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Make it with Micromite Phil Boyce – hands on with the mighty PIC-powered, BASIC microcontroller Part 14: Using Bluetooth to set your Micromite free S o far in this series, if you want to interact with your Micromite Keyring Computer (MKC) you have to physically connect it (and the Development Module (DM)) to your computer with a USB cable. Then, you run a terminal application such as TeraTerm on your computer. The terminal application acts purely as a ‘console’ which provides the Micromite with a screen (for output), and a keyboard (for input). You can think of this set-up as the Micromite being ‘USB tethered’ to a screen and keyboard – see Fig.1. Note that the physical length of the USB cable, which for technical reasons is usually no more than one metre, determines the maximum distance between the Micromite and computer. This month, we are going to show you how to ‘set your Micromite free’ by replacing the USB physical link with a wireless link. Using Bluetooth technology to create this wireless link, it becomes possible to separate your Micromite and computer from each other by up to 10m. First though, why would you want to use a wireless link instead of having the Micromite tethered to within a metre of your computer? Well, a wireless link opens up all kinds of remote-control projects and capabilities; for example:  Several sensors could be connected to a Micromite, and assembled into a waterproof enclosure that you locate outdoors. Sensor data can then be formatted in your Micromite code (with PRINT commands and Escape codes – see Part 8, September 2019) for display on your computer screen, which is located conveniently indoors.  A battery-powered robot-buggy could be created that incorporates an on-board Micromite. A Bluetooth link would Questions? Please email Phil at: contactus<at>micromite.org Practical Electronics | March | 2020 Computer Development Module (DM) Console Terminal app 3.3V Reg Screen D+ Keyboard COM x USB cable tether D− USB BoB USB port USB-to-serial Tx Rx Rx Tx 5V 3.3V Reg Micromite Micromite Keyring Computer (MKC) Fig.1. Using a USB cable to connect your MKC/DM to your computer results in them being tethered together. Distance apart is limited by length of USB cable – typically no more than 1m. allow the robot to roam freely, totally untethered; yet it can be fully controlled from your computer’s keyboard. (A Bluetooth-controlled robot-buggy will be a future project).  You could modify any of your existing projects to enable them to be accessed remotely. For example, adding Bluetooth to last month’s Mood Light project means that it can remain where you want it to be positioned, while customising the code from the comfort of your ‘remote’ computer. Computer These examples have probably inspired you with some ideas for wireless interaction with your Micromite. Let’s get started by understanding the design of this Bluetooth link. Design concept In Fig.1, you can see the familiar method we have used so far in this series to connect the MKC to the computer’s USB port via the USB-to-serial module inside the DM. Electrically, the USB-to-serial module deals with the complex USB Development Module (DM) Console Terminal app 3.3V Reg Screen D+ Keyboard COM x USB port D− USB-to-serial Tx Rx Serial link tether 5V USB BoB USB cable USB PSU USB BoB Rx 3.3V Reg Tx Micromite Micromite Keyring Computer (MKC) Fig.2. Rearranging the elements in Fig.1 results in a serial link tether. Theoretically, this means the computer and Micromite can now be separated by more than 1m. 53 Computer Development Module (DM) Console Terminal app 3.3V Reg USB-to-serial Screen D+ D− 5V USB 5V BoB Keyboard COM x 5V USB cable USB port Tx Rx Rx Tx Wireless tether Serial-towireless Serial-towireless USB PSU USB BoB 3.3V Reg Tx Rx Rx Tx 5V Micromite Micromite Keyring Computer (MKC) Fig.3. Adding a pair of USB-to-wireless modules to Fig.2 allows for an untethered wireless link between the computer and the Micromite. protocol, and provides a much simpler serial protocol that has two physical connections: Transmit (Tx) and Receive (Rx). These are the connections that the Micromite serial console uses. Now, without changing any connections, let’s reposition the elements shown in Fig.1 to create Fig.2. This version highlights that we’re using a ‘serial-link tether’ as opposed to a ‘USB cable tether’. The important point here is that a wired serial link is much easier to convert into a wireless link compared to converting a USB-tether link. We do this by introducing a pair of serial-to-wireless modules, one at either end of the serial-link – see Fig.3. Note that in this new layout, power and connectivity to the DM require the addition of a USB break-out-board (BoB) at the computer end. This is because the DM is no longer plugged into the MKC, which is