Gregor – Page 3 – Maker Projects

RC model control with web browser – improved user interface

A few days ago I came across the ESP8266 MikroE Buggy project.

In this project, a web server is implemented on the ESP8266 – similar to my blog Model Remote Control with Web browser. Using this concept, a browser based (and therefore operating system neutral) radio control could be easily made available. In this project, especially the HTML5 based user interface implementing a joystick caught my attention.

The software is open source and so I was able to change the program for use with a PiKoder/SSC wRX. Additionally, I adapted the code for controlling a ‘normal’ car or boat (one channel for speed, one channel for direction). The customized source code is available in a github repository.

The programming of the ESP8266 is also described in the web browser model remote control blog. An additional feature of the ESP8266 MikroE Buggy project is that the Arduino file system is used. The installation and use is described here.

Digital and precise servo tester

Overview

The servo tester presented here is equipped with a PIC controller to provide for very accurate pulse generation (pulse width: 1 ms – 2 ms) especially in comparison with a simpler construction with RC links. For this purpose, the internal oscillator is used, which is specified in the selected range of the supply voltage with an accuracy of 1 %.

Furthermore, the servo tester is characterized by the fact that, in contrast to other simpler digital devices, the supply voltage range is specified form 4.8 V – 6 V. With this, the servo tester can also be connected to the BEC connection of a speed controller. The polarity of the pulse for servo control can be adjusted by hardware (jumper setting).

In addition, the Servo Tester enables the use of servos for other applications, such as for rotating and panning surveillance cameras.

Circuit

The circuit is based on the PIC12F675, which controls the servo tester. The supply voltage of the controller is lowered to 3.3 V by a corresponding controller; this ensures the highest accuracy of the internal oscillator on the one hand and the large supply voltage range of the tester on the other hand.

However, this approach requires a driver transistor Q1, which performs the level adjustment to control the servo. The supply voltage of the servo is directly looped through, so that servos or motor controllers can be tested either with the already existing battery / BEC supply by the speed controller or by means of an additional power supply (in this configuration it must be ensured that no power is provided via the servo plug).

The jumper JP3 determines the polarity of the control pulse for the servo. Please note that the LED is a bi-color LED.

Operation

The operation is simple and intuitive. The servo tester has two different operating modes: the manual mode, in which the servo is controlled by a rotary knob P1 and the neutral position can be adjusted and the exercise mode, in which the servo is continuosly moving between the end points. The change between the two operating modes is carried out by pressing the button S1. The LED will indicate the active mode of the servo tester.

After switching on, the device is in manual mode and the servo position is adjusted by rotation of the potentiometer P1. In the pulse area outside the window of 1.45 ms and 1.55 ms, the LED lights up in green. To move the servo to the neutral position, the color of the LED within the window of 1.45 – 1.55 ms changes to yellow or both colors of the LED light up and when the neutral position of 1.5 ms is reached, red is finally displayed; no button has to be pressed and both hands are free to perform adjustment work if necessary.

The Exercise Mode offers two speeds to choose from. The LED flashes red in this mode and shows which speed was selected via its flashing frequency (0.25 s corresponding to 2 x flashing/second or 15 s (correspondingly once 2 s on, then 2 s off) from final rash to final rash). The speed is switched by turning the potentiometer: if a pulse length greater than 1.5 ms is set, then the Exercise Mode is selected at high speed, otherwise the servo is controlled slowly.

Software Download

The firmware for the servo tester (Release 1.0) is freeware, which can be used without restrictions for private, non-commercial purposes according to the underlying End User License Agreement (EULA).

Download Servotester HEX-File einschließlich EULA

Servotester kit and components

In my shop you will find a complete kit for the tester.

Open Source Arduino Digital RC Transmitter

The sketch ArduinoDTX implements a feature rich RC addressing all needs of a state-of-the-art transmitter on an Arduino. It is based on fully digital encoding of all control information in the miniSSC – protocol rather than using a PPM frame. This fully digital encoding enables transmitting over a transparent serial channel such as Bluetooth, Wifi, and XBee. As a receiver for e.g. Bluetooth a PiKoder/SSC RX would be deployed.

