I recently tried to connect a ezUHF receiver to the ppm input of the APM2. I soldered the jumper on the back and connected the cable to ch5. This setup was working fine with a Simprop 2G4 receiver in ppm mode. When I now connect the ezUHF receiver two things are happening (on two different APM2 hardware). The first APM does not boot correctly. the A B C LEDs are blinking in a row A B C fast and then remain blinking slow in the same order - what does this mean)? The second APM2 starts and I can connect via Mission Planner but in the config tab there is no input from my transmitter visible.
The support of ezuhf told me that it outputs a 3V logic level. Maybe this is not working for the APM so anyone any hint where the problem could be?
I tested it with two differnt ezUHF recievers - same game.
3v logic probably isn't going to work with a 5v system. Trying to use 3v logic with a 5v processor is notoriously unreliable and I wouldn't suggest it.
Your ezUHF probably isn't putting out true 3.3v logic. It might have a pulldown resistor that is eating some of the voltage. You could try running the RX at 3.6v if you can change that. Otherwise you'll have to get a proper level converter or search the internet for alternatives. It can be done with a diode and a pullup resistor supposedly.
I wouldn't take chances with this sort of thing though. Receivers are cheap compared to a crash.
Just buy a simple level translator like this one - https://store.diydrones.com/I2C_SMBus_Voltage_Traslator_I2C_Level_S... or http://www.sparkfun.com/products/8745
Note it has 2 supply voltages - 3.3V and 5V and also 3.3V datalines and 5V datalines.
Also you can make your own by using 2N7002( BSS138 ) +2x10k resistors for each channel....see the attached schematics.
ok thanks a lot for your answers this helps me a lot. ill try it with the given scematic.
thanks again to you jake ad nick :-)
ok. I watched the links nick gave me; can you tell me which of the connectors would i have to connect? I get from the reciver the gnd, + volatage and signal line; where shoud i connect it eg to the levl shifter from diydrones? sorry for askin, but i have to get into this first...
Thanks in advance
The connections you have to make are:
1. 5V side ( 5V electronics ):
a/ autopilot 5V power supply -> 5V power supply of the level shifter board;
b/ autopilot 5V dataline -> 5V dataline of the level shifter board;
c/ autopilot GND -> GND of the level shifter board.
2. 3.3V side ( 3.3V electronics...in your case receiver ):
a/ receiver 3.3V power supply -> 3.3V power supply of the level shifter board;
b/ receiver 3.3V dataline -> 3.3V dataline of the level shifter board;
c/ receiver GND -> GND of the level shifter board.
Thank you very much Nick!
Greetings from Germany
can someone please help me how to input PPM in APM2 board. which jumper has to be enabled on APM2. thanx
Short input pins ch2&3 (the signal pins) with a strap and insert PPM on ch1.
hi john, thanx for the guide for giving PPM IN. i would be using frsky FASST receiver with PPM out on PIN 1. i am using Futaba 7C. by default the mode channel is on channel 8 of Rx. but 7C has only 7 channels. earlier i used to input channel 7 of Rx to CH8 IN of APM. how do i assign mode to channel 7 in APM. since i am using PPM IN so i cannot change channels just by switching the servo connectors form Rx.