where it got these connections previously. So, referring to Fig.2 and Fig.3, you can see that by adding a USB BoB at the computer end, the required power and data signals (D+ and D−) can be routed directly to the DM. At the Micromite end, we just need to power the MKC from a 5V STATUS LED USB power source. That’s the theory; now a quick look at a suitable serial-to-wireless module. HC-05 Bluetooth module The HC-05 is a low-cost Bluetooth serial-towireless module with all the functionality we need (see Fig.4). For now, simply consider a single HC-05 module as having two interfaces: a serial interface (Tx-pin and Rx-pin), and also a wireless Bluetooth interface. In use, any serial data sent (from an external device) to the HC-05’s receive pin (Rx) is wirelessly transmitted via Bluetooth (ideally to a paired Bluetooth device). Likewise, any Bluetooth data received by the HC-05 (from a paired Bluetooth device) is sent out serially on the transmit pin (Tx). Note that all of this happens without us having to worry about any of the technicalities of the Bluetooth protocol. Now consider having two HC-05s paired to each other via Bluetooth – see Fig.5. What the above translates into is that any serial data sent to the Rx pin on the left-hand HC05 is then automatically outputted on the Tx pin of the right-hand BUTTON c) d) EN VCC TXD GND RXD b) STATE a) Fig.4. (a) Pinout of the HC-05 serial-to-Bluetooth module. Some have the button soldered in place (b), and some don’t (c). Pins are labelled on the reverse of the module (d). 54 HC-05. Likewise, serial data received on the Rx pin on the right-hand HC-05 is automatically outputted from the Tx pin on the left-hand HC-05. In effect, we have created an untethered-wireless seriallink; and this is exactly what we need to replace the hard-wired ‘serial-link tether’ (see Fig.2 and Fig.3). Some of you with Bluetooth built into your computer may be wondering why we’re not using it at the ‘computer end’ of the wireless link, and therefore just use a single HC-05 at the ‘Micromite end’. You can indeed do this, but in practice there are many potential complications, such as: incompatible Bluetooth versions, driver issues, drop-out problems, other Bluetooth device(s) already paired to your computer’s Bluetooth… and so on. In the design presented here we will eliminate all of these potential issues by simply using a pair of low-cost HC-05 modules that form a dedicated wireless link to your Micromite. HC-05 hardware overview Referring to the diagram in Fig.4a, the hardware elements of the HC-05 that we need to concern ourselves with are the:  Six pins on a 0.1-inch single-row header (discussed below)  Small red status LED (flashes at different speeds to indicate various things – useful during testing)  Miniature button (to put the unit into configuration mode). Note that not all HC-05 modules come with the miniature button soldered into place (but the two solder pads will always be there – Fig.4c). If it is absent, use the two solder-pads to connect a 2-way 0.1-inch pin header, and use a jumper to mimic the button being pressed (required when we come to configure the HC-05 modules). Turning to the six pins on the module:  EN is the enable input. If left unconnected (as we are doing), or if tied high (+V) it will allow the HC-05 to operate. If taken low (linked to GND), the unit is disabled (and enters lowpower mode)  GND and VCC supply the required power (3.6V to 6V)  TXD and RXD are the two serial-interface pins  STATE is an output (active high) that indicates successful connection status of the Bluetooth module (a totally different function to the small on-board red LED). Notes regarding Bluetooth and the HC-05 If you have used Bluetooth before you will no doubt recognise terms such as: ‘master’, ‘slave’, ‘paired’, ‘bind’, and ‘passkey’. Several of these terms will become relevant when we initially create our Bluetooth link Practical Electronics | March | 2020 If any of the above is unclear, please don’t worry; we will cover most of Practical Electronics | March | 2020 these points as we work through the assembly and configuration of the Bluetooth link. After you have finished reading this article, do reread the above list. HC-05 HC-05 Tasks to implement the Bluetooth link EN VCC GND TXD RXD STATE EN VCC GND TXD STATE In order to create the wireless Bluetooth seriallink in Fig.5, we need to configure one HC-05 as a master, and the other HC-05 as a slave. Then we need to ensure that Fig.5. Using two HC-05 modules to create a wireless we bind them together so Bluetooth serial-link; effectively replacing a wired serial link that they automatically (represented by the dotted lines). connect to each other. Note that once they are both configured, adaptors will require a 6-way socket to it does not matter which HC-05 module allow the HC-05 module to be plugged