Using a JR radio as a trainee's radio with a 9X

McKenzie · Post by **McKenzie** » Mon Feb 17, 2014 11:59 pm

I need help to set up an old JR radio to use as a trainee's or student radio with my TG 9X using the er9x firmware.
I have the trainer system working using an old WFly fm radio but I can't get the 9X to register a signal from the any of the JR radios I have tried. Am I mising something or is the signal from the JR to week or is the protcol different.
Thanks in advance George.

Post by **Kilrah** » Tue Feb 18, 2014 8:26 am

The signal from the JR is too weak indeed, I remember there was a schematic for an amplified cable somewhere or a mod for the 9x to accept the low level.

McKenzie · Post by **McKenzie** » Tue Feb 18, 2014 10:21 am

Thanks for the reply.
I thought that might be the problem. I'll do a bit of a search or try and design a little single transistor amp.

Post by **jhsa** » Tue Feb 18, 2014 10:35 am

Try this:
Also you can read the thread a bit more.. there are more examples.

viewtopic.php?f=5&t=976&p=48927&hilit=t ... tor#p46918

João

kaos · Post by **kaos** » Tue Feb 18, 2014 9:32 pm

Can someone take a look at this please. Thx.viewtopic.php?f=95&t=5057#p71396

McKenzie · Post by **McKenzie** » Wed Feb 19, 2014 11:53 am

I tried the simple circuit from the other thread but couldn't get anything to work. I tried a 2 transistor circuit to correct the inversion of the signal and even tried an PNP transistor which on the scope gave quite a good looking signal but still nothing. I havn't tried the capacitive type circuit yet.
Does the added resistor to TX module help at all in this case?

Post by **ShowMaster** » Wed Feb 19, 2014 4:21 pm

I thought this was fixed in a er9x FW upgrade MikeB did several years ago?
I have revisited this since buying extra 9x transmitters. I do know I could never get the external circuits to work with my jr or Spektrum TXs as my old posts indicate. The only thing that did work for me at the time was to add the internal 1 transistor inverter into time 4066 IC circuit of the master 9x. That works!
It was MikeB or Eraz that posted it maybe 2 years ago on RCG. It may however disable the 9x from being a trainer or sim tx.
I still have one 9x with the added circuit and again, it works with all my Spektrum/JR radios.
It's worth bringing up again if just to finalize a working fix.

Sent from my iPod touch using Tapatalk

Post by **Kilrah** » Wed Feb 19, 2014 4:56 pm

ShowMaster wrote:I thought this was fixed in a er9x FW upgrade MikeB did several years ago?

The FW fix is only for output (sim/student), not for input.

Post by **ShowMaster** » Wed Feb 19, 2014 5:38 pm

Ok, output only.
Then the internal mod is the way to go with possibly a bypass switch to short out or jump out the 1 transistor circuit. The switch or jumper could be installed in the battery compartment.
It does work!
Now to find it in all the posts and forums from 2 years ago if it's needed.
FYI
As I remember it's a 3904 npn or equiv inserted in series in pin 8 of the 4066 IC.

Sent from my iPod touch using Tapatalk

Post by **MikeB** » Wed Feb 19, 2014 7:43 pm

I've just tried this circuit:

: Trainer.png (2.42 KiB) Viewed 12639 times

This seemed to work with quite a low input signal (0.4V swing).

Edit: The idea of this is to build it into the cable, not inside the Tx.

Mike.

Post by **ShowMaster** » Thu Feb 20, 2014 1:11 am

Is this a circuit that was used some time ago or is it a new one Mike? I never had success but I'm very happy to try this one. It'll be of good use.
I don't remember the cap in the input circuit in the past circuit.

Post by **ShowMaster** » Thu Feb 20, 2014 1:15 am

This is what I tried from posts in the past.
I found a saved copy.

McKenzie · Post by **McKenzie** » Thu Feb 20, 2014 1:26 am

Mike Thanks for posting that circuit.
I put one together and it only worked with the input to the 9X reversed.
I don't know how to do a drawing on here to show the reversed connection. Hopefully anyone else trying to do a bit of buddy box work with a JR radio will find this post.

Thanks again

George.

Post by **MikeB** » Thu Feb 20, 2014 8:50 am

Showmaster: The idea behind my circuit is it DOESN'T need the +5V, so just wires in the cable.

McKenzie: How do you mean reversed? Did you swap signal and ground? There are many different possibilities of resistor values and capacitor values that might be needed. As an experiment, could you try a larger value capacitor without using a reversed connection (I don't have a JT to test with).

Mike.

McKenzie · Post by **McKenzie** » Thu Feb 20, 2014 10:22 am

Mike.
I had to swap the ground and signal wires going into the 9X. I believe it is needed because the transistor inverts the signal.
I have already built the bits into a cable all shrinked up but I have some spare bits so I will do another test with different caps.
I think having to swap the connections is not the end of the world, in my final I used sheilded wire and the sheild is connected to the ground pin of each jack plug but on the the small piece of vero board with the components they don't connect.

McKenzie · Post by **McKenzie** » Thu Feb 20, 2014 11:24 am

After a bit more testing I'm totaly confused.
With a .047uf the circuit work with output wires both ways but the scope showed the grounds connected a much better looking signal, the the tops did have a small curve at the switch piont though.
With a 63uf it only worked with the output to the 9x swaped.
Tried it without the cap, it worked only with the swaped connection and gave a very clean looking signal only inverted with the trace spending most time at ground.

