JR X3810 interface - Interfacing the JR X3810

[alexraws]

Hi,

I have finished an AVR design that works with Airtronics. I now want to interface an JR X3810. I used an oscilloscope to view the output of the buddy cable when the tx was off and can't see the traditional PWM signal. Does any one know what the output is from this radio, and is it the same for JR's. I have looked on the net but haven't had any success.

Alex :0

[Steve Lewin]

Sorry I'm confused. What do you mean by asking if the output from a JR X3810 is the same as JR's ? Anyway, there is no output when the Tx is off. Try switching it on. JR has the same basic PPM signal as other makes but AC coupled and lower voltage.

Steve

[alexraws]

Thanks Steve,

The Output to the buddy cable output is activated when you push the Mono jack into the transmitter i.e. when the Transmitter is off. When you switch it on, it assumes that it is the master and the buddy cable is an input.

If I look at the signal coming out of the buddy cable, there doesn't seem to be a long delay >> (2msec) after the PWM signal. i.e. I can't trigger the scope properly. I can see that it is an AC signal, is it inverted perhaps ?

My qusetion about other JR's is, is this a standard for JR radios, or do they differ ?

Alex

[Eric Brouwer]

I see you refer to PWM, and not the normal PPM signal. Info below is with the radio in PPM mode. Do not know if it changes when using PWM mode. Is your design for PWM, or PPM?

JR radios differ from other type of radio's, as their PPM signal level is below 1V, compared to around 12V for other radios.

Looking at most interfac es, a high value resistor is placed between the PPM input and 0V to prevent spurious operations when no radio is connected. You can try removing this resistor, and use a pull-up resistor of 100k, connected between PPM in and 5V of the interface. This will ensure that a transistor can be turned on hard enough with the lower voltage level of JR radio's.

[Steve Lewin]

Eric, PWM and PPM are just different names for the same thing. Most commonly called PPM.

Alex, you're right about the switching on, I never noticed (I don't use JR normally).

I don't have any Airtonics/Sanwa Tx to check. All the JRs I've seen have had the same signal and the signal has the same sense as Futaba and Hitec i.e. the synchronise is a long high level pulse, the channels are variable length highs with fixed length low between them as shown at (look under PPM signal).

Perhaps Airtronics is inverted ? From what I've seen of Airtronics I wouldn't be surprised.

Steve

[ringram2077]

Alex
You refer to an AVR design, I assume you mean one using an AVR device. If so, could you share the circuit with me ? I have used those devices on other projects.
Richard

[alexraws]

All,

Thanks for your replies ! I will give it a bash tonight.

Yes, Airtronics is inverted ! It has fixed high time and the low time varies according to the stick position - hence my confusion. There is also a long dead time between the start of the pulse train, and yes it's 10V - much larger than the JR signal.

Richard, I am using the Tiny12 AVR processor from ATMEL with 6 other components. I will gladly share the design with whoever wants it. At the moment it works only with Airtronics/Sanwa. I am not sure how the guys on the net captured their schematics, but I will see if I can get something together for you. If you know what the best way is - let me know. I want my design to cover as many TX's as possible and the software will sense what Tx is connected. I have made a PCB which will need a slight mod now, and if you want one let me know and I'll send it to you.

Alex

[alexraws]

All,

I have just realised that the transmitter must be in PCM mode as I have just checked with my friend and he is using a PCM receiver. This explains why I am not seeing an analogue PPM signal ! Now all I need to do i work out how to change it !

Regards

Alex

[Eric Brouwer]

[alexraws]

All,

I have everything working with JR now. Thanks for all your help. It makes a big difference decoding the PPM signal instead of the PCM signal ! I will publish the circuit and code when I know how. I have also made a small single sided PCB.

Alex