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Get Started with Data Comms and the Raspberry Pi Pico

The Raspberry Pi Pico would be a great Internet of Things device but for one thing: it has no Internet connectivity. Fortunately, we can fix that with a Super SIM and an add-on cellular module such as Waveshare's Pico SIM7080.

Raspberry Pi Pico and Waveshare Pico SIM7080.

In our tutorial Get Started with SMS Commands and the Raspberry Pi Pico, we combined the Pico, the Waveshare Pico SIM7080 cellular module board, an MCP9808 temperature sensor, and a four-digit, seven-segment LED display into a prototype Internet of Things (IoT) development device.

This device uses Super SIM's SMS Commands API to receive commands over-the-air and, when instructed, to send back information. This works very well for device-to-user communications routed through your cloud, but what if you want the device to be able to reach out to other Internet resources? For that you need a data connection and the ability to make HTTP requests — GET, POST, PUT, etc. — and parse the remote server's response.

This tutorial will take you through the process of adding exactly this functionality to your IoT application.

(warning)

Warning

This guide requires a Twilio account. Sign up here now if you don't have one. It also requires a configured Super SIM. If you haven't set up your Super SIM in the Console, please do so now. Our Super SIM First Steps guide has extra help if you need it.

1. Set up the hardware and software

If you have already completed Get Started with SMS Commands and the Raspberry Pi Pico, you're ready to jump straight to Step 2, below. If not, run through the SMS Commands tutorial's first four steps, which cover the crucial hardware and software setup that you will need to undertake in order to complete this tutorial.

Head there now and then come back here when you've completed Step 4.

2. Prepare the initial Python code

Throughout this tutorial, you'll be pasting code from this page into a text editor, first the code below and then additional functions as you progress through the guide. At each stage, you'll copy the current code from your editor and paste it across to the Pico. The code included here entirely replaces hat from the previous tutorial in the series.

At this point, you should have a Pico with MicroPython installed. It should be fitted to the Waveshare board and connected to your computer by USB cable. You should have fired up Minicom (Mac/Linux) or PuTTY (Windows) and have the MicroPython REPL prompt, >>>. Hit Ctrl-C to exit the running program, if you don't see the prompt.

As a reminder, hit Ctrl-E to enter MicroPython's 'paste mode', paste in code copied from your text editor, and then hit Ctrl-D to start running it.

Alternatively, if you're a Mac or Linux user, you can use the pyboard.py tool to beam it over for you and relay the output to your terminal.

Here's the base code listing. Copy it — click on the copy icon in the top right corner of the listing; it'll appear as you mouse over the code — and paste it into your text editor.

(information)

Info

You can find the a complete listing of the code, including all subsequent additions, at our public GitHub repo.

Don't send it over to the Pico just yet — you'll need to complete Step 3 first.