It seems to me that the problem is not the low level signal from the JR that is the problem. It looks more like the 9X has a base 5v on the signal wire and when connected to the JR it pulls the signal above ground which stops the 9X from registering a signal.
Anyway the I guess the best option would be to use the most simple circuit that works and for me that is just the 2 resistors and transistor but I won't cut up the lead I already made as it seems rock steady.

Thanks again Mike for all your good work.
George Mckenzie.

Post by **MikeB** » Thu Feb 20, 2014 12:57 pm

The transistor inverting the signal is not a problem for the 9X, it works with either polarity signal input. The transistor input is much more sensitive to the polarity of the input. As long as you have the capacitor in place, there is no problem to swapping the input wires over.

For information, the input thresholds of the processor are over 3 volts for a '1' and under 1 vol for a '0'. The processor has an internal pullup resistor enabled on the signal, which is why you see 5V on it when idle.

It looks like this might be a solution for low amplitude trainer signals.

Mike.

McKenzie · Post by **McKenzie** » Fri Feb 21, 2014 1:02 am

: JR to 9X trainer cable

I have attached a scan of what I think would be a final working version.
With the values shown the scope trace is a very clean 0-5volt signal at the 9X. The circuit without the capacitor and the inverted output only give a 1.2 - 2.8volt signal. Which shouln't work but it does.
I will change my cable to match to attached curcuit and give it a good test this weekend as I have to do some training.
I will report back after the weekend.

Regards George.

The cap valve in the above diagram is 4.7nf or .0047uf the drawing is not as clear as I'd hoped. This gave the best looking scope trace out of all the caps I tried.

McKenzie · Post by **McKenzie** » Sun Feb 23, 2014 7:10 am

Just returned from today's training session with 7 different students having one flight each, the cable and the ER9X software couldn't be faulted.

Post by **ShowMaster** » Sat Apr 09, 2016 6:36 pm

MikeB wrote:I've just tried this circuit:
Trainer.png
This seemed to work with quite a low input signal (0.4V swing).

Edit: The idea of this is to build it into the cable, not inside the Tx.

Mike.

Old post but good info. I'm trying to use a JR S400 tx as a trainer Tx with a USB simulator adapter. I believe its suffering the same issue, low output as this post originally dealt with. The JR was purchased to use as the trainer tx for the club's original dx7's to free them up as masters. They never worked with the dx7 so the club was going to trash it recently. I'd like to mod it or a cable to be able to use it, and now we have a few USB sim adapters.
I'm planning on having bench time and I'm just revisiting this past discussion.
I never used your circuit because about that time your 9x mods and the pro and Taranis came along and pretty much solved it for me.
About your circuit. The cap coupled input from the trainer (JR) removes the DC component? I'm assuming the JR trainer out doesn't need to see an external pull-up or load?
No power is needed on the output to the master because it's assumed there's a pull-up resistor on the trainer input circuit?
To verify this I would want to measure the trainer input line for 5v or level?
This would also be the case on the USB sim input Jack tip to be able to power the circuits collector?
I'll of course measure and try all this, but having you review my theory on this can't hurt.
It'll be interesting to see how long it'll take before you read this old post.

Post by **MikeB** » Sat Apr 09, 2016 6:43 pm

There is a pull-up resistor on the trainer input of the 9X, which is why the circuit doesn't need one or power.
The cap on the input centres the input signal, by removing the DC level, at the base voltage of the transistor.

Mike.

Post by **ShowMaster** » Sat Apr 09, 2016 8:41 pm

Wow that was fast Mike.

I wonder why JR uses such a low level?
Ok, time for me to do some actual hands on with a scope and also build up this circuit.
Thanks

Daedalus66 · Post by **Daedalus66** » Sun May 01, 2016 5:23 pm

The S400 was always stated to be the odd one out in the JR series, not compatible with many other transmitters, even in the FM days when it was made. I never saw a real explanation but always assumed it was signal level or polarity. Please let us know what you find as I have one languishing in the basement.

Post by **ShowMaster** » Sun May 01, 2016 6:25 pm

It's on my to do list. I've just revived a Taranis B that was a parts bucket from someone else. Good education for sure. It'll probably be my trainer and loaner tx.
MikeB did post several times, a transistor buffer circuit for low level JR's to the er9x and sky9x builds. I'll have to try it. I've never tried the 400 with an actual JR. I have a pcm10 and older unlimited 8. I know it won't work with a DX7.
I'm curious as to what the 400 trainer out circuit looks like and if my JR's will work with it?
This 400 I have is in perfect condition with a good tx battery. A shame it's shelved by my club using dx7's for training. Maybe I'll solve that. More as time permits.

Post by **ShowMaster** » Wed May 11, 2016 7:38 am

I've solved the S400 trainer level problem but may have posted it in the wrong thread? Rather than cross post, look at this link to it.
I have done $99 12c buffer boards on order and they may make it even easier to convert the 1.8v to 5v Ppm. The bss138 specs dies list 1.8 to 5v in its specs.
The values in my schematic are what I threw together fast. It worked so I installed it. Room for a redesign by anyone motivated. If the 12c buffer works I'll use it.

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