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Apr 13, 2010, 05:34 AM
SILURIA / UK
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Modding the Corona RP8D1 and RP6D1 for the PPM & RSSI output / Long range


Modding the Corona RP8D1 and RP6D1 for the PPM & RSSI output / Long range

WARNING!! - read this first.... https://www.rcgroups.com/forums/show...36&postcount=3

This method is based about getting the outputs out onto a plug that a servo extension cable can be made up to suit your particular plane layout. i've also used direct wires - and added and extra set of servo pins too, but have found this method quite neat too.

Ground wire
Depending upon your setup, you may need a ground wire conenction from the rx.
referring to attached photo, solder up as you can see

PPM output - Mikrocopter / DOSD+
Referring to the picture, locate the gold test point that the red wire connects too.
Now quickly "tin" the test point with an iron and some solder.
Now take a servo lead as per the photo and "tin" the end of the red wire ready to solder to the rx.
Place the red wire onto the PPM test point you "tinned" earlier.
Place the Iron onto the joint until it melts. As soon as it solders onto the test point, remove the iron quickly.
Now put some hot glue around the joint.

NOTE: Some instances may require additional resistors and / or capacitors to connect up to the OSD. Depends upon the model. Usuallya 10k in line resistor is a good start.
NOTE: There are apparently now 2 versions of this rx, but even ones I purchased in last few weeks are still the same. PPM output may be in a different location.
NOTE: Test range before flying

NOTE: For the DOSD+ I found that the Corona rx signal is not strong to connect directly and required a 100k resistor (10k upwards probably fine) in order to allow the rx to work. I am concerned about losing this control in flight so have elected to disconnect it after initial config and instead run with the OSD on permanently. If this does not suit you then I suggest a small op-amp type circuit, or a different rx is the way to go.
here is link to best way for PPM...

https://www.rcgroups.com/forums/atta...mentid=3234581


RSSI output - FPV OSD
Referring to the picture, locate the capacitor covering the chip that the RSSI signal connects too.
Carefully bend the capacitor back 45 degrees - making sure the bend is at the point where the capacitor legs touch the board - not the capacitor itself as the leads are very fragile. You will probably have to remove some hot glue first. Pick it off with a sharp knife bit by bit.
Now locate the loop wire on the chip under the capacitor you just moved and gently scrape along the centre of it to clean ready for soldering.
Now quickly "tin" the loop wire with an iron and some solder. Take care to avoid disconnecting the loop
Now take a servo lead as per the photo and "tin" the end of the red wire ready to solder to the rx.
Place the white wire onto the RSSI loop wire than you cleaned and tinned earlier.
Place the Iron onto the joint until it melts. As soon as it solders onto the wire, remove the iron quickly to avoid the loop wire coming off.
Now put some hot glue around the joint and press the capacitor back down into place.

NOTE: Some OSD's will require additional resistors and / or capacitors to connect up to the OSD. Depends upon the model.
NOTE: There are apparently now 2 versions of this rx, but even ones I purchased in last few weeks are still the same. RSSI output may be in a different location.
NOTE: Test range before flying



Increasing range - FPV
Referring to the picture, remove the existing thin aerial wire. May need to remove some hot glue.
Measure the length of the wire and make up another the same length with slightly stronger cable.
Add a 2mm corally style connector as per photos, taking care to ensure the overall length with connector is the same. i.e. will need to shorten the cable slightly.
Some heat shrink tubing will strengthen the joint for longer service.
Now you can make up some extension cables.
Recommended lengths are 1/4 or 1/2 wavelength

72mhz - 1.98m max total length. Not sure of start length, but add 49.5cm segments to make up 1.98m total length
35mhz - 4.04m max total length. Add 1.01m or 3.03m extensions
(for purists, liberties taken to make simple)

I might be incorrect, but for me, disabling the fail-safe has considerably increased range and reduced lockouts. This may be something peculiar to the Corona DSP rx and the tolerances to which they operate.
Last edited by Shikra; Apr 23, 2011 at 03:47 AM.
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Apr 13, 2010, 07:56 AM
SILURIA / UK
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I really think a buffer is necessary for the PPM output of a Corona RX. I am concerned about using a resistor to present the signal to another device (i.e. DOSD+) because changing that signal can trigger the rx into non-operation. RF, fluctuations etc in flight could trigger the rx to glitch of fail completely.
It is not an issue if only used to set up only and then leave disconnected (as I did)

Updated - here is the circuit I now use.............

I have fitted fine inside the RX case to keep RX side of the RSSI and PPM buffers as short a possible.
A 0.1uf cap between the RSSI out and ground on the output side of the buffer chip may help stabilise RSSI fluctuations on teh OSD. Personally I have not found the need.

It might be easier to take a servo cable outside with gnd, 5v and the PPM signal. The buffer could then be put in line and the gnd/PPM out put continued to the OSD.
Last edited by Shikra; May 10, 2010 at 08:09 AM.
May 10, 2010, 07:45 AM
SILURIA / UK
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Special note - RSSI and PPM buffers for Corona RP8D1 rx

WARNING!! - unless you use a buffer - or follow the notes below you will either loose range (RSSI mod)- or worse loose complete control of all channels (PPM mod)
RSSI
It appears that the RSSI line on the Corona RX is used as part of it's failsafe triggering process. Using it with an OSD that does not have an high impedance input - or without a suitable value resistor will probably affect it's range.

