Understanding the growth of new technologies and keeping in mind of giving an added value to its existing product eStorm-L1, Embien launched an Android app named “DAQ Suite”. With experience in developing Android app for many segments such as IoT, healthcare, automotive etc we have developed “DAQ Suite” for enhancing user experience in multiple industrial applications such as remote control, remote data acquisition/logging, etc.

This blog is the sequel of the blog “eStorm-L1 as GSM based remote switch” demonstrating the relay control and sensor monitor via an Android app. The following video shows the remote monitoring and control application typically applicable in industrial domain and many other verticals. The demo is setup using the GSM based remote switch and android application controlling the device through SMS command.

For the demo purpose we have connected two LED’s and two switches for demonstrating the relay control and sensor monitor functionality respectively. In the real time application, the LED could actually be a relay with suitable external DC supply for coil excitation and switch could be a sensor/transducer output preferably a digital high/low signal or even a pulse type output. The device stores all the configuration settings corresponding to the user, IO, etc in the EEPROM and hence preserved even on power cycling. Also the device has an option to erase the memory on site and start the user settings from the initial factory default.

The DAQ Suite android app includes the following menu options

  1. Device type selection setting – To select the type of the device need to be monitored or controlled. Available device will be listed in the Device model list box.
  2. User settings – To set the user details such as name, phone number, password, device description, and phone number to be taken for call actions etc.
  3. Relay settings – To set the on duration, ON/OFF delay etc. For multiple relays, the name of the device attached to the relay can be set.
  4. Update settings – To set the update interval for how much time interval the user need to receive the SMS about the current status of the relay and digital input. Many options can be chosen from the list view such as on change, periodic, both and none.
  5. Call actions settings – To set the action to be done on the relay upon calling the device. Either the relay can be switched ON/OFF.

The main screen of the DAQ suite includes the status of the SMS command being sent and time information of the last received/sent SMS. The control switch to toggle the relay and the status LED of the digital inputs is also included in the main screen.

Upon every operation, a SMS will be sent to the device with the predefined command set and the respective status of the digital inputs and relay will be displayed on the main screen based on the acknowledge SMS from the device.

About Embien: Primary focus of Embien technologies lies in the Industrial Automation segment. We have a rich experience in working on industrial automation and control systems with customers across geographies to enable their factories and assembly lines run efficiently. Our team have developed protocol stacks for various industrial protocols and enabled them in customer devices. We have created various Human Machine Interfaces (HMI) systems to make easier the interface with the machine. Our Machine to Machine (M2M) service offering includes developing system capable of remote monitoring and controlling of machines, PLC’s, etc.

Displays are primarily an output device used for presentation of information in text or image forms. In any processing system, it is mostly necessary to have a display to communicate the processed information to the user. Different types of displays are available ranging from a small LED (Light Emitting Diode) to large LCD/LED monitors with touch. The former typically can show only a status of the system while the later can display more information graphically.

In this blog, we discuss about one type of display, the Dot Matrix Displays, more commonly called as DMD, which is essentially a LED based display but packed together tightly to enable basic graphical rendering. We will cover the technology in detail including the principle behind its operation, interfacing techniques and its applications.

Dot Matrix Display (DMD)

Dot Matrix Display is the simple and more commonly used displays for showing advertisement information in shops, clocks, railway departure indicators, bus routes, etc where low cost displays are required with limited resolution. Further it is used extensively by electronic enthusiasts in their hobby projects.

Daisy chained DMD panels

Three 16X32 DMD panels

DMD’s are now becoming more popular in industrial segments due to low cost and durability when compared to LCD technologies. Following are the advantages of the DMD displays used in industries

  1. Easy update and dynamic message display to diverse audience
  2. Can display in any fonts/languages as generated by software
  3. Basic graphics and animation effects possible
  4. No need of powerful MCUs
  5. Relay messages to employees through one board or company-wide communication system
  6. Easy integration with the existing setup with just a tiny gateway between the system and the DMD panel
  7. Durable and practically no maintenance
  8. Low cost compared to LCD displays

Commonly available display configurations are from 3X5 (15 LEDS) to 128X64 (8192 LEDS). Large sized DMD panels for industry require special design considerations both in hardware and software which is discussed in detail below.

