Servers by jDrones

PixHawk telemerty Ports - is there anyway to add more Telemetry ports?

(Asim) #1

The limit of Two telemetry ports on PixHawk limits the number of devices that require telemetry port use.

Is this due to Electronics design limitations or is it possible to externally add more telemetry ports if needed? Has anyone experimented with this so far?

Any ideas or solutions comes to your mind?

Thanks for your help…

(David Buzz) #3

(Andre-K) #4

That depends on your needs, read-only devices can read stream from the same port, and once you run an onboard computer, MAVProxy will give you nearly unlimited number of serial, and IP ports.

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(Asim) #5

@Andre-K - My need is as follows;

  1. ADSB - Supposed to be plugged into TELEMETRY 2 - a.k.a Serial 2
  2. Minimum OSD - Supposed to be only Plugged into TELEMETRY 2 - a.ka. Serial 2
  3. RFD 900X modem - Suppose to be only plugged into TELEMETRY 2 - a.k.a Serial 2
  4. GPS - Dedicated port - a.k.a Serial 3.
  5. LIDAR - e.g… We can use Serial 4 for that one.

Serial 4/5 - Serial 4 is for second GPS and Serial 5 is for debugging.

So as you can see, I am short on ports.

One idea I had was to design a serial break out board for PixHawk, however I don’t have the;

  1. PixHawk Complete Circuit Diagram.
  2. I don’t think a breakout board can be plugged in externally, unless I completely redeisgn the PixHawk PCB??
  3. Over all processing capacity of the micro processor to understand limitations as far as how many serial ports simultaneously can be supported. May be consider a higher power processor?

I see a need for much more serial ports on Pixhawk down the road with embedded OSD for sure.

If I want to get into such development, what is the process to get the community involved as long I am doing all the funding? Any suggestions…

(Asim) #6

Thanks David…I am aware of that page. See my message below to Andre-K

(David Buzz) #7

if 5 serial/s isn’t enough, use CAN, there’s a bunch of CAN peripheral/s available now. Also, you can put at least one of your GPS’s on CAN 9 if u insist on having 2 ), and your OSD can share a serial port with the telemetry radio under most circumstances, and you absolutely don’t have to leave “serial 5” for debugging, it’s fine to use it as a normal serial port too. Finally, I’ll mention that UC4H is 'UAV-CAN-FOR-HOBBIYISTS" and I hear that the UC4H “General Node” can allow u to attach all sorts of things to the CAN bus that would normally use serial or i2c or gpio’s.

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(Asim) #8

@DavidBuzz - Thanks!. I will check out UC4H. Is there a compiled list available for all the CAN supported PixHawk Peripherals out there somewhere?

When you said share OSD with telemetry on the same serial port, little confused. You mean physically wired both devices pins (Tx, Rx, GND and Vcc)?

In the Ardu pilot documentation it enforces that ADSB, OSD and telemetry all should be Serial 2 due to some power constraints. is that a typo “or” just a recommendation?

(Andre-K) #10

For example;
Adsb on telem2, tx shared with OSD
Rf900, preferably not powered by pixhawk/cube on telem1
GPS on serial3
If you use I2C for LiDAR, you even have serial4 to free.
No problem at all.

(Asim) #11


So if I understand you correctly;

  1. Direct connect ADS-B to Telemetry 2, (all wires).
  2. Only Connect OSD, GND, +VCC, and Just the TX wire to Telemetry 2. Are we sure this will not violate any TTL circuit law?
  3. RFD 900 to Telemetry one, but use a BEC or something to power the RFD 900. (Due to power limitations on Telemetry 1)
  4. GPS 1 to original GPS port (Serial 3) and 2nd cable to I2C.
  5. LIDAR either on Serial 4 or find a LIDAR that works off I2C.

I can give that a shot.

One more question. the I2C expansion board typically gives you 4 x I2C ports. Can we use two boards cascaded to gain 8 x I2C ports? What is the limitation as far as I2C ports that can be cascaded?

Thanks for your help.

(Andre-K) #12

Pixhawks TX pin to OSDs RX pin, yes.
No TTL problems.
And I2C maximum limits is a complex topic, the total length, topology, shielding, choice of cable, where the termination is, all affect the maximums… Still, usually one is limited by addresses and practical need for sensors/devices rather than electrical properties, as long one make neat and functional network.

(Asim) #13

@Andre-K - Thanks. I am an electronics Engineer, so I can handle the electronic complexities. To me I2C is nothing more than the good old RS485 (master/Slave protocol). One device can be active at time.

I found a good source

Any other recommendations?

By the way where can I find detailed schematic of PixHawk and complete write up of how it works. Are there any detailed engineering documents available? It’s open source but I just can’t find one central depository.