1from machine import UART, Pin, I2C
2from utime import ticks_ms, sleep
3import json
4
5class MCP9808:
6    """
7    A simple driver for the I2C-connected MCP9808 temperature sensor.
8    This release supports MicroPython.
9    """
10
11    # *********** PRIVATE PROPERTIES **********
12
13    i2c = None
14    address = 0x18
15
16    # *********** CONSTRUCTOR **********
17
18    def __init__(self, i2c, i2c_address=0x18):
19        assert 0x00 <= i2c_address < 0x80, "ERROR - Invalid I2C address in MCP9808()"
20        self.i2c = i2c
21        self.address = i2c_address
22
23    # *********** PUBLIC METHODS **********
24
25    def read_temp(self):
26        # Read sensor and return its value in degrees celsius.
27        temp_bytes = self.i2c.readfrom_mem(self.address, 0x05, 2)
28        # Scale and convert to signed value.
29        temp_raw = (temp_bytes[0] << 8) | temp_bytes[1]
30        temp_cel = (temp_raw & 0x0FFF) / 16.0
31        if temp_raw & 0x1000: temp_cel -= 256.0
32        return temp_cel
33
34class HT16K33:
35    """
36    A simple, generic driver for the I2C-connected Holtek HT16K33 controller chip.
37    This release supports MicroPython and CircuitPython
38
39    Version:    3.0.2
40    Bus:        I2C
41    Author:     Tony Smith (@smittytone)
42    License:    MIT
43    Copyright:  2020
44    """
45
46    # *********** CONSTANTS **********
47
48    HT16K33_GENERIC_DISPLAY_ON = 0x81
49    HT16K33_GENERIC_DISPLAY_OFF = 0x80
50    HT16K33_GENERIC_SYSTEM_ON = 0x21
51    HT16K33_GENERIC_SYSTEM_OFF = 0x20
52    HT16K33_GENERIC_DISPLAY_ADDRESS = 0x00
53    HT16K33_GENERIC_CMD_BRIGHTNESS = 0xE0
54    HT16K33_GENERIC_CMD_BLINK = 0x81
55
56    # *********** PRIVATE PROPERTIES **********
57
58    i2c = None
59    address = 0
60    brightness = 15
61    flash_rate = 0
62
63    # *********** CONSTRUCTOR **********
64
65    def __init__(self, i2c, i2c_address):
66        assert 0x00 <= i2c_address < 0x80, "ERROR - Invalid I2C address in HT16K33()"
67        self.i2c = i2c
68        self.address = i2c_address
69        self.power_on()
70
71    # *********** PUBLIC METHODS **********
72
73    def set_blink_rate(self, rate=0):
74        """
75        Set the display's flash rate.
76        """
77        assert rate in (0, 0.5, 1, 2), "ERROR - Invalid blink rate set in set_blink_rate()"
78        self.blink_rate = rate & 0x03
79        self._write_cmd(self.HT16K33_GENERIC_CMD_BLINK | rate << 1)
80
81    def set_brightness(self, brightness=15):
82        """
83        Set the display's brightness (ie. duty cycle).
84        """
85        if brightness < 0 or brightness > 15: brightness = 15
86        self.brightness = brightness
87        self._write_cmd(self.HT16K33_GENERIC_CMD_BRIGHTNESS | brightness)
88
89    def draw(self):
90        """
91        Writes the current display buffer to the display itself.
92        """
93        self._render()
94
95    def update(self):
96        """
97        Alternative for draw() for backwards compatibility
98        """
99        self._render()
100
101    def clear(self):
102        """
103        Clear the buffer.
104        """
105        for i in range(0, len(self.buffer)): self.buffer[i] = 0x00
106        return self
107
108    def power_on(self):
109        """
110        Power on the controller and display.
111        """
112        self._write_cmd(self.HT16K33_GENERIC_SYSTEM_ON)
113        self._write_cmd(self.HT16K33_GENERIC_DISPLAY_ON)
114
115    def power_off(self):
116        """
117        Power on the controller and display.
118        """
119        self._write_cmd(self.HT16K33_GENERIC_DISPLAY_OFF)
120        self._write_cmd(self.HT16K33_GENERIC_SYSTEM_OFF)
121
122    # ********** PRIVATE METHODS **********
123
124    def _render(self):
125        """
126        Write the display buffer out to I2C
127        """
128        buffer = bytearray(len(self.buffer) + 1)
129        buffer[1:] = self.buffer
130        buffer[0] = 0x00
131        self.i2c.writeto(self.address, bytes(buffer))
132
133    def _write_cmd(self, byte):
134        """
135        Writes a single command to the HT16K33. A private method.
136        """
137        self.i2c.writeto(self.address, bytes([byte]))
138
139class HT16K33Segment(HT16K33):
140    """
141    Micro/Circuit Python class for the Adafruit 0.56-in 4-digit,
142    7-segment LED matrix backpack and equivalent Featherwing.
143
144    Version:    3.0.2
145    Bus:        I2C
146    Author:     Tony Smith (@smittytone)
147    License:    MIT
148    Copyright:  2020
149    """
150
151    # *********** CONSTANTS **********
152
153    HT16K33_SEGMENT_COLON_ROW = 0x04
154    HT16K33_SEGMENT_MINUS_CHAR = 0x10
155    HT16K33_SEGMENT_DEGREE_CHAR = 0x11
156    HT16K33_SEGMENT_SPACE_CHAR = 0x00
157
158    # The positions of the segments within the buffer
159    POS = (0, 2, 6, 8)
160
161    # Bytearray of the key alphanumeric characters we can show:
162    # 0-9, A-F, minus, degree