DMD – Design Considerations

Let us assume a case of a DMD panel of size 16×32 i.e. with 512 LED’s. To show an image/display of our liking, it is essential to control the LEDs individually. We should be able to power on or off any particular LED independently of others. Simplest method is to dedicate a control line from MCU for each LED. This calls for 512 GPIO’s from the MCU to control a single panel.

The problem with this approach is that not only it is practically possible to have a MCU with so much GPIO’s but there might be many display which will call for much more pins. It will be cumbersome to manage the wiring as well.

Second easiest way to reduce the number of GPIO’s needed to control the LED’s, Dot Matrix Display panel can be organized as a two dimensional array of LEDs. The LED’s in the Dot Matrix Display can be wired together in such that the anodes of LEDs in a row are tied together and cathodes of LED’s in a column are tied together.

Now that they are organized in a 2D matrix format, it is possible to switch on a particular LED by closing the circuit for the row and column corresponding to that LED. Even as we have control over individual LEDs, still we will not be able to use the model because of the following reasons:

  1. Considering 16×32 DMD (i.e. 16 rows and 32 columns, in total 512 LEDs), in a matrix configuration we will still need 16 (row control) + 32 (column control) = 48 GPIOs per panel. Using 3 panels increases this to 144, way beyond pins available in a low cost MCU.
  2. Even if we have enough pins, it is not possible to have individual control of LEDs. For example, as shown in the below circuits, turning ON only the first LED in row 1 and both first, second LEDs in row 2 is not possible as closing row and column circuits will illuminate all those connected in common.
    2D Matrix display configuration

    Expected to switch ON only three LEDs

    Row column intersection in DMD

    Four LEDs ON instead of three

  3. Another major consideration is the power requirement. With a 2.1V forward voltage and a typical current consumption of 20mA, each LED will consume 4.2mW. So with all the 512 LEDs powered on simultaneously, the consumption will be around 512 * 20mA * 2.1V = 21.5 Watts. A 3 panel set up will draw upward of 60 W.
  4. And none of the MCU’s can power this much.

DMD – Design Philosophy

Considering all these factors, we are in need of a mechanism to work with a sub set of LEDs at a time. First and foremost factor taken in account is that only “we” the humans are going to see the display. We take advantage of a shortcoming in human vision called the “persistence of vision”.

According to this phenomenon, when light strikes the retina, depending on the brightness of the image, retinal field of view and color, the brain retains the impression of that light for about 100 to 60 milliseconds even after the source of that light is removed. So, the eye cannot clearly detect changes in light that occur faster than this retention period and they either go unnoticed or they appear to be one continuous light to the observer.

So based on this, if we power on the LED’s for a brief period of time and keep it off for more time but do it very fast that our human eyes are not able to differentiate it, we will be able to achieve the necessary effect. Let us assume that the 512 LED’s are managed in 4 groups of 128 each, if we can say switch on each 128 LED for 5 ms and keep it off for 15 ms, we will be able to refresh each LED in 20 ms much faster that the eye can notice. Further the power consumption is reduced to a quarter of that when all are illuminated to around only 5.4 W, much manageable.

This is how actually DMD displays are built. The LEDs are organized to smaller groups that are cyclically powered on as needed. Even though this seems to be a lot of work for MCU, actually it is not and even an 8 bit MCU with 6 pins can control the panel with few more tricks. More of this is presented in our next blog.

 

eStorm-L1 is a commercial off the shelf product from Embien. Loaded with many features, it is mainly crafted to support quick realization of customer requirements. eStorm-L1 has been currently deployed across industries for various functional applications.

This blog captures one of the most popular applications of eStorm-L1 as a GSM Remote Control Switch. Being based on our proven and reliable platform, the GSM remote switch brings to the industry a low cost solution and help reducing the man power. With just a SMS command to the device, multiple loads can be switched on and off. It also supports acquiring the current status of analog /digital sensors attached to it. Apart from industry applications, this remote switch can also be used for home automation purposes.

eStorm L1 – Device Information

eStorm-L1 based GSM remote control switch is a remote monitor and control device equipped with GSM connectivity and external digital IO interfaces.

Powerful MCU: The device is powered by industrial grade ARM Cortex M0+ micro-controller. It holds rich IO interface supporting multiple digital inputs and relay control outputs. The core can run at 48 MHz that is quite powerful for remote control and monitor application.