in. in Fig.5 is the ‘master’, and which is the In addition, we will use an LED on each ‘slave’. This is because the two modules adaptor to show when the two Bluetooth together form a two-way (duplex) serialmodules are connected to each other (this link (Tx>Rx and Rx<Tx). Do not fall into will prove very useful when the modules the misconception that one module is a are positioned in different locations). ‘transmitter’, and the other is a ‘receiver’ Everything else on each adaptor is just – each is both. the required pins and/or sockets, to make To be able to configure the two HC-05 the relevant connections. Fig.6 shows the modules in the first place, and then go assembled adaptors. on to physically use them with our DM A really useful bonus (or rather, part and MKC (as shown in Fig.3), we need to of the design) is that the adaptor board at work through the following sequence of the computer end will also double up as tasks, T1 to T9: the HC-05 configuration unit. Let’s begin T1 Build an HC-05 Bluetooth interface with the first assembly task. (with BoB) for the DM (computer end) T2 Build an HC-05 Bluetooth interface T1: HC-05 adaptor for the DM for the MKC (Micromite end) This adaptor is designed to be plugged T3 If either HC-05 is without the miniature into the DM (from above) and needs the following specific requirements: button, then add a jumper link T4 Set terminal application settings to n  Correctly positioned pins (downward facing) allowing the adaptor to be HC-05 requirements plugged into the DM. T5 Configure one HC-05 as a slave T6 Configure the other HC-05 as a master n  A socket for the HC-05 module. This is just a 6-way socket and allows T7 Set terminal application settings back easy insertion, and removal, of an to Micromite requirements HC-05 (especially useful during the T8 Plug everything together configuration process). T9 Test the wireless Bluetooth link n  An LED and current-limiting resistor, which indicates that the HC-05 has Keeping the hardware simple successfully connected (via Bluetooth) Looking through the list above, you will to the other HC-05 module at the see that only the first three tasks involve Micromite end. Since we are creating any hardware construction – the rest is a Bluetooth link, we will use a blue configuration and testing. Referring back LED (you can use any colour, but do to Fig.3, you can see that the serial-touse the appropriate resistor value) wireless module (HC-05) at the computer end connects directly to the USB-to-serial n  A USB socket – this allows connection module (in the DM). Likewise, the HC-05 to the computer and is required because at the Micromite end connects directly to the DM does not have its own USB the MKC. So to keep the theme of ‘simple socket. We will use a USB BoB identical plug-in modules’ for the MKC and DM, to the one used in the MKC (see Fig.3). and also to keep construction to the bare minimum, we only need to assemble two You can see from the schematic (Fig.7) straightforward adaptor boards: one for that there is nothing complex – it’s just a the computer end that plugs into the matter of making the required connections DM (T1); and another for the Micromite between the USB BoB, the HC-05, the end that plugs into the MKC (T2). Both LED, and the DM (as outlined in Fig.3). RXD because they are part of the configuration that we will need to perform. Before we discuss the configuration in detail, there are several points that we need to highlight regarding Bluetooth and the HC-05 module: n  Bluetooth is a one-to-one wireless link that connects two devices n  To form a Bluetooth link, one end must be the ‘master’ Bluetooth device, and the other must be the ‘slave’ Bluetooth device. This means that two masters will not connect to each other, nor will two slaves n  For a master and a slave to connect to each other, they need to have the same ‘passkey’ (sometimes referred to as ‘passphrase’, or ‘password’) n  When two devices are communicating with each other via Bluetooth, they are regarded as being ‘connected’ and ‘paired’. No other device can join in the communication (remember, Bluetooth is a one-to-one connection) n  The HC-05 has two modes of operation: ‘configuration’ (also known as AT mode), and ‘communication’ (also known as Data mode) n  In configuration mode, there are several settings that can be altered. These settings ultimately affect how the HC-05 behaves when in Data mode n  To enter configuration mode, the HC-05 module is powered up while pressing the module’s button (or shorting the link on modules without a button) n  Configuration settings are sent to the HC-05 via the serial link (Rx and Tx pins) at a fixed baud rate of 38,400 n  Configuration settings can be sent to the HC-05 from any terminal application, such as TeraTerm (use the same terminal app you currently use when connecting to