An Auxiliary RC Control Unit
FOR THOSE WHO BOLDLY GO
and wish to do things a little differently ... IC3 is a hex inverter. I
was not sure whether I would need more inverters downstream.
As it turns out, one was enough. If the pulses are positive going,
you can leave out the inverter stage or use two stages in series.
Or you can use a LM311 for the inverter stage. The PPM regenerator stage uses the NE558. You could use four 555s or two
556s. Just remember that these devices produce negative going
pulses so you need to rework the output stage, as well. Whatever
you do, build it as shown or a variation of it, like it or dislike it, let
me know. I’ll be glad to hear from you. You can reach me at
IC5B is a D type flip
flop. With the clock and
data inputs grounded,
it becomes a simple set-reset circuit. The output
of IC1B is a positive
pulse indicating that the ■ FIGURE 4. Hybrid arrangement
missing pulse detector has found the positive pulse of
end of a pulse train and the beginning 300 microsec-of the next pulse train. This pulse sets onds. The nega-
IC5B forcing the Q output to go positive tive going edge
and Q\ to go negative. The trigger pulse of this pulse
from IC4C to the reset input of IC5B triggers IC6C,
forces Q to go negative and Q\ to go another one to two millisecond delay.
positive. To sum this up, the Q output The last stage, IC6D, outputs again a
of IC5B is positive and Q\ negative 300 microsecond pulse. To sum it up,
for the first five pulses of the original we have a positive pulse one to two
signal from our transmitter. Conversely, milliseconds delayed with respect to
Q will be negative and Q\ positive for pulse five of the original pulse train
the remainder of the pulse train.
■ FIGURE 5. ACU waveforms
and another positive pulse again
delayed by the requisite one to two
milliseconds. These two pulses are
combined, or to put it properly, they
are OR’ed via R18 and R19. Diodes D1
IC6 is an NE558 quad timer.
There are four independent
stages inside the NE558. The outputs are open collector. The first
timing element is IC6A. It is triggered on the negative going edge
of the trigger produced by IC4A.
Timing components are (R6+R7)
x C4. R6+R7 are either a total of
1K ohm or 2K ohm. Combined
with C4, this stage produces a
positive output pulse with duration of one to two milliseconds.
The next stage, IC6B, is triggered
by the negative going edge of this
pulse. The timing RC combination of IC6B, R8 x C5, gives us a
All resistors are 1/4 watt, 5% tolerance, and are available from
any of the usual suppliers. For C1 through C7, use non-polarized,
1% mylar or ceramic types. These are part of the timing sequences and should be quite
stable. C8 is an electrolytic used for bypassing the battery voltage.
The integrated circuits are CMOS. This choice is dictated by the fact that the nominal
supply voltage from the transmitter is 9. 6 volts. The same functions can be obtained with
TTL but it would require the use of a five volt regulator and would put considerably more
demand on the transmitter’s battery. Note that in North America these CMOS devices
are CD**** but in Europe, notably the same devices from Philips are named HEF****.
All of the data sheets for the ICs can be found on the Internet.
DESCRIPTION DATA SOURCE
CD4538 Retriggerable multivibrator Fairchild
CD4017 Divide by 10 counter Fairchild
CD4049 Hex inverter Philips or RCA
CD4093 NAND Schmitt trigger National
CD4013 D type flip-flop RCA
NE558 Quad timer Fairchild
LM311 Voltage comparator Texas Instrument
PP0308 Six-pin line plug Jaycar Electronics
January 2006 35