163    CHARSET = b'\x3F\x06\x5B\x4F\x66\x6D\x7D\x07\x7F\x6F\x5F\x7C\x58\x5E\x7B\x71\x40\x63'
164
165    # *********** CONSTRUCTOR **********
166
167    def __init__(self, i2c, i2c_address=0x70):
168        self.buffer = bytearray(16)
169        super(HT16K33Segment, self).__init__(i2c, i2c_address)
170
171    # *********** PUBLIC METHODS **********
172
173    def set_colon(self, is_set=True):
174        """
175        Set or unset the display's central colon symbol.
176        """
177        self.buffer[self.HT16K33_SEGMENT_COLON_ROW] = 0x02 if is_set is True else 0x00
178        return self
179
180    def set_glyph(self, glyph, digit=0, has_dot=False):
181        """
182        Present a user-defined character glyph at the specified digit.
183        """
184        assert 0 <= digit < 4, "ERROR - Invalid digit (0-3) set in set_glyph()"
185        assert 0 <= glyph < 0xFF, "ERROR - Invalid glyph (0x00-0xFF) set in set_glyph()"
186        self.buffer[self.POS[digit]] = glyph
187        if has_dot is True: self.buffer[self.POS[digit]] |= 0x80
188        return self
189
190    def set_number(self, number, digit=0, has_dot=False):
191        """
192        Present single decimal value (0-9) at the specified digit.
193        """
194        assert 0 <= digit < 4, "ERROR - Invalid digit (0-3) set in set_number()"
195        assert 0 <= number < 10, "ERROR - Invalid value (0-9) set in set_number()"
196        return self.set_character(str(number), digit, has_dot)
197
198    def set_character(self, char, digit=0, has_dot=False):
199        """
200        Present single alphanumeric character at the specified digit.
201        """
202        assert 0 <= digit < 4, "ERROR - Invalid digit set in set_character()"
203        char = char.lower()
204        char_val = 0xFF
205        if char == "deg":
206            char_val = HT16K33_SEGMENT_DEGREE_CHAR
207        elif char == '-':
208            char_val = self.HT16K33_SEGMENT_MINUS_CHAR
209        elif char == ' ':
210            char_val = self.HT16K33_SEGMENT_SPACE_CHAR
211        elif char in 'abcdef':
212            char_val = ord(char) - 87
213        elif char in '0123456789':
214            char_val = ord(char) - 48
215        assert char_val != 0xFF, "ERROR - Invalid char string set in set_character()"
216        self.buffer[self.POS[digit]] = self.CHARSET[char_val]
217        if has_dot is True: self.buffer[self.POS[digit]] |= 0x80
218        return self
219
220'''
221Send an AT command - return True if we got an expected
222response ('back'), otherwise False
223'''
224def send_at(cmd, back="OK", timeout=1000):
225    # Send the command and get the response (until timeout)
226    buffer = send_at_get_resp(cmd, timeout)
227    if len(buffer) > 0: return (back in buffer)
228    return False
229
230'''
231Send an AT command - just return the response
232'''
233def send_at_get_resp(cmd, timeout=1000):
234    # Send the AT command
235    modem.write((cmd + "\r\n").encode())
236
237    # Read and return the response (until timeout)
238    return read_buffer(timeout)
239
240'''
241Read in the buffer by sampling the UART until timeout
242'''
243def read_buffer(timeout):
244    buffer = bytes()
245    now = ticks_ms()
246    while (ticks_ms() - now) < timeout and len(buffer) < 1025:
247        if modem.any():
248            buffer += modem.read(1)
249    return buffer.decode()
250
251'''
252Module startup detection
253Send a command to see if the modem is powered up
254'''
255def boot_modem():
256    state = False
257    count = 0
258    while count < 20:
259        if send_at("ATE1"):
260            print("The modem is ready")
261            return True
262        if not state:
263            print("Powering the modem")
264            module_power()
265            state = True
266        sleep(4)
267        count += 1
268    return False
269
270'''
271Power the module on/off
272'''
273def module_power():
274    pwr_key = Pin(14, Pin.OUT)
275    pwr_key.value(1)
276    sleep(1.5)
277    pwr_key.value(0)
278
279'''
280Check we are attached
281'''
282def check_network():
283    is_connected = False
284    response = send_at_get_resp("AT+COPS?")
285    line = split_msg(response, 1)
286    if "+COPS:" in line:
287        is_connected = (line.find(",") != -1)
288        if is_connected: print("Network information:", line)
289    return is_connected
290
291'''
292Configure the modem
293'''
294def configure_modem():
295    # NOTE AT commands can be sent together, not one at a time.
296    # Set the error reporting level, set SMS text mode, delete left-over SMS
297    # select LTE-only mode, select Cat-M only mode, set the APN to 'super' for Super SIM
298    send_at("AT+CMEE=2;+CMGF=1;+CMGD=,4;+CNMP=38;+CMNB=1;+CGDCONT=1,\"IP\",\"super\"")
299    # Set SSL version, SSL no verify, set HTTPS request parameters
300    send_at("AT+CSSLCFG=\"sslversion\",1,3;+SHSSL=1,\"\";+SHCONF=\"BODYLEN\",1024;+SHCONF=\"HEADERLEN\",350")
301    print("Modem configured for Cat-M and Super SIM")
302
