Make it with Micromite
Phil Boyce – hands on with the mighty PIC-powered, BASIC microcontroller
Part 35: Mini-Project: iButton-controlled Electronic Door Lock
T
his month, we are going to
n If the iEDL display is also a touchscreen,
begin the iButton Electronic Door
Lock (iEDL) mini-project. The idea
is to bring together the topics covered in the
last three articles (January – March 2022)
of the Make it with Micromite (MIWM)
series and put all we learnt to practical use.
Do note that we will not be describing
details of the various electromechanical
door solenoids (or ‘holding magnets’) that
are typically used for locking/releasing
a door. Our iEDL will simply provide a
set of change-over relay contacts that
can either be interfaced with an existing
electromechanical lock, or alternatively
used to control any new mechanicalhardware that needs to be installed.
The concept behind the iEDL is simple
– issue an iButton key to anyone that
is permitted to open (ie, access) one or
any selected door(s) in a building. For
example, doors around the home, in
an office environment or even a large
commercial business premises. An iEDL
is located next to each restricted door,
and on presenting a valid iButton key, a
person can unlock the door. This might
sound the same as any other simple
electronic door lock, so what makes the
iEDL so special?
then for extra security a PIN can also
be requested (in addition to presenting
the iButton-key)
n Using a ‘master Configuration Button
key’, the iEDL can be triggered to enter
a configuration mode. The ability
to switch the iEDL to behave as a
configuration tool avoids the need
to link the iEDL to a computer, and
creates a standalone solution
n In configuration mode, the name of the
keyholder can be programmed into an
EEPROM iButton key
n In configuration mode, an iButton
key can be reassigned to a new user
or wiped from the system
n In configuration mode, an iEDL can be
programmed with a descriptor (such
as ‘Staff Entrance’), and this can be
shown on the iEDL display
n This project really comes to life when
more than one iEDL is implemented on
a site. Each iEDL can be programmed
with a single Category ID, which can be
set when the iEDL is in configuration
mode. If access settings (ie, one or more
Category IDs) are also programmed
into an EEPROM key (as well as the
keyholder’s name), then a user can be
granted access to certain category doors,
but denied access to other category
doors. This also means that an iEDL does
not need to contain a list of valid key
numbers – instead, the single Category
ID programmed into the iEDL is checked
against the Category IDs programmed
into the presented EEPROM iButton,
and access is then either permitted, or
denied, accordingly.
iEDL features
The simple answer is there’s a Micromite
at the heart of our iEDL, so it can easily be
programmed in MMBASIC with as many
features and options that we can dream
up; and thus we can create a much more
intelligent and flexible lock. For example:
n Incorporate a TFT display in the iEDL,
so the name of the person trying to gain
access can be shown – this creates a
better user experience
Micromite code
The code in this article is available
for download from the PE website.
66
Fig.1. Three MIWM modules are used in
the iEDL prototype: (from top to bottom)
a) The Micromite Keyring Computer
(MKC); b) The Development Module
(DM); c) The TFT-adaptor (complete with
piezo sounder).
Practical Electronics | April | 2022
From the above list of examples, it
can be seen how the functionality of the
solution could be made to behave in an
intelligent way. All that is required is
a change to the main program-code in
the iEDL; with the hardware remaining
exactly the same. We will be incorporating
many of the above features (next month),
but first we need to discuss how to
assemble an iEDL.
Hardware
As mentioned above, the iEDL hardware is
built around a Micromite; so, in keeping
with the original concept of this series,
the prototype iEDL was based on the
following modules:
n Micromite Keyring Computer (MKC –
from MIWM Part 2, PE March 2019)
– see Fig.1a
n Development Module (DM – from MIWM
Part 3, PE April 2019) – see Fig.1b
n TFT-adaptor (MIWM Part 15, PE April
2020) – see Fig.1c. This contains the
touchscreen, as well as a piezo sounder
n iButton reader (from MIWM Part 32,
PE Jan 2022) – see Fig.2
n LED (if not built into the iButton
reader), plus current-limiting resistor
n Low-cost relay module – see Fig.3.
