4PL 3 Position Momentary Switch Mod

[YJ_Driver]

If there's one feature that is missing in the Futaba 4PL for scalers, it's a 3 position momentary switch. Even though the DT switches are mechanically momentary, Futaba didn't deem it important to let us use them as such.

I'd been thinking about modding my radio for a while and I finally came up with a circuit that requires just 3 resistors, a transistor and 4 wire connections to convert one of the DT switches to momentary with only one minor drawback, you can't use the 3 position slide switch SW2 at the same time as the modded DT. That's it, otherwise you can program any model to use the DT as before, or as momentary, or use SW2 as normal. Plus, there's no changes to the radio components so you can pull out the circuit anytime to go back to stock.

What this mod does is connect a set of DTs which are two momentary switches to the SW2 circuit which provides 3 positions. Here's the schematic; the thick lines are wires about 2" long with the indicated colours that match my installation pictures below:


I installed this on DT4 though DT3 should work the same. I didn't check whether DT1 and DT2 operate the same.

Using this setup is simple: let's say you wired up DT4, for 3 pos. momentary operation make sure DT4 is programmed to OFF in the *TRIM.DIAL menu, and program SW2 as CH3 or CH4 in the >SWITCH> menu. Keep SW2 in the middle position for momentary operation, or slide SW2 for holding that position.

If you want to use SW2 normally program it as normal but don't use DT4. If you want to use DT4 program it normally and don't use SW2 but set it to the left position (this is the 3.3V position which will pull up the DT signal to keep it operating normally).

For those interested the SW2 switch is made by COMAX and operates like this one (I don't know the exact p/n):
Comax Slide Switches
Although it has a complex scheme, it's used as a single pole on-off-on switch connecting either ground or 3.3V to the signal going to the decoder chip. As far as I can tell the pins that I show as unconnected on my schematic are actually unconnected.

The transistor is a PNP type, I used a MPSA92 but just about anything will do. A TO92 package is small and works well, but if you use something other than a MPSA92 check the datasheet for pinout as it may differ.

Here's my installation. First the components before putting lots of heat shrink on all the exposed conductors.


Here's a closeup of the connections. The green and black wires can be reversed if you desire, though you can also reverse the channel on the radio.


And with everything in place. Note again that this is to DT4, the DT3 connections are right above it.


I did quite a bit of testing such as measuring voltage thresholds to determine a good resistor value, and to ensure that this mod is safe for your radio. I left out some details but I'll be happy to answer questions.

Richard

[hotwheels000]

Bravo Sir that is a much needed option on the radio

Time to get to it on mine now Hope i dont goof it up....

[ninja turtle]

Yes! Thank you very much for this. It's a bit over my head at the moment but I'm ready to jump in.

[jthellfire911]

I'm good at soldering and working with electronics.. But I Don't think I wanna tear apart my new 4pl lol.
I'd rather pay somone to do that.

Amazing work though! If I had the cahones to do it I would. haha

[YJ_Driver]

Originally Posted by jthellfire911

I'm good at soldering and working with electronics.. But I Don't think I wanna tear apart my new 4pl lol.
I'd rather pay somone to do that.

Amazing work though! If I had the cahones to do it I would. haha

Well when your warranty is over you should check out this one too
4PL Throttle Trigger Travel Mod

[losikid]

... i thought that would be a given option on a high end radio

[badhoopty]

Originally Posted by losikid

... i thought that would be a given option on a high end radio

you would think... i bought a 4pk thinking it would be the last radio i would buy for awhile.

a week later i bought a hacked flysky, just for the momentary switch...

[808DA6]

Thanks YJ. Gonna try this one.

[YJ_Driver]

I edited the first post: the transistor is a PNP, not NPN.

[808DA6]

Just finished the mod on my 4PL. I have to say, its nerve racking to break into this radio, but all seems to be well. It operates exactly as a momentary toggle should. I need to bind this radio to my crawler and actually use it. Can't wait.

THANK YOU!!!


15min update:
Radio bound. Momentary toggle is a winner!!

Oh and, this is the cheapest mod by far. $.30 for the transistor. $.06 for each resistor.

[YJ_Driver]

You're welcome, I'm glad it worked out for you.

[ninja turtle]

Just ordered what I need to get this done. YJ_DRIVER, would you mind going into detail about how you packaged the resistors and transistor? Thank you very much for this write up.

[rcscaler]

By the way,
we need to get 4.7K resistor, but are we going to use 1/2 watt or 1/4 watt?

[anuthabubba]

Very nice how to post but why would you want a 3 position momentary switch?

[doublej]

Originally Posted by anuthabubba

Very nice how to post but why would you want a 3 position momentary switch?

For winches on scalers....

[JokersWild]

Originally Posted by losikid

... i thought that would be a given option on a high end radio

I would have thought too.....



Good write up tho!

[YJ_Driver]

Originally Posted by ninja turtle

Just ordered what I need to get this done. YJ_DRIVER, would you mind going into detail about how you packaged the resistors and transistor? Thank you very much for this write up.

I used shrink wrap of varying sizes over all soldered wire connections both for isolation and prevent flexing that may lead to a break. I used one piece on the transistor's middle lead for isolation, then put a large piece over the whole thing to isolate it from anything inside the radio, and again to keep it together and strong.

Originally Posted by rcscaler

By the way,
we need to get 4.7K resistor, but are we going to use 1/2 watt or 1/4 watt?

Get 1/4 watt.



And thanks for all the comments.

[nsimps]

Thank you!

This radio should have been this way from the factory, but alas with this mod it works! I'm fairly new to the soldering world and with patience this wasn't too bad at all and well worth the time and effort.

I ended up using PN2907 from Radio Shack as the PNP transistor. So far with 5 min of out and back with the winch no smoke coming from the radio.

Thanks again for taking the time to put this up, it will make my next comp so much better!

[joshsmith512]

thanks for this, I just did this mod and it is sweet but I think I did something wrong as the momentary only works one way and nothing the other way. I was able to just put the winch constant above on dt3 and use dt4 just for momentary winch in, any ideas why did I possibly pop a resistor?

[joshsmith512]

ok just redid it and still does the same thing? even tried clearing a model memory and started fresh on the radio program. so i am modding a 4pls but it looks exactly the same. any ideas?