303'''
304Open/close a data connection to the server
305'''
306def open_data_conn():
307    # Activate a data connection using PDP 0,
308    # but first check it's not already open
309    response = send_at_get_resp("AT+CNACT?")
310    line = split_msg(response, 1)
311    status = get_field_value(line, 1)
312
313    if status == "0":
314        # Inactive data connection so start one up
315        success = send_at("AT+CNACT=0,1", "ACTIVE", 2000)
316    elif status in ("1", "2"):
317        # Active or operating data connection
318        success = True
319
320    print("Data connection", "active" if success else "inactive")
321    return success
322
323def close_data_conn():
324    # Just close the connection down
325    send_at("AT+CNACT=0,0")
326    print("Data connection inactive")
327
328'''
329Start/end an HTTP session
330'''
331def start_session(server):
332    # Deal with an existing session if there is one
333    if send_at("AT+SHSTATE?", "1"):
334        print("Closing existing HTTP session")
335        send_at("AT+SHDISC")
336
337    # Configure a session with the server...
338    send_at("AT+SHCONF=\"URL\",\"" + server + "\"")
339
340    # ...and open it
341    resp = send_at_get_resp("AT+SHCONN", 2000)
342    # The above command may take a while to return, so
343    # continue to check the UART until we have a response,
344    # or 90s passes (timeout)
345    now = ticks_ms()
346    while ((ticks_ms() - now) < 90000):
347        #if len(resp) > 0: print(resp)
348        if "OK" in resp: return True
349        if "ERROR" in resp: return False
350        resp = read_buffer(1000)
351    return False
352
353def end_session():
354    # Break the link to the server
355    send_at("AT+SHDISC")
356    print("HTTP session closed")
357
358'''
359Set a standard request header
360'''
361def set_request_header():
362    global req_head_set
363
364    # Check state variable to see if we need to
365    # set the standard request header
366    if not req_head_set:
367        send_at("AT+SHCHEAD")
368        send_at("AT+SHAHEAD=\"Content-Type\",\"application/x-www-form-urlencoded\";+SHAHEAD=\"User-Agent\",\"twilio-pi-pico/1.0.0\"")
369        send_at("AT+SHAHEAD=\"Cache-control\",\"no-cache\";+SHAHEAD=\"Connection\",\"keep-alive\";+SHAHEAD=\"Accept\",\"*/*\"")
370        req_head_set = True
371
372'''
373Make a request to the specified server
374'''
375def issue_request(server, path, body, verb):
376    result = ""
377
378    # Check the request verb
379    code = 0
380    verbs = ["GET", "PUT", "POST", "PATCH", "HEAD"]
381    if verb.upper() in verbs:
382        code = verbs.index(verb) + 1
383    else:
384        print("ERROR -- Unknown request verb specified")
385        return ""
386
387    # Attempt to open a data session
388    if start_session(server):
389        print("HTTP session open")
390        # Issue the request...
391        set_request_header()
392        print("HTTP request verb code:",code)
393        if body != None: set_request_body(body)
394        response = send_at_get_resp("AT+SHREQ=\"" + path + "\"," + str(code))
395        start = ticks_ms()
396        while ((ticks_ms() - start) < 90000):
397            if "+SHREQ:" in response: break
398            response = read_buffer(1000)
399
400        # ...and process the response
401        lines = split_msg(response)
402        for line in lines:
403            if len(line) == 0: continue
404            if "+SHREQ:" in line:
405                status_code = get_field_value(line, 1)
406                if int(status_code) > 299:
407                    print("ERROR -- HTTP status code",status_code)
408                    break
409
410                # Get the data from the modem
411                data_length = get_field_value(line, 2)
412                if data_length == "0": break
413                response = send_at_get_resp("AT+SHREAD=0," + data_length)
414
415                # The JSON data may be multi-line so store everything in the
416                # response that comes after (and including) the first '{'
417                pos = response.find("{")
418                if pos != -1: result = response[pos:]
419        end_session()
420    else:
421        print("ERROR -- Could not connect to server")
422    return result
423
424'''
425Flash the Pico LED
426'''
427def led_blink(blinks):
428    for i in range(0, blinks):
429        led_off()
430        sleep(0.25)
431        led_on()
432        sleep(0.25)
433
434def led_on():
435    led.value(1)
436
437def led_off():
438    led.value(0)
439
440'''
441Split a response from the modem into separate lines,
442removing empty lines and returning all that's left or,
443if 'want_line' has a non-default value, return that one line
444'''
445def split_msg(msg, want_line=99):
446    lines = msg.split("\r\n")
447    results = []
448    for i in range(0, len(lines)):
449        if i == want_line:
450            return lines[i]
451        if len(lines[i]) > 0:
