[Bob Small]

I'm looking for some way to "boost" the actual DCC signals.

The QSI GWire receiver outputs a DCC signal, but because the GWire is limited to a 5V input, the DCC output is correspondly low.

What I would like to do, is to boost the DCC signal to around 12 - 15V and then use that to drive a DCC decoder.

Any ideas?

I think that some combination of opto-isolator and amplifier would do the job.

 

[Road Foreman]

Bob,

Why not hook it up to the QSI decoder, either the Aristo or the Magnum??

BulletBob

 

[Bob Small]

/DesktopModules/NTForums/themes/mls/emoticons/sad.gif Too big. I need something a lot smaller.

 

[Greg Elmassian]

You need an engineer to make you a small bipolar amp...

It's just a couple of transistors and a power supply... a little switcher, but you did not say what power was available...

by the way, what size do you want this to be (give x y z dimensions)... I think you actually cannot beat the size of the QSI...

Regards, Greg

 

[ConrailRay]

Bob,

I remember reading when the Gwire unit first came out, that someone took the signal off of it and hooked it up to a Digitrax or similiar decoder.

The signal coming out of the Gwire is probably just the 5v DCC signal (or some version of a DCC signal), not what you would normally see on the track of a dcc system (DCC signal on top of square AC wave or similiar), which is why you would need to build a booster here. However, you can probably take this 5v DCC and send it directly to the uProc pin on the decoder.

I did something similiar last year as an experiment with a different DCC system and a function only decoder. Basically I sent the DCC signal from an NCE command station over RF. Then captured the signal with the reciever RX, and sent this digital signal directly into the uProc of a function only decoder. I had to hack this decoder. I forget the specifics, but basically somewhere in or right after the diode bridge rectifier on the decoder, a line comes off and goes through a resistor setup or two (think it is a voltage divider setup to convert to the 0/5v DCC signal) and directly into the uProc. This line is filtering out the DCC signal, droping the voltage so the uProc can handle it, and sending it to the uProc. So you need to cut out and isolate this line and feed it from RF reciever or possibly Gwire unit.

I was going to try this with a motor decoder but never got around to it. Note that motor decoders may be a little more complex, in that it will take the DCC signal from both sides of the rail and feed it into 2 different pins on the uProc. The signals on each side of the rail I believe are bi-polar or opposite of each other, and I beileve many motor decoders compare these signals as a safety check to ensure its getting a clean and accurate signal. I think the way to get around this is to branch the single signal and send one side through an inverter, but not sure.

-Ray

 

[Greg Elmassian]

Ray, I think it was Stan Ames, and it was either a Digitrax or Lenz. I agree with all you posted, and it will work on a motor decoder, you just have to find the right place for input, you might be able to "level shift" the unipolar signal to a bipolar, though not sure all decoders need it.

Yep 5 volts, because that is the power supply voltage to the LINX receiver, and also standard TTL levels.

Still would like to hear from Bob about target volume of the electronics and the available voltage to run it.

Regards, Greg

 

[Bob Small]

Here are my options and thoughts.

My next project is to battery power a small 4 axle switcher (similar to a Aristo Lil Critter, more like an LGB 20910 field railway diesel).
It is currently running on DCC with a Digitrax DH123D and SoundTraxx DSX

It is intended for the grand kids to play with.

By way of experiment, I have used battery + GWire + TCS FL4 to light a caboose. So I know that idea works.

Option 1.

I thought that I'd like to try Stan Ames' ideas of DCC with UPS

The concept is battery + Lenz Gold decoder + GWire which seems to be workable.

The Lenz has a SUSI sound interface, but getting any kind of SUSI sound decoder is proving difficult. The only one seems to be Uhlenbrock. And they are expensive.

Option 2.

The DSX gets all it power from the DCC signal. I have tried connecting the DSX direct to the GWire, but no success. This is why I then asked if there is a way of "boosting" the DCC signal. Primarily to feed the DSX.

