My enormously complicated, enormously fun DC throttle project

[mmagliaro]

I'm interested, but two questions..... or maybe if I just read more I'd figure it out.

DC output - is this a 'pure' DC, or a square/pulse transistor, or otherwise modified output?

Power in - every walkaround throttle I have is set up for DC voltage in and DC voltage out on a 4-pin connector.    I'm having difficulty figuring out what your input power supply is.
If got a collection of conventional wired throttles, some commercial, some home-brew, varying from a pair of ancient CAMA throttles to a pair of PS550 cabtrollers to a pair of home-brew pure DC throttles with internal additional resistors.  Getting rid of the cable here would be nice, so I'm interested.

Output is either completely smooth DC, or smooth DC with a 4v half-wave 60 Hz since pulse riding on top of it that gradually declines as you increase the speed.  The original Thorne design did not reduce the amplitude as you increased the speed, and it didn't turn the pulses of at zero throttle, so it "leaked" a little and modern engines would creep at zero throttle.  I fixed both of those things in my redesign.  I also added my own since wave generator to it, so that my board doesn't have to rely on the 60 Hz waveform from an AC input power supply (although I can still build it that way). 

There is place on the board to connect an SPST switch to turn the pulses on or off.  But seriously, I recommend always just leaving it on.  Not a single engine I have ever run on this, coreless, DCC equipped, etc, has ever had a problem with the pulses.  No noise, no weird "crazy" behavior from the DCC decoder, nada.  And motors just plain run a little better at low rpms with that gentle pulsing in there --- yes, even Faulhaber coreless motors will run just an edge slower and more steadily, with some pulse in there.

Power supply:
16VAC or 18VDC input is my strong recommendation.  You can use lower voltages, especially if you aren't loading it heavily (like, loading up to 1A instead of 3A), or if you don't care that your top end output voltage is only about 10.5 instead of 12.  I wouldn't go below 12VAC or 14VDC, though.

And I would not go higher!  No no no no!  All that will do is create more heat and put 14-15 or more volts onto the track.  Who needs that?   You can use any AC power transformer (or the AC "accessory" terminals from an old power pack --- although
I hate that idea because those accessory outputs are notoriously too high a voltage and are very unstable).

A really good thing to use for a DC supply is a surplus laptop computer "brick".  You can get 3-5 AMP laptop power supplies like that for $10 these days.  They are switching power supplies, and have very accurate, stable outputs.   You can just cut the laptop plug off the end, strip the wires, and hook them up to my board.  Performance wise, the AC transformer is more efficient because my input goes through a 4-diode bridge whether you use AC or DC, and the AC load will be shared by 4 diodes, whereas the DC will only go through two of them.  But since I used monster 12 AMP Schottky rectifiers, it's not going to be a problem either way.

Input is 2 wires... AC or DC.   Output is 2 wires to the track.

It has an on-board direction control DPDT relay, operated by an SPST toggle or 2 momentary  push buttons.  It has an on-board current threshold protection, which is a comparator with Schmitt trigger style circuit that triggers QUICKLY and ACCURATELY - not like a thermal power pack breaker that can sit there letting the throttle bake in its own juices for 30-60 seconds before it finally trips.    Overcurrent trip turns on an output on the board that can drive an LED, which you could put on your control panel (if you don't want it on the board itself).  Reset is just via a nomally-closed momentary pushbutton.

[mmagliaro]

Max,
Going by the large filter caps, my guess that your throttle can output filtered "pure" DC voltage.  You also mention pulse option and that it can use a "pulse module"  That sounds rather complex.  I'm curious why didn't you just use a simple on-board pulse generator (either made up from discrete transistors or something like a 555 timer IC)?

Back in the day I built the TAT V throttle (from the plans in Model Railroader), and it uses that kind of simple pulse generator. It features adjustable frequency and pulse width, and that really works well to finr tune it to make every motor crawl at slow speeds.  That throttle works really well,

Correct on the big caps.  The smooth DC is seriously smooth, as in less than 0.1v ripple at full 3A load.

Pulse generators made from a 555 are easy.  SINE WAVE pulse generators based on the 555 are pretty awful.
I wanted to stick with smooth sine pulses because I know from practical use that those do not freak out decoder-equipped
engines.

The "pulse module" is my own little board that plugs into my main board.  You
can power the throttle from AC, and it will use the 60Hz sine from the AC as the pulses, which was the original
Thorne design.  But the sine wave from the power transformer gets "topped" (tops chopped off) under load.
That does not seem to bother any motors.  I've run that version for decades. 

But I added the sine generator especially in case somebody wants to power this thing off DC, where there would be no "wave" to derive from the input.   And since higher-current AC "wall warts" are going the way of the dodo bird, that became even more important (to support a DC input).  You can get  cheap DC high-current switching wall warts these days anywhere.  AC, not so much.

The "module" is based on the ICL 8038 wave generator IC (a 14 pin DIP).  That chip with a few resistors and caps
outputs a really nice full-wave sine with adjustable frequency.  I then put it through a little add-on circuit of my own with some transistors and voltage dividing resistors to allow me to cut the wave off anywhere I like, and also adjust the amplitude.  So twiddling two trimmers I can get any duty cycle and any amplitude.
 It did take me a while to figure it all out.  But now that that's all done, we're talking about soldering a handful of components to a little board and plugging it in. 

[peteski]

That's pretty clever Max!  I like it.

[mmagliaro]

Per a suggestion of Peteski's earlier on, I did add some user-configuration to the hand-held. 
For now, you can only set the momentum rate and the top maximum speed.  Those seemed like the most useful for now.

From the hand-held itself, you click the power button 3 times, putting it in "parameter set mode".  Then you turn the speed dial to set where you want the maximum speed to be, and click 3 times again to exit the mode.  The setting is saved in EEPROM, so it is persistent.   This lets you set a top voltage to, say, 8v ( or whatever you want ).  Then the speed dial has a smooth range from 0-8v, which gives a much nicer feel for a lot of N Scale engines that run way too fast on 12v anyway.
I haven't done something for setting the momentum rate directly on the hand-held yet.

I wrote an app to do this by plugging the hand-held into a USB port on a Windows machine.
It's not a thing of beauty, but it is simple enough to write and maintain.  And if I (inevitably) get carried away with settable parameters, it will be a lot easier to view and manage them on something like this than on an obtuse series of button clicks on a hand-held device.   It's your basic capability that can download the parameters on the hand-held, populate widgets on a display, let you change them, and upload them back to the hand-held.

[Cajonpassfan]

That's pretty clever Max!  I like it.

Yes, quite clever! Holy Cow!
Otto

[peteski]

Excellent, excellent!