PPM & PWM Tester/Analyser

[Phil_G]

One of them is the Multiplex Royal SX 16, so the question is what happens if the number of channels is more than eight?. The SX does deliver a ppm stream, I am not sure that it delivers all 16 channels

To achieve 16 channels MPX must use non-standard timing Max, as sixteen periods of two-milliseconds plus a few milliseconds synch simply wont fit in a standard 20ms PPM frame.
I dont know how they do it, they could send alternate frames of channels 1-8 and 9-16, or maybe they use short channel timing - or it could be a 'standard' channel timing in a 40ms frame.
The tester would do one of three things:
Alternate frames - each channel would rapidly flicker between 1/9, 2/10, 3/11 etc and would be unreadable
Short channel timing - it woudlnt recognise the signal without timing changes to the code
Standard channel timing in a 40ms frame would read all channels ok and would display ch1 to ch6

I altered Phil's sketch to show the "Americanized" spelling of "analyser" to "analyzer"

English is wonderfully strange Dave, in fact the OED supports both spellings but the preferred spelling of any past particlple ending in "...ized" such as 'synthesized' or 'analyzed' is with the Z. Yet 'analyser' and 'synthesiser' have the preferred S.

Cheers
Phil

[MaxZ]

Thanks Phil, I have ordered the bits and I am going to build it. Maybe something useful comes out of it in case of the MPX tranny, but I am sure I will have other projects. At least I can use it as a display for my servo tester.

Max.

[MaxZ]

Phil, I have been looking at the Arduino sketch, as I am always trying to understand these things to improve my knowledge of the programming language (as best as possible, my skills here are limited).
The sketch compiles fine, so there should be no problems. But what puzzles me is that the variable "signal" appears in orange, which suggests it identifies a function:

Schermafbeelding 2019-03-27 om 12.56.11.png (8.27 KiB) Viewed 19427 times

The rest of the sketch does not substantiate that, and I don't find it in the standard library. Do you know what is happening?

Max.

[MaxZ]

I have now completed the tester, but unfortunately nothing is displayed on the screen. I have not used vero board, but basically wired everything up. I have checked the layout twice, and cannot find a mistake, short circuit or anything. The screen lights up, but that is all. I have reloaded the sketch to be sure, and it uploaded fine.
The only thing I have not done is wiring up both GND pins of the Nano, but just the one on the analog pins side. The schottky is wired directly to the minus bus. Any ideas?

Max.

PS: I see my supply voltage is only 4.25 V, maybe that is the culprit. Let's see what a fresh charge of my 4s NiMh will do.

[MaxZ]

Did you twiddle the contrast pot Max? the display is very sensitive to voltage changes.
That is to say it works fine over a wide range of supply voltages but the contrast setting will need adjusting to suit. It only needs to be a gnats out and the display is unreadable.

Yes, I did twiddle the pot, but maybe not all the way. I only had a multi-turn pot available, so I installed that. I will try again tomorrow when my battery is charged.

[MaxZ]

Yessss!
With the freshly charged battery connected, still nothing but a nice backlit empty screen. But after screwing the pot almost all the way down the characters started to appear! I am guessing it was the pot all the time, thanks Phil.

I can also report that the ppm stream from my MPX Royal SX shows up fine, 6 stable channels and a frame size of 18 ms.

Max.

[RON]

I’ve just built this tester using an i2c 20x4 lcd display. It’s identical to a normal 20x4 display apart from it only uses 4 wires instead of the usual 16, plus the contrast pot is built in. Makes this project much easier to wire up. You can also turn the backlight on or off in the software. May be of some use that feature, possibly as a battery saving system.

Here is a photo of the display working. Not very neat as it was just a quick wire up job to test. Obviously this can be neatened right up.
I had to change the lcd library in the sketch for an i2c version.
Ron

[RON]

Neatened up the i2c ppm tester, looks a bit better.
Just ordered a new case for it from RS. its 125mmx85mmx25mm Part number PF13-3-9D. Ive used these cases before and they are superb quality, they have slip in end cheeks.bargain at £6.69. They come in all sorts of sizes too.
Its in dark grey and should compliment the blue led display.
I never bother using the servo outputs so they have been omitted.
Mine is self powered so it runs from the encoder or RX battery.
Great little project, and very useful, Thanks Phil

Ron

[Adrian_H]

I've done an update for the sketch to use I2c and also multi-screen & servo-output in case of >6 channels.

In case its useful, I have put the sketch here and related documentation here.