2.4 Conversion Idea - on the cheap - troubleshooting

[sweli]

I have a few Eflite MLP4DSM 2.4 radios around that we fly foamies with.
They are had on Ebay very cheaply.

I will have to use AR#### receivers versus those for surface radios.




When you pull them appart, there is a little 2.4 transmitter board with 3 pins to the main board.
3.4v+
3.4v-
PPM/PWM

[sweli]

So I pulled the defunct FM transmitter board out of an old Futaba 3PDF radio.
(I know the radio works, because I tested it with another FM board)
Installed a cheap regulator to dial the voltage from 12 down to 3.4.
And connected the signal line.

[sweli]

The down side, is that these 2.4 modules do not have a hard switch to put it in program mode. Instead the radio uses a detent position on throttle stick.

So, I wired in a servo harness on both the module (as seen above), and the donor radio.

[ik632]

I have a few of those radios too. Do they work with the Spektrum surface receiver?

[sweli]

So now the trouble shooting (any radio gurus, please jump in here............).

With the 3PDF off, I plug in the donor radio with the servo extensions.
I am using a known good receiver already in a foamie.
I plug in the receiver, and let it enter program mode after not detecting a Tx signal for 10 secs.
Then hold down on the throttle stick and turn the donor radio on. This puts it in program mode.
After a few seconds they bind, and the donor radio can control the plane.

Turn off the donor radio and unplug it.
Turn on the 3PDF.
An LED comes on on the transmitter (as usual, no error flashes).
But nothing?? Wheel or throttle do not respond on the plane.

The foamie Rx that I am testing with, is a ParkZone PKZ3351.


So is the PPM/PWM signal from the Futaba something different that the module cannot interpret to pass on?

Is it worth picking up a used Spektrum AR400 and trying it?

[sweli]

Anyone have some tech input?

[sweli]

Originally Posted by ik632

I have a few of those radios too. Do they work with the Spektrum surface receiver?

As far as I know, you need a Spektrum AR#### receiver.

[losikid]

3.4 volts seems kinda low...are you sure it doesn't need 5 volts?

[sweli]

I thought that also. The donor Tx takes 4AA (4.8v), but when I put a meter across the pins before removing the transmitter module, it came back 3.45v.
I'll pull another one apart and check it.

thx

[sweli]

Looks like earlier on, the DIY module you can buy from FRSKY had concerns with "Potential overdriving on the PPM line". So they installed a Schottky Diode to limit it. I would not even begin to know what value is needed.
Thoughts?