452            results.append(lines[i])
453    return results
454
455'''
456Extract the SMS index from a modem response line
457'''
458def get_sms_number(line):
459    return get_field_value(line, 1)
460
461'''
462Extract a comma-separated field value from a line
463'''
464def get_field_value(line, field_num):
465    parts = line.split(",")
466    if len(parts) > field_num:
467        return parts[field_num]
468    return ""
469
470'''
471Blink the LED n times after extracting n from the command string
472'''
473def process_command_led(msg):
474    blinks = msg[4:]
475    print("Blinking LED",blinks,"time(s)")
476    try:
477        led_blink(int(blinks))
478    except:
479        print("BAD COMMAND:",blinks)
480
481'''
482Display the decimal value n after extracting n from the command string
483'''
484def process_command_num(msg):
485    value = msg[4:]
486    print("Setting",value,"on the LED")
487    try:
488        # Extract the decimal value (string) from 'msg' and convert
489        # to a hex integer for easy presentation of decimal digits
490        hex_value = int(value, 16)
491        display.set_number((hex_value & 0xF000) >> 12, 0)
492        display.set_number((hex_value & 0x0F00) >>  8, 1)
493        display.set_number((hex_value & 0x00F0) >>  4, 2)
494        display.set_number((hex_value & 0x000F), 3).update()
495    except:
496        print("BAD COMMAND:",value)
497
498'''
499Get a temperature reading and send it back as an SMS
500'''
501def process_command_tmp():
502    print("Sending a temperature reading")
503    celsius_temp = "{:.2f}".format(sensor.read_temp())
504    if send_at("AT+CMGS=\"000\"", ">"):
505        # '>' is the prompt sent by the modem to signal that
506        # it's waiting to receive the message text.
507        # 'chr(26)' is the code for ctrl-z, which the modem
508        # uses as an end-of-message marker
509        r = send_at_get_resp(celsius_temp + chr(26))
510
511'''
512Make a request to a sample server
513'''
514def process_command_get():
515    print("Requesting data...")
516    server = "YOUR_BEECEPTOR_URL"
517    endpoint_path = "/api/v1/status"
518
519    # Attempt to open a data connection
520    if open_data_conn():
521        result = issue_request(server, endpoint_path, None, "GET")
522        if len(result) > 0:
523            # Decode the received JSON
524            try:
525                response = json.loads(result)
526                # Extract an integer value and show it on the display
527                if "status" in response:
528                    process_command_num("NUM=" + str(response["status"]))
529            except:
530                print("ERROR -- No JSON data received. Raw:\n",result)
531        else:
532            print("ERROR -- No JSON data received")
533
534        # Close the open connection
535        close_data_conn()
536
537'''
538Listen for incoming SMS Commands
539'''
540def listen():
541    print("Listening for Commands...")
542    while True:
543        # Did we receive a Unsolicited Response Code (URC)?
544        buffer = read_buffer(5000)
545        if len(buffer) > 0:
546            lines = split_msg(buffer)
547            for line in lines:
548                if "+CMTI:" in line:
549                    # We received an SMS, so get it...
550                    num = get_sms_number(line)
551                    msg = send_at_get_resp("AT+CMGR=" + num, 2000)
552
553                    # ...and process it for commands
554                    cmd = split_msg(msg, 2).upper()
555                    if cmd.startswith("LED="):
556                        process_command_led(cmd)
557                    elif cmd.startswith("NUM="):
558                        process_command_num(cmd)
559                    elif cmd.startswith("TMP"):
560                        process_command_tmp()
561                    elif cmd.startswith("GET"):
562                        process_command_get()
563                    else:
564                        print("UNKNOWN COMMAND:",cmd)
565                    # Delete all SMS now we're done with them
566                    send_at("AT+CMGD=,4")
567
568# Globals
569req_head_set = False
570
571# Set up the modem UART
572modem = UART(0, 115200)
573
574# Set up I2C and the display
575i2c = I2C(1, scl=Pin(3), sda=Pin(2))
576display = HT16K33Segment(i2c)
577display.set_brightness(2)
578display.clear().draw()
579
580# Set up the MCP9808 sensor
581sensor = MCP9808(i2c=i2c)
582
583# Set the LED and turn it off
584led = Pin(25, Pin.OUT)
585led_off()
586
587# Start the modem
588if boot_modem():
589    configure_modem()
590
591    # Check we're attached
592    state = True
593    while not check_network():
594        if state:
595            led_on()
596        else:
597            led_off()
598        state = not state
599
600    # Light the LED
601    led_on()
602
603    # Begin listening for commands
604    listen()
605else:
606    # Error! Blink LED 5 times
607    led_blink(5)
608    led_off()

