diff --git a/README.md b/README.md
index fcba0c7d..ee41490a 100644
--- a/README.md
+++ b/README.md
@@ -34,9 +34,7 @@ Includes configuration for a google container OS instance.  Runs a small Rocket.
 
 ## Resources 
 
-- Background: https://twitter.com/Terkwood/status/1044992354178994178?s=19
 - pH sensor wiring and example code: https://www.element14.com/community/docs/DOC-89396/l/arduino-projects-for-arduino-day-water-and-irrigation-projects-part-2
-
 - LED with scrolling text tutorial: https://gustmees.wordpress.com/2018/04/08/first-steps-with-the-arduino-uno-r3-maker-makered-coding-scrolling-text-with-8x8-led-matrix/amp/?__twitter_impression=true
 - Cross compiling rust for armv7 from MacOSX using vagrant: https://medium.com/@wizofe/cross-compiling-rust-for-arm-e-g-raspberry-pi-using-any-os-11711ebfc52b
 - Cross compiling OpenSSL: https://assil.me/2017/09/30/cross-compile-openssl-arm-zynq.html
diff --git a/microcontrollers/README.md b/microcontrollers/README.md
new file mode 100644
index 00000000..ddf24195
--- /dev/null
+++ b/microcontrollers/README.md
@@ -0,0 +1,4 @@
+# Microcontroller gadgets
+
+[PH and Submersible Temp Sensor](ph_temp_sensor_esp8266) are implemented using a DF Robot SEN0169, which [has documentation here](https://wiki.dfrobot.com/Analog_pH_Meter_Pro_SKU_SEN0169).
+