Note that the MKC and DM can be
substituted with an alternative Micromite
module, as has been discussed elsewhere
in this series. For example, it is possible
to use an Explore28 (or Explore64), but
this would need to be hard-wired to a
touch-TFT. To avoid having to hardwire a TFT, it is better to use a 28-pin
Micromite BackPack module (version 2
– see PE, May 2018; PCBs are available
from the PE PCB Service) which would
just need the required iButton reader,
LED, piezo sounder and relay module
to be connected.
Once you have chosen your preferred
Micromite to build the iEDL, you just need
to add the required external parts. To
assist with assembly, please refer to Fig.4;
Fig.2. The DS9092L is our preferred
iButton reader. It contains a centremounted LED which assists in locating
the exact position for where to present
the iButton.
Practical Electronics | April | 2022
this summarises the
Micromite pin number
connections to all the
other parts of the iEDL.
A point worth
noting here is that
the cost of an iEDL is
around £50 (uncased),
so it is a much cheaper
solution compared
to commercially
available door-access
systems – but, can
be fully configured
(ie, programmed) to
behave as you need
it to. (Do note that
questions relating to
compatibility of the
iEDL with your home
or work insurance
provider are your
responsibility!)
a)
b)
26
T_IRQ
15
T_DO
14
L S1
Piezo buzze
T_DI
3
r
T_CS
7
22
T_CL K
SDO
(MISO )
L ED
SCK
25
SDI (MO SI)
2
R1
1
c)
3.3V
iButton reader
R2
7
D/ C
23
RESET
6
9
iButton
CS
0V
G ND
5V
V CC
d)
5V
J4
TFT
0V
R3
1
e)
NO
21
L ED1
CO M
0V
NC
5V
10
Circuit assembly
Fig.4. Pin connections between the Micromite and the five main
The most complex elements of the iEDL: a) The TFT has 14 contacts connected
connection inside as shown (note the 10Ω backlight resistor); b) the piezo is
the iEDL is between connected between pin 26 (PWM 2A) and I/O pin 22; c) The
the Micromite and the iButton reader (with 4.7kΩ pull-up) is connected between I/O
touchscreen. If you pin 9, and 0V; d) An LED (and series current-limiting resistor)
are using an MKC, DM is connected between I/O pin 10, and 5V; e) The relay module
and TFT-adaptor, then needs 5V power. I/O pin 21 controls the change-over contact.
these connections are
channel 2A, and I/O pin 22 is set low (or
already made for you (and likewise if
high, rather than left ‘floating’), then a
using a 28-pin Backpack). However,
tone will be heard. Unless you are using
if you are building an iEDL with an
an MKC with the TFT adaptor (which
Explore28 (or Explore64) module,
has a built-in piezo), you will need to
then you will need to make the ten
connect an external piezo sounder to
connections shown in Fig.4a, plus the
the Micromite.
10Ω current-limiting resistor required for
The iButton reader is connected to Pin 9,
the TFT backlight. These connections
as shown in Fig.4c. This requires a 4.7kΩ
ensure all aspects of the touchscreen
pull-up resistor to function correctly (as
work when using the Micromite’s builtexplained in MIWM Part 32, PE Jan 2022).
in TFT driver.
Whether the iButton reader has a builtTo provide audible feedback to the user,
in LED, or you use an external LED,
a piezo sounder is connected between
you will require the usual LED currentpin 26 and pin 22 (see Fig.4b). Pin 26
limiting resistor to be connected in series.
is a PWM output, and when MMBASIC
The exact value will depend on the
is set to output a square wave on PWM
LED being used, but a typical value is
somewhere between 330Ω and 1kΩ. This
LED is useful for highlighting where
the iButton reader is located in dark
conditions. It is connected to pin 10,
as shown in Fig.4d; setting pin 10 low
turns the LED on.