To test if you have an issue: with tx on and off, measure the voltage of the RSSI line with is connected to the OSD and then without. If the voltage doesn't change you will be OK.

Options are:
1 Disable failsafe
2 Use with an OSD that has a very high input imedance
3 Isolate with a high value resistor - verify with digital voltage meter that the rs side of the rssi line is not being pulled down. Looking for maximum voltage swing on the OSD side of the resistor to minimum "pull down" on the inpout side
4 Ideally - use an RSSI buffer



PPM
Similar to the RSSI, it was never intended that this signal will be used externally and it is clear that this signal will get pulled down unless you have an high impedance and unclamped input on your OSD.
My first Corona modded for PPM could drive a DOSD+ OK with a simple resistor. The signal was pulled down slightly, but not enough to cause it to operate. It may not be suitable for long term use. I chose to only use it for setting up the DOSD+

Options are:
1 (Not recommended) Try various values of resistor between the RX and OSD. 10-100k. Need a value which does not pull down the PPM signal, but gives enough to drive the OSD
2 Ideally - use a PPM buffer

Summary
What is clear from testing is that a "Buffer" is the only safe way to go if PPM output is needed. Variations in RX and the possibility of loosing signal in flight makes it not worth it.
If you can live without failsafe, then RSSI can be used wthout a buffer.
Last edited by Shikra; May 10, 2010 at 07:50 AM.
Jun 09, 2010, 02:47 PM
RC Wannabe!
areis81's Avatar
hello shikra, i bought this receiver to make your mod but.... my rp8d1 does not have any jumped chip!!!

what should i do? how is that possible?

thanks for your help....
Jun 10, 2010, 10:44 AM
SILURIA / UK
Shikra's Avatar
Thread OP
I believe the RSSI uses the same pins on the IC. The wire link is now part of the board.
I hope your good at soldering! some use superglue on those small chips.

For the PPM I do not know as have not seen one - the baord layout looks very different. I also ordered new one from HK to help others, but still get 8 channel. They do not offer 35mhz 9 channel on their pages. What frequency are you?


It is really best to use the buffer circuit - using direct ppm / RSSI connection can affect the rx. All info in the notes!
Jun 10, 2010, 12:22 PM
RC Wannabe!
areis81's Avatar
thnaks. i gave the rx to a friend of mine, electronic engineer... i really can't solder those small pins! i will check as you specified in the notes, thanks!
Jul 04, 2010, 10:14 AM
Registered User
noppita's Avatar
Dear shikra

I am flying with william tricopter and i am using corona rx + TT-RecEnc (convert rx signal to single pulse train signal) and the send signal to my tricopter controller board. Now, i want to get rid of TT-recEnc (converter) and modified my corona rx so that it will send out signal of sinble pulse train. The above modification mehod from you is to do what i need right?
Jul 04, 2010, 12:05 PM
Registered User
noppita's Avatar
I have question, please help me answer

If i convert my corona RP8D1 to PPM signal to my tricopter controller board with 6 channel using. what about channel 7 and 8? will i still be able to connect normal servo to 7 and 8 and control my camera mount?


Anyone has picture of RP6D1 location where to connect white, red and black wire.
Jul 05, 2010, 04:11 AM
SILURIA / UK
Shikra's Avatar
Thread OP
Using the LM358N OPamp is good - it works very well. Small, cheap and easy to build.
Can still use all the channels for conecting servos directly - so yes for your pan/tilt

The PPM signal from the Corona is very weak and quite small. It works perfect if you use OP-amp buffer circuit, but may also work with a simple resistor - I cannot recommend that due to variations in the receivers though. Best avoided

I have not seen the 6 channel one so do not know the location points.


Hope that helps!
Jul 05, 2010, 07:10 AM
Registered User
noppita's Avatar
Thank you Shikra

do you happen to have a photo of how to connect LM358N OPamp circuit to the corona board?
Aug 05, 2010, 10:31 AM
Registered User
noppita's Avatar
dear shika

i need your help

looking at your buffer circuit for corona, 5 v and ground is connect to what? outside 5 v or connect to 5 v leg and ground within the corona
Apr 06, 2011, 04:51 PM
Dax
Dax
There is no spoon
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Sorry to bump such an old thread.

If I want to do the RSSI mod on a new Corona Rx without the "loop" wire which pin should I be aiming for? I can't quite tell from your picture what two pins the loop is connecting. I understand I could use either of the 2 pins the loop is connected to, I just need to know what two pins those are.

Also, if I disable failsafe I can use RSSI without a buffer correct?

Thanks!
Apr 06, 2011, 04:57 PM
O <- this a ground loop
Hi Dax,

This is just to help people do the small work.



more details if you're interested


Ren
Apr 06, 2011, 05:38 PM
Dax
Dax
There is no spoon
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Thank you so very much.
Apr 06, 2011, 07:55 PM
O <- this a ground loop
Quote:
Originally Posted by Dax
Thank you so very much.
you are most welcome
I'm actually getting some PCB made up for the buffers.

about 9mm x 9mm
(any smaller and it would be a pain to use)

Ren


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