Make it with Micromite
Phil Boyce – hands on with the mighty PIC-powered, BASIC microcontroller
Part 26: Having fun with a Micromite Plus
L
ast month, we discussed the
main differences between the various
versions of MMBASIC (Standard,
Plus, and eXtreme). We also highlighted
some of the different hardware modules
that are available for use with these different
versions of MMBASIC.
Throughout this series, we have used
the Standard version of MMBASIC. There
are two good reasons for this; first, it is
the ideal starting point when learning
about MMBASIC; and second, it is the
only version of the firmware that loads
onto an easy-to-solder DIP IC – ie, the
28-pin PIC that we used in the easy-tobuild Micromite Keyring Computer (MKC).
Over this month, and next, we are going
to work through a fun (and hopefully
useful) project based around the more
powerful Micromite Plus. Ultimately,
this means that we have more I/O pins
available than the MKC, which in turn
means we can add hardware modules that
have more than just the usual handful of
pins. In this project we will be connecting
to various hardware modules including
a 64x32 RGB LED matrix display panel
(see Fig.1), which requires 13 I/O pins.
Using Micromite Plus also means we
have many new MMBASIC commands at
our disposal; so, in this project we will be
adding access to an SD card. We will show
you how to write data to an SD card (which
effectively means we will be creating a data
logger), and also show you how to use a
bitmap image that is stored on the SD card
and display it on the 64x32 RGB panel.
In addition to the RGB panel and the SD
card, we will also use a couple of items
that we have previously used elsewhere
in this series: an infrared (IR) receiver and
a real-time clock module (RTC). By now,
you will be familiar with using these on the
MKC, and you will see just how easy it is
to migrate them from the MKC for use with
a Micromite Plus (it’s the same MMBASIC
commands, just different pin numbers).
Project overview
If you haven’t already guessed from the
introduction above (and the photo opposite),
we are going to create a smart clock that uses
an RGB LED matrix panel as the display
(Fig.2). This is the type of panel that you
see in electronic signage that is appearing
everywhere. However, those signs typically
use many tens or hundreds of panels to
form the overall display, whereas we will
just be using a single panel. Nevertheless,
our single-panel display allows the time to
be easily viewed from several metres away,
making it extremely useful in larger rooms.
It also looks fantastic!
In addition to the date and time, it also
displays the current temperature. The
temperature, date and time are all logged at
regular intervals onto an SD card. The SD
card can then be inserted into a computer
and the data viewed in another application,
such as a spreadsheet or graph. To add a
fun element to this project, we will also
incorporate the Mastermind game that
we created earlier in the series (Part 15).
Incorporating an IR receiver means we
are able to use an IR remote transmitter to
control everything – so here we will use
it to select a function from a simple menu
in order to switch between the clock and
the Mastermind game; and yes, you will
be able to play the Mastermind game by
remote control while sitting several meters
away in your favourite chair. One other
menu option will allow you to display a
bitmap file stored on the SD card, albeit the
resolution will be limited to the display’s
pixel resolution of 64x32.
Building blocks
This project will require the following main
hardware items:
• Micromite Plus Explore 64 module
• 64x32 RGB LED panel
• RTC module
• IR receiver
• IR transmitter
• 5V PSU.
In addition, you will require a piece of
stripboard to mount everything on, along
with some wire-links, and various pin-strips,
sockets and a couple of screw terminals.
You will also need a micro-SD card to
Fig.1. A typical 64x32 RGB LED matrix panel (LR): a) front, b) rear, c) connection to it is via a 2x8 connector (ribbon cable) with the
pinout as shown.
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Practical Electronics | March | 2021
Fig.2. This fun project looks amazing
when housed in a photo frame that uses
a dark, LED-friendly front panel.
store the temperature data and any 64x32
bitmap image files.
Optionally, you can add an HC-05
Bluetooth module (as discussed in Part
14), allowing you to remotely access the
Micromite Plus and make code changes
from the comfort of your armchair!
You may have noticed that there is
no temperature sensor listed above – so
how can it display the temperature? The
answer is that the RTC module is based on
the DS3231 chip, and this has a built-in
temperature sensor, so no separate sensor
is required. Access to the temperature
value within the RTC is via software, more
on that next month – this month, we will
just focus on hardware. First, let’s discuss
how to source the above items.
Micromite Plus
Explore 64 module
Various versions of the Explore 64 module
(also known as the E64) have been released
over the last few years. However, they all
comprise a 64-pin PIC pre-programmed
with MMBASIC Plus, and they all have an
onboard microSD socket. The E64 has two
rows of downward-facing pins that allow
it to be easily plugged into a breadboard,
or alternatively plugged into your own
custom-board via two rows of sockets
(as in this project). All versions of the
E64 have the same footprint, and pinout
sequence for all of the I/O pins and power
pins. Hence, any version can be use in
this project. It’s available from micromite.
org for just £29.95 plus shipping. For
further technical details, including a
circuit diagram of the original E64, please
visit: https://geoffg.net/Explore64.html
64x32 RGB LED panel
The RGB panel is the focus of this project
and they’re available from many places.