Finally, the relay module is connected
to Micromite pin 21 (and 5V power),
as shown in Fig.4e. Setting pin 21 low
turns the relay on (and hence switches
the relay’s change-over contacts).
Hardware assembly is straightforward
Fig.3. This low-cost relay module is
whichever Micromite module you use;
readily available online. It contains a set
and it’s easy to understand how the
of change-over contacts, and hence can
Micromite interacts with each element.
be interfaced to the electromechanical
Remember, it is the MMBASIC code
hardware that in turn controls the locking/
which makes everything come to life (and
releasing of the door.
enables the intelligence and features).
67
Fig.7. GUI TEST TOUCH allows you to test the accuracy of the calibration. If it’s too
inaccurate, simply use GUI CALIBRATE again.
Fig.5. GUI TEST LCDPANEL should
result in this built-in test-pattern animation
appearing on the TFT screen.
Configuring the iEDL
Once you have completed the required
connections between the Micromite and
each iEDL element, perform all the usual
visual checks. When everything looks
correct, apply power to the iEDL, and then
connect the Micromite to your preferred
terminal program (eg, TeraTerm). When
a connection is established, you will
need to configure two specific Micromite
OPTIONs, followed by careful calibration of
the touchscreen. So, assuming that the two
OPTIONs aren’t yet set, start by configuring
the TFT display driver with the command:
OPTION LCDPANEL ILI9341,L,2,23,6
On pressing Enter, the TFT should go
blank (rather than appearing whiteish/
grey). If it doesn’t, then power down,
recheck everything, then power back up.
The TFT’s backlight should flash briefly,
and then the display will go blank. Now
type GUI TEST LCDPANEL and you
should see the usual built-in animated
test pattern (a circles patterns – see Fig.5).
Next, you need to configure the
touchscreen. This is carried out with the
command OPTION TOUCH 7,15 followed
by the command GUI CALIBRATE
On pressing Enter, the TFT will
display the calibration screen, as shown
in Fig.6. Follow the onscreen instructions
using a plastic stylus to touch the four
crosshairs that pop up, one at a time.
Once this step is completed, you can
check the accuracy of calibration by
typing the command GUI TEST TOUCH
On pressing ENTER, the screen will clear,
and you can use a stylus to write words
on the screen (see Fig.7). If the position of
the pixels appearing are offset too far from
the tip of the stylus, then you will need to
recalibrate the screen (GUI CALIBRATE).
Once accurate screen configuration has
been completed you can proceed to testing
the piezo sounder, the LED, the relay
module and the iButton reader.
Testing the iEDL
Fig.6. The touchscreen is calibrated with
the command GUI CALIBRATE. Use a
plastic stylus and simply follow the onscreen instructions to complete calibration.
68
To test the piezo sounder, begin by setting
PWM channel 2A (pin 26) to output a
square wave with a frequency of 1kHz.
This is achieved by typing the command:
PWM 2,1000,50 (1000Hz with a 50%
duty cycle). Nothing should be heard at
this point since you also need to set pin
22 to 0V, which is achieved by typing the
command: SETPIN 22,DOUT
On pressing Enter, you should hear
the piezo sounder (if not, then check the
commands have been typed correctly, and
also the piezo’s two pins are connected to
pins 26 and 22. The tone of the sounder
can be changed by altering the relevant
PWM parameter. To see this (or rather to
hear it), type: PWM 2,500,50
This will change the frequency from
1kHz to 500Hz. The piezo is silenced
by typing: SETPIN 22,OFF (which
causes pin 22 to float). Alternatively,
the piezo sounder can be silenced by
typing: PWM 2,STOP
The LED is tested by setting I/O pin
10 to a digital output. To turn it on, set
pin 10 low by typing: SETPIN 10,DOUT
If the LED does not light, first
check the command has been entered
correctly, then check the connections
to the series resistor, and to the LED. Be
sure to check the value of the resistor
is somewhere in the region between
330Ω to 1kΩ. If it is too high (possibly
due to mis-reading the resistor’s colour
bands) then the chances are the LED
could be so dim, that it appears not to
be working at all. If after these checks it
still doesn’t light, then ensure that the
LED is installed correctly (remember,
LEDs are polarised components and
hence they must be inserted the correct
way round).
