PWM to PPM converter

This converter was designed to support PPM signal to MNAV. Modern 2.4 GHz RC receivers don’t have PPM output so converter devices have to be used to generate it.

This converter was designed for Futaba R608FS receiver but it can be used with any 8 channel receiver.

Schematic:

Description:

The microcontroller captures every PWM channels and generates the PPM signal. The input signals are connected to resistor ladders (R21-R36). Value of these resistors should be chosen according to the signal level of the receiver. Sum of value of ladder elements should be around 10 Kohm. PWM signal of Futaba R608FS has 3 V amplitude so R22 R24 R26 R28 R30 R32 R34 R36 aren’t used. The PPM signal is connected to PIN46. It was configured as an open drain output with a 4,7 Kohm pull up resistor. Supply voltage: max 5 V.There is a LED on the board which is blinking during normal operation.

PIN out:

Receiver CH1-CH3

NC

Servo CH1-CH8

GND NC PPM Signal ICSP

GND +5V Receiver CH4-CH7

Receiver CH8+5V

GND

Converter with receiver:

Notes:

Channel 8 is unimplemented by the firmware of the controller. Value of channel 8 remains constant on the PPM signal. If channel 8 is necessary firmware modification has to be done. After the modification channel 8 have to be connected with a separate servo cable.

If the noise of supply voltage is grater then 500 mVP-P following things should be done: Support 5 V supply on not connected pin of PPM connector.Break the supply line of LM1117Connect PIN3 of LM1117 with PIN2 of PPM connector.Unsolder pull up resistor of the PPM output.Solder a new pull up resistor between PPM output and PIN2 of the PPM

connector