{"id":2014,"date":"2015-01-23T20:45:37","date_gmt":"2015-01-23T20:45:37","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=2014"},"modified":"2015-03-06T04:38:51","modified_gmt":"2015-03-06T04:38:51","slug":"esp8266-analogue-input","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2015\/01\/esp8266-analogue-input\/","title":{"rendered":"esp8266 analogue input"},"content":{"rendered":"

\"esp1_analogue\"<\/a><\/p>\n

The esp8266 contains a 10bit ADC. There are apparently various issues, including instability when transmitting over Wifi, and the lack of a voltage reference. However it is usable. The analogue input is labeled “tout” on the pinout below:<\/p>\n

\"esp8266_pinout\"<\/a><\/p>\n

Unfortunately this isn’t broken out on the cheapest esp8266 boards (the esp1) but it’s possible to get access to it with some wirewrap wire and careful soldering (see image above).<\/p>\n

The ADC input can then be read using some relatively simple C code as shown below. This code was adapted from an old version of the SDK (it doesn’t seem to be present in the current version).<\/p>\n

I’ve also attached a complete working example that uses the function below: adc_test.tar<\/a><\/p>\n

\r\nuint16 ICACHE_FLASH_ATTR adc_read(void) {\r\n  uint8 i;\r\n  uint16 sar_dout, tout, sardata[8];\r\n\r\n  rom_i2c_writeReg_Mask(0x6C,2,0,5,5,1);\r\n\r\n  \/\/ disable interrupts?\r\n  SET_PERI_REG_MASK(0x60000D5C, 0x200000);\r\n  while (GET_PERI_REG_BITS(0x60000D50, 26, 24) > 0); \/\/wait r_state == 0\r\n  sar_dout = 0;\r\n  CLEAR_PERI_REG_MASK(0x60000D50, 0x02); \/\/force_en=0\r\n  SET_PERI_REG_MASK(0x60000D50, 0x02); \/\/force_en=1\r\n\r\n  os_delay_us(2);\r\n  while (GET_PERI_REG_BITS(0x60000D50, 26, 24) > 0); \/\/wait r_state == 0\r\n  read_sar_dout(sardata);\r\n\r\n  \/\/ Could this be averaging 8 readings? If anyone has any info please comment.\r\n  for (i = 0; i < 8; i++) {\r\n    sar_dout += sardata[i];\r\n  }\r\n  tout = (sar_dout + 8) >> 4; \/\/tout is 10 bits fraction\r\n\r\n  \/\/ I assume this code re-enables interrupts\r\n  rom_i2c_writeReg_Mask(0x6C,2,0,5,5,1);\r\n  while (GET_PERI_REG_BITS(0x60000D50, 26, 24) > 0); \/\/wait r_state == 0\r\n  CLEAR_PERI_REG_MASK(0x60000D5C, 0x200000);\r\n  SET_PERI_REG_MASK(0x60000D60, 0x1); \/\/force_en=1\r\n  CLEAR_PERI_REG_MASK(0x60000D60, 0x1); \/\/force_en=1\r\n  return tout; \/\/tout is 10 bits fraction\r\n}\r\n<\/pre>\n
UPDATE: There’s also a system_adc_read function in the library symbols, I’ve not used it but it could be worth looking at.<\/p>\n
<\/p>\n
This is a continuation of my notes on the esp8266 microcontroller, you can find a complete list of my esp8266 posts here<\/a><\/h4>\n","protected":false},"excerpt":{"rendered":"
The esp8266 contains a 10bit ADC. There are apparently various issues, including instability when transmitting over Wifi, and the lack of a voltage reference. However it is usable. The analogue input is labeled “tout” on the pinout below: Unfortunately this isn’t broken out on the cheapest esp8266 boards (the esp1) but it’s possible to get […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-2014","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1RRoU-wu","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2014","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/comments?post=2014"}],"version-history":[{"count":3,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2014\/revisions"}],"predecessor-version":[{"id":2204,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2014\/revisions\/2204"}],"wp:attachment":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/media?parent=2014"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/categories?post=2014"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/tags?post=2014"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}