the Micromite via the DM) n  To configure a setting, use the format: AT+setting_name=value (this is why configuration mode is also referred to as ‘AT mode’) n  To interrogate a setting’s current value, use the format: AT+setting_name? n  All settings on the HC-05 are stored in Flash memory. This means that they will be remembered even when the HC-05 is powered off n  Settings only need to be set up once; when all settings have been configured correctly, the HC-05 only needs to be used in Data (communication) mode n  However, any setting(s) can be changed at any time by re-entering configuration mode n  Two correctly configured HC-05 modules can be made to automatically pair with each other (by ‘binding’ the master to the address of the slave). 55 Fig.6. (left) The completed adaptors: note here that the buttons are not in place on the HC-05 modules and hence one horizontal, and one vertical 2-way pin header has been added onto each HC-05. (right) The adaptors in use: the one with the USB BoB plugs into the DM, and the other adaptor with the 3-way IR socket plugs into the MKC. The USB socket (on the USB BoB) has five pins broken out onto a 0.1-inch header – although only four are used. The outer two pins supply 5V power to the HC-05 module and the DM. Two other pins from the BoB (D+ and D−) are routed directly to the DM (to the USB-to-serial module). The Rx/Tx from the USB-to-serial module (DM) are routed directly to the HC-05’s serial pins (RXD and TXD). Finally, the activehigh output from the HC-05’s STATE pin directly feeds the blue (connection status) LED via a 1kΩ current-limiting resistor. Fig.8 shows the stripboard, along with the relevant track-cuts, wire-links, and component placements. We will not go into J3 5V 5V D– D+ ID 0V NC J1 0V USB BoB To DM D+ / D– 5V 0V J2 Power to DM 11 12 EN VCC TXD GND To DM Rx / Tx RXD STATE J6 J4 J5 Support and alignment only R1 1kΩ 0V D1 11 12 5V 0V Fig.7. Block diagram for DM. Note the additional USB BoB that is required. 56 step-by-step detail – it’s a straightforward build. Simply cut the correct size board (19 tracks by 10 holes); make the seven trackcuts; insert the six wire-links, 1kΩ resistor, LED (long lead (anode) into hole H7) and mount the four banks of downward-facing pins (that will plug into the DM). Next, mount the 5-way pinstrip (for the BoB), and the 6-way socket (for the HC-05). Finally, solder the BoB onto the 5-way upward-facing pinstrip – be careful to get the correct orientation (the USB socket is upper-most, meaning the GND pin should be closest to the left edge of the stripboard). It is also worth soldering two pieces of wire to strengthen the USB BoB onto the stripboard (positions B1 and B5). And that’s all there is to it. Throughout construction, do the usual checks to ensure that track-cuts are across the full width of the track, and that there are no shorts between adjacent tracks. Correct anything that doesn’t look right. To test the adaptor, carefully insert it into your DM with the orientation shown in Fig.6, but do not install an HC-05 yet. Connect it via your micro-USB lead to your computer, and launch your terminal app exactly as if you were using the MKC. Press some keys and you should see the DM’s red LED (data) flash as you press them. However, nothing should appear on the screen. If you do not see the DM’s red LED flash then stop and check everything. There is not much that can cause an issue, so start by ensuring that the DM’s green LED (power) is lit; ensure that the adaptor is inserted into the DM correctly; check the soldering on the adaptor, as well as the track-cuts and wire-links; and finally check that the terminal app is connecting to your usual COM port (as if you were connecting to your MKC). Once you can see the red LED flash each time you press a key, then you can continue. Grab a short piece of wire (or a component leg off-cut) and temporarily insert it between the second and third holes on the 6-way HC-05 socket (link E8 to E9). This will connect the Tx output from the USB-to-serial module (on the DM) back to the Rx input. So now when you press keys you should see the characters appear (echo) in your terminal app. Note that the Enter key does not move down A B C D E F G H I J J I H G F E D C B A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 A J1 J2 B BoB C D J3 E J4 F R1 G k a H I D1 J5 J6 J 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 J I H G F E D C B A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Fig.8. Stripboard for DM: (top) component side (bottom) conductor strip side. (Blue indicates downward facing connector pins on underside – see photos in Fig.6.) Practical Electronics | March | 2020 n  Upward facing sockets that J8 0V 5V J2 J5 0V 17 18 15 16 5V To MKC J1 EN VCC 21 To MKC TXD 22 23 GND 24 25 STATE 26 RXD J4 J3 5V 0V 0V J6 J7 1 3 2 5 4 7 6 9 8 A B C D E F