Simple audio encoding... how?

[MooseFET]

---
Maybe even better, since it gets rid of the peak detector!

The down side I see, in hardware, is the need for 16 bit adders to do
the integration for an 8 bit input.

You don't need real 16 bit adders because the ADC is much slower than
HC logic. You can use a serial adder.

Another idea would be to have a 20MHz clock and a 20KHz saw tooth.
Any time the voltage is greater than the sawtooth, the counter is
enabled. By using a somewhat perverted sort of ADC, you get the
summing action with just counting. It is only good to about 10 bits
on the ADC but perhaps that is enough.

Here's what I've got so far:

news:[email protected]

Unfortunately I can't deal with the URL. Perhaps if I wasn't so lazy
I would have a real news reader, but if a sled had wheels it would be
a wagon too.

I did it in 4 bits instead of 8 because I thought that would make it
simpler but, in actuality, doing it in 8 ( using an HC688 for the
magnitude comparator, a couple of HC273's for the input latches, an
HC40103 for the counter and a single HC175 instead of the HC74's) would
have resulted in one less chip.

If I get ambitious I'll redraw it...

Did someone already say "use a PIC" yet?. This sort of thing would be
falling off a log simple with something like Cygnal F120 processor.
You could sample the ADC at 40KHz and use one of the DACs to make the
output pulses. With just some lightning protection and a 3.3V
regulator, the who thing would be done.

 

[MooseFET]

---
Geez, where's the fun in that?

Besides I seem to recall the OP (who seems to have dropped off the face
of the earth) asked for a hardware solution.

I find myself losing interest now that the problem appears to be not
all that hard to solve. If I had to do it with all hardware, I would
look at the ramp ADC method I suggested elsewhere but it has too many
parts in it even at that.

Was there some reason that analog oneshot like circuits got
abandoned? It seems like they would do what the OP wanted well
enough.

 

[MooseFET]

I don't have a complete one but I did sketch out the high points.

The trickiest part seems to be making an integrator with a reset that
has a very low offset voltage. There are conflicting requirements on
the op-amp involved.

Low bias current and fast together usually means a JFET but the low
offset suggests a bipolar.

Basically this part started out looking like this:


---/\/\---O O----------------------
^ HC4053 1/3 !
! !
+----------!!------------+
! C1 !
--!-\ !
! >------------------+---- To Amplitude
GND---!+/ Sample and hold


Instead of having to put a sample and hold circuit on the amplitude, I
came up with the idea of making more than one of the integrators. I
settled on a total of four such circuits. They take turns like this:

A - running up
B - Holding while we make this pulse
C - Resetting down to zero
D - Settling

I was looking at a 5uF film capacitor as C1. 10V means full amplitude
at 20Hz so:

I(C1) = 5uF * 20 * 10 = 1mA

This is a reasonable output current for an op-amp.

 

[MooseFET]

See below:

My schematic is at:


and since you get abse I've emailed you a copy as well.

I'm not sure we're on the same page since, after querying the OP and
finding out that what he wanted was a circuit which would output a pulse
with a width proportional to the amplitude of an input sine wave, I
posted a circuit which would do that regardless of (well, there is a
high-frequency limit) the frequency of the input signal, on a
cycle-by-cycle basis.

I was aiming at a duty cycle that depended on the amplitude and not a
pulse width that did so.


A comparator that looks like this:


R1 R2 C1
GND ---/\/\---+---/\/\--!!--
! !
-!+\ !
! >--------+--- "IsLow"
Signal ---------!-/
!
GND



The R1 and R2 are picked based on how much HF noise there is on the
signal. C1 makes a time constant that is short enough that the
comparator switches very near zero volts for the intended signal.

The IsLow signal goes to three places. One is the 4053 section here:


Signal
---+----/\/\-----+-----/\/\---------
! ! !
! --!-\ !
O ! >------------+--- Rectified
<--------------!+/
O HC4053
!
GND

One other place the IsLow goes is to a counter that divides by 4.
This counter via logic gates does the sequencing on the analog
switches in the 4 resetable integrators.

The switches in the integrators reset the integrator half the time,
cause it to integrate up 1/4th the time and hold steady for 1/4th the
time. This means that two 4053 sections are needed per integrator.


