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https://github.com/redoxcode/micropython-ppm_reader

A micropython library to decode PPM signals coming from a RC receiver
https://github.com/redoxcode/micropython-ppm_reader

micropython ppm rc-receiver

Last synced: 2 months ago
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A micropython library to decode PPM signals coming from a RC receiver

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README 

        
[![pypi version shield](https://img.shields.io/pypi/v/micropython-ppm_reader)](https://pypi.org/project/micropython-ppm_reader/) [![pypi downloads per month shield](https://img.shields.io/pypi/dm/micropython-ppm_reader?color=brightgreen)](https://pypi.org/project/micropython-ppm_reader/)

## Description

A micropython library to decode PPM signals coming from a RC receiver (as used for rc planes and drones).



This library is focused on savety and includes functions that can be used to detect a faulty or lost signal.

**For this it is required to init the PpmReader class with the correct number of channels in the PPM signal. This might be a different number than the amount of servo connectors on the RC receiver hardware!**



Created for the use with pi pico, but should work on other boards as well.

You can find the [API documentation](https://github.com/redoxcode/micropython-ppm_reader/#API) and a few [examples](https://github.com/redoxcode/micropython-ppm_reader/#Examples) below.



## Examples



### Print the values of all channels

```Python

from ppm_reader import PpmReader

ppm_pin_id=28

ppm_channels=8

ppmReader=PpmReader(ppm_pin_id,ppm_channels)

while True:

    time.sleep(0.5)

    print(ppmReader.get_values())

```

### Find the number of channels

```Python

#the number of channels should be known before you init PpmReader

#if the channel number is incorrect only guess_channel_count will work

from ppm_reader import PpmReader

ppm_pin_id=28

ppmReader=PpmReader(ppm_pin_id,channels=0)

while True:

    time.sleep(0.5)

    print(ppmReader.guess_channel_count())

```

### Find values for min_value and max_value

```Python

#move the controls to the extreme positions and observe the values

from ppm_reader import PpmReader

ppm_pin_id=28

ppm_channels=8

ppmReader=PpmReader(ppm_pin_id,ppm_channels)

while True:

    time.sleep(0.5)

    print(ppmReader.get_raw_values())

```

### Check for a loss of signal

```Python

from ppm_reader import PpmReader

ppm_pin_id=28

ppm_channels=8

ppmReader=PpmReader(ppm_pin_id,ppm_channels)



#wait initial connection with the remote

while ppmReader.get_valid_packets() == 0:

    print("waiting for connection ...")

    time.sleep(0.5)

print("connected.")



#got signal, continue to main loop

while True:

    last_packet_time=ppmReader.time_since_last_packet()

    print(last_packet_time)

    if last_packet_time>25000: 

        #25ms without a new packet

        #take security measures here (for example stop all motors)

        print("connection lost")

        #wait for connection

        while ppmReader.time_since_last_packet()>25000:

            pass

        print("connected again")

    else:

        #connection ok. Do something here

        print(ppmReader.get_values())

```



## API

### class PpmReader(pin_id,channels,min_value=1000,max_value=2000,packet_gap=4000)

- pin_id: GPIO pin connected to the PPM signal comming from the RC receiver.

- channels: Number of channels in the PPM signal. if the channel count is wrong the packts will be considered invalid.       

- min_value: Minimum timeframe per channel in us (this should be around 1000us for standard equipment).

- max_value: Minimum timeframe per channel in us (this should be around 2000us for standard equipment).   

- packet_gap: Minimum time gap between packets in us (4000us should be used for standard equipment).



```time_since_last_packet()```

- returns the time passed since the last valid packet arrived in us. This will stay below about 5000us if every packet is received correctly. Missing 2 or 3 packets is usually not a problem.



```get_valid_packets()```

- returns the number of valid packets received



```get_inalid_packets()```

- returns the number of invalid packets received

    

```reset_packet_counters()```

- resets counters for valid and invalid packets received

    

```get_raw_values()```

- returns a list of all raw timeframes in us in the last valid packet received



```get_raw_value(channel)```

- returns the raw timeframe in us in the last valid packet received for a given channel

- channel: channel to get the value from



```get_values()```

- returns a list of all values in the last valid packet maped to a range of 0.0 to 1.0 (values are not clipped)



```get_value(channel)```

- the value for a given channel in the last valid packet maped to a range of 0.0 to 1.0 (values are not clipped)

- channel: channel to get the value from



```get_values_bi()```

- returns a list of all values in the last valid packet maped to a range of -1.0 to 1.0 (values are not clipped)



```get_value_bi(channel)```

- the value for a given channel in the last valid packet maped to a range of -1.0 to 1.0 (values are not clipped)

- channel: channel to get the value fro



```guess_channel_count()```

- returns the number of channels in the last packet (incase you are not sure how many channels your signal has)