Flight instrument sensor dongle for Kobo and XCSoar

[peter50763]

If you fly or have an interest in flying a Sailplane, Paraglider or Hang Glider, you may have heard of a common DIY flight instrument made by a hacked Kobo book reader and XCSoar software (XCSoar.org).
The Kobo does not have any sensors built in, and so needs data such as GPS, and pressure sensors to feed into XCSoar software. So a dongle with sensors is required. A common and very good Australian built device is the BlueFly (http://blueflyvario.com/) which has a serial comms version suitable for this job.
But if like me you like to build stuff, here’s an idea which has lots of possibilities.

The Kobo has Wifi, and XCSoar will accept input from a device on a UDP or TCP port, so the PICO-W presents some interest possibilities.
(Also I should mention here that there is a Android version of XCSoar, so you don’t need to have a Kobo to test of use this.)

Overall concept;
The PICO-W is setup as an Access Point, the Kobo connects to this, the PICO reads the sensors, packets up the data, and sends it to the Kobo via a UDP broadcast packet.
(If using an Android phone, it has all the data already, except for the Airspeed sensor, so this would be a way of having airspeed data on the phone app.)

Basic hardware;
RPi PICO-W
Barometric pressure sensor, MS5611 in the form of a GY-63 breakout PCB.
A GPS module, with ttl serial comms. I used here the TEL132, but almost any will do.
LiPo battery with a charger with in my case a 5v output. The PICO-W plus bits is a bit heavy on the battery in this configuration, but there obvious fixes to address this.

For audio vario I use a simple switching transistor with diode protection, in case I connect a standard speaker.

In addition to this you could add a SDP3x digital mass flow pressure sensor for Air Speed. However the airspeed range will determine if the ‘x’ is a 1 or 2. These are really small and SMD, so I had to make a breakout pcb for it.

Software;
Micropython, because it’s easy and fun. The almost the whole of the development system is on the chip, just add Thonny or similar and away you go. Because of this I have not made any attempt to add user preferences setup interface, just hack the code you wrote.

You may note that there are pins labels with unused signals, such as BUSY, RST, DIN, CLK etc. That’s because I’m in the process of adding a small epaper display directly to the PICO-W and plan to ware in on my wrist as well as it supplying data to the Kobo and XCSoar.

Nothing to show of the hardware at the moment as I keep pulling it apart, in this case to add the epaper display. Still working on the software for that to run in the back ground.

Happy to share the code I have done. Should I just cut and paste in this forum?

Happy Making.
Cheers.
Pete L.

[James]

Hi Pete,

Suuuper cool project here! I’m sure we’d love to see more of it when the hardware is done

As for code, surrounding the start and end of the code with 3 backticks (```) will format your code in a scrollable box like so.

How are you getting your airspeed data? A pitot tube arrangement with a pressure sensor? Or something fancier like one of these:

SparkFun Air Velocity Sensor Breakout - FS3000-1015 (Qwiic)

Keen to see how you go on this one!
-James

[peter50763]

Hi James, interesting device, wonder how it works…, might be OK for paraglider air speeds.
I’m using a pitot system. The SDP32 is a 0-500Pa differential pressure sensor, using mass flow method. That gives it a basically 0 offset, and a max airspeed detection of ~95kph. But an effect of the mass flow method is it ‘leaks’, so air flowing down the plumbing reduces the pressure at the sensor. There is a linear section to this “error” so it can be used to increase the effective range. Not sure if it would go to sailplane airspeeds, 80-350kph. But should be pretty good for what I fly, hang gliders.
I’ll sort out all the versions of software I have messed with, and paste it here as you suggest. There are basically 6 small files. And there is heaps of room for improvement.
Not sure that it will ever be a finished project, as there are many options to explore.
But that’s the fun of it!
P

[peter50763]

OK, some photos and code.

• main1.py (copy to main.py when you want it to boot)
• WAP.py Wireless Access Point
• audio.py Makes beeping noise when going up in lift (A joy to a pilot!)
• sensors.py Sets up and read the pressure sensors Barometer (Altitude and Vario), and ASI
• gpsuart.py Sets up uart and manages the GPS data
• lxnav.py LXNAV protocol sentence generator, returns the assembled string.

