Make it with Micromite
Phil Boyce – hands on with the mighty PIC-powered, BASIC microcontroller
Part 40: Simple PicoMite GPS tracker
T
his month, we will demonstrate how easy it is
to build a simple GPS tracker based around a PicoMite. To
do this, we will connect a low-cost Pico GPS module to
a PicoMite BackPack. The GPS module that we will use in this
article is the Waveshare Pico-GPS-L76X (see Fig 1) – however,
you could substitute this with any other model of Pico (or nonPico) GPS receiver with only minor changes to the program code
(and possibly the physical connections). There are three main
reasons for choosing this specific GPS module, it is:
1. Cheap (approx. £15, incl magnetic GPS antenna mount)
2. Available from many online suppliers
3. Plug-and-play, so no wiring or soldering is required.
We will use the 2.8-inch version of the PicoMite BackPack,
which incorporates the Waveshare Pico-ResTouch-LCD-2.8
module (discussed in Part 38). Many other screens could be
used, but we have chosen this one since not only does it have
a suitable pixel-resolution for displaying lots of GPS data, but
also it incorporates an onboard micro-SD socket, which is useful
for saving logged GPS data to a micro-SD card.
The GPS tracker program code is easy to build thanks to
MMBASIC’s built-in set of GPS commands. So, grab yourself
these three modules (or equivalent) and let’s begin.
Setting up the PicoMite BackPack
First, you need to set up a PicoMite BackPack with the
Waveshare Pico-ResTouch-LCD-2.8. If you already have this
BackPack set up then simply jump to the next section (GPS
module overview); however, in case you missed Part 38, we
will quickly describe the necessary steps.
1. Download the latest PicoMite Firmware (for free) from:
https://geoffg.net/picomite.html (Note: scroll to the
‘Downloads’ section at the bottom of the page and click on
the ‘DOWNLOAD’ button for: PicoMite firmware V5.07.0x
(includes the manual). Remember to ‘Extract all’ to unzip
the folder’s contents.
2. Install the PicoMiteV5.07.0x.uf2 Firmware file (from step
1) into the Pico module. Refer to Make it with Micromite,
Part 37 or the Getting Started section in the User Manual
from step 1 for details on how to do this.
3. Connect the Waveshare Pico-ResTouch-LCD-2.8 display
module. You can either use an expander board (recommended),
Micromite code
The code in this article is available for download from
the October 2022 page of the PE website.
46
Fig 1. The low-cost Waveshare Pico-GPS-L76X is designed
for use with the Pico. This module has both pins and sockets,
enabling us to sandwich it in a stack between the PicoMite and a
display module, thus creating a simple GPS Tracker.
or plug the display module directly into the PicoMite. Note
that if you connect them directly together then you will need
to separate them again when you insert the GPS module later.
The GPS module is sandwiched between the PicoMite and
the display module, so an expander board makes it a little
easier to initially set things up – see Fig 2.
4. Connect the PicoMite to your preferred terminal app (eg,
TeraTerm), and configure the following OPTIONS:
OPTION CPUSPEED 252000 (to run the PicoMite at 252MHz)
OPTION SYSTEM SPI GP10,GP11,GP12 (configure the
SPI bus)
OPTION LCDPANEL ST7789_320,L,GP8,GP15,GP9,GP13
(configure the display module)
GUI TEST LCDPANEL (check the screen is set up correctly)
OPTION TOUCH GP16,GP17 (configure the touch)
GUI CALIBRATE (calibrate the touch)
GUI TEST TOUCH (check the touch calibration)
OPTION SDCARD GP22 (configure the micro-SD card)
The above is just a summary of the required configuration to
create a PicoMite BackPack. If you have any issues, or would
like to configure a different display module, then please refer
to the User Manual (or read Make it with Micromite, Part 38).
Practical Electronics | October | 2022
Fig 2. By using an expander board, it is much easier to connect the PicoMite,
display module, and GPS module to initially set up the GPS Tracker. Note the
orientation of each module.