G H I J K 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 J1 J2 D1 J4 J5 k 19 20 21 22 23 24 J3 a R1 J6 J7 J8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 A B C D E F G H I J K K J I H G F E D C B A K J I H G F E D C B A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 D1 R1 1kΩ mimic those on the MKC (allowing access to the Micromite’s I/O pins, and other hardware modules to be plugged in) n  A socket for the HC-05 module. This is oriented horizontally so that when the HC-05 is inserted, it is not going to prevent other plug-in modules from being inserted (see Fig.6) n  An LED and current-limiting resistor for visual indication that the HC-05 has successfully connected to the HC-05 module at the computer end. 11 10 13 12 14 To MKC Fig.9. Block diagram for the MKC adaptor a line (ie, it does not perform a line feed (LF)). Instead, it will just position the cursor at the beginning of the current line (ie, perform a carriage return (CR)). If you don’t see the characters appear when you press keys then perform the usual checks. Next, remove the temporary link from the second and third position and insert it between the first and fifth holes on the 6-way socket. This should result in the adaptor’s LED being lit. If it isn’t lit then check the LED circuit, and if you have access to a multimeter, carefully check that you have close to 5V present at the fifth position. Correct anything wrong, and ensure that you do see the LED on the adaptor lit (when positions 1 and 5 on the HC-05 socket are linked) before moving on. As a final test, remove the temporary test link and carefully insert an HC-05 module (see Fig.6 for orientation). You should see the small red LED on the HC-05 flash. That concludes testing for now. We will come back and use this adaptor in task T5; but for now, unplug everything from your computer, and let’s build the other adaptor. T2: HC-05 adaptor for the MKC This adaptor is designed to be plugged into the MKC (from above). However, it must also allow other hardware modules to be plugged in (normally other modules would be plugged directly into the MKC). So this is a pass-through adaptor and needs to have the following requirements: n  Correctly positioned pins (downward facing) allowing the adaptor to be plugged into the MKC Practical Electronics | March | 2020 The schematic for this adaptor is shown Fig.9. Once again, it Fig.10. Stripboard for the MKC: (top) component is just a matter of making the side (bottom) conductor strip side. (Blue indicates required connections between downward facing connector pins on underside – see the MKC, the HC-05 and the LED photos in Fig.6.) J3 soldered directly to copper strips. to check that the adaptor’s LED turns (as outlined in Fig.3). The 5V power for on. Perform the usual checks and rectify the HC-05 on this adaptor board is taken errors before moving on. directly from the MKC. The HC-05’s serial Now you may carefully insert an HC-05 pins (RXD and TXD) feed directly to the module with the correct orientation (see MKC’s Tx and Rx (console) pins. And, Fig.6), and check the small red LED on as before, the active-high output from the HC-05 flashes. If it doesn’t flash then the HC-05’s STATE pin directly feeds you will need to ensure you have a 5V the connection status LED via a 1kΩ supply going to the GND and VCC pins current-limiting resistor. Note that a 3-way on the HC-05 socket. If 5V is there but socket (J8) has been added that allows an the LED does not flash then it may be a infrared receiver to be inserted. This is not faulty HC-05. (I mention this because I a requirement for the Bluetooth link, but have had one – out of approximately 30 it adds useful functionality if we want to purchased – that turned out to be faulty.) use an IR receiver in a project. That concludes testing this adaptor; we The stripboard requirements are shown will come back and use it in task T8 when in Fig.10 – it uses a slightly bigger board (24 we set up the complete Bluetooth link. tracks by 11 holes). Make the 14 track-cuts; insert the six wire-links, 1kΩ resistor, LED (with the long lead (anode) in hole B19); T3: No Button? Simply add a link mount the three banks of downward-facing By default, when you power up the HC-05 pins (that will plug into the MKC); and it will be in communication (Data) mode; mount the 6-way socket (for the HC-05). ie, it acts as a serial-to-wireless module – Note the HC-05 socket (J3) is soldered to albeit one that may not actually be paired the underside of the stripboard (not through to another Bluetooth device. However, as holes), and with a horizontal orientation mentioned above, to enter configuration (see Fig.6). Finally, solder the four upward mode you need to hold down the miniature facing sockets. Perform the usual checks button while powering up the HC-05. If along the way to ensure the track