The third place IsLow goes is to a one-shotting circuit that resets a
ramp generator once per cycle.

The ramp is compared to whichever integrator is holding the voltage
and this comparison becomes the output.


I hope that is clear enough for you to follow. It is a bit complex
but I think it gets the job done.

 

[MooseFET]

Spice biffs every time I put the comparitor in but you'll get the
idea.

I'm sure it is more complex than needs be

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RECTANGLE Normal -640 2752 -800 2640
RECTANGLE Normal 11168 -4048 11008 -4160

 

[Jasen Betts]

Spice biffs every time I put the comparitor in but you'll get the
idea.

it seems LTs chips like to have the inputs at close volages
(max difference 0.6 or 1.2 v)

I'm sure it is more complex than needs be

and less complex. using voltage controlled switches is cheating!
real parts only.

I've been playing with (a simulation) of a simpler (and less capable)
version but had problems with max differential input, bias current,
and oscillations. (and a glitch on rising zero crossing)

this was my starting point:

.-------------+---->|--[R]-.
| | |
| |\ | |\ |
`--|-\ +----|-\ | |\
| >--->|--+ | >----+-| >O-- out
in---+--|+/ | .-|+/ |/
| |/ === | |/ -+-
| | | |
| -+- +5 /// | [1K]
| |\| +-----'
`--|-\ |/
| >---[1k]-|
.--|+/ |>
| |/| |
| -+- -5 /// gnd
///

this circuit has max output duty cycle of 50%
only measures the amplitide of the positive half-cycle
and is only approximately linear (but R could be replaced with a
better current source)

if I can find some ideal op-amps and comparitors
and install a flip-flop (or delay line?) to squash the
glitch it might even work!

 

[MooseFET]

it seems LTs chips like to have the inputs at close volages
(max difference 0.6 or 1.2 v)

Many of the op-amps have diodes across the inputs.

and less complex. using voltage controlled switches is cheating!
real parts only.

The real parts are HC4053s. I have an only partial model of them.
The supply voltages are +/- 5V so that the switches can be used.

I've been playing with (a simulation) of a simpler (and less capable)
version but had problems with max differential input, bias current,
and oscillations. (and a glitch on rising zero crossing)

this was my starting point:

          .-------------+---->|--[R]-.
          |             |            |
          |  |\         |    |\      |
          `--|-\        +----|-\     | |\
             |  >--->|--+    |  >----+-| >O-- out
     in---+--|+/        |  .-|+/       |/  
          |  |/        === | |/ -+-
          |             |  |     |
          |   -+- +5   /// |    [1K]
          |  |\|           +-----'
          `--|-\         |/      
             |  >---[1k]-|        
          .--|+/         |>
          |  |/|           |
          |   -+- -5      /// gnd
         ///              

 this circuit has max output duty cycle of 50%
 only measures the amplitide of the positive half-cycle
 and is only approximately linear (but R could be replaced with a
 better current source)

 if I can find some ideal op-amps and comparitors
 and install a flip-flop (or delay line?) to squash the
 glitch it might even work!

There is a trick to doing the op-amp and diode rectifiers. You want
to keep the op-amp from flying to the rails on the other half cycle.
In real life, op-amps tend to take a long time to recover from being
crashed against the rails.

 

[Jasen Betts]

Spice biffs every time I put the comparitor in but you'll get the
idea.

it seems LTs chips like to have the inputs at close volages
(max difference 0.6 or 1.2 v)

Many of the op-amps have diodes across the inputs.

I'm sure it is more complex than needs be

and less complex. using voltage controlled switches is cheating!
real parts only.

The real parts are HC4053s. I have an only partial model of them.
The supply voltages are +/- 5V so that the switches can be used.

I've been playing with (a simulation) of a simpler (and less capable)
version but had problems with max differential input, bias current,
and oscillations. (and a glitch on rising zero crossing)

this was my starting point:

          .-------------+---->|--[R]-.
          |             |            |
          |  |\         |    |\      |
          `--|-\        +----|-\     | |\
             |  >--->|--+    |  >----+-| >O-- out
     in---+--|+/        |  .-|+/       |/  
          |  |/        === | |/ -+-
          |             |  |     |
          |   -+- +5   /// |    [1K]
          |  |\|           +-----'
          `--|-\         |/      
             |  >---[1k]-|        
          .--|+/         |>
          |  |/|           |
          |   -+- -5      /// gnd
         ///              

 this circuit has max output duty cycle of 50%
 only measures the amplitide of the positive half-cycle
 and is only approximately linear (but R could be replaced with a
 better current source

that's right...