GPS module overview
The Waveshare Pico-GPS-L76X GPS is a low-cost, plug-andplay module that is widely available. It has useful benefits
such as fast positioning (with battery back-up), high accuracy,
low power consumption and various LEDs for indicating the
modules operating status. A close-up of both sides of the
module is shown in Fig.3.
Like most other GPS modules, it has UART for (serial)
communication, with a selectable baud rate of between 4800
and 115200bps (9600bps by default). This makes it easy to
connect to the PicoMite since the program code just needs
to communicate via an MMBASIC COM port. All we need to
know is the relevant pin numbers used for serial
transmit (Tx) and serial receive (Rx). Refer to
Fig.4 for a detailed pinout of the Pico-GPSL76X GPS module – you will see that only four
connections are used.
Note that there is one small disadvantage of this
module – the onboard battery holder supports an
ML1220 rechargeable cell. These are hard to source;
however, the good news is that a battery is not
essential; it just means that on power up the GPS
module takes a bit longer to get the initial satellite
fix (typically between one and two minutes). (If
you find a source of the ML1220, then do please
drop me an email with the details.)
Connecting the GPS module
If you use an expander board, then simply insert the GPS
module into any available header. It is important to plug it in
the right way round – refer to Fig.2 to see the correct orientation.
The alternative is to create a stack of boards. To do this, you
will first need to carefully separate the PicoMite from the display
module, and then insert the GPS module between them. Again,
it is important to get the GPS module the right way round, so
refer to Fig.5 to see the correct stack orientation.
Once the GPS module is installed, carefully screw the antenna
into the larger end of the supplied adaptor, and then insert
the smaller end of the adaptor into the
socket on the GPS module (item number
3 in Fig.3). Ensure that you position the
antenna so that it has a good line of sight to
the sky. This is so it stands a better chance
of seeing multiple GPS satellites, which in
turn means it will receive a better signal
containing more accurate data.
GPS data
1. L76B module
6. Backup mode wakeup button
2. Battery holder – supports ML1220 rechargeable cell,
for preserving ephemeris information and hot starts
7. RT9193-33 – power chip
3. GNSS antenna connector
4. Raspberry Pi Pico header
5. Standby mode switch
8. Status indicators
RXD/TXD: UART TX/RX indictor
PPS: GPS status indicator
PWR: power indicator
Fig 3. Top and bottom view of the various on-board elements of the Waveshare
Pico-GPS-L76X.
Fig 4. Pinout of the Pico-GPS-L76X module. Just four pins are required, two for power,
and two for serial communication. Note that the GPS Rx pin is on GP0 (PicoMite
COM1 Tx pin), and GPS Tx is on GP1 (PicoMite COM1 Rx pin).
Practical Electronics | October | 2022
Before we explore MMBASIC’s built-in GPS
commands, let’s first look at the format of
GPS data. Fig.6 shows a snapshot of actual
raw data grabbed directly from the Pico
GPS module (via a USB-to-serial module,
and displayed in TeraTerm which was set
to a baud rate of 9600). GPS raw data is
made of multiple ‘sentences’, each one
containing various GPS data. Typically,
a set of sentences is output every second
from the GPS receiver. The type of each
sentence is indicated by the characters at
the start of the line (after the initial ‘$’).
For example, the second line in Fig 6 is a
GNGGA sentence (technically referred to
as a ‘Global Positioning System Fix Data’
sentence). A GNGGA sentence contains
useful GPS data such as time, latitude,
longitude, number of satellites and altitude.
The content of this (and other) sentences
is well documented online (a worthwhile
reference is: http://aprs.gids.nl/nmea/) so
we won’t go into further detail here. Note
that it is not essential to understand the
exact format of sentences for our tracker,
we are just providing a reference for
readers who want to read more about the
specific details. So how do we go about
extracting the relevant elements of GPS
data in MMBASIC?