Digital Inputs and outputs: The device supports up to 4 digital inputs mainly to acquire the data from the sensor/transducers. There are option for up to 8 digital outputs in relay mode and 4 digital outputs in digital switch mode. Digital switch mode supports direct control of the load connected across the terminals whereas the relay mode supports the external relay control which controls the load connected it.

GSM Communication: The device includes dual band GSM modem with on board antenna and SIM card holder. The device supports standard 6-pin SIM card with 1.8V and 3V operating voltage.

Storage: EEPROM available in the device supports storing configurations and user account details such as user name, phone number, password etc.

Field upgrade: USB device and configuration switch is provided for field upgrade. Connecting to the PC/Laptop with the provided application and firmware will be sufficient to do the upgrade task.

Enclosure: The device is carefully designed and enclosed inside an ABC plastic enclosure to sustain under rugged industrial environment. It can be mounted on the wall through the protruded flanges in the sides of the enclosure lid.

Remote Control Switch – Operation

Device requires a valid SIM card to be inserted in the SIM card holder. User should carefully connect the load / sensors to the respective terminals. Load connected to eStorm-L1 can be controlled remotely by just sending a SMS command or a missed call for relay control. There are options for configuring one admin and up to 10 users. Only the admin has rights to add, delete the user accounts etc. Password and phone number should be valid to control the device.

Configuring the device is very simple. Just a missed call to the device will provide the administrator, a user name and password through SMS. This user name and password should be added in all the commands for valid operation and the same can be changed by the admin through SMS command. Following are the command groups and available commands that are supported by the device for remote switch application.

  1. Relay commands
    1. Group switch on/off relays
    2. Individual switch on/off relays
    3. Setting ON/OFF delay
    4. Setting ON duration
    5. Setting Relay status update option/period
    6. Setting missed call control action
  2. Inputs commands
    1. Group of inputs enable/disable
    2. Particular input enable/disable
    3. Setting ON/OFF de-bounce
    4. Setting input status update type and period
  3. Admin commands
    1. Add user
    2. Delete user
    3. Change password
    4. Change user phone number
    5. Getting user list
  4. Query commands
    1. Query device information
    2. Current relay and inputs settings
    3. Current status of inputs and relays
    4. Device network signal strength
  5. Help commands
    1. Missed call action command format
    2. Relay command format
    3. Input command format
    4. Admin command format
    5. Query command format

For all the above command types there are shortcut commands which supports easy and quick control actions for the user handling the device. Except the admin commands all the users have rights to use the commands providing a better hierarchy in control.

Following figure depicts example SMS command sent to the device and response received from the device respectively.

Example 1: Consider all relays are in off state. Issuing a command with user name and password to switch on relays connected to digital outputs 1, 3, 5, 7 at a time. The response confirmation message from the device will describe the list of relays in ON state i.e. 1, 3, 5, and 7 and the list of relays in OFF state i.e. 2, 4, 6, and 8.

Relay On command

GSM Relay On command

Example 2: Consider the relays 1, 4, 5, 8, inputs 1, 4 is ON and relay 2, 3, 6, 7, inputs 2, 3 is OFF. To get relay and input status information’s, sending query command to the device. The relay and inputs status will be sent by the device as shown in the figure upon the SMS command reception.

Status Query Command

GSM Switch Query Command

Applications of the GSM Controller

GSM based remote switch applications are generally numerous and with Embien’s device designed specifically for operating in -40 to 80 degrees, the net get even wider. Some of them include the remote control of industrial lighting, exhaust fans, engine/machine pre-heaters, cabin heaters, water well pumps, single phase/ 3-phase irrigation systems, power cycle and reboot of remote servers, routers and computers, HVAC – heating and air conditioning in holiday homes, aviation engine heaters, pumping stations, etc.

About Embien: Primary focus of Embien technologies lies in the Industrial Automation segment. We have a rich experience in working on industrial automation and control systems with customers across geographies to enable their factories and assembly lines run efficiently. Our team have developed protocol stacks for various industrial protocols and enabled them in customer devices. We have created various Human Machine Interfaces (HMI) systems to make easier the interface with the machine. Our Machine to Machine (M2M) service offering includes developing system capable of remote monitoring and controlling of machines, PLC’s, etc.