cuts are both of your HC-05 modules have the correct, and no solder shorts have been button in place, then you can jump this introduced between adjacent tracks. section and move straight on to task T4. When you are happy that everything However, if either HC-05 has no button looks correct with this adaptor, carefully (and you do not have any spare miniature insert it into your MKC with the orientation buttons to solder into position) then solder shown in Fig.6. Again, do not install an a two-way pin-header across the button HC-05. Then connect your MKC to your pads. You can mount this header either computer (or any 5V USB PSU) using your horizontally, or vertically (see photos in usual USB lead. Note that we are only Fig.6). Then, whenever you need to put testing for 5V on the adaptor, so there is the HC-05 into configuration mode, simply no need to launch your terminal app for place a jumper link onto the header (to this test. If you have access to a multimeter short out the button pads) before you you can carefully check that you have close power up the HC-05. to 5V present at the fifth position on the Now that all the hardware has been HC-05 socket (J3) (effectively point A23). assembled, and some basic tests have been Insert a short piece of wire into the first performed, we need to prepare your terminal and fifth positions of the HC-05 socket app to configure the two HC-05 modules. 57 T4: Preparing the terminal app (for HC-05) Until now, whenever you used your MKC for development, you first inserted the DM into it, and then connected this duo to your computer, from which you launched your terminal app. Everything (should have) then worked, and you saw either the usual Micromite welcome message, or cursor, or your running program. This all happens because you initially went through the process of making the necessary settings in your terminal app. These settings were then saved, allowing you to do a ‘single click’ (this was discussed in Part 4, May 2019). In essence, the terminal app only talks to the USB-to-serial module (on the COM port assigned by the operating system). Nothing happens in the terminal app until something intelligent (ie, your MKC) is connected to the Tx and Rx pins on the USB-to-serial module. Whenever something is connected to these pins, successful communication can only take place if the settings in the terminal app match those required by the connected device (remember we had to set the speed to match the Micromite’s OPTION BAUDRATE setting). So currently, your terminal app is specifically set up for communicating with your Micromite. However, we have now replaced the MKC with an HC-05. This means we need to adjust some terminal app settings to allow successful communication with the HC-05 bcause its parameters are different to those used by the Micromite. In the following discussion, we will be referring to TeraTerm as our terminal app. If you use a different terminal app then don’t worry – you will use the same settings, but they will be found in different places within the menus. (Useful tip: before making any changes to the terminal app settings, take a picture of the screen showing the current settings – we will need to set them back to what they currently are once we have configured the two HC-05 modules. A camera on a smartphone can help here. Otherwise, simply write them down or take (and save) a screen grab.) Before we adjust the terminal app settings, let’s first connect some hardware for it to communicate with. Take the smaller adaptor and insert it carefully into your DM. Now connect this up to your computer in exactly the same way as if you were plugging in the MKC/DM combination. Check that the green power LED on the DM is lit. If an HC-05 module was already inserted into the adaptor, carefully remove it. Now launch your usual terminal application (exactly as if you were connecting to your MKC/DM). If everything goes well, then you will see your terminal screen open up (and it will 58 be connected to the USB-to-serial module in your DM). Do not expect to see anything on the terminal screen yet. The position we are trying to get to is: terminal app open and connected to your DM. If your terminal app doesn’t connect for some reason, then check which virtual COM port your operating system has assigned (shutting down any open sessions of your terminal app first). Remember, at this stage simply treat everything Fig.11. TeraTerm settings highlighted here need to be as if you are connecting to the MKC/ altered to enable successful communication with the DM (all we have done is replace the HC-05. Also set TeraTerm’s baud rate to 38400. MKC with a Bluetooth module). performed up to this point (ie, DM green Next, take one of the HC-05 modules power LED on, slow flash on HC-05 and press the button (or add the jumper small red LED, 38400 baud, echo