************/char SHT_WriteByte(unsigned char bytte){ unsigned char i,error=0; DDRC = 0b00000011; // for (i=0x80;i>0;i/=2) //shift bit for masking{ if (i & bytte) DATA_OUT=1; //masking value with i , write to SENSI-BUSelse DATA_OUT=0; SCK=1; //clk for SENSI-BUSdelay_us(5); //pulswith approx. 5 us SCK=0; }DATA_OUT=1; //release dataline DDRC = 0b00000010; // DATA is OutputSCK=1; //clk #9 for ack delay_us(2);error=DATA_IN; //check ack (DATA will be pulled down by SHT11)delay_us(2);SCK=0; return error; //error=1 in case of no acknowledge}//----------------------------------------------------------------------------------// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1" //----------------------------------------------------------------------------------char SHT_ReadByte(unsigned char ack){ unsigned char i,val=0;DDRC = 0b00000010; // DATA is Inputfor (i=0x80;i>0;i/=2) //shift bit for masking{ SCK=1; //clk for SENSI-BUS delay_us(2);if (DATA_IN) val=(val | i); //read bit delay_us(2);SCK=0;} DDRC = 0b00000011; // DATA is OutputDATA_OUT=!ack; //in case of "ack==1" pull down DATA-Line SCK=1; //clk #9 for ackdelay_us(5); //pulswith approx. 5 us SCK=0;DATA_OUT=1; //release DATA-line //ADD BY LUBING return val;} //----------------------------------------------------------------------------------// generates a transmission start // _____ ________// DATA: |_______|// ___ ___// SCK : ___| |___| |______//----------------------------------------------------------------------------------void SHT_Transstart(void){ DDRC = 0b00000011; // DATA is OutputDATA_OUT=1; SCK=0; //Initial statedelay_us(2);SCK=1;delay_us(2);DATA_OUT=0;delay_us(2);SCK=0; delay_us(5);SCK=1;delay_us(2);DATA_OUT=1; delay_us(2);SCK=0; DDRC = 0b00000010; // DATA is Input} //----------------------------------------------------------------------------------// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart// _____________________________________________________ ________// DATA: |_______|// _ _ _ _ _ _ _ _ _ ___ ___// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______//----------------------------------------------------------------------------------void SHT_ConnectionRest(void){ unsigned char i; DDRC = 0b00000011; // DATA is outputDATA_OUT=1; SCK=0; //Initial statefor(i=0;i=1 in case of no response form the sensor} //----------------------------------------------------------------------------------// makes a measurement (humidity/temperature) with checksum//----------------------------------------------------------------------------------char SHT_Measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode){ unsigned error=0;unsigned int temp=0;SHT_Transstart(); //transmission start switch(mode){ //send command to sensorcase TEMP : error+=SHT_WriteByte(MEASURE_TEMP); break;case HUMI : error+=SHT_WriteByte(MEASURE_HUMI); break;default : break; } DDRC = 0b00000010; // DATA is inputwhile (1){ if(DATA_IN==0) break; //wait until sensor has finished the measurement} if(DATA_IN) error+=1; // or timeout (~2 sec.) is reached switch(mode){ //send command to sensorcase TEMP : temp=0;temp=SHT_ReadByte(ACK);temp