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Old Mar 28, 2007, 06:12 AM
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Help!
optoglo with PCM

I have done a few of the C.Brent Dane's optogloII onboard glow drivers - and nice they are too
However, a friend has tried one of them with his futaba and says it will NOT work on his PCM receivers I have a ZPCM JR receiver, and that is fine on it, but is there an issue with trying to use these units with Futaba PCM ? IF so...what is the workaround guys ? TY
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Old Mar 28, 2007, 06:22 AM
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Hi,

do not forget Futaba's Rx have a Low servo signal output voltage ... ( ~ 2v7 ). A level shifter might be needed. ( Already had these problems with Schmitt trigger inputs of Pics ÁP )

PCM has nothing to do with that kind of problems ... as the servo signals are the same shape, PCM or Not ...

Alain
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Old Mar 28, 2007, 06:57 AM
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Hi Alain, so are the output signals lower on PCM futaba than on PPM futaba ? It works fine on his futaba ppm stuff
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Old Mar 28, 2007, 07:20 AM
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I do not know if it is linked to PCM Rxs production ... but the Futaba's level problem is well known !!!

Here is an adapter scheme I did for a friend ...

Alain
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Old Mar 28, 2007, 08:02 AM
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I made one about 5 or 6 years ago and it was fine with Futaba PCM (129DP RX)
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Old Mar 28, 2007, 11:05 AM
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Thats interesting....Anyhow, in the meantime I have a friend bringing me a futaba PCM set over tomorrow, and I am going to try it out.
Ace - thanks for the circuit, I read this ( not being very techie really ) as a simple 2 transistor amplifier Yes?
I take it that this would be inserted in the input lead to the optoglo, and boost the level to the circuit? sorry for being a bit thick
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Old Mar 28, 2007, 12:05 PM
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Hi, Tim

You understood everything ... nothing to add !!!



Alain
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Old Mar 29, 2007, 09:45 AM
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Well, received the unit back today, and have tried it on a friends Futaba PCM receiver, and it does NOT work. The led flashes intermittently, but never goes out, or comes on "strong" unless of course I reverse the jumper, when everything stays the same, but at opposite ends of the throttle stick movement.
I am wondering whether having slightly deviated from the capacitor specs has affected the onbord signal generation enough to cause the problem ?
It works fine with all my JR stuff, PCM and PPM, as well as with my Spektrum 2.4Ghz set.
Capacitors called for are C1 = 0.056uf C2 = 0.010uf
I used C1 = 0.068uf ( 68nf) C2 = 0.01uf

Do you think this may be the problem ?
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Old Mar 29, 2007, 10:28 AM
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Hi,

1) did you see the little note about 74HC123 ... at the bottom of page 8 ???

2) if it works with one receiver, it might work with EVERY receiver ... respect to that input level problem ...

You could check datatasheet for your own HC132 ... may be truth here, in the
datas :

Philips HC132 shows, 6v supply, thresolds of 3.14v and 2.26 ..., 4.5v : 2.38 and 1.67 v

those are typical ... not so far from our critical 2.7v !!!

AND Won't work with 5 cells

Try the adapter ...

Alain
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Old Mar 29, 2007, 12:30 PM
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I was reading about the driver on RC_U just now. The original links to the docs is broken, so I only understand what was being discussed. I noted that they were using a gear channel for a function. IF this one also monitors the throttle channel, I think I know what's going on. Futaba (side note: a little girl at the field pronounces it Foo-Ta-Ba ) uses parallel timing of (I think) 4 channels at a time. That is, it sends out 4 channels at the same time (EDIT: Web says 2 channels - never question The Web ), then sends out the next 4. This is true ONLY on their PCM receivers in the PCM mode. If, for example, you need to 'read' the throttle channel AND read the aux (gear) channel, they might be presented at the same time. IF it's setup to read first one, then the next, this driver might get lost, unable to do both at the same time.

I ran into this problem with my Hamster, where I needed to read the rudder channel and read the aux channels. When they were presented at the same time, it messed up what I was expecting in the code and it failed.

Just thinking out loud - I've made a lot of assumptions about the driver. Still, note that Futaba dose pair channels to drive at the same time on a PCM system.
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Old Mar 29, 2007, 01:13 PM
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Quote:
Originally Posted by Acetronics
Hi,

1) did you see the little note about 74HC123 ... at the bottom of page 8 ???

2) if it works with one receiver, it might work with EVERY receiver ... respect to that input level problem ...

You could check datatasheet for your own HC132 ... may be truth here, in the
datas :

Philips HC132 shows, 6v supply, thresolds of 3.14v and 2.26 ..., 4.5v : 2.38 and 1.67 v

those are typical ... not so far from our critical 2.7v !!!

AND Won't work with 5 cells

Try the adapter ...

Alain
Hi Alain - yep noted the difference in capacitor spec if NOT using the HC123.
Mine are "genuine" labelled MM74HC123 AN
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Old Mar 31, 2007, 04:32 AM
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sorted !

Well after changing C1 from 47 nf to the original specified .056 it works.
I actually used 2 x in parallel, a 47 and a 10nf, as I didnt have any 0.056
Incidentally, math ( maths as we say in the UK ) was never my strong point, and decimal classes seemed to be held every time I was playing truant but please just confirm a couple of things for my brain regarding the very confusing world of capacitor markings and stuff......

0.010uf is effectively the same as 0.01uf or indeed .01uf , which is also 10nf

am I correct ? TYIA
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Old Mar 31, 2007, 09:28 AM
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Hi,

Surprising result ...

Might that mean there's a small difference in the signal repeating freq. ??? ( no sync. delay needed with PCM ... ) a look with a scope would confirm ...

Alain
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Old Apr 21, 2007, 05:04 AM
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more info and surprises !

Having got the unit to work at home with all my receivers, PCM and PPM, I sent it back to the guy. He claimed it would still not work
We then hit on the answer !! he was using a 5 cell receiver pack
when he used a 4 cell, all was fine. Seems like the unit does NOT like 5 cell packs ( apologies Alain...but just noticed you mentioned something about this in an earlier post )
As a fix...which seems to work, and allows useage on either 4 or 5 cell, I added a couple of small diodes in series with the the positive supply from the receiver output, just to drop the voltage slightly and it appears fine.
What do you guys think to this mod ?
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Old Apr 21, 2007, 06:35 AM
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Hi, Tim

This mod is the other way to have it running ... I do so with a pair 1N400x when using PIC's ( max voltage is 5.5v !!! ) with 5 cells , and it works fine !!!

but you must short them if using 4 cells

you could also think to use a LM2940-5 reg. ( low drop ) or MIC 29150-5 ( Ultra low drop ) and it would work fine with both voltages ...

Alain
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