In earlier versions of the Micromite
firmware, serial communication with
47
Fig 5. Here, the
PicoMite, GPS
and display
modules
can be seen
stacked
together. Note
the correct
orientation of
each module.
a GPS module meant receiving serial data into a COM port
input buffer. The program code then searched for the start of
a sentence (indicated by a ‘$’ character), and/or the end of a
sentence (Carriage Return and Line Feed). Once detected, the
program code would then work through the first few bytes in
the sentence to check the type of sentence (and hence, what
data follows). In brief, the program code looks for a required
sentence match (for example ‘GNGGA’). Only when the required
sentence type is found can the relevant data be extracted in
a meaningful way. This whole process is quite complex to
code, but it is possible.
The great news is that everything has now been made so much
easier with the PicoMite Firmware thanks to the set of GPS
commands (or more specifically, GPS functions). These remove
all the programming complexities since all you now need to
do is use the appropriate parameter, and the relevant data will
automatically be returned. For example, to extract the time you
would use GPS(Time); likewise, GPS(Satellites) will return
the number of satellites being detected by the GPS antenna.
However, before using any of the GPS functions, it is important
to include the following two lines of code somewhere near
the start of the program:
SETPIN GP1,GP0,COM1
OPEN "COM1: 9600,256" As GPS
The first line defines the PicoMite’s Rx pin and Tx pin for use
with serial port COM1 – in Fig.4 you can see these are GP1
and GP0 respectively.
The second line opens up COM1 for use with a serial GPS
receiver. The parameters define the baud rate as 9600bps, and
a receive buffer size of 256 bytes.
MMBASIC’s GPS functions
With the above two lines near the start of the program code,
we are then able to use any of the GPS functions. The most
important function is GPS(VALID). This function should be
used before any of the other GPS functions are used to ensure
that any subsequent data requested is valid. It returns a value
of 0 for invalid data (triggered when a sentence’s checksum
value is incorrect), and a value of 1 for valid data (ie, the
sentence’s checksum value is as expected). Your program
code just needs to check for a value of 1, then it can safely use
the required GPS function(s) knowing that the returned data
represents a true value.
The following is a list of the more common GPS functions
available (all are used in our GPS Tracker code):
GPS(DATE) Returns the normal date string corrected for
local time; eg, 28-08-2022
GPS(TIME) Returns the normal time string corrected for
local time; eg, 12:22:53 – note that daylight saving is not
taken into account and has to be adjusted in program code
using (for example) the EPOCH command
GPS(SATELLITES) Returns number of satellites in view
GPS(LATITUDE) Returns the latitude in degrees as a floatingpoint number, values are negative south of the equator
GPS(LONGITUDE) Returns the longitude in degrees as a
floating-point number, values are negative west of the
Greenwich meridian
GPS(ALTITUDE) Returns the current altitude
GPS(SPEED) Returns the ground speed in knots as a floatingpoint number
GPS(TRACK) Returns the track over the ground (degrees
true) as a floating-point number
GPS(FIX) Returns non-zero (true) if the GPS has a fix on
sufficient satellites and is producing valid data
There are two further functions available for more advanced
users (neither are used in our GPS Tracker code):
GPS(DOP) Returns DOP (dilution of precision) value
GPS(GEOID) Returns the geoid-ellipsoid separation
You can try any of the above at the command prompt to see
what a function returns. Begin by typing these two lines:
SETPIN GP1,GP0,COM1
OPEN "COM1: 9600,256" As GPS
Next, type the relevant function at the command prompt, for
example:
PRINT GPS(DATE)
You can then try the other functions
without having to type the first two lines
again. So continue with something like
PRINT GPS(SATELLITES) to see the
number of satellites.
Remember that in our program we
should always check that GPS(VALID)
returns a value of 1 (we have not used
it at the command prompt as we are
just demonstrating the output from the
various GPS functions).
Fig 6. A sample of GPS raw data as it outputs from the GPS receiver. Note that each
sentence starts with a ‘$’ character, followed by the type of sentence, and then all the
GPS data follows to the end of the line.