Once the LED is lit, then check it is turned
off by typing the command: PIN(10)=1
The relay module is tested in a similar
way as the LED – simply replace the
reference to pin 10 with pin 21. Thus,
to energise the relay, type the following
command: SETPIN 21,DOUT
You should hear the relay click; if not,
perform the usual checks. Once this is
working correctly, ensure you can switch
the relay off again by typing: PIN(21)=1
(again, you should hear a click as the relay
coil is de-energised).
Finally, you need to test the iButton
reader. To do this, you will require at least
one iButton; this can be either a DS1990
(ID only), or a DS1971 (EEPROM) iButton.
Type in the following program into
the EDITor:
DO
ONEWIRE RESET 9
TEXT 160,120,MM.ONEWIRE,CM,1,3
PAUSE 10
LOOP
Practical Electronics | April | 2022
Fig.8. The AZTouch enclosure is
an attractive wall
mounted case.
a) (left) the image
that convinced
me to try and fit
an iEDL inside.
b) (right) my first
attempt at fitting
the iEDL into a
modified AZ-Touch
enclosure. Note
the iButton reader
lower right.
Next, RUN the program and check that a 0 character is
displayed in the centre of the TFT. Then tap (and hold) an
iButton onto the reader and make sure that the 0 changes
to a 1 while the iButton is in contact with the reader. If this
test fails, then check the code is entered correctly, and also
that the iButton reader is connected to pin 9. Also check the
value of the pull-up resistor; it needs to be 4.7kΩ.
Once the above tests have been successfully completed,
then we can be guaranteed that the iEDL has been assembled
correctly. The iEDL is now ready for the main program
code to be loaded; however, this will have to wait until
next month. So, in the meantime, why not try and modify
some of the recent iButton demo code so that it displays
information (such as the iButton’s unique ID number) on the
TFT display instead of in the Terminal screen. Essentially,
this means replacing the relevant PRINT commands with
TEXT commands, along with using the correct parameters
that the TEXT command requires. Refer to the simple DO...
LOOP program listed above for such an example, and also
refer to the Micromite User Manual to check the parameters
used – for example, to add some colour.
that the version of the iEDL shown in the photo is based
on an Explore64, and is positioned behind the front panel,
rather than installed inside the enclosure. I just thought that
I would share this first attempt at trying to fit an iEDL into
an AZ-Touch enclosure. I hope this inspires you to think
about how to house your iEDL.
Next time
Now that we have assembled, configured, and tested the
iEDL mini-project, next month we will discuss how the
program code works. Until then, stay safe, and have FUN!
Housing the iEDL
One thing to think about is how to install the iEDL into a
suitable enclosure. Many technically brilliant electronic
projects are let down by being housed in a poor casing. Custom
3D-printed enclosures have become more popular over the
last few years; however, this approach is only practical if
you have access to a 3D-printer (and arguably have lots of
spare time to print the numerous prototypes that you’ll end
up printing so that you get everything positioned correctly).
However, one nice looking (and readily available) enclosure
that grabbed my attention recently was the AZ-Touch (see
Fig.8). This is a wall-mounted unit with a cut-out for either
a 2.4-inch or 2.8-inch ILI9341 touchscreen. As a bonus, a
compatible ILI9341 TFT is included in the AZ-Touch kit
(Google for a list of AZ-Touch sources).
Although many pictures online show the AZ-Touch
mounted in a portrait orientation, there is nothing stopping
us from using this enclosure in a landscape orientation. So,
I decided to purchase a handful of these kits and attempted
to modify things to see if I could successfully house the iEDL
inside. An early prototype is shown in Fig.8b, but do note
Practical Electronics | April | 2022
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