It's more parts than the above ascii but it seems to work.

Version 4
SHEET 1 1176 680
WIRE -336 -272 -352 -272
WIRE -320 -272 -336 -272
WIRE 416 -272 240 -272
WIRE 576 -272 480 -272
WIRE 720 -272 656 -272
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WIRE 896 192 768 192
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WIRE -96 208 -352 208
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WIRE 640 496 640 464
FLAG -64 -64 vcc
FLAG 624 -64 vcc
FLAG -512 160 0
FLAG -336 -272 vcc
FLAG -368 -160 0
FLAG -240 -160 vee
FLAG -64 32 vee
FLAG 624 144 vee
FLAG 240 192 0
FLAG -16 208 vcc
FLAG -16 304 vee
FLAG -208 304 0
FLAG 400 384 0
FLAG 544 192 vcc
FLAG -240 -64 vcc
FLAG -240 32 vee
FLAG 640 496 0
FLAG 336 -112 vcc
FLAG 336 -16 vee
FLAG 272 64 cap
FLAG 992 -64 0
FLAG 1040 64 out
SYMBOL Opamps\\LT1097 -64 -80 R0
SYMATTR InstName U1
SYMBOL Opamps\\LT1097 624 -80 R0
SYMATTR InstName U2
SYMBOL Misc\\battery -240 -272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5v
SYMBOL voltage -512 16 R0
WINDOW 3 -189 100 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 .2 2000)
SYMATTR InstName V2
SYMBOL Misc\\battery -336 -272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 5v
SYMBOL cap 224 96 R0
SYMATTR InstName C2
SYMATTR Value 1µf
SYMBOL diode 48 0 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL Opamps\\LT1097 -16 192 R0
SYMATTR InstName U3
SYMBOL res -368 80 R0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL diode 416 -256 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL res 672 -288 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 1K
SYMBOL res -64 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 100
SYMBOL res 48 368 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 100meg
SYMBOL npn 336 224 R0
WINDOW 3 56 60 Left 0
SYMATTR Value 2N2222
SYMATTR InstName Q1
SYMBOL res 544 192 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 1K
SYMBOL res 816 -32 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R7
SYMATTR Value 1k
SYMBOL Opamps\\LT1097 -240 -80 R0
SYMATTR InstName U4
SYMBOL res 176 64 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 51 49 VBottom 0
SYMATTR InstName R10
SYMATTR Value 100
SYMBOL res 192 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 28 56 VBottom 0
SYMATTR InstName R12
SYMATTR Value 1k
SYMBOL diode 624 400 R0
SYMATTR InstName D3
SYMBOL diode 624 336 R0
SYMATTR InstName D4
SYMBOL res 544 0 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R14
SYMATTR Value 1K
SYMBOL Opamps\\LT1097 336 -128 R0
SYMATTR InstName U5
SYMBOL res 544 -80 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R11
SYMATTR Value 1K
SYMBOL res 96 -144 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL diode 0 96 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D5
SYMATTR Value 1N914
SYMBOL res 224 -208 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R16
SYMATTR Value 1k
SYMBOL diode -80 -96 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D6
SYMATTR Value 1N914
SYMBOL diode 80 -176 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D7
SYMATTR Value 1N914
SYMBOL diode -16 -176 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D10
SYMATTR Value 1N914
SYMBOL diode 720 -128 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D11
SYMATTR Value 1N914
SYMBOL res 736 -208 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R19
SYMATTR Value 47K
SYMBOL diode 576 -176 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D8
SYMATTR Value 1N914
SYMBOL diode 656 -128 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D9
SYMATTR Value 1N914
SYMBOL diode 624 272 R0
SYMATTR InstName D12
SYMBOL pnp 832 32 M180
SYMATTR InstName Q3
SYMATTR Value 2N2907
SYMBOL res 880 64 R0
SYMATTR InstName R8
SYMATTR Value 1k
TEXT -568 392 Left 0 !.tran 0 .006s .001s startup