This way I could do either
a) Battery + GWire + Lenz + booster + DSX (with Lenz battery powered and only the DSX connected to the boosted DCC signal) or
a) Battery + GWire + booster + Lenz + DSX (with both decoders in parallel connected to the boosted DCC signal) or
c) Battery + GWire + booster + Digitrax + DSX (with both decoders in parallel connected to the boosted DCC signal)

The advantage of all of these ideas is that the decoders are all very small. I have just enough space to fit the GWire and battery. A 7805 can provide the +5V for the GWire. I was hoping that I could make up a "booster" with no more than a 7812 and a couple of ICs or "transistors". This would provide a 12V DCC signal which was also cable of supplying around 1/2amp

Having said that, there is possibly enough space to fit the QSI decoder and in the end that may well be the solution, but I'd still like to explore the possibility of reusing the existing decoders.

 

[Greg Elmassian]

The QSI is 2.3" x 1.2" x .75" not counting the pins, which could be bent over or eliminated, wiring directly to the board. Also, half the board is 1/4" thick. You can rearrange the 2 electrolytic caps, and remove the polyswitch.

Seems to be smaller than the total of what you are proposing (motor decoder, sound decoder, 5v regulator and electronics to amplify DCC) and it works out of the box, and less wiring, easy to program, large library of sounds, works on DC and DCC...

Regards, Greg

 

[ConrailRay]

Bob, Just out of curiosity, how did you connect the Gwire to the TCS function decoder? A hack like I described or some other method??

Well, the CVP decoders have a 1 amp DCC booster on board, so its just a matter of finding a simple and small circuit to recreate it. Might be able to check on the merg website to get some ideas.

-Ray

 

[Bob Small]

Ray,

The GWire output is a 5 wire FFC - 2 ground, 2 DCC and +5V. I made no changes to the GWire. And no changes to the TCS FL4.

The FL4 is wired up with the red and black direct to the GWire DCC, the black/white to ground, and all the function wires through the lighting LEDs and dropping resistors.
There is no connection to the FL4 blue wire. All light power comes from the 5V regulator.
The FL4 is ideal for this application because it already has a ground wire.

I made up a small PCB with all the bits. It has a 7.2V li-on battery, a 5V regulator, a SLW5S FFC conector for the GWire and a few resistors.

I did find that the voltage was critical. The original breadboard test used a 14V battery and an LM7805 and gave 5.02V and worked fine. I then changed to a 7.2V battery and an LM2940 low dropout regulator. This gave 4.94V and nothing worked. So I added a 1N5818 ground bias diode to the regulator and bumped it up to 5.17V. All works OK. Need to be careful as the output buffers on the GWire have a max voltage of 5.5V

As far as a booster is concerned, I have found a dual channel optoisolator that will handle 20V output with a gain around 150. Fairchild HCPL-2530. So that might be promising.

 

[CapeCod1]

In Re Bob Small's comment:
"The Lenz has a SUSI sound interface, but getting any kind of SUSI sound decoder is proving difficult. The only one seems to be Uhlenbrock. And they are expensive."
For what ever its worth, I'm using Stan Ames' circuit (DCC + batteries) in my 6 locos. They all use SoundTraxx units. (Easy installs.)
CapeCod1

 

[Bob Small]

Capecod1,

Is your DCC through the track or through the air?

 

[ConrailRay]

Hey Bob,

Your set up is interesting. Having a separate ground wire on the FL4 definately helps this set up, but if you can find the diode bridge on a standard decoder, you can hack into this.
So basically what you're saying is that the 5v DCC bit stream from the Gwire unit is constant enough to obviously supply the DCC stream and power the FL4 decoder??
Any idea why there are 2 DCC wires? Is one signal inverted, or is it just redundency? I don't have a Gwire or QSI decoder yet, but I know there's a few transistors on the Gwire board that may be doing something.

Thanks!
-Ray

 

[Bob Small]

Posted By ConrailRay on 03/04/2008 7:27 PM
So basically what you're saying is that the 5v DCC bit stream from the Gwire unit is constant enough to obviously supply the DCC stream and power the FL4 decoder??
Yes.
Or at least enough power to switch the functions.
I'm using the battery to power the lights. Just using the decoder to switch them to ground. So that way the GWire doesn't handle any of the function loads.

