PPM decoder

Arduino projects on the go
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: PPM decoder

Post by bluejets »

Lost me I'm afraid.
Seems a post number # would be much easier.
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: PPM decoder

Post by Pchristy »

If you have a PPM output, why not just use a NE5045 or NE5046? These were single chip decoders made by Signetics back in the 70s. Although long obsolete, they are still available. The 5045 is a 7-channel decoder, and the 5046 two channel IIRC.

I may have some 5045s kicking around somewhere, though I would have to dig for them! I switched to using CMOS shift registers (CD4015), but the Signetics chips have input amplifiers and sync detectors built in - as well as a regulated supply for the receiver!

Dead simple, and no programing needed!

:D

--
Pete
User avatar
Eric_B (KraftyOne).
Posts: 2
Joined: 14 Mar 2021, 05:30
Location: The Shoalhaven, NSW, Australia.

Re: PPM decoder

Post by Eric_B (KraftyOne). »

I agree, in fact I have just built a 5045 powered PPM decoder to make use of a TGY-1A6C receiver I was given by a club mate, (actually 3 of them, he had "goofed-up" an order and didn't get what he really wanted), and as dedicated recycler (and hoarder), I can't bear to throw anything out.

So I have a few old Kraft 7FM receivers laying around from the 1970's, when we were flight-testing FM stuff down here in OZ for KSI. We, (KSA) could use FM modulation here before it become legal in the US, and we also had a permit to use 35 and 72MHz for limited testing purposes.

My first thought was to sweep all the 72MHz RF components off the 7FM boards and re-jig the decoder to accept the negative CPPM pulse input. This worked quite well, but removing the unwanted components. entailed a fair bit of work. I was about to start on the other Rx when I remembered I had some 4045 chips somewhere in the spares bins.

A little scrap of Veroboard, a few components, a bit of solder, and another PPM encoder is born, also in a 7FM Rx case. The 5045 input can be set up for either P or N pulse streams, and I have 2 "New" receivers for my TGY-i10 Tx. (Not all my transmitters have a Gold Case)... :)

Cheers All, (My first post).
Eric, (the KraftyOne)
Attachments
Kraft-7F-iA6C_Rx.JPG
NE-5045-1A6C_Rx.JPG
NE-5045-schematic.png
Tx_2Rx.JPG
MaxZ
Posts: 330
Joined: 31 Jan 2019, 11:48
Location: Boskoop, Netherlands

Re: PPM decoder

Post by MaxZ »

Hi Eric, welcome to the forum.
Funny that, the same goof-up AND the same receiver type (TGY-iA6C) that got me thinking about an external ppm decoder, and starting this topic.....

Cheers,
Max.
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: PPM decoder

Post by Pchristy »

Here you go - data sheet for Ne5045 attached!

--
Pete
Attachments
NE5045_ETC.pdf
(502.13 KiB) Downloaded 139 times
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: PPM decoder

Post by bluejets »

Hope somone has a couple in their back pocket ......price is rather expensive for what one can find.

Think I have a couple somewhere. 8-)
Martin
Posts: 744
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Re: PPM decoder

Post by Martin »

According to the data sheet, the chip looks for a 6ms sync pulse. That might be a problem with some modern receivers that put out 8 channels of PPM with a fairly fast frame rate.

The FrSky D4R-II puts out 8 channels of PPM, and its standard frame time is 18.5 ms. In the exceedingly unlikely event that all 8 channels are simultaneously at their maximum position (2.011 ms) then the sync pulse is only 2.412 ms long, and virtually indistinguishable from all the other pulses.

FrSky released a firmware update for the D4R-II when this was pointed out to them, slowing the frame rate to 22.5 ms. This makes the shortest possible sync pulse 22.5 - 8 x 2.011 = 6.412 ms.

Beware if you have 8 channels of PPM being transmitted and the frame rate is 50 frames per second or faster - synchronization might be lost! That's why my sketch treats anything longer than 2.5 ms as a sync pulse.

Of course, in reality, you never get the situation where all 8 channels are all at their maximum value at the same time, but to make things safer, on computer sets, it's worth setting any unused channels to be fixed at the minimum value of about 0.988 to 1.000 ms. :)

The Digispark or Pro Mini Arduinos are usually cheaper than an NE5045 now, and like the chip, they have a built-in voltage regulators. :D
User avatar
Eric_B (KraftyOne).
Posts: 2
Joined: 14 Mar 2021, 05:30
Location: The Shoalhaven, NSW, Australia.

Re: PPM decoder

Post by Eric_B (KraftyOne). »

Hi Martin,

This project come about because I have a dozen or so NE-5045 chips on hand, (I never throw anything out), otherwise I would be using Arduino. Yes, I watch your videos, thanks for sharing all your interesting work.

The 5045 sync pause can be adjusted if necessary, but my i10-iA6C combo runs a 20ms frame, and I seldom use more than 5 channels anyway. I built a test circuit with 50K pots in place of R9 and R10, to optimise values to the nearest std. value, and the V/D pair at pin 13 can make fine adjustments to the comparator switch point.

All the complex noise reduction circuitry can be removed when using CPPM input, its' already been taken care of by the 2.4GHz radio system.


Eric,
(a DIY Hacker from way back).
Post Reply