JR Vs Futaba Buddy output - RC Groups
Thread Tools
Nov 04, 2001, 04:52 AM
Official Old Git!

JR Vs Futaba Buddy output


Does anyone know the format / polarity etc of the signals coming out of the JR and Futaba TX (via the buddy box output).

I'm trying to get some electronics to recognise both outputs, so need to know the format.

Sign up now
to remove ads between posts
Nov 04, 2001, 12:26 PM
Registered User
Mr.RC-CAM's Avatar

Some basics:

This link will offer some basics: http://www.geocities.com/heliguy99/radio/

The two signals are similar, only differing in signal level and channel order. They are both positive going pulses. Each pulse's width represents a servo's position. Pulse widths can range from 1.0mS to 2.0mS, where 1.5mS is center. A complete group of pulses is called a "frame." Frame rates can range from 20 to 70 Hz.

Here is a sample of the channel orders.

Radio Ch1 Ch2 Ch3 Ch4
Fut Ail Elev Thr Rud
JR Thr Ail Elev Rud

The JR vs. Futaba electronic interface is somewhat different for the two radios, but the differences are easily accommodated.

(1) Futaba Tx's must be supplied with external power to use it as the trainer (slave mode). If you expect to turn it on to use it, then it will transmit RF (master mode). The encoder's output drive impedance can be as high as 100K, so a signal buffer is required (two resistors and a NPN transistor).

(2) JR does not required external power. When you plug into the DSC jack, some internal contacts close and enable the encoder, but leave the RF amp off (slave mode). This is for trainer operation. If you need RF (master mode), then turn on the main power switch. The output drive is often capacitively coupled, so a high impedance signal buffer is required. This is as simple as three resistors and a NPN transistor. You may have seen posts from FMS simulator cable builders that complain of "weak" JR signals and intermittent cable operation. Their troubles are due to their use of the wrong interface design. In most cases their grief could be fixed with a weak pullup resistor on the base of the buffer transistor in their cable interface.

This is about all I can offer you. Your best bet is to just put a o-scope on the trainer port and wiggle the sticks. The mysteries will be revealed if you do.

Home of the R/C Wireless Video Project
Nov 05, 2001, 07:28 AM
Electrics rule
risto's Avatar
For Futaba look:

for whole text:

(JR do not know unfortunatly)

Last edited by risto; Nov 05, 2001 at 07:31 AM.
Nov 05, 2001, 08:34 AM
Registered User
A couple of corrections/additions to RC-CAMs useful information.

1. Futaba Txs do not actually need external power. To stop them transmitting RF you can remove the crystal or module.

2. At least some JR Txs do need to be switched on. Certainly the JR Max 6 I checked did. Again to prevent it transmitting remove the crystal.

3. When you are decoding the signals it's necessary to find the synch pulse in order to find channel 1. The synch pulse is longer than any channel pulse, usually around 4ms but it may be as low as 2.5mS.

I think the reason people refer to the JR signal as "weaker" is probably because it is of considerably lower amplitude particularly in the older models. It's also often capacitively coupled and that combination means it will not work with many of the interface designs which work fine with Futaba/Hitec Txs. However any interface that works with older JR Txs will probably work with anything else.