eddiewebb · July 7, 2022 01:23 · Jul 7, 2022
diff --git a/dht sensor fix.md b/dht sensor fix.md
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+### What
+  A 'fix' for the notoriously poor reading issues of DHT hygrometer sensors from Python / Raspberry Pis.  
+
+### Why
+I've used the cheap DHT sensors on a few projects and always find the "yeah they're unreliable, just keep trying"
+ and that sucks.  How do opther devices work using these sensors? Priority. 
+
+ So these process changes have, for me, worked to give my python process the realtime CPU & IO access to meet the strict 
+timing requirements of a DHT sensor.
+
+ Super useful: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/monitoring_and_managing_system_status_and_performance/tuning-scheduling-policy_monitoring-and-managing-system-status-and-performance
+
+### How
+Just add these cpu & io priority settings to your systemd file.   
+You may be able to lower priority but since I use dedicated zeros I want all the priority possible. 
+
+```
+
+[Service]
+...
+#give cpu scheduling priority to help timing issues reading DHT sensor
+CPUSchedulingPolicy=fifo # fifo or rr are 2 realtime options
+CPUSchedulingPriority=99 #highest
+Nice=-20 # highest
+IOSchedulingClass=realtime # only realtime option
+IOSchedulingPriority=0 #highest
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Even when using read_retries for the DHT Adafruit library I saw **success rate jump from ~60% to 90%+**