If I write a class or even just a bunch of code in a file, I try and leave an “Example of usage” at the end of the file, this can be used to demo/modify/develop the code in the file above it. But don’t forget to comment it out again.
(Also I find it good to help refresh my fading memory!)
There is also a lot of hardcoded setup in this these would be best moved to passed args in the startup of main1.py. But I have left it this way for clarity.

main1.py

## XCsoar WiFi Data Dongle
## main file.
## This starts up all the parts
## and then does the final part of sending data to XCSoar

## Written specifically for the RP PICO-W
## could run on an ESP32 or similar,
##  but the audio tone generator will need to be ported to an ISR,
##  as this uses the PICO PIO module

## sensors run in a _thread on core1 (PICO specific as it has 2 cores)
## but _thread works on the ESP32 as well


## If changing hardware arrangement,
##     remember to update sensors and gps to any new pins used
## Code has been written to be as simple as possible

## Low level imports
import machine
from machine import Pin, Timer
import time
import sys
## Application specific imports
import sensors
import lxnav
import gpsuart
import WAP
import audio

## some links that may be useful
#https://forums.raspberrypi.com/viewtopic.php?t=310062
#https://hackspace.raspberrypi.com/articles/raspberry-pi-picos-pio-for-mere-mortals-part-3-sound

##############################################
## for development, this will try and  #######
## end the process neatly              #######
button = Pin(0, Pin.IN, Pin.PULL_UP)
global loop
loop = True
timer = Timer(-1)

def checkButton(t):
    global loop
    if(button.value() == 0):
        loop = False

timer.init(period=100, mode=Timer.PERIODIC, callback=checkButton)
##############################################

# Should exit a booting "main.py", on power up, hold the "button"
time.sleep(0.5)
if(loop == False):
    print("Exit")
    sys.exit()
    
## define the parameters that setup the network and hardware
# Wireless Access Point WAP
ssid = "W-ap"
password = "123456789"

## startup the various parts
print("Starting Systems")
aud = audio.audio()
aud.doStartBeep()
ap =  WAP.wap(ssid, password)
gps = gpsuart.gpsUart()
sensors.startSensors()
lx  = lxnav.LXNAV()  ## the protocol format in which to send the data to XCsoar
print("All started")

message_to_xcsoar_udp = ''
time.sleep(2.0)

aud.doStartTune()

a = 0.0
v = 0.0
asi= 0.0
while(loop):
    gps.readUart()
    if(gps.messages() > 0):
        while(gps.messages() > 0):
            message_to_xcsoar_udp = gps.getNMEA() # get one awaiting NMEA sentences
            ap.udpSend(message_to_xcsoar_udp)     # and send it
#             try:
#                 print(message_to_xcsoar_udp.decode('UTF-8'))
#             except Exception as e:
#                 print(e)
            aud.do(bario.readVARIO())

    a = sensors.readALTI()
    v = sensors.readVARIO()
    asi =sensors.readASI()  ## make sure there is not data for ASI below just'' 
    message_to_xcsoar_udp = lx.get('{:.2f}'.format(asi), '{:.2f}'.format(a), '{:.2f}'.format(v))
    ap.udpSend(message_to_xcsoar_udp)
    print(message_to_xcsoar_udp.decode('UTF-8'))
    aud.do(v)
    time.sleep(0.1)


## if button is low loop exits and preforms a shutdown
print("shutting down")

aud.doEndTune()
print("1")
gps.end()
print("2")
ap.end()
print("3")
aud.end()
print("4")
rp2.PIO(0).remove_program()
print("5")
timer.deinit()
print("6")
sensors.endCore1() # this is not returning ???
print("shutdown")
sys.exit()

WAP.py

import network
import socket
import machine
import time

######################################################
class wap:
    def __init__(self, ssid, password):
        print("Starting WAP")
        self.ssid = ssid
        self.password = password
        self.ap = network.WLAN(network.AP_IF)
        self.ap.config(essid=ssid, password=password)
        self.ap.active(True)
        
#         print(self.ap.config("mac"))
#         print(self.ap.config("essid"))
#         print(self.ap.ifconfig())

        conf = self.ap.ifconfig()
        UDP_IP = str(conf[0])
        print(UDP_IP)
        UDP_IP_list = UDP_IP.split('.')[0:3] + ['255']
        self.UDP_IP = '.'.join(UDP_IP_list)
#        self.UDP_IP = '192.168.4.16'
        print(self.UDP_IP)

        self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    def udpSend(self, msg):
        XCSOAR_UDP_PORT = 4353
        self.sock.sendto(msg, (self.UDP_IP, XCSOAR_UDP_PORT))
        
        self.sock.sendto(msg, (self.UDP_IP, 2000))

    def end(self):
        self.ap.active(False)


    def rex(self, p):
        UDP_PORT = p
        self.sock.settimeout(0.10)
        try:
            data, address = self.sock.recvfrom(1024)
            print(address, data.decode())
        except:
            pass