on and link) while you insert the HC-05 into Transmit as CR+LF). the adaptor board. This should result in the small red LED on the HC-05 initially T5: Configure the slave HC-05 coming on, and then it should start flashing In this task, we will first reset the HC-05 to slowly. If this is the case, then the HC-05 original factory defaults (just in case any is now in configuration mode. If the LED settings have previously been changed). is flashing quickly, then either the button Then we will set the HC-05 to be a slave, wasn’t fully pressed, or the jumper link followed by setting the baud rate of the wasn’t in place correctly. Remember, HC-05 to the same value the Micromite the button needs to be pressed while the uses (ie, what we noted down from the HC-05 is inserted. If you’re using a link, previous section). Finally, we will find it can remain in place for now. the unique address of this HC-05 module Once you have the small red LED so that the address can be programmed flashing slowly, you are ready to move into the other HC-05 (the master). Doing on and adjust the terminal app settings. this ensures the master only connects to First, we need to ensure the baud rate is set this slave HC-05. correctly. In TeraTerm, go to Setup/Serial So, with an HC-05 inserted into the port... and make a note of the current Speed adaptor and in configuration mode (slow setting – it is likely to be either 38,400, flashing red LED), let’s now configure or 115,200. This is the speed that your it to be the slave. You’ll need to type terminal app communicates at with your in the commands ensuring you see an Micromite. Now ensure that the Speed OK response at each stage (see Fig.12). Note that if you make a mistake when is set to 38,400, which the HC-05 uses entering a command, using the Delete (remember to record all current settings key, BackSpace key, or cursor keys will prior to changing them). Press OK to save. result in an error upon pressing the Enter Now go to Setup/Terminal and tick the key. If you do not see an OK response, Local echo option to set it. On this same or if you see any error message, then screen, set the New-line, Transmit: option simply repeat the relevant command. to CR+LF (see screenshot in Fig.11). Press So now type the following commands, OK to save. These are the only settings each followed by Enter: that need to be adjusted. Note that if you AT+ORGL Assigns original factory were to close your terminal app then these modified settings will be lost. So to save settings them more permanently, go to Setup/Save setup and then click the Save button. Henceforth, whenever you launch your terminal app, the settings will be pre-set for communicating with the HC-05. Now for the crucial test – in the terminal window type AT, then press Enter; you should see an OK response. Note that it is case insensitive, so at is also valid. If you just see a blank line returned then simply repeat AT (Enter) until you see OK. Once you see this, it means that you are successfully communicating with the HC-05 module and you are now in a position to configure it (leave it plugged in for now). If you do not see an OK response Fig.12. The commands used to configure then you will need to repeat the checks one HC-05 as the slave. Practical Electronics | March | 2020 the Bluetooth link will just not work. If it is different, then simply re-enter the above BIND command, but this time with the correct address. This completes configuration of the master HC-05. If you used a link to enter configuration mode, then now is the time to remove it. Next, temporarily remove the HC-05 from the adaptor, then reinsert it. This takes the HC-05 module out of configuration mode, and puts it into communication mode. Fig.13. The commands used to configure the other HC-05 as the master. T7: Set terminal application settings back to Micromite requirements AT+ROLE=0 Defines slave mode AT+ADDR? Returns the unique address; write it down exactly as shown, for example: 98d3:51:fd967d AT+UART=115200,0,0 Sets the baud rate which must match your Micromite (ie, use the Speed value noted from the previous section); 115200 is just an example, you may be using a different speed. The last thing to do before testing the Bluetooth link is to reinstate the terminal app settings back to what they were originally (ie, what they were set to when used with your MKC/DM). In your terminal app, first set the correct baud rate (Setup/ Serial port...) so that it matches what your Micromite uses. Then in Setup/ Terminal, switch off echo (un-tick box) and also return Transmit: back to CR (and not CR+LF). Be sure to save the settings so that they are not lost when you shut down the terminal app. And that’s it – we are now ready to test the Bluetooth link. Once all these steps have been completed, remove the HC-05 module and insert it into the MKC adaptor