This digital RC transmitter is based on the Open Source project arduinorc by Richard Goutorbe and thus inheriting the respective full feature set such as:

up to 9 proportional channels (Nano), 6 channels by default (Uno)
up to 6 additional digital channels (switches)
9 model memories
Dual rate/Exponential switch
Throttle cut switch
2 programmable mixers
End point adjustment, Potentiometer and Servo calibration
Throttle security check at startup
Optional Transmitter battery low voltage alarm
Programmable with Linux or Windows via USB (terminal application)

The original arduinorc-sketch has been modified and became the ArduinoDTx sketch, which outputs all channel information in the miniSSC-format rather than a PPM-pulse frame on Arduino pin D6. Every time a stick position would change a miniSSC message is generated. The PPM output has been removed completely.

The ArduinoDTx sketch is open source and provided through a respective github repository under the terms of the GNU General Public License Version 3.

Prototype setup: Digital four channel RC

Schematic setup of the Arduino Digtial RC transmitter

An RC transmitter with four channels will serve as a prototype project. As shown in the image two Thumb-Joysticks are evaluated by the Arduino (Pot 1/2 and Pot 3/4 in the above schematic). The connection to the Arduino’s analog pins is through a proto-shield. This shield does also accomodate the mode switch and the LED with the respective 270R resistor.

The RC is designed for battery operation. To guarantee the required minimum voltage of 6 V for the Arduino – even when using rechargeable batteries with a nominal voltage of 1,2 V – a battery holder for five AA elements has been selected. The two side panels support your palm operating the remote control and would enhance the user comfort significantly.

Please note that the USB port of the Arduino is easily accessible. This allows you to download software upgrades but also to customize the RC to your application.

Commissioning and testing

Test setup Arduino Digtial RC transmitter

For commissioning the RC you would download the arduinodtx sketch (.ino-file) which is provided through an respective github repository. Please note that building the sketch requires the Arduino “TimerOne”-library.

After you have uploaded the sketch to your Arduino the easiest way to test the RC would be to build the “wired remote control” shown to the right using a PiKoder/SSC evalutation board. In the standard configuration the pots 1-4 would control the respective servo channels 1-4 of the PiKoder/SSC.

If you wanted to customize your RC transmitter then you would hve to follow the steps described on the arduinorc-page. All commandos for programming the arduinorc are still available to you – for more information please refer to the (arduinorc command documentation).

Using Bluetooth communication

Bluetooth shield configuration for Arduino Digtial RC transmitter

You can easily customize the digital remote control to a Bluetooth RC with an ITEAD-Bluetooth Shield and then use the PiKoder/SSC RX as a readily available and fully compatible 8 channel receiver. Since the transmission is based on a tranparent serial protocol there are no changes needed in the sketch and the complete feature set is also available for the Bluetooth RC.

The transmitter setup is shown in the image. Prior to operating the RC the connection between the wifi modules has to be configured. Please refer to the PiKoder/SSC RX User Manual for a detailed description.

Using WLAN communication

You can also easily customize the digital remote control to a Wifi RC by adding a logic level converter, a dc-dc converter, two jumpers as UART multiplexers (to allow for programming the wifi radio) and an ESP8266-01 Wifi module and then use the PiKoder/SSC wRX as a readily available and fully compatible 8 channel receiver. The hardware setup and the programming of the wifi radios is described in great detail in the blog Arduino WLAN RC Transmitter.

Additional Application Examples

In order to increase the range of your radio control you can upgrade from Bluetooth to XBee. The setup is described in the blog Arduino based XBee radio control and in the PiKoder/SSC Application Note #3: XBee Communication.

Arduino WLAN RC Transmitter

The Open Source Arduino sketch arduinodtx implements a feature rich state-of-the-art RC transmitter with a serial command output (PiKoder/SSC compatible). The transmitter commands would be sent via a transparent serial channel.

Therefore, a wifi communication module such as an ESP8266-01 can be used in concert with a PiKoder/SSC wRX wifi based receiver to easily build a feature rich radio control.

In addition to the components for the basic setup of the arduinodtx you would need a logic level converter, a dc-dc converter, two jumpers as UART multiplexer and the wifi module as shown in the image above. The wiring of these building blocks is shown below (you would have connect all signals with identical names):

The setup is fairly simple and can be easily done on a prototype board. Please note that Arduino signals are shown in blue.

Then you would have to configure the transmitter’s wifi radio to establish a transparent link to your receiver radio – similar to binding a transmitter and receiver in a standard rc environment. This would be done by setting the jumpers as shown above to connect the radio directly to your computer. Please refer to ESP8266-01 Sketch for the PiKoder/SSC wRX for more information. If you would want to program the ESP8266-01 while in place you would have to add the additional components for the programmer to the prototype board.