###########################################################
# 
# ap = wap("W-ap", "123456789")
# x =100
# 
# while(x):
# #    ap.udpSend(MESSAGE)
#     ap.rex(4353)
#     print('.')
#     time.sleep(1.0)
#     x -= 1

###########################################################
###########################################################
###########################################################
###########################################################

class station:
    def __init__(self, ssid, password):
        print("Starting joining wifi WAP")
        self.ssid = ssid
        self.password = password
        self.wlan = network.WLAN(network.STA_IF)

#        self.wlan.config(essid=self.ssid, password=self.password)
        self.wlan.active(True)
        res =self.wlan.scan()
        for each in res:
            print(each)

#        self.wlan.connect(self.ssid, self.password)
        

#         conf = self.wlan.ifconfig()
#         UDP_IP = str(conf[0])
#         UDP_IP_list = UDP_IP.split('.')[0:3] + ['255']
#         self.UDP_IP = '.'.join(UDP_IP_list)
#         print(self.UDP_IP)
# 
#         self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    def udpSend(self, msg):
        XCSOAR_UDP_PORT = 4353
        self.sock.sendto(msg, (self.UDP_IP, XCSOAR_UDP_PORT))

    def end(self):
        self.wlan.active(False)

###########################################################
#         
# w = station("Galaxy A71B468", "jcye9075")
# x = 10
# while(x):
#     print(x)
#     time.sleep(1.0)
#     x-=1
# w.end()
# print("end")

audio.py

import machine
from machine import Pin
from rp2 import PIO, StateMachine, asm_pio
#from machine import Timer
import time
import utime

# to fix ENOMEM error
#rp2.PIO(0).remove_program()
#############################################################################
# PIO code from https://hackspace.raspberrypi.com/articles/raspberry-pi-picos-pio-for-mere-mortals-part-3-sound
#############################################################################
## importing this will load and prep the PIO code.
## The audio class below will activate it as required for the tone to sound
#############################################################################

@asm_pio(sideset_init=PIO.OUT_LOW)
def square_prog():
    label("restart")
    pull(noblock) .side(0)
    mov(x, osr) 
    mov(y, isr)
    
    #start loop
    #here, the pin is low, and it will count down y
    #until y=x, then put the pin high and jump to the next secion
    label("uploop")
    jmp(x_not_y, "skip_up")
    nop()         .side(1)
    jmp("down")
    label("skip_up")
    jmp(y_dec, "uploop")
    
    #mirror the above loop, but with the pin high to form the second
    #half of the square wave
    label("down")
    mov(y, isr)
    label("down_loop")
    jmp(x_not_y, "skip_down")
    nop() .side(0)
    jmp("restart")
    label("skip_down")
    jmp(y_dec, "down_loop")
    
max_count = 5000
freq = 1000000
#square_sm = StateMachine(0, square_prog, freq=freq, sideset_base=Pin(0))
square_sm = StateMachine(0, square_prog, freq=freq, sideset_base=Pin(28))

#pre-load the isr with the value of max_count
square_sm.put(max_count)
square_sm.exec("pull()")
square_sm.exec("mov(isr, osr)")

#############################################################################
class audio:
    def __init__(self):
        ''' usinf a POI state machine for the signal generator, calculate the freq, on time and off time of the audio vario '''
        print("Starting Audio")
        self.freq = 4000
        self.freqLast = 4000
        self.pause = 10
        self.beep  = 200
        self.beepOntime = time.ticks_ms() + self.pause
        self.beepOfftime = time.ticks_ms() + self.beep
        self.vario = 0.0
        self.tune = True
        self.beat = 0
        square_sm.put(4000)
        
