WARNING: Raspberry pi GPIO is designed for 3.3V: five volts will damage GPIO.
A short 20cm cable and 3.3V powered a successful DHT11 test. I would like to reproduce this effort with 3 DHT22 sensors at distances of 20cm , 12m and 24m.
- Aosong marketing material indicates the possibility of 20m
- akaj9's forum entry #9: 5V Arduino forum indicates success at 60M with UTP wiring;
- measure temperatures at a distance from 12 and 24 meters from the rPi via DHT22
- wire (CAT5E) to power and receive data from two DHT22s per CAT5E cable to the rPi
- ensure the sensors are provided enough voltage, despite the voltage drop across the 12m and 24m CAT5E cable
- minimize (eliminate) the use of level converters (3.3v <=> 5.0V)
To clarify, two cables of 12 and 24 meters, each endpoint will have two temperature sensors.
I seek to avoid:
- damaging GPIO and stay by ensuring that it is not driven by greater than 3.3V
DHT22 sensors are powered by 12m and 24m ethernet cables:
- Will the sensors have enough voltage if powered at 5V?
- Will the data voltage returned to the rPi be at a safe 3.3V?
- If not, what can be done to ensure a safe 3.3V data return to the pi?
- The calculations below show no voltage drops at 0.1 A What (if any) flaws are in the calculation?
Any references to the topic or experience is appreciated.
Voltage drop calculations
25 meter with 2-twisted pair calculation:
12 meter with 1-twisted pair calculation: