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Re: [Paparazzi-devel] Xbee 868 uplink

From: Jeremy MICHEL
Subject: Re: [Paparazzi-devel] Xbee 868 uplink
Date: Wed, 29 Apr 2009 09:34:20 +0200
User-agent: Thunderbird (Windows/20090302)

This morning, I tried a 19200bps datalink instead of a 57600bps one.
19200 is under the RF bandwidth of the Xbee which is 24kbps.
It didn't solve my problem. I always have difficulty to send data to the aircraft. The downlink frame uses about 30ms every 100ms of the RF link. So the RF link is not saturated by the downlink.

Is there any software flow control for the uplink in the paparazzi uart code, which sends data until it has been recorded, or which waits for a downlink frame end to send uplink data?


Jeremy MICHEL a écrit :
I had the problem of the 10% duty cycle which stops the transmission after 5,40 minutes at 57600bps. I solved that by resetting the Xbee every 5 minutes before the problem appears. And it work very well. I have connected the Xbee reset pin to the Tiny P0.14 pin with some modification in the main_ap.c in order to control this pin periodically.
I lost only 18ms of transmission every 5 minutes…

I tried to reduce the amount of data sent using the minimal.xml file but it had no effect.
The Xbee bandwidth isn’t fully used by the telemetry (Data every 100ms).

Next step : try to reduce the bandwidth but let me doubt about this.


Gareth Roberts a écrit :

I bought one, but the device is apparently designed for burst, not streaming. It only has a 10% duty cycle, so after about 5 min it just stops working for me. I switched back to 2.4ghzs until I work around it...

----- Original message -----

There is an example of such low-bandwidth telemetry file available in



Gautier Hattenberger wrote:

> Hi,

> The bandwidth of a 868MHz modem is much smaller than the one of a

> 2.4GHz. If you use the same telemetry file, the result can be an

> overloading of the downlink that will prevent the uplink to work very

> well. Removing some of the messages or at least increasing their

> sending period could solve your problem. I should be able to test this

> new modem next week I hope.


> Gautier


> Jeremy MICHEL a écrit :

>> Hello,


>> I am trying to use the new Xbee pro 868 MHz.

>> Downlink works well however I couldn't get the Uplink working reliably.

>> Sometimes I succeed in live changing aircraft's settings by multiple

>> fast double-clicks... Not user friendly...


>> Datalink is configured in transparent mode which worked well with

>> Aerocomm modems.


>> The code I used in "my_airframe".xml in order to configure the datalink:

>> ...

>> <section name="DATALINK" prefix="DATALINK_">

>>    <define name="DEVICE_TYPE" value="PPRZ"/>

>>    <define name="DEVICE_ADDRESS" value="...."/>

>> </section>

>> ...

>> ...




>> -DUART0_BAUD=B57600

>> ap.srcs += downlink.c $(SRC_ARCH)/uart_hw.c datalink.c pprz_transport.c

>> ...


>> Any help is welcome,


>> Jeremy




>> _______________________________________________

>> Paparazzi-devel mailing list

>> address@hidden <mailto:address@hidden>




> _______________________________________________

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