        ## setup and start the time that will call the do function
#        self.timer = Timer(-1)
#        self.timer.init(period=100, mode=Timer.PERIODIC, callback=self.do)
        ## once setup simply update the vario variable. Usage show below

    def setV(self, v):
        self.tune = True
#        print(v)
#        print(v, self.freq, self.beep, self.pause)

    def setTune(self):
        self.tune = True
        self.beat = 0
        
#    def do(self, tm):
    def do(self, v):
#        self.tune = True
        self.vario = v
        ticks = time.ticks_ms()
        baseF = 4000
        liftPosThres = 0.2
        sinkNegThres = -1.1
        if(self.vario >= liftPosThres):
            self.freq = int(baseF + int(self.vario * 100.0))
            self.pause= 75
            self.beep = 1000 - int(self.vario * 100)
            
        elif(self.vario > sinkNegThres):
            self.beep = 0
            self.freq = 500
        elif(self.vario < sinkNegThres):
            self.freq = int(baseF/2 + int(self.vario * 100.0)) # v is negative
            self.pause = 50
            self.beep =  3000
        else:
            print("error v out of range")

        if(self.beep <= 0): self.beep = 0
        if(self.freq != self.freqLast):  # not pulling from the buffer
            square_sm.put(self.freq)     # when we put there
            if(square_sm.tx_fifo() > 2): # requires a 
                square_sm.exec("pull()") # pull to stop it blocking up
            self.freqLast = self.freq
            
        if(self.beep > 0):                # should beep be working
            if(square_sm.active()):         # is it on now
                if(utime.ticks_diff(ticks, self.beepOfftime) >= 0):
                    square_sm.active(0)   # turn off and calculate next on time
                    self.beepOntime = utime.ticks_add(ticks, self.pause)
            else:
                if(utime.ticks_diff(ticks, self.beepOntime) >= 0):
                    square_sm.active(1)    # turn onand calculate next off time
                    self.beepOfftime = utime.ticks_add(ticks, self.beep)
        else:
            square_sm.active(0)
        
    def doTune(self):
        if(self.beat < 5):
            square_sm.put(4000)
            square_sm.active(1)
            self.beat += 1        
        elif(self.beat < 10):
            square_sm.put(3000)
            self.beat += 1        
        elif(self.beat < 20):
            square_sm.put(4900)
            self.beat += 1        
        elif(self.beat < 40):
            square_sm.put(4000)
            self.beat += 1        
        elif(self.beat < 50):
            square_sm.active(0)
            self.beat = 0         
            self.tune = False

    def doStartBeep(self):
        square_sm.put(3000)
        square_sm.active(1)
        time.sleep(0.2)
        square_sm.active(0)
        time.sleep(0.1)
        
    def doStartTune(self):
        square_sm.put(3500)
        square_sm.active(1)
        time.sleep(0.05)
        square_sm.active(0)
        time.sleep(0.1)
        square_sm.active(1)
        time.sleep(0.1)
        square_sm.active(0)
        time.sleep(0.1)
        square_sm.put(4500)
        square_sm.active(1)
        time.sleep(0.2)
        square_sm.active(0)

    def doEndTune(self):
        square_sm.put(4500)
        square_sm.active(1)
        time.sleep(0.05)
        square_sm.active(0)
        time.sleep(0.1)
        square_sm.active(1)
        time.sleep(0.1)
        square_sm.active(0)
        time.sleep(0.1)
        square_sm.put(3500)
        square_sm.active(1)
        time.sleep(0.2)
        square_sm.active(0)

    def end(self):
#        self.timer.deinit()
        square_sm.active(0)
#############################################################################
## usage example
#import random
# aud = audio()
# var = 0.0
# 
# x=5
# while(x):
#     aud.doStartTune()
#     time.sleep(1.0)
#     
#         
# #    var += 0.00 + float(random.randrange(-10,10)/100.0)
# #     aud.setV(0.2)
# #     time.sleep(0.1)
# #     aud.setV(0.0)
# #     time.sleep(0.1)
# #     aud.setV(-2.0)
# #     time.sleep(0.1)
#     x-=1
#     print(x)
# # to stop the noise!!! run this only
# square_sm.active(0)
# aud.end()
# rp2.PIO(0).remove_program()

sensors.py

#import machine
from machine import Pin, I2C
import _thread
import utime
import time
import math