48
Tracker software
Now that we have all the hardware
connected, it’s time to load the GPS
Tracker software into your PicoMite.
Practical Electronics | October | 2022
As can be seen from Fig 7, the basic GPS data is formatted
onto the 2.8-inch display so that you can continually see
what is happening in terms of received data. (Note that the
data logged to the SD card is limited to a maximum of one
record per second).
A useful test at this point is to mount the GPS set up in a
vehicle, and then go for a drive with the purpose of gathering
a good set of data on the SD card. Please do take all necessary
precautions while driving – or put it another way, keep your
eyes on the road and not on the GPS tracker’s display! Once
a set of data is obtained, remove the SD card from the display
module, and insert it into a computer. Open the log file which
will be named trkDATA_yymmdd_hhmmss.csv (but with the
current date and time values) and you will be able to view
the logged data.
You can use something like Google maps to plot the longitude
and latitude co-ordinates to see the precise location plotted
onto a map – doubtless some websites can plot all the data
points in one go to show the path taken on your test drive
(more on this next month).
That’s it. You can see how everything works. Why not edit
the program code to make your own custom version of the GPS
tracker? Try adding some new features – here are a few ideas:
Change the layout of the screen to show only the data you’re
interested in
Add a ‘logged-record’ counter to indicate how many entries
have been logged onto the SD card
Add a parameter to the program code that determines how
often data is logged to the SD card
Limit logging to the SD card based on a change of position
rather than logging every second
Change the data logged to only include the fields you’re
interested in
Practical Electronics | October | 2022
removed (or is missing), show a warning message
Make a covert tracker unit that does not require a display.
Instead, use the PicoMite’s green ‘heartbeat’ LED as a
status indicator.
Next time
When I ordered the GPS module for this article, the supplier
accidentally sent me a finger-print reader module instead. They
let me keep it (and subsequently sent me the GPS module I
had originally ordered). I’ve examined the finger-print reader’s
datasheet, and it seemed like something that could easily be
connected to the PicoMite, so I challenged myself to see if I
could get the PicoMite to communicate with the reader, and
sure enough, the PicoMite easily interacted with it. However,
the complex part is to get the hardware to learn different
fingerprints, store the patterns internally, and then compare
any finger (touched onto the reader) against the stored patterns
and thus identify the user. Thankfully, all this intelligent
functionality is built into the finger-print reader, but that
means it is essential to have a thorough understanding of the
reader’s datasheet. Data communication between the PicoMite
and the reader is quite complex and has to be performed in
a very specific way for successful operation. Hence, it is all
down to the PicoMite program code which is currently a work
in progress. I hope next month to be able to show you how to
integrate a low-cost finger-printer reader module into your next
project – fingers crossed! Until then, stay safe, and have FUN!
Questions? Please email Phil at:
contactus<at>micromite.org
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The file you need is GPS_Tracker.txt which is available for
download from the October 2022 page of the PE website.
Once installed, it is worth taking a quick look at the program
code to see how it works. As usual, it is well commented so
it should be easy to follow what is going on. In summary, the
following steps occur:
1. COM1 is set up as a serial port for use with a GPS receiver
2. A welcome message is displayed briefly (it fades in, then
fades out)
3. The value of GPS(VALID) is checked:
a. If 0 (invalid data), then grey out any current data shown
on the 2.8-inch display and make the screen’s border red
b. If 1 (valid data) then:
i. Extract various GPS data (date, time, satellites, lat,
long, altitude, speed, tracking)
ii. Make the screen’s border green
iii. Display the various GPS data on the 2.8-inch display
(see Fig 7)
iv. Check if Time is different to last time:
If Time is still the same, then do nothing
If Time is different, then log GPS data to the SD card
4. Go to step 3
Add error checking; for example, when the SD card is
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Fig 7. The GPS
tracker program
displays various GPS
data on the 2.8-inch
display. All data is
also logged to the
micro-SD card.
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