Fitting a knob to the Procab, (instead of the wheel), Im a knob man.

The Main North HOME.


After purchasing my NCE system with an encoder wheel in my radio Procab, I found I was not completely happy operating with the speed buttons or encoder wheel. In the System manual I found instructions that explained how to fit a potentiometer instead of the encoder.


For those that dont understand, a potentiometer has min and max physical stops just like were used to on our DC cabs and the encoder has no stops. Operate up to increase speed and the rate that the wheel is move determines the rate of speed step changes until max. The wheel still turns but the display stays on max. When decreasing to stop, the same method applies.


I figured that this potentiometer could be fitted some where else with a knob. I pulled my Procab apart and found a really convenient location and only making a small change to the circuit board to fit it in, under the right hand lower corner of the display, next to the momentum button.






I purchased the recommended potentiometer as stated in the System  Manual.


Removed the circuit board and cut off the unused corner for potentiometer access.


Connected the potentiometer to the circuit board with 3 core shielded wire with the shield connected to the negative battery terminal.


I initially wired up the potentiometer with 3 loose wires and I had a display problem, that sometimes when reducing throttle speed to stop, the loco stopped but the display still showed about 020 030. Strange, I thought that is was a shielding problem, so I wired with shielded wire, but made no difference. This problem still exists but does not cause any operational problem.





The new Procab has a newer different circuit board.


The radio board harness connection to the main board is where I previously removed the corner to allow fitting of the potentiometer.


The blue potentiometer is shown placed in the position similar to where I fitted in my modified Procab.


I am not sure about the capability of adding a potentiometer to this Procab.


Will let you know with by placing the information here.






I drilled a hole in the Procab top cover, determined by the available access for the potentiometer.


Securing the knob onto the potentiometer shaft will require a matching sleeve to allow knob fitment.


Glue the sleeve onto the shaft with super glue making sure no glue flows into the internals of the pot.


Secure the knob with its screw. Be careful not to apply too much pressure on the delicate potentiometer stops.


May be a good practice not to glue, just have a tight fit so any pressure the knob rotates as I have done wit mine.





When fitting the potentiometer you have to add a 2.2 K ohm resistor to the circuit board where config is written on the board. This now tells the PIC that you have a potentiometer.






A newer REV D circuit board. Ill let you know when I fit the pot/knob as shown in the newer position below.


I seem to remember asking Larry at NCE about fitting potentiometers to later throttles and I think he said NO.




The Procab now operates one handed in the left hand, thumb operating the knob and direction button. I really like this knob installation. For new operators they hold the Procab in their left hand and operate the knob with their right hand.


I fitted a 23 mm knob, could be a little smaller, But this size allows for easy one fingered operation.




Another Knob location for the Procabs using both the Encoder and Potentiometer.





In this installation the knob was placed where the speed wheel is.


The original encoder was used, that is the right size to fit without too many modifications.


With the knob like this, the encoder is easily bumped and could cause inadvertent movement of the selected loco.


A better arrangement would to use an encoder similar to what is in the Cab04E that has mechanical clicks that result in a little resistance to movement. The Cab04E encoder would only fit with quite a bit of modification of the circuit board around the wheel slot.


Looks a bit more professional than my first attempt. Ill let my operators be the judge and see which of all the Procabs, is better.




I had to cut out some of the housing around the slot to fit the encoder in, so the circuit board would sit down correctly.


The flanges that centre the wheel and what it rolls on can foul the encoder. If you remove these, putting the Procab back to its original position, if not youre not happy with the knob encoder, may cause a problem.







The encoder in the wheel slot. I filed off some of the encoder housing and the edge of the circuit board, for more clearance, too much, hence the white double sided tape over the encoder.


Wired the encoder up to the circuit board as shown. If speed the wrong way, swap end wires.


As can be seen, the 9.5 mm wide encoder just fits in. If the wider 12.3 and higher 5.3 mm Cab04E encoder is used, the 2 circuit board tracks on the left and maybe one on the right will have to be replaced with wire links.




The 13.2 x 12.3 x 5.3 mm Cab04E Encoder on the left and the 9.5 x 9.5 x 4.5 mm Procab Encoder on the right showing the larger size of the Cab04E

Clicker encoder. The slot in the circuit board will have widened and 2 to 3 tracks replaced by wire links.


I will fit a 20 K potentiometer 9.5 x 9.5 x 4.5 mm (same size as the encoder), Part No 3310-001-203 to my Procab later as I prefer the stops and 300 degrees of rotation of a potentiometer. 




The completed Knob Encoder Procab showing how easy it is to use. With the correct knob without a line would be better as it may give the wrong impression of loco speed for the unwary.


It works quite well, as far as encoders go.


To tighten up the encoder, fit a felt washer or one made out of sponge, under the knob. 


A 22 mm diameter knob, just fits inside the speed buttons allowing button operation.


An easy modification, that can easily be returned to the original configuration, if not happy.