Battery Eliminator for Futaba TX on XTR

[AndyOne]

There was a thread a while ago where someone was complaining about having to charge the TX battery to use in on their sim so this set me thinking. When I got XTR, I noticed that the plug that goes into the trainer socket powers up the transmitter by connecting two pins which don't turn on the RF output. These two pins just connect the battery to the encoder. If you were to feed the encoder circuit from an external source you wouldn't need the battery in the Tx. You can get enough power from the USB port but it's at the wrong voltage. USB power output is at 5V and you need around 9V to power a Futaba transmitter. Iwas looking at junk on my desk at work the other day and I found some free samples of DC to DC converter chips that just happened to convert 5V to 9V. My initial thought was It can't be that easy, they will require lots of external components or they won't be powerfull enough. When I looked at the datasheet I was wrong on both counts. So I hooked up the circuit below took the battery out of my Tx and went flying.

The battery eliminator requires a plug and socket set so you can make an intermediate lead between the XTR lead and the Tx and you will need to sacrifice a USB lead by cutting off one end. See below...

[HankF]

You can just use a 9v wall wart as I do. Make sure it's not over about 10.5v.

Hank

[AndyOne]

Hank,

I thought of that approach but I wanted a supply that went on and off with the computer and that could also be used from a laptop.

Andy.

[FredericG]

Which Futaba transmitter do you have?
On my FC-16 the trainer connector on the PCB is a 4 pin molex connector. I was wondering how these pins relate to the pins of the round plug you describe.

Frederic

[e-sailpilot86]

The FC-16 and other European models of futaba/robbe transmitters are significantly different. He has any of the older futaba radios, except for the 4YF, 6EXA, 7C, 9C, and 14MZ.

[AndyOne]

Fredric,

I'm using a 8UP but I'm fairly certain the circuit will work with any Futaba Tx with the 5pin Din trainer socket. As for the European style transmitters, I haven't seen the pin-out of it's trainer socket. If it works on the same system where power is supplied by the instructor's Tx then is should be possible to make it work.

Andy.

[Kwok_Yu]

Andy,

Are you 100% sure the encoder needs 9V? For example the multiplex evo TX run on only 6 cells, which is a few volts lower. Could it be that the higher voltage is for the rf section and there is a voltage reg that drop the voltage to 5 volts for the encoder? Have you tried just supplying 5 volts?

-Kwok

[AndyOne]

Kwok,

I tried it on a power supply before I made the circuit, my 8U Tx encoder section won't power up much under 8 volts as it uses 8 cells in its battery pack. You may be able to get away with feeding the 5V out of the USB straight into a 6 cell Tx though.

Andy.