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1 # CPPM Multi module hardware modification
3 By default Multi uses the telemetry line to send the received channels using a RX protocol (FrSky, DSM, AFHDS2A, Bayang) to the radio.
4 But this does not work on FrSky radios since the telemetry lines of the internal and external modules are shared.
5 On a STM32 module and with a simple hardware modification, you can go around this hardware limitation by using CPPM to send the trainer information to the radio.
7 There are 2 ways to connect the module CPPM trainer signal available on the STM32 USART1.TX pin (BOOT0 programming TX pin) to the radio:
8 1. Use the trainer jack input which is supported by all radios.
9 1. Use the heart beat module bay pin 2 which is currently supported by erskyTX but not yet by OpenTX. FrSky ACCESS and X10/X12 radios do not support this mod.
11 For the hardware modification you need:
12 1. 1K resistor
13 1. Wire
14 1. Shrink tube to isolate the resistor
15 1. For an external trainer, a 3.5mm mono jack plug
16 1. Soldering iron and solder
18 ## Trainer jack
20 ### Here is the modification on a Banggood 4-in-1 or an iRangeX IRX4 / IRX4+:
22 
24 ### Here is the modification on a Jumper 4-in-1:
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28 ## Heart beat within the module bay
30 ### Here is the modification on a Banggood 4-in-1 or an iRangeX IRX4 / IRX4+:
32 
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35 ### Here is the modification on a Jumper 4-in-1:
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39 