Develop Reference

Arduino pyfirmata analog reading problems

I am having some problems reading analog values from my Arduino Mega using pyfirmata.
I use Arduino Mega with a Mega Sensor Shield.
I would like to read analog values from a HW-201 IR sensor (pin A5).
I have uploaded the Standard firmata sketch on Arduino IDE, and I am running the following code using Anaconda Spyder:
import serial
import serial.tools.list_ports
from pyfirmata import ArduinoMega, util
from time import sleep
def readArduinoPort():
COM = []
ports = list(serial.tools.list_ports.comports())
for p in ports:
if "Arduino" in p.description:
COM.append(str(p.device))
return COM
COM = readArduinoPort()
board = ArduinoMega(COM[0])
pin = board.get_pin('a:5:i')
it = util.Iterator(board)
it.start()
try:
while True:
print(pin.read())
sleep(0.1)
except KeyboardInterrupt:
pass
Now, this code runs just fine the first time I use it, generating numbers close to 1 when the sensor is detecting proximity and numbers close to 0 when not detecting anything.
However, whenever I try to run the Iterator a second time (without restarting the kernel), the code generates seemingly random numbers (almost like the pin was floating, like nothing was connected to it).
Any idea why this is happening? Is this a normal behavior?
Thank you!
I already checked these questions that do not entirely address my issue:
arduino pyfirmata analog reading
Analog readings on Arduino returns wrong values
I have the same result by not having anything pinned to pin A5 of the Arduino Mega.
I wasn't sure, but I tried adding:
board.analog[5].enable_reporting()
before the iterator and then:
board.analog[5].disable_reporting()
but nothing changed.

Board Differences
I ran into the same problem. I own both a Mega and an Uno and needed to select the appropriate Board and Processor in the tools menu:
Tools > Board > _board_
Tools > Processor > _processor_

BME280 on Raspberry Pi using Python 3 - Odd first reading

I have 2 x Pimoroni BME280 and they both produce the same initial reading of 21.95*C 698.09hPa 76.34% humidity.
Using this simple code
import time
from smbus2 import SMBus
from bme280 import BME280
bus = SMBus(1)
bme280 = BME280(i2c_dev=bus)
while True:
temperature = bme280.get_temperature()
pressure = bme280.get_pressure()
humidity = bme280.get_humidity()
print('{:05.2f}*C {:05.2f}hPa {:05.2f}%'.format(temperature, pressure, humidity))
time.sleep(1)
and I always get as the first line of output as...
21.95*C 698.09hPa 76.34%
followed by the correct data for example...
18.70*C 993.54hPa 55.88%
18.70*C 993.53hPa 56.12%
18.71*C 993.54hPa 56.06%
18.71*C 993.54hPa 55.95%
Does anybody know why this is?
Currently I have the same thing on both of my BME280 so presume it's some sort of initialization thing on the first reading which must be discarded. If I run my program the only solution I can see it to ask twice what thr readings are and discard the first reading..
Thanks for reading and helping...

I would presume that this is caused due to an initial transient value being outputted by the sensor as a result of initialising your sensor.
It would be interesting to see how an Arduino would handle the initialisation process
vis-à-vis said transient value with your sensor.
As you said, if your continuous readings are 'correct', I would try to perhaps delay the output process or omit the first reading in some way or another.

Issue with daisychaining MCP3008 SPI on Raspberry Pi with Python

At the moment I am trying to let two MCP3008's communicate through SPI with my raspberry pi and a Python script. A potentiometer should send a certain analog value to the MCP3008 input channel.
Here is my setup in Fritzing:
Breadboard Schematic
and here is the schematic overview:
Schematic Overview
The SPI wiring is based upon a standard daisychain schematic as shown in:
SPI Daisy Chain
The Python Code I am using is:
import spidev
import time
spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 1000000
def read_spi(channel):
spidata = spi.xfer2([0,(8+channel)<<4,0])
return ((spidata[1] & 3) << 8) + spidata[2]
try:
while True:
channeldata = read_spi(0)
print (channeldata)
time.sleep(.1)
except KeyboardInterrupt:
spi.close()
I am getting values, but they fluctuate a lot with every value possible between 0 and 1023.
I've tried it with one MCP3008 without daisychaining of course and it worked fine, so my guess is that it has something to do with either the daisychain being incorrect, or the addressing of the MCP3008.
Can you guys help me out? Thanks alot!!
Cheers,
Devatu

Might be a late response, but according to the data sheet this chip can't be daisy-chained at all.
I am also looking for an ADC which can be daisy-chained.

arduino read in pyfirmata gives output as none

I wrote a basic code for reading values from analog pin 0(I have a light sensor attached to it and the output is coming at analog pin 0) in python3 using pyfirmata, but it is giving the output as none no matter what. I tried the same code in arduino IDE and that is giving the right answer. Please help.
Code is :
from pyfirmata import Arduino, util
import time
board = Arduino('/dev/cu.usbmodem1411')
it = util.Iterator(board)
it.start()
board.analog[0].enable_reporting()
while True :
print (board.analog[0].read())
time.sleep(1)
Even when it gives an output after few seconds, it gives 0.29 which isn't actually the sensor value that comes on serial monitor. That value varies between 0 and 1023 and is relatively quite larger than this.

The analog pins of Arduino linearly translate the input voltages between 0 and +5V to 0
and 1023. However, in pyFirmata , the values between 0 and +5V are linearly translated
into the float values of 0 and 1.0. For example, if the voltage at the analog pin is 1V, an
Arduino program will measure a value somewhere around 204, but you will receive the
float value as 0.2 while using pyFirmata’s read() method in Python.

You'll need to start an Iterator thread before reading
board = pyfirmata.Arduino("COM5") # change com port
board.digital[3].mode = pyfirmata.INPUT
it = pyfirmata.util.Iterator(board)
it.start()
board.digital[3].read()
Most of the time it work, but sometimes None still show up. Sometimes time.sleep can help.

You have to do an if conditional first, something like this (and try running analogfirmata):
while True:
if board.analog[0].read() == None:
pass
else:
print("board.analog[0].read()")

Raspberry Pi python serial FT232 not receive 8bytes

I FT232 module connected to the Raspberry Pi (with USB cable). I want to receive 8bytes (1 byte). On Windows, Terminal draws me correctly beats (eg. 00001011). In the following python script:
#!/usr/bin/python
import serial
import binascii
ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1)
while True:
str1 = ser.read(1)
if str1 == '':
print ''
else:
print bin(int(binascii.hexlify(str1),16))
returns only 2 bits at the end:
0b11111100 ,
0b11111101 ,
0b11111110 ,
0b11111111
What am I doing wrong that draws me just 2bits at the end?
Below please find screen how to receive data on Windows:
http://mateok.ovh/windows.jpg
And on Raspberry Pi:
http://mateok.ovh/linux.jpg
I would like to get on the Raspberry Pi received data were the same.
Edit:
I was able to find a solution! It turned out that the reason is ... that the device had been connected before starting the Raspberry Pi! If they Disconnect and reconnect only when the Raspberry Pi starts - values are returned well! Maybe someone knows the cause of this? And how can I fix it? I do not want every time you re-connect the converter ..