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On Mon, 26 Oct 2020 15:03:52 -0700 (PDT), in
gmane.comp.hardware.beagleboard.user Julian Reyes
<julian.messier31-re5jqeeqqe8avxtiumw...@public.gmane.org> wrote:
>What about sensors? Do you have an example? I have a Seeed Temperature
>Sensor, using node-red how can I get temperature?
Seeed/Grove has many types of temperature (and humidity) sensors.
https://www.seeedstudio.com/Grove-Temperature-Sensor.html
Is a thermistor design. It outputs an analog voltage which you then scale
(using parameters provided in the documentation) to determine the
temperature. PROBLEM: Beaglebone ADC inputs max at 1.8V; if you power this
version with a 3.3V feed, you will need to use a voltage divider to reduce
the 0.0-3.3V output into 0.0-1.8V. You also need to connect it to one of
the pins that is configured as ADC input, NOT GPIO.
https://www.seeedstudio.com/Grove-Temperature-Humidity-Sensor-DHT11.html
uses a DHT-11. The DHT-11 has a very complex protocol in which one has to
measure the length of high/low pulses to determine if a 1 or 0 bit is being
output. Using compiled (C/C++ or assembler) MAY allow a program running in
the Linux realm to successfully read such a unit, but native Python or
Javascript (which, as I understand it, is what gets run through the
Node-Red interface) is not fast enough to reliably read one of these.
https://www.seeedstudio.com/Grove-BME280-Environmental-Sensor-Temperature-Humidity-Barometer.html
uses the BME280 chip. This sensor has both I2C and SPI interface modes.
Reading such requires connecting to pins that are configured for either I2C
or SPI, and issuing commands followed by reading the return data. The good
news, the data IS in binary (it may need some scaling, but has no analog to
timing based problems).
https://www.seeedstudio.com/Grove-I2C-High-Accuracy-Temperature-Sensor-MCP9808.html
is another I2C interface type
https://www.seeedstudio.com/DS18B20-Temperature-Sensor-1-Wire-Digital-Thermometer-p-4281.html
is a Dallas Semiconductor (now Maxim) "1-wire" protocol
https://en.wikipedia.org/wiki/1-Wire
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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