But what I have also found is that the GWire doesn't have enough power (either not enough voltage, or not enough current, or both) to power a SoundTraxx DSX. Which is why the booster question.

Any idea why there are 2 DCC wires? Is one signal inverted, or is it just redundency? I don't have a Gwire or QSI decoder yet, but I know there's a few transistors on the Gwire board that may be doing something.

Thanks!
-Ray

The output from the LINX is a single wire. This is then inverted to create a second output. Each output is then put through a buffer. So basically each output is 5V with one the inverse of the other.

It would be interesting to see the GWire DCC signal on a scope.

 

[ConrailRay]

Bob,

Thanks, good info. It will be interesting to see if you can use an opto-coupler to boost the voltage/current enough to power the DSX chip instead of using mosfets. I guess the function only decoders are different, but I thought decoders had a minimum voltage input of 8 or 9 volts (trying to remember from when I was messing around in Z scale). I was told by soundtraxx that the max draw on the DSX chip is 400mA, which is probably more then what the Gwire signal was planning to provide.

Also, 4 or 5 years ago, I cut a DSX chip in half and resoldered all the connections back together in a different shape so I could get it to fit into a Z scale loco, and it actually works (after a few attempts    I have dawings of all the traces/components I made somewhere around here, but can't find them at the moment.
So I was just looking at another DSX I have here. If you cut the wrapper off and hold it so that the plug is facing downward, you can see 4 small black diodes and a zenor diode right above the plug. This is the diode bridge to convert the power to DC. I forget which one, but one of the caps on there is a buffer cap to help provide power over dirty track (underneath is also a + and - connection where you can connect more buffer caps). Now if you look on the right side of the plug, the red wire comes in and the trace goes into the diode bridge and also splits off to the two resistors to the right of the plug which looks like the voltage divider. This trace then goes directly into the uProc and is probably the 5v DCC signal. If you look on the left side of the plug where the black wire comes in, it also has solder pads for resistors in a voltage divider setup, where that lead also goes into the uProc, but there's no resistors there, so it seems like they may only be taking one side of the signal. So theoretically, you might be able to take the 5v DCC signal from the Gwire and tap into the DSX chip dirrectly after the voltage divider (this lead needs to be isolated from the red wire) and then simply connect higher voltage from your batteries to the red/black wires.

-Ray

 

[Bob Small]

Ray,

You're the man

I removed the two resistors from the DSX and soldered a single wire to the common junction.
This isolates the DCC input signal from the red and black input.

I connected 12V DC to the DSX black and red wires.

So now the DSX has three inputs - +12V (red wire), ground (black wire) and DCC (the new wire)

The DCC input was then connected to one of the DCC outputs from the GWire. The GWire is connected to +5V.

And it works fantastically.
The GWire controls the DSX

 

[ConrailRay]

Bob,

That's great! All this hacking talk makes me want to go back and hook up the compatible linx TX chip to my NCC commancd station and see if I can get it to talk to the Gwire, QSI and other decoders A dream of controlling the layout with wireless NCE hammerheads to wireless DCC/battery locos Plus since all the wireless throttles go into the NCE command station and merge together to a single DCC signal, wouldn't have to worry about selecting 1 of 8 channels on the linx chips on the CVP throttle and recievers...

Not to mention building my own Gwire unit, as the linx RX chip is relatively cheap compared to the price (and new price hike) they just put on the board!

I'm still wondering if the CVP TX is sending out a full blown DCC signal or some sort of limited signal that still works?

-Ray

 

[DKRickman]

Ray,

Have you managed to get the above combination working yet? Even tried?

A question about the Gwire reciever. Can it control multiple decoders with different addresses, or is it basically a single address decoder on its own?If the former, could you concievably feed its output into a DCC booster, and thus control a layout less expensively than the common wireless systems on the market?

 

[John J]

Remember Linier Amps from CB days. They use to cause the lights on your car to dim when you keyed the mic?. What about a linier amp on a smaller scale?
Anyone know how to make one? It's been so long since I graduated from De Vry I forgot all of that stuff. ( They were still teaching vacuum tube theory back then)