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Frog Juicers compatible with RailPro?

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Dean:

--- Quote from: JJ Crooke on June 01, 2016, 09:18:02 PM ---Hi everyone,

I had the chance to go down in my basement to work on my layout this past weekend for the first time in several months so I'd like to give a quick update on Tam Valley's Frog Juicers compatibility with RailPro. I was able to install an LM-2S decoder in one of my locomotive and the verdict is...

Tam Valley's Frog Juicers are NOT compatible with RailPro's PWR-56. The locomotive can run fine in one of the turnout's alignment but will create a short on the alternate alignment. The Frog Juicers will not change the polarity of the frog as it can't detect the short.

Oh well... I'll have to sell my Frog Juicers and look at the other options listed in this thread.  :-\

--- End quote ---

You might try an auto-reversing device.

Alan:

--- Quote ---I'm glad you liked my idea. I was thinking a bit more basic than your description though. I was thinking of simply detecting/using the voltage somehow; when a locomotive first bridges the insulating gap from the powered rail to the frog (same side of the locomotive) the frog will either have ~14v or 0v applied to it
--- End quote ---

I've got it!!! The solution hit me out of the blue last night - a voltage divider network. I'll whip up a schematic later but here is the general idea: A series network consisting of 2 sense resistors sized to develop a 1.7 volt drop at 20mA and 2 limit resistors sized (combined) to limit current to 10mA at 14.2V.

Arranged thusly: VCC --> RSENSE --> RLIMIT --> Frog --> RLIMIT --> RSENSE --> Gnd

Connect an optoisolator across each sense resistor. When no wheel is on frog then only 5mA flows across the network. Insufficient RSENSE VDROP to meet optoisolator LED turn-on voltage. When a wheel connects frog to either polarity rail then effectively the network is cut in half raising the current flow to 20mA creating a 1.7V drop across the corresponding RSENSE and firing the respective optoisolator.

Now with a clean optoisolator output signal we can trigger anything we want. I'm thinking a pair of NAND gates controlling a quad switch like a CMOS4066 that disconnects the RNETWORK from the frog to solve the permanently-on problem. The logic output would initiate the correct charge pump MOSFET combination and start a short duration timer to temporarily hold 1/2 network at 20mA. The logic gates serve to prevent both polarity transistors from being on at the same time.

Wheel bridges rail to frog --> current jumps on one side of resistor network --> optoisolator triggers --> timer starts --> frog to network disconnect --> charge pump fires transistor --> timer expires --> transistor shuts down --> frog to network connect.

Tim, you are a genius!

 

G8B4Life:
Alan you've put a smile on my face this cold winters night  :); I've been called many things before but never a genius. I do think the title of genius should go to you though for figuring out the way to implement my idea, something I would not be able to do.

I really look forward to seeing the design you come up with.

- Tim

Alan:
The credit is all yours. I was satisfied to explain why off-the-shelf juicers work but are not ideal. Mostly because I practice another religion where there is no need for them - switch motor control. Your statement caused me to think about the problem, a problem I don't have <snide wink>, from a different angle. It is all about occupancy detection not short detection. Kudos to you.

The dots you helped me connect were "Hey, I've already done this!" My circuit breakers sense current flow and current ramp. Accurately. My occupancy detectors use measured voltage drop to trigger optoisolators. Sensitively. Together they form the foundation of the solution. Instead of shutting down high current circuits or sending logic pulses to a signalling system, we use the same basic sensing but do something different with the output - switch circuit polarity. At least we know the sensing side is probably doable!

Circuit breaker on the right - Sensing current rise via voltage across resistor (big brown resistor) to trigger a charge pump (IC) to turn on a MOSFET (transistor with the heat sink).
Occupancy detector on the left - Using voltage drop via current across a device (3 big diodes) to trigger an optoisolator (far IC) that starts a timer (near IC) to put out a signal (LED).
Many of both devices are functioning on my layout today. Proof the sensing scheme works. Exciting.

JJ Crooke:
I have finally received the SmartFrog V.5 (AP003) that I had ordered directly from Ane Model. It took 3 weeks to receive (Taiwan to Canada) and I was anxious to see if it would work with the RailPro system. As I explained elsewhere in this thread, I am looking for a replacement for the Tam Valley Frog Juicer as it is not compatible with the PWR-56. The wiring is the same as a Mono Frog Juicer (left rail, right rail and frog) but it must also be powered by a separate set of wires. Since my turnout was already wired for the Mono Frog Juicer, I've added two additional feeder wires (16 gauge) from the bus (14 gauge) to power the SmartFrog.

I am happy to report that the AP003 SmartFrog V.5 works like a charm with the PWR-56! The polarity of the frog changes automatically when a locomotive enters the isolated frog area and there is no jerking or hesitation from the locomotive. Everything is very smooth. You can hear a "click" when the polarity is changed or when you turn the PWR-56 on or off. Each SmarFrog is $14.95 USD (ordered directly from Ane Model's website) and shipping is free on orders over $100 USD.

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