Practical Electronics | March | 2021
However, the cost varies considerably,
from about £20, up to just over £100. Do
not let this put you off; an online search
for ‘RGB LED Matrix Panel 64x32’ will
lead you to places where you pay the
lower end of this price range. You will see
references to the ‘pitch’, which essentially
means the distance in mm between the
pixel centres. The pitch is often referred
to as the ‘P’ number, so an ‘LED matrix
64x32 P4’ means the pixels are 4mm apart.
Multiply this by 64 (and add a bit for the
edges) and this gives an approximation to
the physical length of the panel (ie, a bit
longer than 25.6cm). So, the higher the P
number, the bigger the panel. Typical P
numbers are: 2.5, 3, 4, 5, 6, 8 and 10. The
panel shown in the photo (Fig.2) is a P3,
which is nice and compact. Two warnings
when choosing a panel; first, do ensure
it is a 64x32 (and do not go for a smaller
or larger one as the display driver won’t
work correctly); and second, do check it
has a 2x8 interface with pins labelled as
in Fig.1. If the pin names are the same,
but in a different sequence, then it will be
fine to use, but you will need to modify
the stripboard wire-links accordingly. It is
far easier to just find a matching pinout.
In the past I have used one from here (no
affiliation): http://bit.ly/pe-mar21-miwm1
RTC module
This is the same small DS3231 RTC module
as used previously in this series for various
other projects. It comes with a pre-soldered
5-way socket. You can search online for
‘RPi GPIO RTC’ to find many places from
which to source this module cheaply. One
example of a reliable UK seller (and no
affiliation) is: http://bit.ly/pe-mar21-miwm2
IR Receiver and Transmitter
This project uses the usual TSOP4840 (or
TSOP4838) IR receiver that we have used
several times in this series. So, you probably
already have one; however, if not, they are
readily available online. Likewise, with the
transmitter, we have used two different
types in this series; a smaller one for the
Electronic Dice (Part 5), and a 44-button
transmitter for the Mood Light (Part 13).
Note that literally any IR Transmitter can
be used providing it meets either of the two
common IR protocols (NEC or Sony). All
we need to do is alter the project’s program
code slightly in order to decipher the various
IR codes from any button presses. This will
be covered next month.
5V PSU
The RGB panel has a total of 2048 pixels (ie,
64x32). Each pixel comprises three LEDs
(R, G, B), meaning that there are 6144 LEDs
in total. Taking into account that each LED
requires circa 15mA, this equates to an
immense amount of power. However, the
RGB panel’s internal circuitry multiplexes
the LEDs, which essentially means that the
potential number of LEDs turned on at any
one moment in time is limited to a finite
number, much lower than 6144. The result
is that multiplexing reduces the maximum
power required significantly. Even so, a
decent 5V power supply must be used for
this project, and you certainly don’t want
to drive it from your computer’s USB port
(which is typically limited to a maximum
of 500mA). We recommend an official
Raspberry Pi 4 Power Supply, available
online for around £7.50. They can reliably
supply 5.1V at up to 3A. They come with
a hardwired USB-C connector on the end,
but we can simply cut this off to expose
the 0V and 5.1V wires which are inserted
into a 2-way screw terminal. Alternatively,
you can use a redundant tablet charger
which should be able to supply 2.1A.
Otherwise just use any 5V power supply
with a minimum delivery of 2A.
SD card
The E64 works with any micro-SD card
that has a capacity between 8GB and 64GB.
There is no need to buy the latest highspecification card, but we do recommend
using a branded one. For example, a 16GB
SanDisk card should cost around £8.
Circuit diagram
As with all our circuits in this series, it is
just a matter of connecting the relevant pins
from the various items to the correct I/O
pins on the Micromite; and then supplying
power to each item. In this project, we need
to connect the MM+ to the RGB panel (13
I/O), the RTC (2 I/O), and the IR receiver
(1 I/O). All the pin numbers used in this
project are shown in Fig.3.
The RGB panel is driven by a display
driver that effectively ‘bit-bangs’ the
required signals over 13 standard I/O pins.
The RTC communicates via I2C and hence
is connected to the E64’s I2C Data and Clock
pins (pins 43 and 44 respectively); and the
IR receiver connects to the E64’s IR input pin
(pin 51). All three items, including the E64,
require a 5V supply, and this is supplied via
the external PSU described above.
Connectors are not shown in Fig.3;
however, they are discussed below in the
construction section.
