Intefacing diagram for JR Radios. - How to interface with JR radios?

[Mike Roberts]

Easier done than said. I've added this to the FMS troubleshooting page on my website.

Mike

[plasoneal]

Mike:
Unfortunately you're not the only one who sometimes has to place work priorities ahead of playtime! ???

I did get around to checking my circuit & TX out last night. Either I'm not doing the tests right, or we've got something here.

First, on the TX, whether I test in DC or AC, I only get an initial spike on the needle which then falls back to zero. I did this test with only the buddy cable inserted into the radio. I also tried this on both my radios, with the same result. I THOUGHT I received a 2 volt AC signal at one time, but when I went back to verify it later, I couldn't repeat it. I may have had my tester set on ohms, and could have misread the dial as 2 volts instead of 20 ohms (that was the only reading I could duplicate).

When I started up FMS and plugged in the i/f, I read about 10 volts "across" R5(I think this was DC?). Not sure if I tested it right, just tested against the leads going into and coming out of the resistor. When I plugged the radio into the i/f, nothing changed. I also made sure the FMS was configured to use the 32 bit Parallel/Serial drivers with the COM port correctly selected.

Neither piece seemed to test out quite right. What do you recommend from here?

Paul

[Mike Roberts]

Paul
It looks like an interface problem. This is a step closer.
I am a bit confused as you have demonstrated that the buddy lead does work.
I am also concerned about the initial spike you see. This suggests that there is some pullup/leakage to the positive rail. This might be holding TR1 on all the time. I recommed that you add a capacitor around 1 - 10uF with the + to your transmitter and - to the 10k input resistor.

let me know if this works.

Cheers

Mike

[Steve Lewin]

The JR Max 6 I test with shows, on DC volts with the trainer lead open circuit, about 6V when first plugged in, dropping to almost 0V over a minute or two. The 'scope shows the same thing, the signal is about 2Vp-p but starts off with about 6V superimposed and gradually drops to +/- 1V. That's why I put a capacitor on the input of the circuit (I found 10nF was plenty in my case and any bigger just rounded the edges too much).

There's something strange going on. Sorry I haven't checked the voltages on my circuit but I've just noticed that I don't own one. I must have sold or given them all away (I normally use the PIC version). Must build another one .

Steve

[plasoneal]

Well, after being quite busy for the past couple of weeks, let me bring you up to date. I did add the capacitor (10nF per Steve's reco) and still have the same results. No signal, still about 10 volts across R5 no matter whether the TX is plugged in or not.

I thought perhaps I wasn't checking voltages quite right on the buddy cord, so I set it up to take an "in-line" measurement while the two transmitters were interconnected. Definitely got some readings, but they were a bit weird. Went off the dial whenever I extended my primary TX's antenna, no matter what the voltage meter was on.... suspect it wasn't really reading volts.

Any other reco's? About to try to resurect an OLD tower hobbies TX (around 20 years old).... It's not a legal TX any more, but it does have a buddy port. Are the Tower systems compatible with (or made by) Futaba? If so, maybe my effort is better spent on an interface for that.

Paul ???

[Mike Roberts]

Paul

I would take the meter readings with the crystal removed. The radiated signal could be picked up by your meter leads.

As to your Tower Hobbies transmitter. It is bound to have the code signal available somewhere. Often the code PCB is separate to the RF stage and connected by three wires - positive, ground and signal. Trace the connections to find the positive and ground. Signal is then obvious. Try my standard IRQ interface first. You will do no damage to either the interface or your tx since the input impedance is high.

Best of luck.

Mike

[plasoneal]

Mike and/or Steve:
I restested my JR radios again, with both the crystals removed. I tested both in-line between the two boxes, as well as across from the signal to the ground while the two boxes were connected. I still get a spike that starts at probably around 6 volts the first time I touch the leads and then it drops almost immediately to near zero. After this drop, I do see some voltage (AC) which on my meter appears to be <0.2 volts, assuming my meter is accurate. (It's an older meter, but to the best of my knowledge works ok.) This fluctuates up and down a bit if I trigger the "trainer" button on either of the two boxes.

This seems to be a lot lower voltage than is documented for the JR radios, yet they both work fine w/each other. (One is 6-7 yrs old, the other about 2 yrs old.) Got any idea what's going on, or if I'm doing something wrong?