## Starting a new thread on the PICO, should put it in Core1
## use a loop to get/process the ASI pressure sensor and the Altimeter/Vario sensor
global ASIfinal
ASIfinal = 0.0
global ALTIfinal
ALTIfinal = 0.0
global VARIOfinal
VARIOfinal = 0.0
global TIMEsample
TIMEsample = utime.ticks_ms()
            
global PRESSfinal
PRESSfinal = 0.0
global TEMPfinal
TEMPfinal = 0.0
global core_one_run
core_one_run = True

def readASI():
    global ASIfinal
    return ASIfinal

def readALTI():
    global ALTIfinal
    return ALTIfinal

def readVARIO():
    global VARIOfinal
    return VARIOfinal

def endCore1():
    global core_one_run
    print("c1")
    core_one_run = False
    print("c2")
    time.sleep(0.5)
    print("c3")
    _thread.exit()
    print("c4")

def sensors():
    global ASIfinal
    global ALTIfinal
    global VARIOfinal
    global TIMEsample
    global core_one_run
    # hardware setup hardcoded for now
    i2cAsix = 0
    i2cAsiAddr = 0x21
    i2cAVx = 0
    i2cAVAddr = 0x77
    
    
    # setup ASI pressure readings
    IAS = 0.0
    i2cAsi = I2C(i2cAsix, scl=Pin(21), sda=Pin(20), freq=100000)
    diffP = 0.0
    temp  = 0.0
    i2cAsi.writeto(i2cAsiAddr, bytearray([0x36, 0x03]), 2)
 
    # setup Barometric pressure sensor for Alti and Vario
    i2cAV = I2C(i2cAVx, scl=Pin(21), sda=Pin(20), freq=100000)
    i2cAV.writeto(i2cAVAddr, bytearray([0x1E])) #        reset_cmd()
    utime.sleep_ms(200)
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xA2, 2)
    C1 = data[0] * 256 + data[1]
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xA4, 2)
    C2 = data[0] * 256 + data[1]
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xA6, 2)
    C3 = data[0] * 256 + data[1]
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xA8, 2)
    C4 = data[0] * 256 + data[1]
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xAA, 2)
    C5 = data[0] * 256 + data[1]
    data = i2cAV.readfrom_mem(i2cAVAddr, 0xAC, 2)
    C6 = data[0] * 256 + data[1]

    ## setupthe kalman filter
    ALTIfinal = 0.0  # x_abs
    VARIOfinal = 0.0 # x_vel
    t = utime.ticks_ms()
    dt = 0.03   # sample interval

    cz = 7000.0 # p_abs_abs
    cv = 0.0    # p_abs_vel
    cdv = 0.0   # p_vel_vel
    vz = 0.1    # var_z_abs

    # setup done now loop doing the read/conversions/processing
    while(core_one_run):
        # do ASI sensor read and process
        def checkCRC(data, size, csum): # this used only for ASI chip 
            crc = 0xff
            for i in range(0, size, 1):
                crc ^= data[i]
                crc &= 0xff        
                for bit in range(8, 0, -1):
                    if(crc & 0x80):
                        crc = (crc << 1) ^ 0x31
                        crc &= 0xff        
                    else:
                        crc = crc << 1
                        crc &= 0xff        
            return (crc == csum)          
            ######################
        data = i2cAsi.readfrom(i2cAsiAddr, 3)
        p = data[0:2]
        pcrc = data[2]
        IAS = 0.0
        press = 0
        if checkCRC(data[0:2], 2, data[2]):
            press = p[0] *256 + p[1]
            if press & 0x8000:       ## handle the signed int
                press -= 0x10000
            press /= 60.0
        else:
            print("err")
        if(press > 0.0):
            IAS = math.sqrt(press * 1.568135)
            if IAS < 1.0:
                ISA = 0.0
        ASIfinal = IAS
#        print(ASIfinal)
        # do Bari sensor reading and process
        i2cAV.writeto(i2cAVAddr, bytearray([0x48])) #pres_conversion()
        utime.sleep_ms(10)
        value = i2cAV.readfrom_mem(i2cAVAddr, 0x00, 3) #         read_pressure()
        D1 = value[0] * 65536 + value[1] * 256 + value[2]
        i2cAV.writeto(i2cAVAddr, bytearray([0x58]))  #        temp_conversion()
        utime.sleep_ms(10)
        value = i2cAV.readfrom_mem(i2cAVAddr, 0x00, 3) #         read_temp()
        D2 = value[0] * 65536 + value[1] * 256 + value[2]
        """Conversion of the read data to get the final output"""
        dT = D2 - (C5 * 256)
        TEMP = 2000 + ((dT * C6) / 8388608)
        OFF = C2 * 65536 + (C4 * dT) / 128
        SENS = C1 * 32768 + (C3 * dT ) / 256
        
