Build your own DSM2 transmitter module (its working!) - Page 4 - RC Groups
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Sep 09, 2007, 07:42 PM
TheSteve's Avatar
The receiver isn't always in bind mode, its like a standard Spektrum receiver, you need to connect a bind plug to put it into bind mode. The receiver will ignore bind packets in normal mode the same as any normal Spektrum receiver.
So to bind a receiver to the original LP5DSM transmitter you simply connect the bind jumper to the receiver you wish to bind and power it on, then power on the LP5DSM and it will bind and set failsafe. You then power off the receiver, remove the bind jumper and you're good to go. Its really no different then any other Spektrum transmitter other then its powers up in bind mode for 2 or 3 seconds everytime you turn it on then goes to normal mode.
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Sep 09, 2007, 07:50 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Got it.

I have an XPS module for outdoor stuff, but this could be a great mod for indoor flying using the small DSM2 Spektrum rcvrs.

XPS is working on a 4 gram rcvr, but their product release schedule can be pretty slow.

Just need to get a LP5DSM. Should be lots left when the CX2 owners wear them out or move on to something else.


Pat MacKenzie
Sep 10, 2007, 01:01 AM
Registered User
the Tx does seem like it should be easily available given how many people are using their CX with a DX7.
Sep 25, 2007, 03:19 PM
Inciting Riots
village_idiot's Avatar
My AVR stuff should arrive any day, and I just rounded up a LP5DSM to give this a whirl. I would be very interested in code set up for 6 channels, or 1-4+6 to be able to use with other helicopters with my 9C.

Since the code is not mine, I will not make it public if you are willing to share.
Sep 28, 2007, 07:33 PM
E-325, E-620 No plastic
Originally Posted by TheSteve
Decided to play with this a little more this evening and everything fell into place.
I tried a serial port rate of 125K instead of 115200. The data is now super easy to see and follow.

Questions or comments let me know!
This is very interesting! I imagine it did take some time to figured it out.. Just for info, would you know if the JR 9 or 10 channels is using something similar?

Thank you in advance.

Happy flying
Sep 28, 2007, 08:26 PM
Inciting Riots
village_idiot's Avatar
Just got one of my transmitters.
Oct 29, 2007, 03:50 PM
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village_idiot's Avatar
Penciled out a rough schematic with some help from Steve. He strongly recommends the 0.1uf cap to ground on the reset line to help prevent unwanted resets. Guys go back and forth over this on AVRFreaks, some swear by it, some not so much. So if you intend on this make provisions to be able to add this cap if you want it to be optional, it just might be needed.

Note that there are a couple of things that have not been proven yet, this is my "working" scheme so there might be changes to things like the power supply filtering, PPM input buffer, RF OK switch, etc. I will be building this very soon to try it. If all goes well then the hex code might show up.
Oct 30, 2007, 10:07 PM
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village_idiot's Avatar
Well if stupidity didn't get in the way, I might have an update on this.

The brown wire for the LED goes low to turn the LED on, so that part of the circuit should be fine.
Oct 31, 2007, 08:07 PM
Inciting Riots
village_idiot's Avatar
I threw together a really crude version of the above. No transistors, chip mounted in the dev board, just really hasty construction. Works fine so now all I have to do is build a more final version that will fit in the nice box that I have ready.

Sorry about the crumby picture, my camera has finally given up.
Oct 31, 2007, 09:14 PM
TheSteve's Avatar
Nov 01, 2007, 10:11 AM
Inciting Riots
village_idiot's Avatar
I'll work on getting the real version done this week, but I foresee few problems. In fact the only thing that I could see happening is that if I used the wrong buffer for the PPM, and that would be a simple fix (but unlikely that I messsed it up).

I think it would be safe to release the firmware if you are able to do so. Also this could be made into a "universal" Futaba/Hitec compatible device simply by changing the buffer to the inverting style, ignoring the RF OK connection, and connecting it to the trainer port. You could also build up a JR version with everything in the above schematic except for the connector pin out (since the PPM buffer is non inverting), and I don't think you need a pull up on the PPM line. So delete R1 and change to the 6 pin that JR uses and it should work. Maybe need to change the RF OK section, I'm not sure how JR handles that feedback.

Also the RF OK portion (Q2) will NOT need a pull up on the brown wire. So that note on the scheme should be ignored too. This should apply to all designs. Q2 is an active low switch (with PNP), which means when the input goes low (on the base), it conducts current across the emitter and collector. Since this is going to ground it turns the Futaba LED on. To make it active high, use the same circuit as the inverting buffer. It is unlikely that JR would use the active high type switch as I'm sure they are grounding the LED to make it turn on (if their radios have an LED for RF OK). Somewhere I have the pinouts for the JR modules that I guess should be dropped in here to complete the information.

An example of an inverting buffer (and active high switch) can be found here:
Nov 01, 2007, 01:28 PM
Inciting Riots
village_idiot's Avatar
A perf board that fits the XPS new style Futaba shells. Note the amount of copper on the edges, this is the best way that I can think of to relate the acual measurements so that the connector lines up.

Radioshack 276-149
Last edited by village_idiot; Nov 01, 2007 at 01:34 PM.
Nov 01, 2007, 06:12 PM
supreme being of leisure
ZAGNUT's Avatar
why not design a board and etch it? would be pretty easy for your simple schematic and could be done up single sided with SMT parts (less drilling).

or if you have to use perf board at least use the FR4 stuff with plated thru-holes.

Nov 01, 2007, 06:40 PM
TheSteve's Avatar
I know in my case it was much quicker to just use perf board. The board I built for this project took less then 2 hours. I would always prefer to use higher quality board but I've used radio shack boards before simply because that is what I had on hand and felt like building something. You have to be more careful with soldering iron heat, aside from that they work fine.
Nov 01, 2007, 08:08 PM
Inciting Riots
village_idiot's Avatar
Soldering iron heat? It's been a really long time since I pulled one of the rings off these boards, even desoldered several and still ok. Mostly it is what I had on hand, and as Steve said, it goes together quickly, even when you are mixing surface and through hole like I will be.

One of these days I need to learn one of the circuit design applications so that it goes a little more quickly, then I'll stop using as much perf board as I do. Double sided etched boards wouls make this simple to put together, all my v+ supply and ground could be on the back side. Depending on what happens at work tomorrow I may have this done by the time I leave for the night. Should be able to knock this together in 2 hours or less now that the connector is mounted.

I'm not loving the XPS cases, probably won't buy them again.

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