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Mar 09, 2011, 07:33 PM
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Converting a PPM 9 channel to PPM 8 channel.......

Converting a PPM 9 channel to PPM 8 channel.......

Guys, I want to convert my Aurora 9 PPM 9 channel to PPM 8 channel so that I could use a Futaba DSM2 Modules on my Aurora 9........I was hoping someone already done this.

The possible solution....
1. use a microcontroller, read a ppm signal and masked of the 9th channel.....which is doable.

2. use a Hardware circuits, use a mono-stable circuit to MASKED-OFF the 9th channel.....

I like the hardware solution, the Circuit is just like a MISSING PULSE DETECTOR, after detecting the Missing Pluse (This is actually a Synchonization pulse)..... the circuit will just produce a Short pulse that is Long enough to MASKED-OFF the 9th channel.......its just a simple 555 Timer circuit and a Gate, the Gate Could be a AND Gate or the OR Gate depending on the signal produce by the Aurora 9.
Last edited by lazy-b; Mar 09, 2011 at 07:46 PM.
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Mar 09, 2011, 09:28 PM
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Stoats's Avatar
Probably the quickest and most reliable would be to use a small PIC or AVR to read the trainer port and output the appropriate pulse train for a module. You could make it autodetect positive/negative shift so it can be generic. Power the module with its own battery so you don't have to ever swap modules (just make a little box to hang off of the handle). I mainly forget what the pulse train looks like coming out of the Futaba that the Spektrum is expecting (do the pulses go low to high or vice-versa).

I've got an idea for an analog/IC solution but it would take longer to make it and test than programming a PIC. You could use NOTs and an AND to make the rising edge pulse which feeds a counter. Set a latch at 8 which cuts off the output AND circuit. At count=9 and the pulse train goes low, then reset counter/latch. Lots of IC's. I'm not a 555 guru so there's probably some interesting ways to do something similar.

If I hadn't loaned out my 9C + Spek module, I could probably knock it out in a couple hours (most of the time spent relearning PIC and getting the uC running).
Mar 10, 2011, 04:07 AM
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Been Thinking it was a Constant Frame Rate, it would be easier to just Simple Masked-off the Last Pulses, but it was a Variable pulse so you need a counter to keep track of the channel.........Ok, its complicated using a Hardware Solution.

using a microcontroller, we need to MASHED-OFF just the Last 9th channel pulse......we need to the INPUT PPM signal should be directly Connected to the OUTPUT PPM Signal that connected to a Single Gate.......the Gate could be a AND or an OR Gate depending if its a Normal High or Normal Low signal..........a Control Bit call MASK-OFF is connected directly to the microcontroller, the Mask-off the last 9th channel.

You could use a DIODE instead of a Gate.

The Main Program will first look for the Channel 1, by looking for a long delay (Sync Pulse)......then start counting from the Edge, until you reach the 8 channel , wait until you able to let the 8th channel finished, then you Activate the Mash-off bit for until the 9th channel have finished.
Mar 10, 2011, 07:32 AM
Registered User
use a 4017 decade counter and recombine only 8 outputs
Mar 10, 2011, 09:07 AM
Registered User
look like the 4017 is Good Idea, its what most FM Receiver decode PPM signal to Individual servo pulses.......Look like I could use The 8th channel Pulses to Produce another Pulses to Mask-out the 9th Pulses.

Anyway, will try to Record The Actual PPM signalof Aurora 9........will try to post it here.

a 4017 and 555 and a DIODE will just do the JOB.

Thanks for all suggestion.
Last edited by lazy-b; Mar 10, 2011 at 09:19 AM.
Mar 10, 2011, 11:22 AM
Registered User
This is a very interesting topic! I hope you guys succeed!

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