I have been enjoying some holiday Arduino learning by implementing Nick Gammon’s Temperature/Humidity logger as a tutorial.
The schematic is as shown here:
http://gammon.com.au/images/Arduino/HHS_Temperature_Logger1.png; except my version is implemented on a breadboard at this stage. And to more easily test the DHT22 in isolation pin 1 of this sensor has been directly connected to the 5V rail rather than the FET switched power source.
An image of the project to the extent it has been implemented thus far is attached.
The processor is an ATMega238PU configured with an 8Mhz Lillypad bootstrap using Mr Gammon’s superb chip programming sketches.
All is working well save the DTH22 will not respond.
I have wired the DTH22 into an Arduino UNO R3 board and tested it with the following DTH22 libraries:
: GitHub - adafruit/DHT-sensor-library: Arduino library for DHT11, DHT22, etc Temperature & Humidity Sensors
: Arduino/libraries/DHTlib at master · RobTillaart/Arduino · GitHub
and, what appears to be a more recent branch of  incorporating a Dew Point calc I was interested in,
: GitHub - dplasa/dht: Arduino library for the DHT11, DHT12, DHT22, DHT33, DHT44 and clone temperature and humidity sensors
Example sketches from all of these libraries work with the DHT22/UNO combination without a hitch. However the DHT22/Lillypad combination will not work with any of them; save with libraries  &  I get an ‘ERROR_ACK_L’ error acknowledgement.
Specifically I’m using a Sosong AS2302 sensor; for which a product manual is available here:
Consulting section 7.4 Step 2 of this manual (top of page 7 including Pic7), in conjunction with reviewing the code within the ‘dh1wire::_readSensor’ routine in dht.ccp (dht library ), specifically at line 183, it appears the host has issued a sensor start-up pulse (Tbe - Tgo) and the sensor has commenced its response signal by pulling the SDA pin low. However the Trel portion of the sensor response signal has not completed; or, due to a timing mismatch, the host has not detected the sensor taking SDA high again within the ‘loopCount’ timeout period.
Not yet being sufficiently adept with C++ Arduino code I’m unsure how to decipher what may be causing this problem and how to rectify it. Can anyone out there perhaps point me towards the best area and methods to focus on?
I have web searched for other responses to 8Mhz timing problems with the DHT22 (e.g. DHT22 not working with 8mhz clockspeed?) but none of them deal with the specific issue I’m encountering. And yes, I do have a 10K resistor between pins 1 & 2 of the DHT22.