Please note also the setting of the jumpers for D0/D1. Please make sure that the Arduino would not interfere with any direct communication with the ESP8266-01 by connecting the Arduino´s RESET signal to GND.

After completing the programming of the ESP8266-01, the adjusting of the jumpers, restarting of the Arduino and rebooting your RC would be fully operational.

ESP8266-01 Sketch for the PiKoder/SSC wRX receiver

The PiKoder/SSC wRX uses the ESP8266-01 module configured as an Access Point (AP) to implement a transparent serial communication channel between a transmitter a PiKoder/SSC. The ESP8266-01 can be programmed as needed based on its default firmware by using respective AT commands. However, given the number of parameters used for the commands this approach is complex and rather error prone. In addition, the verification of the programming is difficult and mistakes very often require to re-flash the ESP8266.

It has turned out to be significantly easier to flash the ESP8266-01 with a dedicated sketch, which implements all the features required for the serial communication and offers an additional command interface for setting the AP parameters needed.

This sketch udpRC_ESP8266-01 is Open Source and is provided via github for download. The sketch will be compiled and uploaded to the ESP8266-01 via the Arduino IDE as described in the blog RC with your webbrowser.

The use of the re-programmed module is very simple and intuitive. After rebooting the sketch would check the non-volatile memory of the ESP8266 for a valid parameter set. If no parameters are found then the default values will be used. After rebooting the the Controller is ready to operate.

The screenshot shows the user interface and the available commends. After rebooting the ESP8266-01 sents a more or less unreadable stream of characters to indicate that it is ready.

Entering the command ‘$?<cr><lf>’ will echo the current parameter setting. The SSID of the AP would be changed with the command ‘$s=’ followed by <cr><lf> and for changing the password you would use ‘$p=’. The revised parameter will be stored right away but will only be applied after a reboot. You can always check the changed parameter settings with ‘$?<cr><lf>’.

Radio control with your webbrowser

If your rc model would offer an access point and run a webserver, then you could control your model with a webbrowser running on your smartphone – no matter whether this is a Windows or Android device or an iPhone.

The PiKoder/SSC wRX (see below) is well suited as a hardware platform for this concept: the ESP8266-01 offers the access point and runs the webserver, the PiKoder/SSC manages all realtime aspects of controlling the servos and the electronic speed control.

PiKoder/SSC wRX

The standard configuration of the PiKoder/SSC wRX requires the ESP8266-01 to act as a transparent bridge. Since we will be needing a webserver, we would have to flash this wifi controller with a new firmware. This can be easily accomplished by using the latest Arduino IDE which is supporting generic ESP8266 modules.

The new controller firmware is open source and would be available through the github repository makerprojects/httpRC. After downloading open the sketch in the Arduino IDE. At the beginning of the source code you will find the settings recommended for compiling the program. [Update December 27, 2018: The httpRC sketch has been completely revised and updated. Please check this blog for more details.]

In order to flash the ESP8266-01 you will need an USB-Serial converter, since the wifi module does not feature a USB port. Please keep in mind also, that the ESP8266 requires a supply voltage of 3,3 Volts – the board is not 5 V tolerant! The offering of USB-Serial converter offering a 3,3 Volt supply as well as 3,3 Volt signal level is limited; therefore it might be easier to use a converter with 5 V supply and 3,3 V signal level such as the PL2303TA readily available at ebay (shown below) and build your own converter from 5 V to 3,3 V.

USB-Serial connector

Since you would need a “reset” and “program” button for flashing the module you might consider to construct the little adapter shown below using a prototype board.

Programming adapter for the ESP8266-01

The schematic for the programming is shown below.

The conversion of the 5 V provided by the USB-Serial adapter to 3,3 V follows the design of the PiKoder/SSC wRX and requires a standard low drop voltage controller LF 33 CV ( please refer to the following excerpt of the PiKoder/SSC wRX schematic; the 5 V input would be to the left, the output is to the right).

Unfortunately the flashing of the ESP8266 does not start automatically as you might be used to when downloading a program into your Arduino but has to be initiated manually. You would push the RST and PROG button simultaneously and release the RST button while still holding the PROG button. After releasing the PROG button, the module would be in flash mode. Now you would start uploading the program. Now you would start uploading the program. Once the upload is complete your controller would require another reset prior to being operational. Once the upload is complete your controller would require another reset prior to being operational.