[ARDF] Montreal fox controllers

[Dale Hunt, WB6BYU]

   Jennifer -

       Hope you saw the other messages on this topic that had
   a different subject line.


       Rather than a fuse on the battery, I prefer to use one
   of the new PTC termisters, designed as a "solid state,
   automatically-resetable fuse replacement".  These look like
   a big disk capacitor or MOV, and come in different current
   ratings.  I use the 2.5 amp ones in some of my boxes:  when
   the current exceeds that value, the thermister shuts down and
   allows just a trickle of current to pass.  When the fault is
   cleared, the thermister resets itself.  This means that the
   field crews don't need to carry spare fuses.  Meanwhile, the
   FAR Circuits boards are set up for two power sources, so you
   can put a 9V back up battery on just the controller that will
   keep it running if the main power is interrupted.  When the
   main power is available it gets used instead.

       And I certainly agree with the idea of using NP0 or C0G
   rated capacitors for C1 and C2 - these have the best temperature
   stability.  Sometimes you can find trimmer capacitors with this
   rating.


       - Dale WB6BYU


Gerald Boyd wrote:
> 
> Jennifer,
> 
> Also don't use the spring type fuse holders between the controller and the
> battery.
> 
> Use the small automotive blade type fuse holders (can get them at radio
> shack).
> 
> The spring type holders can break contact during transport into the field
> and reset the controller! Not a good thing to have happen on event day when
> people are ready to start.
> 
> We don't have an ON/OFF switch. We use power pole connectors to power
> everything up and issue a master reset with a sync cable (a box with a
> pushbutton and a cable to each controller).
> 
> Our controllers have been very stable. As on both event days they came up on
> time and stayed in sync.
> 
> Jerry
> -----Original Message-----
> From: ardf-bounces at kkn.net [mailto:ardf-bounces at kkn.net] On Behalf Of
> Charles E. Scharlau
> Sent: Friday, February 17, 2006 6:27 AM
> To: ardf at kkn.net
> Subject: [ARDF] Re: Montreal fox controllers
> 
> Hi Jennifer,
> 
> I've built (or re-built) about ten of the old version of Jacques & Francois'
> Montreal fox controller. Based on my experience, and what I've heard about
> the alternatives, the Montreal controllers have proved to be the most
> reliable and accurate controller available; and the least expensive to boot!
> I am not sure what improvements are in the newer version, but whatever they
> are, they are not mandatory for having good reliable controllers.
> 
> There are a few things you can do to ensure that your Montreal controllers
> work reliably and keep their timing relative to one another:
> 
> 1. Use a high-quality IC socket for the PIC. You want to be able to remove
> the PIC for re-programming, and a quality socket will ensure that the
> processor stays put when shaken, and stays reliably installed through
> changes in temperature and humidity.
> 
> 2. Solder each part carefully. Soldering is the number 1 source of problems
> in my experience. Only for that reason would I recommend a PCB instead of
> hand-wiring on a perf-board. Also, if you really want to ensure that each
> controller has an identical clock frequency, a PCB helps ensure identical
> parts layout, and prevents random stray capacitance from affecting clock
> synchronization. Otherwise, perf-board wiring should work just fine.
> 
> 3. Program your PIC with software that stores ALL controller parameters in
> non-volatile memory. Earlier versions of software (and perhaps the more
> recent ones, too) read data (such as fox number) from the DIP switch at
> power up. The DIP switch is a definite weak link, and is best used only for
> initial programming, not for setting controller parameters on the fly. I
> prefer to never use the DIP switch at all, and simply reprogram each PIC
> before installing it in the controller. I have software available should you
> need it.
> 
> 4. Use identical, high-quality, crystals and oscillator circuit capacitors
> in all the controllers you build. The capacitors (C1 and C2 in Jacques'
> schematic diagram, I believe) are especially key. Do not use standard
> ceramic caps having a tolerance of +/- 20% and which are not stable over
> temperature. Instead, use the "COG" ceramics (+/- 5%) available from
> Digi-key: 399-1890-ND. (Also, I don't recommend trying to use a trimmer
> capacitor to tweak the oscillator frequency. If you carefully adjust each
> oscillator circuit you will have them "perfectly" aligned only so long as
> they are at the same temperature and they don't get jostled. You are better
> off just using quality fixed-value caps and identical crystals. An added
> plus: no alignment or frequency counter required!)
> 
> 5. Use a minimum number of connectors, and where you must use a power or
> audio connector, use a high quality type, and solder carefully.
> 
> All of the Montreal controllers I've built have been 100% reliable, and keep
> their timing (relative to one another) within ~3 seconds for more than a
> week of continuous use. They will be used for the US Champs in April... and
> they are the least of my worries!
> 
> What a great V-day gift!
> 
> 73,
> Charles
> NZ0I
> 
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