LP4DSM won't bind! help Plz!

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tuxit09
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LP4DSM won't bind! help Plz!

Post by tuxit09 » Tue Oct 14, 2014 7:34 pm

Hello everyone.

I was trying to install the LP4DSM module removed from a parkzone champ boxed transmitter.

I'm having trouble getting it working. The lp4dsm module was working fine in the original transmitter. My turnigy 9x has er9x Ver r813 (latest i believe)

I followed all the treads I could find relating to the install. I have used the 3v3 regulator pad on the 9x main board. I believe this is ok without the dedicated regulator for this low power module. I have sampled voltage at the lp4dsm module to be exactly 3v3 powered up.

So, that in mind I have power and ground is established and checked for continuity at various ground points.

For signal I have a 5K (didnt have 4k7) pull up between 3v3 and SIG on the lp4dsm. Also on SIG we have the diode. I am using 1N4005 (didnt have 1N4001) should be fine right? I also tried 1N4148 (sub for 914 diode) neither diodes let me bind.

Let me assume and correct me if I'm wrong. But the pullup 4K7 resistor should have our SIG line floating high at 3v3 correct? with the diode from SIG >| to PPM pin on the 9x backboard. This being said its expected a low signal on the PPM pin on the backboard would draw the 3v3 float down to a lower voltage.

At least that is what I expect to see happen based on the schematics and instructions I have seen.

Of course In the model menu I set it for proto = DSM2 and set fot LP4/LP5 (also tried dsm2 only and dsm2/dsmx) I also updated the chennel order to the specified TAER.

TROUBLESHOOTING.

Checked 3v3 supply at lp4dsm module 3ve pad.
Checked GND connections.
Check value of pullup = 5K exactly.
Check PPM signal on backboard with O-scope and PPM is present. looks like 12channels?
Check PPM signal at SIG pad of lp4dsm on other side of diode = NO PPM Signal!!!!!
Check SIG pad voltage =0.55v

OK, so I remove diode and PPM conection from lp4dsm and check for 3v3 at SIG. I get only 0.55v after the pullup resistor. This tells me something internal to lp4dsm has it pulled low constantly.

IF lp4dsm has a steady low wouldnt the diode as SIG |< PPM allow PPM to pass through as HIGH pulse from the PPM backboard? I know this is reverse to the intended operation.

Let me note that when I power up with the TRN switch held to enter a BIND mode I get no LED activity on the lp4dsm IF I invert the diode I get 3 flashes from the lp4dsm with the TRN switch held at start up for BIND mode. Yet I dont get my little chanp to bind.

I now a little electronics and it sure seems like everyone else has 3v3 at SIG after pullup?

thanks for your time and help!!!

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Philipp
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Re: LP4DSM won't bind! help Plz!

Post by Philipp » Tue Oct 14, 2014 8:15 pm

How recent is the module you are using? There are some posts here and on RC Groups mentioning problems with very recent DSM modules where Spektrum might have changed some parts of the serial protocol rendering these modules useless with the current implementation of this protocol in er9x. I've not run into this problem myself though, but it might be worth to look into this.

Obvious question: did you get the diode polarity right? You might want to add a photo for the guys who are familiar with this exact mod.

tuxit09
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Re: LP4DSM won't bind! help Plz!

Post by tuxit09 » Tue Oct 14, 2014 8:54 pm

Maybe a year old.

Tried another lp4dsm. Same exact results.

Continuing with my thoughts on an internal pull down in lp4dsm I removed diode removed pull up. Straight wire ppm to sig from back board.

We have bind and controls active. The protocol can't be the problem at this stage. I can't explain the difference between everyone else install and this one. I did do a current sample and I see about 3ma on the ppm line. I'm going to throw in a 1K current limiting resistor and see how that fairs.

One thing to note is we are driving a 5v ppm line into a 3v3 input. Maybe I'll try a diode just for its drop.

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Philipp
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Re: LP4DSM won't bind! help Plz!

Post by Philipp » Tue Oct 14, 2014 10:07 pm

I'm not familiar with the LP modules, but good that you got it working! Please let us know the results of your tinkering, so that others experiencing the same problems can benefit from it in the future.

tuxit09
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Re: LP4DSM won't bind! help Plz!

Post by tuxit09 » Tue Oct 14, 2014 10:43 pm

Well its certainly not an elegant fix. There are problems with it for sure. Like 5v output to a 3v3 input.

Before removing the 2nd module from my only remaining park zone I powered it up. Check input voltage and sig voltage. Both were at 3.45v I forgot to get a snapshot of the ppm signal with the Oscilloscope :( should have done that for comparison.

Bottom line is all I have done here is crudely ran all straight up. 3v3 to the 3v3 pad on 9x sig to ppm on 9x backboard. Gnd to gnd.

I'm not sure what is going on. Be really nice if someone could chime in and compare some data.

I can't help but feel like there is a cancer in there waiting to take my 9x out with the uncertainty.

What I did do is as I said before. I tried a 1.5K,1k,700ohm, and finally 250 ohm resistor in line on ppm. Hoping to limit current. Unfortunately only the 250 ohm resistor was able to pass ppm to lp4dsm to its satisfaction. A couple different diodes proved to break connectivity every time.

Now we know the module was accepting 3.45v happily in its previous radio case. I'm wondering if there is some small timing thing happening. Maybe in that protocol change you mentioned. Maybe we are only working for the moment by attenuating or due to voltage difference forcing it's acceptance of a messy signal to lp4dsm.

I have the notion to continue toying around inside the 9x as long as the smoke holds in. I'll build a clean micro 3v3 regulator that can be dedicated to the lp4dsm and future 3v3 peripherals. I wanted the easy way but this sounds like one more step to solving this particular problem.


tuxit09
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Re: LP4DSM won't bind! help Plz!

Post by tuxit09 » Wed Oct 15, 2014 3:17 pm

UPDATED: DON'T DO AS I HAVE DONE ABOVE!!

I believe that the lp4dsm model is cutting out due to overvoltage on SIG. I flew 3 flights with little champ and last flight intermittent on rc control. Upon inspection the led would go on and off on the lp4dsm module. I'm pulling the plug on my efforts unless someone has something to add.

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