        T2 = 0
        OFF2 = 0
        SENS2 = 0
        
        if TEMP >= 2000 :
            T2 = 0
            OFF2 = 0
            SENS2 = 0
        elif TEMP < 2000 :
            T2 = (dT * dT) / 2147483648
            OFF2 = 5 * ((TEMP - 2000) * (TEMP - 2000)) / 2
            SENS2 = 5 * ((TEMP - 2000) * (TEMP - 2000)) / 4
            if TEMP < -1500 :
                OFF2 = OFF2 + 7 * ((TEMP + 1500) * (TEMP + 1500))
                SENS2 = SENS2 + 11 * ((TEMP + 1500) * (TEMP + 1500)) / 2
        
        TEMP = TEMP - T2
        OFF = OFF - OFF2
        SENS = SENS - SENS2
        
        PRESSfinal = ((((D1 * SENS) / 2097152) - OFF) / 32768.0) / 100.0
        TEMPfinal = TEMP / 100.0
#        print(PRESSfinal, TEMPfinal)
        
        QNH = 1013.25
        alti = 44330.0 * (1 - (PRESSfinal / QNH)** 0.190295)
        
#        print(alti)
#        avkalman(alti) now inline
        tn = utime.ticks_ms() # Manage the time between samples dt
        dt = float(utime.ticks_diff(tn, TIMEsample))/1000.0
        TIMEsample = tn
#        print("dt ", dt)
        
        var_accel = 1.0  # a constant, never get changed?
        ALTIfinal += VARIOfinal * dt  ## expected Alti
        # update state covariance, calculated from last samples variables
        cz += (2.0 * dt * cv) + (dt**2 * cdv) + (var_accel * dt**4) /4.0  # static local
        cv += dt * cdv + (var_accel * dt**3)/2.0                 # static local
        cdv += var_accel * dt**2                                      # static local
        # update
        y = alti - ALTIfinal  ## error, difference between actual and expected Alti
        s_inv = 1.0 / (cz + vz)                                  # local
        k_abs = cz * s_inv   # Kalman gain od alti                    # local
        k_vel = cv * s_inv   # Kalman gain od vario                   # local
        # update state estimate   ## no need to check lock as this is the only locking
        ALTIfinal += k_abs * y    ## Alti and 
        VARIOfinal += k_vel * y   ## vario
        # update state covariance
        cdv -= cv * k_vel  ## as above these are static value to be used to test adjust next sample
        cv -= cv * k_abs
        cz -= cz * k_abs
#        print(ALTIfinal, VARIOfinal)
        time.sleep(0.1)        
    print("Endcore1")
    
def startSensors():
    print("Starting Sensors _thread")
    try:
        _thread.start_new_thread(sensors, ())
    except Exception as e:
        print("err ", e)

    

## usage example
#startSensors()
# x=50
# while(x):
#     time.sleep(0.05)
#     print(readASI(), readALTI(), readVARIO())
#     x-=1
# endCore1()
# print("end")

gpsuart.py

from machine import Pin
from machine import UART
#from machine import Timer
import time
import utime

######################################################
class gpsUart:
    def __init__(self):
        print("Starting gpsUart")       
#        self.prefixes = ['$GNGGA','$GPGSA','$GLGSA','$GNRMC','$GNVTG']
        self.msgs = []
        self.rxData = bytes()
        
        #### Start Uart for the GPS ####
        self.uart = UART(0, baudrate=9600, tx=Pin(16), rx=Pin(17)) ## changed from original for veroboard unit (PL)
#         self.timer = Timer(-1)
#         self.timer.init(period=50, mode=Timer.PERIODIC, callback=self.readUart)

    def messages(self):
        return len(self.msgs)

    def getNMEA(self):
        if(len(self.msgs) > 0):
            return self.msgs.pop(0)
    
    def readUart(self):
#        rxData = bytes()
        while self.uart.any() > 0:
            b = self.uart.read(1)
            self.rxData += b
            if (b == '\n'.encode('UTF8')):
                self.msgs.append(self.rxData)
                self.rxData = bytes()
                while(len(self.msgs) > 10):
                    self.msgs.pop(0)
                    print("gpsUart msg buffer > 10, popping")
#            utime.sleep_ms(1)
            
    def dummy(self, x): ## call with x = 0 to 4
        def gpstimeStr():
            return (str(time.gmtime()[3]) + str(time.gmtime()[4]) + str(time.gmtime()[5]))

        if x == 0:
            # generate GNGGA sentence
            ggaSuffix = ",3731.575481,S,14525.516744,E,1,4,2.07,374.105,M,-2.272,M,,"
            gga = "GNGGA," + gpstimeStr() + ggaSuffix
            crcgga = self.crcCalc(gga)
            ggaStr = "$" + gga + "*" + '{0:x}'.format(crcgga)+ "\r\n"
            return ggaStr