This is the basis of the code you'll work on through the remainder of the guide. What does it do? Much of it is the code you worked on last time, so let's focus on the additions.

To communicate with Internet resources, the modem needs to establish a data connection through the cellular network, and then an HTTP connection to the target server. Lastly, it creates and sends an HTTP request to that server, and reads back the response.

The function open_data_conn() handles the first part, by sending the AT command CNACT=0,1. The 0 is the 'Packet Data Protocol (PDP) context', essentially one of a number of IP channels the modem provides. The 1 is the instruction to enable the data connection.

When the data connection is up, the code calls start_session() to open an HTTP connection to a specific server, which is passed in as an argument. The server is set using AT+SHCONF="URL","<SERVER_DOMAIN>" and the connection then opened with AT+SHCONN.

Requests are made through the function issue_request(). It calls start_session() and then sets up the request: we build the header on the modem (and keep it for future use) and then send AT+SHREQ= with the path to a resource and the value 1 as parameters — the 1 indicates it is a GET request.

The response returned by the modem contains information about the data returned by the server, which is stored on the modem. The code uses this information to get the HTTP status code — to check the request was successful — and the response's length. If the latter is non-zero, the code sends AT+SHREAD= to retrieve that many bytes from the modem's cache. issue_request() extracts any JSON in the response and returns it.

All this is triggered by the receipt of an SMS command, GET, which causes the function process_command_get() to be called. This function calls open_data_conn() and then issue_request(). It parses the received data as JSON and displays the value of a certain field on the LED display using code you worked on in the previous tutorial.

(information)

Info

When the code runs, it turns off the Pico's built-in LED. The LED will flash rapidly five times if there was a problem booting the modem.

The LED is turned on when the device is attached to the network. If the LED is flashing slowly, that means it has not yet attached. Please be patient; it will attach shortly.

3. Set up a data source

Before you can run the code, you need to set up the data that will be retrieved. You're going to use Beeceptor as a proxy for the Internet resource your IoT device will be communicating with. In a real-world application, you would sign up to use a specific service and access that, but Beeceptor makes a very handy stand-in. Let's set it up to receive HTTP GET requests from the device.

