A Microprocessor Based Sequencer For
Transverters 
Now updated with
the PWM version that can be used as a pump circuit for the negative supply for
fet biassing etc - Please see the bottomof this page for more
details .
As mentioned in
one of my other links, I have built a 1296 transverter. When making any sort of
system that is either a PA or Transverter that is external to the radio driving
it, I like to have some form of orderly sequence for the TX/RX relays in the
system.
This is very important
when making high power linears due to the possibility of arcing the contacts on
the busy end of the amp. A sequencer can get over these issues by switching over
the relays before drive is applied. Some switching of bias supplies is needed to
do this if a total solution is needed.
In the past – I
have used linear circuits to do this. Typically with a quad OP Amp and a time
constant. As the voltage rises, the OP Amp compares the rising voltage against a
reference and turns on the outputs as the voltage rises.
A good friend
of mine, Keith ZL1BQE is a gun with the little Motorola 68HC908-QT1 (as well as
many others). I asked him if he could code up a chip with 3 outputs and have a
100mS delay between each output. He said it was an easy task so he set about
doing it and all has been done.
Normally for serial comms in this unit,
the oscillator needs calibrating for the software UART. In this case, no
calibration was needed, as the timing is not that critical.
I had to add some outboard circuitry for this
and this as mainly relay switching and RF sniffing
componentry.
It has the capability for PTT switching by RF or a PTT line that goes to ground for TX.
Please see the circuit
diagram for details
.
If you want to program your own
device - Here is the Code Image for the Micro
Thanks to Keith
ZL1BQE for the code and micro. It all works a treat and is a great little unit
when space is at a premium as in my transverter.
As I needed to use the sequencer for my updated 1296 transverter, I had to also get a negative supply for biassing the 30dB gain preamp stage so that I could get 30dBm to drive my BLV93 to get +36dBm - 4 watts.
I had the idea of waggling a pin on the micro to then drive a complementary pair to feed the charge pump circuit. Keith obliged and here we now have a pin that uses a PWM to drive at about 50kHz. This is used to chop up the dc in the right polarity to then give the - volts.
In addition to this, there is
an inhibit pin that allows the voltage to be sensed. It is fairly basic in the
fact that the pin has to be pulled low to enable the sequencing. This pin is
quite high impedance so I feed the pin from a potential divider, 100k to +5v and
100k to the -5v (I regulated the supply to -5 by a zener or 3 terminal reg like
a 79L05). If the supply is lost due to a short on the supply rail or the pump
components fail, the pin will go high and inhibit DC supply going to the
drain of the power FET and stop it from turning on and blowing up!!
Please see
the circuit
diagram and the S19 code image
for the micro.
73,s de Simon
ZL1SWW.