DC throttle for NCE and how
it works.
Mark Gurries 20Dec05
>Yes
and no. Mostly no. There was a diagram of how to make
a throttle for DC locomotives in the old NCE manual. Haven't
looked at the new manual, yet. Nice thing about NCE is I don't really
need the manual to operate.
Your right
Joe...but the ability to run a analog Loco on the NCE
system was silently dropped many years ago.
There is no circuit diagram in the latest manual since nor will there
ever be one given the hardware support is gone.
>
>The
home made throttle connected to the serial connector and was intended to run
only one loco. Don't know why you couldn't run more than one but all would be
controlled by the one throttle, like a consist. It
worked but not well, and NCE didn't recommend it.
The analog
throttle bypasses the command station completely. The command station has no knowledge of it
usage active or not. The analog throttle
talks to a completely different chip (A dedicated microcontroller called the Rx
chip) that is solely responsible with generation of all the DCC packets being
sent to the tracks as directed by the command station processor. (See note
1). The analog cab speed setting is
simply blended in dynamically with what
ever DCC packet is being sent at the moment and all other data after that such
that is looks like DC to a DC motor sitting on the track. (See note 2).
>I
think it also required some modifications to one of the circuit boards inside
the command station, something I personally wouldn't do.
Correct. There is a jumper wire needed to activate
this feature on the command station that supported. The idea was to allow NCE a
marketing backdoor to claim DC/analog loco support. But at the same time, NCE intentionally made
it very hard to set up, control and use in a meaningful way compared to his DCC
competitors.
Note 1: The
command station processor tells the Rx chip to send this packet this many times
(more or less) and then moves on to do something else. The Rx chip schedules the DCC packet, because
you must first finish sending the current active DCC packets going out at that
moment, and then puts out the track at the next opportunity. In short, the command station lets the Rx
chip worry about the details of keeping the DCC packets flowing down the track
per the NMRA standards so command processor can do all the system management,
cab control & consist management functions asynchronously.
Note 2: The
Rx chip has an A to D converter and reads the analog
throttle Pot position. Analog throttle
control use a DCC packet Feature called "zero bit stretching" that
makes the DCC packet look like a DC signal to a DC motor sitting on the track
without a decoder. It does not actually
alter the DCC data in terms of the information being sent. But is does slow down the effective overall rate
at which DCC packets can be sent. This can have a dramatic effect on large
layouts. The response time of all the
OTHER DCC locos will go down inversely proportionally to the speed of the
analog loco running on the track. This
has actually happen on many times on Digitrax layouts
become major problems....hey what going on...sometime resulting in a required
system reset when in fact all that happened is that someone left the analog
loco throttle wide open by mistake but took the loco of the layout. Most people do not know the "Dark
Side" consequences of running a DC locomotive on DCC.
Best
Regards,
Mark Gurries
Linear
Technology
Power Supply
& Battery Charger Applications Engineer/Manager
---------------------------------------------------------
Model
Railroad Club and NMRA DCC presentations are at: