Improved R2LC/R4LC Serial Data Buffer

John,

Could you post some examples on when to use this item? 

What to look for to determine need, etc.?

Very interesting.

Dave

Hey John,

I'm thinking that this may be the solution to a problem I've been having with a K-Line GS4 that I upgraded the motor driver board to Cruise Commander M unit. When I power up the transformer, if the voltage is set to 0 and I bring it up to operating track voltage which is what I've done for years, the locomotive has only one speed and its pretty fast and no matter what I do, the sound stays at one chuff rate and the speed is either off or on. But, if I preset the voltage on the transformer to what I run at and then put power to the transformer, it works exactly as expected with all speed steps and chuff rates. From what You posted up top, this sounds like it may be the solution.

Are  you going to be selling these? 

I use it whenever I am doing an installation and upgrade and I run into serial data issues.   A common place is when trying to use an IR tether and the ERR Cruise Commander M.  A serial port buffer circuit has been around for years, but none of them amplified the serial port data.  I found that attenuation of the serial data stream was a primary cause of issues with seeing the serial data.  This is my attempt to put that issue to bed.

@Norm Odsather posted:

Are  you going to be selling these? 

Norm, I doubt I'll be building them for sale, I can't imagine getting enough sales to justify having them built in quantity.  I may do a re-spin of the board a bit larger and make it easier to assemble, then I could offer the boards and maybe the parts.  As you can see from the actual board, I may have gone overboard making it small, the little resistors and cap are 0.06" x 0.03" in size, I suspect most folks would have issues soldering them.  The op-amp is also pretty tiny, the spacing of the leads is less than a millimeter.

This is probably what the one for the masses to build would look like.  In order for it not to get really large, I did keep SMT for the op-amp, but it's a SOIC with leads spaced a 1.27mm, they're pretty easy to solder.  Functionally, it would be identical to the SMT version I posted previously.  It also is the same schematic as the SMT version, just the device footprints are different.

Not that I think I will ever build one, but this caveman would need to know the value of C1 first.

John,

I have more than a couple of the MTH PS1 large steam and large diesel engines that I am considering converting to ERR.  Would you think one of these would be needed in those "upgrades"?

@GregM posted:

Not that I think I will ever build one, but this caveman would need to know the value of C1 first.

Yep, forgot to turn on the value display.  As you can see, it's just a power bypass, so a .1uf ceramic would do fine there, that's what I'm using.

@DaveGG posted:

I have more than a couple of the MTH PS1 large steam and large diesel engines that I am considering converting to ERR.  Would you think one of these would be needed in those "upgrades"?

Only if you have issues with loading the serial data line.  It's somewhat hit or miss.

Having only done a few upgrades, I have not run into an issue - everything "works".

Just how does one "know" that loading the serial data line is the issue when things don't work?

Thanks,

Jim

Well, the most obvious symptoms I run across most of the time are the ERR cruise module taking off at full speed even when programmed, or the RailSounds coming up in conventional mode.  I've also noticed in some TMCC engines with smoke regulators that the regulator doesn't get all the serial commands and the buffer sometimes will fix that as well.

I don't think I've had any serial issues but I would buy a few kits or PCBs if you make them. Either the smd or the combo smd-thru hole.

You'll know if you run across serial data issues, something won't work right.

I will be interested in several of these built ups or kits when you finish up your prototyping. I've seen some odd problems with Cruise M installations and this might be the solution. In any case it would be good to have several on hand in case of unexpected problems with future installations.

Also, wouldn't this be a good addition to Scott's ERR lineup? If there are some Cruise M installations that will not work because of serial data issues, it seems like he would need to be able to sell a solution.

Ken

I have the thru-hole boards on order now, and the parts are also coming.  I'll offer some kits that include the board, parts, and instructions of how to wire and use the buffer.  Obviously, they won't be that expensive considering the few parts needed.

I build up a handful of the small SMT versions and realized that was probably going to challenge many folks putting tiny .06" x .03" parts on the a .3" x .4" PCB.   The little SOT-23 op-amp is actually easier than the tiny chip parts.

Same here.  I'll take a couple kits when available.

Dave

Well, I got my prototype boards back from OSHPark, and built a couple of the thru-hole versions.  Note that it's not totally thru-hole, but I went with a larger footprint surface-mount op-amp to make them easier to solder.  The resistors and caps are thru-hole.  This one is quite easy to build, so I'll order a larger quantity of PCB's now that I've actually seen it function.  The actual board is only .4" x .7", and about 1/4" thick at the thickest part.

It took a little longer as the first set I somehow got the wrong footprint for the op-amp and it was too wide!  Had to deep-six those and try again.

Here's a couple of the assembled boards.

To finish the build, I encase them in heatshrink so they can just tucked in where they fit.

This illustrates the performance with a 220 ohm load, still has almost a 2:1 gain.

John,

I would be in for 5 of the kits when ready.

I'm in for several of these kits as well.

Count me in for 6 or so - good to keep in inventory for repairs.

I just went digging for a previous posted design I'd made a few of.  Still have about 8 of them, took me almost a hour to find what I'd done with them.  Thanks for killing my time today guys!

Jim

Thank heavens we have good people like GRJ supporting us with these trickier microelectronics issues! 

The boards are on order, to keep the costs reasonable, they're shipping by slow boat from China, so it'll be a few weeks.

@Jim Sandman posted:

I just went digging for a previous posted design I'd made a few of.  Still have about 8 of them, took me almost a hour to find what I'd done with them.  Thanks for killing my time today guys!

We love to waste time, especially if it's not ours.

I have some previous buffers that didn't amplify, but the silver bullet for these issues turned out to be boosting the amplitude of the serial data signal so that everyone receiving the data gets the word.  I had failures with the previous designs that didn't boost the data, lesson learned.

I think I've used 3 of the previous design, and so far it has fixed the issues.  Wasn't the old one just a optical isolator repeater type design?

I'd still take some of the new improved ones!

Jim

Jim, the old one was a repeater, but it didn't address one of the significant issues, that being the amplitude of the serial data stream.  I finally realized after doing a little detective work, that was the one issue that kept the previous design from solving some of the problems.  So I figured it was time for a "final" cut to address that issue, and then the request for a thru-hole version came along and I went half-way.   The one SMT part has pretty wide lead spacing, and shouldn't be a major issue to solder.

I made up a few of the buffer kits, contact me on my profile address if you'd like one or more. 

The kits come with everything you need to build one buffer board.

All the parts and PCB are included.

And an instruction sheet with a schematic on the back.

You should end up with something that looks like this.   If you stick to the color codes shown, it'll match the diagram and the connection table.

Still have a few of these kits.