In a web browser tab, go to Beeceptor.
Enter an endpoint name in the large text field and click Create Endpoint:
On the screen that appears next, click on the upper of the two clipboard icons to copy the endpoint URL:
Keep the tab open.
Jump back to your text editor and locate the process_command_get() function in the Python code. Paste the endpoint URL you got from step 3, in place of YOUR_BEECEPTOR_URL.
Save the file and then transfer it over to the Pico.
Hop back to Beeceptor and click on Mocking Rules (0) in the page shown above and then click Create New Rule.
In the third field, add api/v1/status right after the / that's already there.
Under Response Body, paste the following JSON, your test API's sample output:
{ "userId":10,"status":1234,"title":"delectus aut autem","completed":false,"datapoints":[1,2,3,4,5,6,7,8,9,0] }
The panel should look like this:
Click Save Rule and then close the Mocking Rules panel by clicking the X in the top right corner.
Again, keep the tab open.

4. Try out the code

Switch over to Minicom (or PuTTY). When you see the Listening for commands... message, open a separate terminal tab or window and enter the following command:

1twilio api:supersim:v1:sms-commands:create \
2  --sim "<YOUR_SIM_NAME_OR_SID>" \
3  --payload GET

You'll need to replace the sections in angle brackets (< and >) with your own information, just as you did last time. Your SIM's SID — or friendly name if you've set one — and the specified account credentials are all accessible from the Twilio Console.

This command uses the Super SIM API's SMS Commands API to send a machine-to-machine message to the Pico. The --payload parameter tells Twilio what the body of the SMS should be: it's whatever comes after the equals sign. In this case, that's GET, the command to which we want the Pico to respond.

The listen() function in your Python code keeps an ear open for incoming SMS messages, which are signalled by the module transmitting a string that includes the characters +CMTI:. If it appears, the code sends a new AT command to the modem to get the message (AT+CMGR) and then awaits a response. When the response comes, the code processes it and extracts the GET — which tells the device to make an HTTP request of that type.

You'll see all this in your terminal window:

The GET request's progress in the terminal.

You should also see 1234 displayed on the LED — one part of the data received from the API you connected to!

(information)

Info

The code listed above will output state messages, but if you want to see the full flow of AT command requests and their responses, you'll need to add a handful of extra lines. To do so, drop in this function:

1'''
2Output raw data
3'''
4def debug_output(msg):
5    for line in split_msg(msg): print(">>> ",line)

and add this line right before the final return in the function read_buffer():

debug_output(buffer.decode())

The output will now look like this:

5. Post data from the device

Reaching out across the Internet and requesting information is only half of the story: you also want to push data out to the cloud. Our Pico-based IoT demo is well prepared to be a source of information: it includes a temperature sensor which you can read and transmit the result by SMS if you send the command TMP by text message.

Not all data receivers accept input by SMS, however. Most will accept POST requests, though, so let's add the code to the application to support that. There are a number of changes and additions to make.

Add the following code right below the def set_request_header(): function definition:

1'''
2Set request body
3'''
4def set_request_body(body):
5    send_at("AT+SHCPARA;+SHPARA=\"data\",\"" + body + "\"")
6
7'''
8Make a GET, POST requests to the specified server
9'''
10def get_data(server, path):
11    return issue_request(server, path, None, "GET")
12
13def send_data(server, path, data):
14    return issue_request(server, path, data, "POST")

Replace the existing issue_request() function with this code:

1def issue_request(server, path, body, verb):
2    result = ""
3
4    # Check the request verb
5    code = 0
6    verbs = ["GET", "PUT", "POST", "PATCH", "HEAD"]
7    if verb.upper() in verbs:
8        code = verbs.index(verb) + 1
9    else:
10        print("ERROR -- Unknown request verb specified")
11        return ""
12
13    # Attempt to open a data session
14    if start_session(server):
15        print("HTTP session open")
16        # Issue the request...
17        set_request_header()
18        print("HTTP request verb code:",code)
19        if body != None: set_request_body(body)
20        response = send_at_get_resp("AT+SHREQ=\"" + path + "\"," + str(code))
21        start = ticks_ms()
22        while ((ticks_ms() - start) < 90000):
23            if "+SHREQ:" in response: break
24            response = read_buffer(1000)
25
26        # ...and process the response
27        lines = split_msg(response)
28        for line in lines:
29            if len(line) == 0: continue
30            if "+SHREQ:" in line:
31                status_code = get_field_value(line, 1)
32                if int(status_code) > 299:
33                    print("ERROR -- HTTP status code",status_code)
34                    break
35
36                # Get the data from the modem
37                data_length = get_field_value(line, 2)
38                if data_length == "0": break
39                response = send_at_get_resp("AT+SHREAD=0," + data_length)
40
41                # The JSON data may be multi-line so store everything in the
42                # response that comes after (and including) the first '{'
43                pos = response.find("{")
44                if pos != -1: result = response[pos:]
45        end_session()
46    else:
47        print("ERROR -- Could not connect to server")
48    return result