Assembly
Apart from the RGB panel and the PSU,
everything is assembled onto a piece of
stripboard which is 36 tracks wide, with 26
holes in each track. The RGB panel is then
attached via a short ribbon cable (supplied
with the RGB panel); and the 5V PSU is
attached via a 2-way screw-terminal. Fig.4
shows the stripboard layout which includes
the wire links, track cuts, and component
(or rather connector) placements.
To begin with, cut the stripboard to size,
and then make the 11 ‘regular’ track cuts
47
Fig.3. (left) This project comprises an E64, RGB panel, RTC
module and IR receiver.
Micromite Exp lore 6 4
21 49 27 2
1 63 62 60
1
64
2
63
3
62
CLK
shown in Fig.4. There are also eight additional track cuts
that need extra care as they are made mid-way between rows
A
R2
R1
P and Q in tracks 1-8 (marked in red in Fig.4). Ensure that
4
61
all 19 track-cuts fully extend the width of the track (either
S K 2
5
60
visually, or ideally by using a continuity tester). Next, use
6
59
D
0V
0V
0V
a pencil to mark out the end positions of the 25 wire links,
58
MCLR
B
G2
G1
8
55
recheck the markings, then go ahead and install them. Two
0V 52 24 3 0V 64 0V 61
11
54
2-way screw terminals (SK1 and SK3) may require the
12
53
stripboard holes to be made slightly bigger – if so, use an
13
52
appropriately sized drill bit.
14
51
SK2 is a shrouded socket to which the RGB panel connects
15
50
R TC
via
an IDC ribbon cable connector. This is 8x2 in size, and
16
49
0V N C C D 5V
if you don’t have one available, then you can use two rows
17
48
of 8-way header pins instead. However, you will then need
18
47
to take great care when you attach the RGB panel’s ribbon
21
46
0V
44 43 5V
22
45
cable connector to ensure it is inserted the correct way round.
23
44
JS1 is a 3-way socket, allowing the IR receiver to be plugged
24
43
in (and removed if needed elsewhere). Alternatively, you can
27
42
solder the IR receiver directly into this position, avoiding the
I R x receiver
28
TS OP 4 8 (3 8 / 4 0)
need for JS1. Do ensure that the IR receiver’s ‘bump’ is facing
29
Data
5V
outwards and away from the stripboard.
3.3V
30
JP1 is a 5-pin header, to which the RTC module is attached,
51
5V
5V
31
0V
and
JS4 is a 6-way socket into which the optional HC-05
0V
32
0V
Bluetooth module can be inserted. Apart from JS2 and JS3,
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now mount all of the screw terminals, header pins and sockets
as required. When it comes to the ‘long sockets’ JS2 and JS3,
extra attention is required. Essentially, they can be
made up of several shorter header sockets that are
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6
A
A
JS1
butted up together to create the 27 positions. However,
B
B
SK1
it is essential that you pull out the contacts from the
C
C
D
D
JP1
socket’s housing for all unused pins. This is easily
E
E
achieved with a pair of nose pliers or side cutters. To
F
F
G
G
JS2
clarify, you should be left with contacts only in the
H
H
I
I
positions marked in Fig.4 (ie, in the top row: G10-14,
J
J
G16, G20-21, G23, G28-29, G34-35; and the bottom
K
K
L
L
row: P10-12, P15, P26, P29-30). If you do not carry
M
M
out this step, then you will certainly run the risk of
N
N
O
O
SK2
JS3
permanent damage to the E64. Once all the redundant
P
Cuts P
contacts have been removed, solder in these sockets.
Q
Q
R
R
As always, do a thorough visual check when you
S
S
have finished assembly. Do not be tempted to insert
T
T
U
U
any modules yet as they will be added gradually next
V
V
month during the testing process.
W
W
SK3
JS4
OE
C
B2
B1
LAT
X
X
Y
Y
1 2
3
4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6
Z
Y
X
W
V
U
T
S
R
Q
P
O
N
M
L
K
J
I
H
G
F
E
D
C
B
A
Z
Y
X
W
V
U
T
S
R
Q
P
O
N
M
L
K
J
I
H
G
F
E
D
C
B
A
1 2
48
Next month
Z
Z
3
4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6
After the hardware assembly, next month we will test
it bit-by-bit, configuring the Micromite Plus as we
go. Then, to finish, we will show you how to make
everything come together by installing the appropriate
program code. In the meantime, why not take a look
at the Micromite Plus User Manual (available for
download from the March 2021 page of the PE website).
and explore some of the many additional features that
your new hardware provides. Until then, have fun!
Fig.4. (left) The top and bottom sides of the
stripboard showing the position of all the required
track cuts, wire links, and connectors.
Questions? Please email Phil at:
contactus<at>micromite.org
Practical Electronics | March | 2021