RE: my old Tower Hobbies TX, it has a seven pin plug in the back. I've found the ground and can find a comination of different readings. I've got one as high as 10 volts DC, about 6 volts DC on another, and then about 2-3 volts DC on a third one. Right next to the 2-3 volts one, there is another socket that reads 2-3 volts, but ONLY when the "trainer" button is depressed. Because of that, I'm assuming the one on constantly @ 2-3 volts is the signal. Sound right? If so, what kind of interface would you recommend? Is this likely PIC instead of PCM?

I won't keep bugging you guys forever on this....but if you have any more leads, I'd appreciate it.

Thanks again,

Paul

[Mike Roberts]

Paul

It is really frustrating that we can only email. I could trace it so fast with a scope!

My guess is that you are getting the signal on the appropriate pin. My coments on voltage are estimates rather than measures as the one time I had access to a JR transmitter I just used my scope to check the signal - which was 1.2v peak to peak. The voltage could be smaller on your meter due to its input impedance or use of diodes to convert to AC.

Suggest you check the operation of each stage of the interface, checking the voltage across the collector resistors both DC and AC (you may wish to do the AC check with a capacitor in series to remove and DC component.

Now to your tower hobbies tx. I would try the standard 2 transisor IRQ interface, and connect the input to 2-3 volt pin that does not change when the trainer button is pressed (logic being that pressing the trainer button connects that pin to the output). If this does not work try all the other pins. With my circuit with 10k input impedance I cannot imagine damage occuring.

Mike
Web :

[plasoneal]

Mike:
Finally got around to test the voltage at the different resistors. Here's what I came up with (all values approximate):

AC DC
R5 23 11
R4 8.5 0
R3 10 4.75
R2 0 0
R1 0 0

Since nothing appears to be happening past TR2 (working backwards from R5), I wanted to confirm it's part #. I have: KS2N3904.

Paul

[Mike Roberts]

Paul

These do not look right. R3, R4 voltages should be 0.7v different (PN junction). Also your 2N3904 is an NPN device while TR2 should be a PNP (any will do). Please replace TR2 with a PNP and try again. What are you using for TR1?

Mike

[plasoneal]

Mike:
I misled you. TR1 is a 2N3904. For TR2 the package I bought says 2N3906, though there is a mixture of #'s stamped on the transistors in that package. I'm not sure what the exact number is on one I'm using there. (Guess my glasses weren't strong enough. ??? )

I believe I have orientation on the transistors and diode correct. What else can I check with my limited equipment?

Where there are multiple connections between components, such as the connections between R2, R3, R4 and TR1, is there any care that must be given? I've just grouped all the leads together and soldered them. Does it take more precision in ordering the leads than that?

Paul

[Mike Roberts]

Paul

Ok so the TRs are OK. The base lead is the middle one in each case. Check the voltage accross the base-emitter of TR2. This should be 0.7v but looks like it might be greater from your individual resistor readings.

This is low froquency stuff to 'layout' will not be critical.

Mike

[plasoneal]

Mike:
Both TR1 and TR2 check out ok. I'm getting what appears to be about the right reading (~ 0.7 v DC) across the base and emitter of each TR. I say 'about right' because my meter's lowest scale is 10v, it looks > 0.5 and < 1.0 v, so I'd say it is about right. This reading is with the IF plugged into the PC. Readings were the same whether the TX was plugged in or not.

Thanks for your continued input....

Paul

[Mike Roberts]

Paul

Please recheck the voltages across the resistors, AC and DC, with/without your tx connected.

Were the earlier references to resistor numbers to those on my JR circuit on my website? I had expected the difference in voltages across R3 and R4 to be 0.7v.



Mike

[plasoneal]

Mike:
I will recheck as soon as I can. However I can tell you that I never have seen any difference whether the TX was plugged in or not. I verified those readings above several times (and yes, the R#'s should equate to your diagram... only messed up the TR#'s the first time.)

Just a process check....when I check the voltage at a resistor, I'm simply putting my test leads on either end of the resistor's leads, before they make any other connections. Is this right? I'm also reversing the leads when I check each one for AC and again for DC. Sound right?