Replace the process_command_get() function with all of the following code:

1'''
2Make a request to a sample server
3'''
4def process_command_get():
5    print("Requesting data...")
6    server = "YOUR_BEECEPTOR_URL"
7    endpoint_path = "/api/v1/status"
8    process_request(server, endpoint_path)
9
10def process_command_post():
11    print("Sending data...")
12    server = "YOUR_BEECEPTOR_URL"
13    endpoint_path = "/api/v1/logs"
14    process_request(server, endpoint_path, "{:.2f}".format(sensor.read_temp()))
15
16def process_request(server, path, data=None):
17    # Attempt to open a data connection
18    if open_data_conn():
19        if data is not None:
20            result = send_data(server, path, data)
21        else:
22            result = get_data(server, path)
23
24        if len(result) > 0:
25            # Decode the received JSON
26            try:
27                response = json.loads(result)
28                # Extract an integer value and show it on the display
29                if "status" in response:
30                    process_command_num("NUM=" + str(response["status"]))
31            except:
32                print("ERROR -- No JSON data received. Raw:\n",result)
33        else:
34            print("ERROR -- No JSON data received")
35
36        # Close the open connection
37        close_data_conn()

When you've done that, copy and paste your Beeceptor endpoint URL into the places marked YOUR_BEECEPTOR_URL.

Finally, add the following lines to the listen() function, right below the code that looks for a GET command:

1elif cmd.startswith("POST"):
2    process_command_post()

Finally, transfer the updated program to the Pico.

5. Set up a data sink

You can't send data without somewhere to post it, so set that up now. Once more, Beeceptor comes to our assistance: you're going to add a mocking rule as a stand-in for an application server that will take in the data the device posts and return a status message.

Switch to the web browser tab showing Beeceptor.
Click on Mocking Rules (1) and then Create New Rule.
Under Method, select POST.
In the third field, add api/v1/logs right after the / that's already there.
Under Response Body, paste the following JSON:
{ "status":4567 }
The panel should look like this:
Click Save Rule and then close the Mocking Rules panel by clicking the X in the top right corner.
Again, keep the tab open.

6. Try out the code — part deux

Switch over to Minicom (or PuTTY). When you see the Listening for commands... message, open a separate terminal tab or window and enter the following command, filling in your details where necessary:

1twilio api:supersim:v1:sms-commands:create \
2  --sim "<YOUR_SIM_NAME_OR_SID>" \
3  --payload POST

This time, you'll see all this in your terminal window:

The POST request's progress in the terminal.

You should also see 4567 displayed on the LED — one part of the data received bacl from the API. Speaking of the API, what did it see? Take a look at Beeceptor. It records the receipt of a POST request to /api/v1/logs, and if you click on the entry in the table, then the JSON icon ({:}) above the Request body panel, you'll see the celsius temperature as received data:

7. Next steps

You now have a Raspberry Pi Pico-based IoT device that can send and receive data across the Internet. In this demo, you've used test APIs for getting and posting data, and triggered both by manually sending an SMS command. Why not adapt the code not only to make use of different APIs — perhaps one you might make use of in your production IoT device — but also to do so automatically, at a time appropriate to the application? For example, you might include a regular weather forecast update, or pull in the output from a Slack channel. You might post device status data to your own cloud.

Wherever you take your Raspberry Pi Pico-based IoT device next, we can't wait to see what you build!

Note

When this was written, of course: the Pico W has been release since then. Back to top