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Old Feb 20, 2008, 02:59 PM
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Hi guys

Hi guys,

Thanks for all input, i think i will buy one of these usb adapter and see how it go
http://www.r2hobbies.com/proddetail.php?prod=rcps81919

Its only cost 7$ so hope i can get something out of it as no mention of number of channel etc.

will keep you updated once i got it

Thanks guys
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Old Feb 20, 2008, 04:37 PM
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That's the thing now, its far cheaper (but less rewarding) to purchase than to build. Fred, you have to remember that when we started these projects (around two - three years ago) most interfaces were serial or parallel, and those USB interfaces that started appearing were typically 50 +, so it was cheaper to build ones own. Now they seem to give USB interfaces away with cornflake serial
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Old Feb 20, 2008, 06:22 PM
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From what I have read the one listed by fred73 has only 7 bit resolution - 128 steps, ouch!
I have used several, Malc - yours has a great feel to it, which is why I am building a few more.
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Old Feb 21, 2008, 01:08 AM
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Cheers Steve, glad to know you like it
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Old Feb 21, 2008, 02:15 AM
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hi fred in case you take the other interface let us know how it works...

anyway I'm really curious to see if rcjoystickng2 can work with this interesting radio so if you could help me... you can also write me on msn messenger (you can find my msn in my rcgroups profile) or in email (you find here: http://alessioandrea.altervista.org/email.html )... I could try also to make a debugging test firmware...

ciao
alessio
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Old Feb 21, 2008, 02:42 AM
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The DX7 is pretty standard(and hugely popular) There should be no issues with it working, its trainer output is the same as all Jr radios. It requires no setup config, if you plug a cable in it will turn on and output PPM. If anything perhaps a slightly lower value resistor as a pullup.
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Old Feb 21, 2008, 05:43 AM
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Quote:
Originally Posted by TheSteve
The DX7 is pretty standard(and hugely popular) There should be no issues with it working, its trainer output is the same as all Jr radios. It requires no setup config, if you plug a cable in it will turn on and output PPM. If anything perhaps a slightly lower value resistor as a pullup.
if it has a open collector output like other jr radios probably you are right, and fred could try smaller resistor values.... 100k for example.... even if I have read somewhere that the resistor was not needed.... I'd really like to know if someone knows for sure if it is open collector or not

anyway it's quite strange that rcjoyng2 does not work with futaba.... there are dozens of people who reported it works on futaba.....
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Old Feb 22, 2008, 05:20 AM
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Hi guys

Should get the new rc usb adapter by next week so finger cross to see how it goes.

BTW this is the one im using right now, built it a year ago and it works both on my futaba and Dx7 straight away, only problem is, its only game port. Thus the reason i wanted to go usb

http://www.rcdesign.ru/eng/electronics/rc2joy

The guy has now done a usb version, maybe u will need to translate with google
http://www.rcdesign.ru/articles/electronics/rcusb

will keep you updated

ciao
fred
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Old Mar 09, 2008, 06:52 PM
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I ran into a problem when building up both M&M's interface and the NG2 by using an "equivilant" transistor. My old Futaba transmitter worked but not my newer 6EXA. See post #142 and those nearby for my exploits.
Jeff
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Old Mar 10, 2008, 06:55 AM
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Quote:
Originally Posted by JDill
I ran into a problem when building up both M&M's interface and the NG2 by using an "equivilant" transistor. My old Futaba transmitter worked but not my newer 6EXA. See post #142 and those nearby for my exploits.
Jeff
thanks for the info and measurement... very useful (unfortunately I don't have a scope )

rcjoystickng2 schematic requires indeed a transistor with a high hfe (but not darlington if you want to keep the Vbe threshold low...) because of the high resistance (R1=22k) that I have put in input as a safer protection for the radio.... high hfe permits to saturate even with a small current at the base.... then a bc107b should be better than bc107a or a 2N3904 and even better should be a bc108c or 109c (and should be also very common).... and the hfe can also change a lot from a transistor to another even in the same family...

anyway in case of problem another solution would be trying a lower value for the input R1=22k resistor (for example replacing with a 10k or even 4.7k one).... another solution would be using an external pull-up for the transistor collector (instead of the internal portb pull-up as in rcjoystickng2 design) and try to use values for example of 22k or more.... but perhaps the most simple solution is to change the transistor or input resistor....

alessio
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Old Apr 16, 2008, 12:35 PM
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DX7 Signals

I also posted this in the "other" USB joystick thread. I think I know why people are having trouble with the DX7 (and possibly other transmitters as well).



