I have been looking at pinouts and docs and code and I must admit Im a little confused by the UARTs. 

I just ordered a Graupner MX-20 HOTT to use instead of my Spektrum DX8i, in the hope I can use the hott-for-ardupilot modules for integrated telemetry.  

I am trying to digest the difference between UART0/2 vs UART0/UART2. Is UART0/2 both UARTS, and UART2 is only available if i do the usb mux solder bridge?  Im a little lost.  

Ideally I would like to use both 3DR Radio (and OSD)/Standard USB and have another serial connection for the HOTT receiver. Is this even possible?

Views: 4871

Reply to This

Replies to This Discussion


I am currently at the same point, can you tell us how you solved it?



It just seems to work. I didnt make any changes what so ever other than adding the headers. If you follow the wiki on creating the cable you should be fine. Sorry for the delay in reply

yes, but the wiki assumes that there is a APM2.0 and I have a APM2.5 where the layout is different, ie the connections of the PINs. But you have also the APM 2.5!?

Can you please tell me what connections and bridge you've set? . Are the Pins TX and GND in the picture below?

thank you

No bridges requred. And yeah. You use GND, TX2 and RX2, as you have in the picture. 

for what is the RX connection, on your picture is see only two cables !?!

You can use PPMSum. You can follow the instructions here: http://www.mkmanual.com/graupner-mx-20

On the APM, bridge pins 2 and 3, and feed the SUMO channel on your RX to pin 1.  Its pretty simple.  You will need to remap channel outputs on your TX to make them match what Ardupilot expects, You do this through the Tx. output swap menu. 

The following works for me:

  • Ch2 -> Output 1
  • Ch3 -> Output 2
  • Ch1 -> Output 3
  • Ch4 -> Output 4
  • Ch5 -> Output 5
  • Ch9 -> Output 6
  • Ch7 -> Output 7
  • Ch8 -> Output 8

yes i still connect my reciever by SUMO. 

my last question belongs to the telemetry connection .... i see only two cables going out from your APM (GND and TX2) to the telemetry input of the reciever ...

i assume that you have not  the 1.5k resistor in series between TX2 & RX2 !?!

It is just tx+rx together (as you want to only have 1 ground to avoid ground loops), and yes... the 1.5k resistor is bridging the 2 as per documentation here: http://code.google.com/p/hott-for-ardupilot/wiki/QuickStartGuideArd...

Works as expected.

thx daniel,

just the resistor pluged - and  it works!

seems important to know ......

Hi Captain Silver

I am really confused and I do not get APM 2.5 with HOTT Gr-24 running.

Question 1:

On Daniels picture above I do see 2 connections - one for Gnd and one for TX.
But as shown in documentation (wiki) there are 3 connections on APM side ... Gnd, Tx, Rx i guess

Question 2:

What about the resistor? I soldered the resistor as shown in 


Means: The middle pin is connected by the resistor. On the APM 2.5 it would be the TX pin, the rx would be connected without resistor and directli to the telemetry port ...

Sorry for my questions - but I cannot get it running ...



No. No ground shown in my picture. This is just the tx+rx together with resistor. This is because the receiver is already grounded to the apm for power input.

Thanks Daniel

But no success till now.

What do I have to do?

- Soldering some contacts? De-solder some contacts?

- how to connect the cable with tx/rx and resistor and the receiver

tx ---|

       |---- resistor ---  t-Signal at receiver

rx ---|

tx --------------- |------  t signal receiver

rx ---resistor--|

Do I have to change anything on the receiver side?



Reply to Discussion



Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2018   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service