        # copy GNPSA and GLSA sentences
        elif x == 1:
            pgsa = "$GPGSA,A,3,25,05,15,29,,,,,,,,,2.29,2.07,0.98*02"  + "\r\n"
            return pgsa
        
        elif x == 2:
            lgsa = "$GLGSA,A,3,,,,,,,,,,,,,2.29,2.07,0.98*13"  + "\r\n"
            return lgsa
        
        elif x == 3:
            # generate GNRMC sentence
            rmcSuffix  = ",A,3731.575481,S,14525.516744,E,1.21,209.33,300822,,,A"
            rmc = "GNRMC," + gpstimeStr() + rmcSuffix
            crcrmc = self.crcCalc(rmc)
            rmcStr = "$" +rmc + "*" + '{0:x}'.format(crcrmc)+ "\r\n"
            return rmcStr
        
        elif x == 4:
            vtg = "$GNVTG,209.33,T,,M,1.21,N,2.23,K,A*29"  + "\r\n"
            return vtg

        else:
            print("Error in dummy gps number")
            return None

    def crcCalc(self, sentence): # sentence in bytearray form
        byCRC = 0
        if type(sentence) != bytes:
            sentence = bytearray(sentence.encode('UTF8'))
        for each in sentence:
            byCRC ^= each
        return byCRC

    def end(self):
#        self.timer.deinit()
        time.sleep(0.1)
        

## Usage example
# gps = gpsUart()
# x = 50
# while(x):
#     gps.readUart()
#     res = gps.getNMEA()
#     if res != None:
#         try:
#             print(res.decode('UTF8'))
#         except:
#             pass
#     x-=1
#     time.sleep(0.1)
#     
# gps.end()
# x = 0
# for each in gps.msgs:
#     print(x)
#     print(each.decode('UTF8'))
#     x+=1
    

lxnav.py

######################################################
class LXNAV:
    def __init__(self):
        ''' create the LXNAV LXZP0 sentence for XCSoar '''

    
    # eg usage string to bytearray  sbytes = bytes(string, 'UTF8')
    #    crc = crcCalc(sbytes)
    def crcCalc(self, sentence): # sentence in bytearray form
        byCRC = 0
        if type(sentence) != bytes:
            sentence = bytearray(sentence.encode('UTF8'))
        for each in sentence:
            byCRC ^= each
        return byCRC

    def get(self, asi, alti, vario):
        # use a list of data to fill in the sentence, end with CRC
        # output format $LXWP0,N,'tas km/h','altutude m', v0 m/s, v1 m/s, v2 m/s, v3 m/s, v4 m/s, v5 m/s, heading, wDir, wSpeed]
        # eg $LXWP0,Y,119.4,1717.6,0.02,0.02,0.02,0.02,0.02,0.02,,000,107.2*5b
        opstr = "LXWP0,N," + asi + ',' + alti + ',' + vario + ',,,,,,,,'  ## initial opstr has to $ nor crc
        sb = bytes(opstr, 'UTF8')  ## make it a bytearray for the CRC
        crc = self.crcCalc(sb)
        ## assemble and return
        return bytearray(('$' + opstr + '*' + '{0:x}'.format(crc)+ "\r\n").encode('UTF8'))

Photos.
This is the latest desktop development arrangement. The code above was tested on this a few minutes ago.

This is how it started;

This is the Epaper version, lots to do yet…

Behind the display.

Having an ASI pitot on my harness or wrist is not going to be useful. So as the Kobo can still be wired up wth a serial port or USB-Serial adapter, I plan to mount the Pitot and interface on the back of the Kobo, facing the airflow. This is using a Seed Studios XIAO-RP2040. But lots of other options. I did try using a second Pico-w and connect to the first WAP to send the ASI data onto the Kobo via the same LXNAV sentence but I could not get 2 Clients to connect to the Pioc-W??

Have fun!
PeteL.