board. If you used a jumper link on the HC-05 to mimic the miniature button being pressed, then remove the link as the configuration for the slave HC-05 is now complete. T6: Configure the ‘Master’ HC-05 In a similar fashion to what we have just done, plug the other HC-05 module into the DM (configuration) adaptor while pressing the button (or placing a jumper on the link). Once you see the slow flashing red LED to indicate it is in ‘configuration’ mode, type in the following commands, one at a time, followed by Enter, and ensuring you see an OK response to each command (see Fig.13): AT+ORGL AT+ROLE=1 Defines master mode AT+UART=115200,0,0 Use the exact same speed as you used for the slave AT+BIND=98d3,51,fd967d Use the slave address returned above – NB, use commas to separate the address (not colons) AT+BIND? Shows the address entered in the previous step. Check that it exactly matches the slave address returned in task T5 – this is an important step. The wrong address means Practical Electronics | March | 2020 T8: Plugging everything together If you have been following the tasks stepby-step, then you should currently have the DM, adaptor, and master HC-05 plugged into your computer (and powered up); and your terminal app successfully up and running. The HC-05’s red LED should be flashing quickly indicating the Bluetooth link is waiting to connect to the Micromite end. The MKC, adaptor, and slave HC-05 should not yet be powered up. If this is not the case, then simply get to this position. Now apply 5V USB power to the MKC – you can use any 5V USB PSU for this, or even a mobile phone battery pack (you are aiming to set up all the elements as shown in Fig.3). Ideally, position the MKC elements a short distance away from your computer (but no more than five metres for now). You should see signs of life as soon as you power up the MKC – this will be in the form of the slave HC-05 red LED initially flashing quickly. If there are no signs of life, then check that the MKC’s blue power LED is lit. If not, then check the power supply. If it is lit, but there are no signs of life on the HC-05, then check that the HC-05 is inserted correctly, and also that the adaptor is inserted correctly into the MKC. If there is still an issue, then something has worked loose from when you tested the adaptor as part of task T2. In this case, perform the T2 checks once again. T9: Wireless Bluetooth link test If all is well, then in just a few seconds of powering up both ends, the two modules should automatically link together. Both adaptor LEDs being lit will indicate this. If this is the case then all is good! If both adaptor LEDs do not light up then you will need to go back and re-run all the checks in tasks T1 to T8. Once both adaptor LEDs are lit you should find that you can now interact with your Micromite in the usual manner. Try typing something like PRINT TIME$ (Enter) and check that all works as normal. If you don’t see any response (but the adaptor LEDs are both lit), then is it because you have a piece of automatically running code? If so, then use Ctrl-C to return to the command prompt. If all has worked out successfully, then congratulations – you have now ‘set your Micromite free’. You are now able to use your Micromite as if it were plugged directly into your computer. If you do have any issues that you just can’t resolve, then simply drop me an email explaining your situation and I will be happy to help you. Upgrading your Mood Light to Bluetooth control Here’s a quick exercise to demonstrate remote interaction with the Micromite. Load the Mood Light software from last month into your MKC (AUTOSAVE, paste, Ctrl-Z). Then use four jumper wires to connect the Blinkt! module to the relevant MKC pins (via the sockets on the MKC adaptor) – refer to last month’s article for the exact pins (SPI Clk, SPI Data, 0V and 5V). Then insert an IR receiver (TSOP) into the 3-way IR socket that we implemented on the MKC adaptor board; and finally type RUN (Enter). You should now see the Blinkt! light up green. Press some buttons on the 44button IR remote and you should see that the Mood Light works as normal. We are not adding any new features here – all we are doing is allowing the Mood Light to be located wherever you want, but with the power to edit the Mood Light code remotely from your computer. Try it – press CtrlC, EDIT, and check that you see the code. Now type in commands at the command prompt to change the colour of the Mood Light remotely (this is an exercise for you to work out...). Now it’s over to you to think of some other uses for your wireless Bluetooth link. Have Fun! Next month Next month, we will show you just how easy it is to add an inexpensive colour touchscreen to your MKC. We will then use it to simulate the classic board game Mastermind – all remotely controlled, of course! 59