.jpg)
Watchdog Timer for Remote BYONICS TT4 Digi-peater
Mike Pinfold ZL1BTB
The Byonics TT4 APRS module has the additional
function as an APRS digipeater and when coupled with a small 2M radio like an
Icom 2a, a 2m j pole antenna , an 18AHr 12v Gel cell, 20 W solar panel with
simple controller is ideal for a remote self contained digipeater .This is the
setup we have ZL1AOR-3 in Rotorua, Cental North Island , New Zealand.
The TT4 functions very well but you must upgrade to the latest firmware which
avoids the dreaded DCD light locked on condition . We have upgraded our TT4's
but we still find the odd dreaded lock up which usually involves a long trip to
the repeater site and a simple flick of the on off switch to set things right
again , but if you digipeater site is up on a hill top, a long drive from
civilisation, then a digipeater lock up is a pain in the arse ! ( at the moment
we are trialing the polish digipeater unit
I noticed it was always the dreaded DCD orange light that jammed on so I thought
we have to have some sort of interface to detect this unwanted configuration and
thus to generate a reset to put the tt4 into operation again .
The problem was that the orange light will normally flicker with normal use so a
“Long on” needs to be addressed . I wanted something simple and easy to build
that wont break down . We had to generate an independent reset pulse . So after
much pondering the situation came up with a simple solution we need to detect a
situation where if the TT4 locks itself up for a determined period of time then
a simple reset timer will switch the TT4 off then on with a simple relay
,rebooting the system.
I had never seen a lockup situation where the
transmit (red) light came on and stayed on ..this would be my activity indicator
. We could have a simple timer that clocks up to a predetermined or selected
time then it automatically switches the TT4 off then on again . We rely on the
packet activity, to toggle the Tx red light off and on and this will "reset" the
count up timer to prevent it from ever switching the TT4 off then on to reboot
the system .
If you select a count up time longer that your beacon repitition rate ,then the
watchdog timer is guarenteed to reboot if there is a TT4 lock up , there will be
no beacon tx light to reset the timer , the timer will eventually time out and
reboot the TT4 ,and the whole cycle starts again with normal operation
repetitively resetting the count up timer
I tried to use a ne555 but it is difficult to acieve repeatible accurate times
as needing high value capacitors and high value resistors so I went to my old
favorate timer application using a CD4060 . It has and onboard oscillator and
can cascade toggle up to 8192 in powers of 2 ( some are missing but thats no
problem) so I arranged a slow oscillator frequency of near 1 Hz, then one merely
taps the reboot relay driver connection to the pin that gives the closest time
to your desired digipeater reset period
simple huh !! But theres a catch. !When the 4060 hits say 1024 seconds, the
toggle output pin goes high and the reboot relay will hold “on” for another 1024
seconds, when the toggle output finally goes low the the relay will letgo and
reboot the tt4 ….not good ! Workable but not good .
So to fix this problem, use a spdt relay connected such that when the reboot
relay switches the TT4 off,I have the N.O. pole that now has +12v on it,
send a reset pulse to the CD4060 Timer . This reset pulse will reset the 4060,
all toggles flip flop outputs will go “low” and the reboot relay will let go and
put 12v back on the TT4, the reboot will occur immediately and not 1024 seconds
later ! The TT4 is immediately back on the air and working !!
cheers Mike ZL1BTB