general project gudance ! if it is possible or not

Kourpetis · 2 Mar 2016, 05:31

I have a some code that I've created in python3 that simulates a virtual button. I have a raspberry pi and I've connected to it a analog sensor. I've created a while loop inside a function that runs for ever and checks if the signal from this sensor passed a threshold variable.

could I create a text window and when ever this threshold is passes to write the character "A" in it, then erase that character and wait until it passes the threshold again so it writes it again.

It works in my terminal but I can't get it to work to qt GUI. It has to do with multithreading but my level in programming is not that advanced. And I don't know any other way to continuously check without the while loop !

A text box of 10 - 20 characters even single line that does that thing, that's all I am asking.

over this code :

#!/usr/bin/python3

import time
import spidev # import the SPI driver
from time import sleep


state="wrt"
DEBUG = False
vref = 3.3 * 1000 # V-Ref in mV (Vref = VDD for the MCP3002)
resolution = 2**10 # for 10 bits of resolution
calibration = 38 # in mV, to make up for the precision of the components
GPIO.setmode(GPIO.BOARD)
GPIO.setwarnings(False)

#start_time=time.time()
#elapsed_time=time.time()

# MCP3002 Control bits
#
#	7	6	5	4	3	2	1	0
#	X	1	S	O	M	X	X	X
#
# bit 6 = Start Bit
# S = SGL or \DIFF SGL = 1 = Single Channel, 0 = \DIFF is pseudo differential
# O = ODD or \SIGN
# in Single Ended Mode (SGL = 1)
#	ODD 0 = CH0 = + GND = - (read CH0)
#		1 = CH1 = + GND = - (read CH1)
# in Pseudo Diff Mode (SGL = 0)
#	ODD 0 = CH0 = IN+, CH1 = IN-
#		1 = CH0 = IN-, CH1 = IN+
#
# M = MSBF
# MSBF = 1 = LSB first format
#		 0 = MSB first format
# ------------------------------------------------------------------------------

# SPI setup
spi_max_speed = 1000000 # 1 MHz (1.2MHz = max for 2V7 ref/supply)
# reason is that the ADC input cap needs time to get charged to the input level.
CE = 0 # CE0 | CE1, selection of the SPI device
spi = spidev.SpiDev()
spi.open(0,CE) # Open up the communication to the device
spi.max_speed_hz = spi_max_speed

#
# create a function that sets the configuration parameters and gets the results
# from the MCP3002
#

def read_mcp3002(channel):
	# see datasheet for more information
	# 8 bit control :
	# X, Strt, SGL|!DIFF, ODD|!SIGN, MSBF, X, X, X
	# 0, 1,	   1=SGL,	  0 = CH0  , 0	 , 0, 0, 0 = 96d
	# 0, 1,	   1=SGL,	  1 = CH1  , 0	 , 0, 0, 0 = 112d
	if channel == 0:
		cmd = 0b01100000
	else:
		cmd = 0b01110000

	if DEBUG : print("cmd = ", cmd)

	spi_data = spi.xfer2([cmd,0]) # send hi_byte, low_byte; receive hi_byte, low_byte

	if DEBUG : print("Raw ADC (hi-byte, low_byte) = {}".format(spi_data))

	# receive data range: 000..3FF (10 bits)
	# MSB first: (set control bit in cmd for LSB first)
	# spidata[0] =	X,	X,	X,	X,	X,	0, B9, B8
	# spidata[1] = B7, B6, B5, B4, B3, B2, B1, B0
	# LSB: mask all but B9 & B8, shift to left and add to the MSB
	adc_data = ((spi_data[0] & 3) << 8) + spi_data[1]
	return adc_data

def main():
	while state == "wrt":
		channeldata_1 = read_mcp3002(0) # get CH0 input
		sleep(0.001)
		channeldata_2 = read_mcp3002(0) # get CH0 input
		sleep(0.001)
		channeldata_3 = read_mcp3002(0) # get CH0 input
		channeldata = (channeldata_1+channeldata_2+channeldata_3)/3
		#
		# Voltage = (CHX data * (V-ref [= 3300 mV] * 2 [= 1:2 input divider]) / 1024 [= 10bit resolution]			 #
		voltage = int(round(((channeldata * vref * 2) / resolution),0))+ calibration
			if ( voltage <= 2500) :	  #key is pressed
				print("A", end="", flush=True) 
				sys.stdout.write('\010')

if __name__ == '__main__':
	main()

jsulm · wrote on 2 Mar 2016, 05:26

Hi and welcome!
The code you provided does not have any GUI related parts.
But one thing you're probably doing wrong is: endless while loop. If you have such a loop in the Qt GUI thread then you block the event loop and your GUI freezes. You should provide your code including GUI, so others are able to help you.
To avoid a loop which polls the sensor you could use a timer to check the sensor regularly. If you really want to poll in a loop then you should move this loop to another thread, but this is more complex compared to timer.

david.hickerson · wrote on 2 Mar 2016, 05:31

@Kourpetis
Hi, it sounds like your code is getting stuck in your while loop. I believe your code needs threading.