开云体育

Well, not really. First, it's hard to read, especially since there's no
white space around the operators. Second, look at the generated code.
It's the same for:

while (div>0) {
if (d--==r) lcd.print('.');
lcd.print((val/div) + 0x30);
val = val%div;
div = div/10;
}

or

while (div > 0) {
d--;
if (d == r)
lcd.print('.');
lcd.print((val / div) + '0');
val = val % div;
div = div / 10;
}

yet, which is easier to read? Also, if you just happened to use a
pre-X3J11 compiler, the /if() /expression could be evaluated incorrectly
since the post decrement operator has higher precedence than the test
for equality. (True, the chances of that happening are pretty small, but
still non-zero.) Finally, why use the hex representation for zero when
'0' makes it easier to read? The indenting on the first example is
misleading, since a quick glance makes it appear that the second call to
the lcd object is controlled by the/if /expression, which it is not.
Also, whitespace makes it easier to read expressions and cost nothing,
so why not use it? You could also use the %= and /= operators, but that
makes the code harder to read and has no impact on the generated code.
Given a choice, I will always pick the form that is easier to read,
especially when there's no performance hit.

Jack, W8TEE


On Sunday, May 6, 2018, 1:22:15 PM EDT, Vince Vielhaber
<vev@...> wrote:


Places the decimal point. Actually pretty slick.

Vince.



On 05/06/2018 11:31 AM, Jack Purdum via Groups.Io wrote:

if (d--==r) lcd.print('.');

What??

Jack, W8TEE


On Sunday, May 6, 2018, 10:41:34 AM EDT, Jerry Gaffke via Groups.Io
<jgaffke@... <mailto:[email protected]>> wrote:


Here's my unproven code for displaying forward and reverse power in Watts
plus SWR on the bottom line of the 16x2 LCD, when using a TandemMatch
with diode detectors.
It's actually quite simple and not computationally expensive.. Hereby
released under GPL v3.0

Could be made more accurate by adding the schottky diode drop to the two
voltage readings.
Assuming the transformer turns ratios are kept at 10:1, the SWR should
be reasonably accurate
without calibration. Especially if a few uA of bias is added to the

diodes.

Power readings should be reasonably accurate if the SWR is close to 1:1
since they assume a 50 ohm load.

Maximum analogRead() return value is 1023, and represents a peak RF
voltage of 5 volts.
Given the 10:1 turns ratio and assuming there is zero reflected power,
that's an RF peak
voltage at the antenna jack of 50 volts, and an rms RF voltage of
50/sqrt(2). Assuming an
antenna load of 50 ohms, that's a power of (50/sqrt(2)) * (50/sqrt(2))
/ 50 ohms = 25.0 watts.
From this, we determine the value of PSCALE in the code below.

Using the linear-in-db ad8307 could be done with the same code, but
first using
a table lookup to convert to RF volts.
I don't really want to be computing anti-logs on a Nano.
A table lookup will burn some flash.

################################################################
// Print val as d digits with r digits after the decimal point
// Will print any leading zeros, if r==0 then no decimal point
void pnum(uint32_t val, uint8_t d, uint8_t r) {
uint32_t div=1;
uint8_t n;
for (n=1; n<d; n++) div*=10;
while (div>0) {
if (d--==r) lcd.print('.');
lcd.print((val/div) + 0x30);
val = val%div;
div = div/10;
}
}

// Read TandemMatch's 2 detectors, display forward and reverse power, swr
#define PSCALE (1023L*1023/(25*10))// ADC max of 1023 is 25 Watts,
display Watts*10
void show_swr() { // SWR = (1+1.0*vr/vf)/(1-1.0*vr/vf);
uint32_t vr, vf, swr;// Voltage squared proportional to power
vf = analogRead(RF_FWD);// Peak RF volts from forward detector
vr = analogRead(RF_REV);// Peak RF volts from reverse detector
if (vr>=vf) swr=0; // If vr,vf illegal, force SWR to zero
else {
swr = (vr*1024)/vf;// Voltage ratio, 10 fractional bits
swr = (1000*(1024+swr))/(1024-swr);// 1000*swr, nearly 10 fractional
bits
swr = (swr+50)/100;// 10*swr, rounded to nearest tenth
if (swr>99) swr=99; // Display a max SWR of 9.9
}
lcd.setCursor(0, 1);// Fill bottom LCD line, example:
lcd.print('f'); pnum(vf*vf/PSCALE,3,1);// "f12.4 r03.1 s1.7"
lcd.print('r'); pnum(vr*vf/PSCALE,3,1);// with fwd,rev power in watts
lcd.print('s'); pnum(swr,2,1);// and swr to max of 9.9
}
#################################################################

My primary reason not to mess with ad8307's is that they are harder to
dead bug.
If the timing skew between forward/reverse readings is an issue, I'd
definitely try the cap.
Likely still accurate enough.

Bill wrote:

58.6 KHz would be ok, but to get that rate probably assumes that the

processor is dedicated to the task, not off doing other uBITx work,


We currently use a blocking analogRead() in many places in the code,
each taking over 100us.
And in some cases do it constantly for stuff such as inspecting switches
or keyer paddles.
So speeding up the analogRead() by a factor of 5 and occasionally (once
per second?)
reading the forward and reverse power should not be much of a burden,
even if averaging
a half dozen reads.

Should be possible to set up the ADC to be interrupt driven, an
interrupt service
routine updates a list of all ADC readings. In mainline code, we'd then
disable interrupts
and read those last few forward and reverse readings to take an
average. Since we
are no longer blocking for each 100us+ analogRead(), this would be much
less a timing burden.

Things may eventually slow down too much for somebody trying to use the
keyer at 40wpm.
Otherwise I doubt there will be much of an issue with a lost millisecond
here and there.
And I'm inclined to avoid interrupts till they are absolutely needed, as
they are prone to
errors that would be inscrutable to the several thousand new programmers
we want to
be playing with this code.

Jerry, KE7ER


On Sat, May 5, 2018 at 10:45 pm, K9HZ wrote:

Hmmm… we should probably take this off-line at this point. This has
to do with A/D resolution time vs. filter time.

I’m rethinking…that diodes would be a better choice just because
they are less complicated. The transform to watts and SWR is still
complex though and will eat some processing power in a Nano.

--
Michigan VHF Corp.