I just took a look at the output of my DX7. Its PPM and about 22mS cycle time.

However, its only about 1.4 Vpp and apparently AC coupled. With the DX7 output connected to the direct coupled scope (10 Meg impedance) the signal goes between +.4 and -1.0 V. The levels are determined by the duty cycle of the signal. That probably explains why it could work for a few seconds (while the coupling cap gets charged) then quit.


I believe the input circuit will need to be revised. A simple diode (Schottky?) clamp might be a solution.
The PIC and XTAL for my NG2 should arrive today so I should be able to take a closer look.

Can anyone comment on whether or not the 22mS time should be OK?
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Old Apr 16, 2008, 04:09 PM
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Andy,

Did you read Jeffs post in the link above

Quote:
Originally Posted by JDill
Problem solved! It turned out to be the apparently not-so-equivilant transistor I had used.

When building up the NG2 I just moved over the 2N3904 I had used in my M&M build, and had similar results. The old Futaba FG worked but the newer 6EXA didn't. The 2N3904 was listed as being a cross for the BC550C.

So then I went with a BC107 as listed on Alessio's schematic (which I had) and it worked for both builds! I then also tried a 2N2222 and it worked just fine too.

Back to the scope. As I mentioned previously the amplitude of the signals at the base of the transistor were the same. But, at the collector/pin 21 of the pic there is a difference. With the BC107 it is 4.9v with both transmitters on both builds. With the 2N3904 it is 4.2v (FG) and 2.8v (6EXA) on the M&M build. On the NG2 it is 3.8v (FG) and 1.7v (6EXA).

I looked at the data sheets for these transistors but I don't know enough to tell what might cause the difference.

At least it made me get out and play around with the scope again. It's been fun building these up, and I might even use them with a simulator now!

Jeff
Changing the transistor seems to make the difference
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Old Apr 17, 2008, 03:43 AM
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Quote:
Originally Posted by Andy64
I also posted this in the "other" USB joystick thread. I think

However, its only about 1.4 Vpp and apparently AC coupled. With the DX7 output connected to the direct coupled scope (10 Meg impedance) the signal goes between +.4 and -1.0 V. The levels are determined by the duty cycle of the signal. That probably explains why it could work for a few seconds (while the coupling cap gets charged) then quit.

...

Can anyone comment on whether or not the 22mS time should be OK?
The 22ms is perfect...

if your measurements are correct you could be right about AC coupled output signal.... even if it seems quite strange because someone seems to get his dx7 working... anyway if you are right a workaround could be to try to invert the polarity (-0.4 to 1V) and try to lower the value of r1=22k if needed (you could try for example with a trimmer...) and if possible use a transistor with a high hfe.... (bc109c for example... test it with a multimeter if you can)

let me know....

alessio
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Old Apr 17, 2008, 03:53 AM
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JDill is comparing two different vintage Futaba transmitters. I also have an old 4 channel Futaba and it puts out 5 volts peak to peak with the the bottom of the pulses at essentially 0V. It should work fine. I don't know what JDill's newer Futaba puts out but, if its just lower amplitude, a higher beta transistor could make a difference. Or, if it puts out 5V p-p and is AC coupled, the output signal would go from approximately +1.4 to -3.6 and that could work but might require a higher beta transistor than the original (my guess is that's what's happening).

In the case of the DX7, look at the picture from several posts ago. That's very similar to what I see if the zero graticule line in the waveform is also zero volts. The signal needs to go at least .7V above zero for the circuit to work. Ain't gonna happen with the present design. I'm sure there's a simple, reliable fix.

As soon as I get a chance, I'll take a look. Unfortunately, I found out today that I need to update my PICSTART Pro programmer's hardware to work with these chips. Its on order but probably won't be here 'til next week.
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Old Apr 17, 2008, 09:42 PM
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My older transmitter does indeed put out a +5v peaked signal. The newer 6EXA is just a lower amplitude, starting at 0v and peaking at 3.9v.
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