The goal of this project was to put an spm9645 Spektrum Satellite Reciever into bind mode without the use of a standard reciever or niche hardware. Instead, the reciever is bound using a microcontroller. The binding protocol for Spektrum DSM2/DSMx remote recievers is as follows:
Within 200ms of powering on, the reciever must recieve a number of falling pulses over the signal pin. The number of pulses determines the communication protocol type as shown in the tables below. If the satellite reciever is to be used as the main reciever, then it should use one of the 'Internal' protocols. There can only be 1 'Internal' reciever. It is recommended to use 9 pulses because if the hardware is unable to support 11ms communication, it will automatically bind as 22ms. See manufacturers documentation for more information:
Remote Reciever Interfacing Documentation
| Pulses | Mode | Protocol | Type |
|---|---|---|---|
| 7 | Internal | DSMx | 22ms |
| 8 | External | DSMx | 22ms |
| 9 | Internal | DSMx | 11ms |
| 10 | External | DSMx | 11ms |
| Pulses | Mode | Protocol | Type |
|---|---|---|---|
| 3 | Internal | DSM2 | 22ms |
| 4 | External | DSM2 | 22ms |
| 5 | Internal | DSM2 | 11ms |
| 6 | External | DSM2 | 11ms |
The binding procedure was implemented in both Arduino (C++) and MicroPython. The scripts perform identical actions, so which one is used is entirely dependent on the users preferences. Pin assignments can be edited in the source code to match the microcontroller used and user preferences.
This code was tested on both a Raspberry Pi Pico, and a NodeMCU ESP8266 microcontroller. The initial goal was to power the reciever from a 3.3V GPIO pin so that the exact time of reciever power application was known and the pulses could be applied within 200ms. However, this was impossible due to the current limits on these microcontrollers. Therefore an external power source was required to power the receiver.
The most elegant solution would be to use a mosfet or a BEC with an enable pin to control power application from the external power source, but this hardware was not on hand. Instead a push button switch was used to power the reciever while simultaneously sending a signal to a GPIO Input pin. When the microcontroller reads a high input signal, it knows to begin sending the pulses. The button must remain pressed throughout the bind process to continue power application to the reciever.
NOTE: SPEKTRUM SATELLITE RECEIVERS ARE 3.3V DEVICES! Application of more than 3.6V will destroy the chip, so a Battery Eliminator Circuit (BEC) may be required depending on power source voltage.
The following schematic details the circuit used for this binding process. The GPIO pins in the diagram do not match the pin assignments in the code!
