Use 27k resistors on the input to create a false ground

This replaces the odd network of 33k resistors; testing shows that
this works 'just fine thanks'.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/chaoskey.pcb b/chaoskey.pcb
index 023194026830d4dab57f3d372d434b2065cbf15a..58b5bed28aa63780337a84494cc3eac615d1c68a 100644 (file)
--- a/chaoskey.pcb
+++ b/chaoskey.pcb
@@ -963,13 +963,6 @@ Element["" "0402" "C4" "1uF" 648.00mil 777.00mil -22.00mil 22.00mil 1 80 ""]
 
        )
 
-Element["" "0402" "R7" "33k" 604.26mil 935.00mil 0.6416mm 70.00mil 2 80 ""]
-(
-       Pad[-15.74mil -3.93mil -15.74mil 3.93mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
-       Pad[15.74mil -3.93mil 15.74mil 3.93mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
-
-       )
-
 Element["" "0402" "R2" "4.7K" 12.7950mm 904.00mil -0.6030mm -23.00mil 0 80 ""]
 (
        Pad[-15.74mil -3.93mil -15.74mil 3.93mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
@@ -1005,7 +998,7 @@ Element["" "0402" "C5" "1uF" 554.00mil 23.3360mm 24.00mil -0.5014mm 3 80 ""]
 
        )
 
-Element["" "0402" "R5" "33k" 17.7480mm 823.00mil -0.5522mm -17.00mil 0 80 ""]
+Element["" "0402" "R5" "27k" 17.7480mm 823.00mil -0.5522mm -17.00mil 0 80 ""]
 (
        Pad[-15.74mil -3.93mil -15.74mil 3.93mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
        Pad[15.74mil -3.93mil 15.74mil 3.93mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
@@ -1156,28 +1149,28 @@ Element["" "0402" "C6" "0.1uF" 677.00mil 777.00mil -84.00mil 31.50mil 1 100 ""]
 
        )
 
-Element["" "0402" "C2" "1uF" 648.00mil 832.74mil 84.00mil -31.50mil 3 100 ""]
+Element["" "0402" "C2" "4.7uF" 648.00mil 832.74mil 84.00mil -31.50mil 3 100 ""]
 (
        Pad[-3.93mil -15.74mil 3.93mil -15.74mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
        Pad[-3.93mil 15.74mil 3.93mil 15.74mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
 
        )
 
-Element["" "0402" "R9" "470" 648.00mil 885.26mil 84.00mil -31.50mil 3 100 ""]
+Element["" "0402" "R9" "4.7k" 648.00mil 885.26mil 84.00mil -31.50mil 3 100 ""]
 (
        Pad[-3.93mil -15.74mil 3.93mil -15.74mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
        Pad[-3.93mil 15.74mil 3.93mil 15.74mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
 
        )
 
-Element["" "0402" "R8" "47k" 687.00mil 894.26mil -84.00mil 31.50mil 1 100 ""]
+Element["" "0402" "R8" "470k" 687.00mil 894.26mil -84.00mil 31.50mil 1 100 ""]
 (
        Pad[-3.93mil 15.74mil 3.93mil 15.74mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
        Pad[-3.93mil -15.74mil 3.93mil -15.74mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
 
        )
 
-Element["" "0402" "R6" "33k" 715.00mil 773.00mil -84.00mil 31.50mil 1 100 ""]
+Element["" "0402" "R6" "27k" 715.00mil 773.00mil -84.00mil 31.50mil 1 100 ""]
 (
        Pad[-3.93mil 15.74mil 3.93mil 15.74mil 19.68mil 20.00mil 25.68mil "1" "1" "square"]
        Pad[-3.93mil -15.74mil 3.93mil -15.74mil 19.68mil 20.00mil 25.68mil "2" "2" "square"]
@@ -1313,8 +1306,6 @@ Layer(1 "top")
        Line[554.00mil 903.00mil 554.00mil 885.00mil 10.00mil 20.00mil "clearline"]
        Line[554.00mil 885.00mil 529.00mil 860.00mil 10.00mil 20.00mil "clearline"]
        Line[529.00mil 860.00mil 506.00mil 860.00mil 10.00mil 20.00mil "clearline"]
-       Line[588.52mil 935.00mil 588.52mil 23.3050mm 10.00mil 20.00mil "clearline"]
-       Line[588.52mil 23.3050mm 574.00mil 903.00mil 10.00mil 20.00mil "clearline"]
        Line[574.00mil 903.00mil 554.00mil 903.00mil 10.00mil 20.00mil "clearline"]
        Line[554.00mil 903.00mil 554.00mil 903.00mil 10.00mil 20.00mil "clearline"]
        Line[715.00mil 20.0340mm 715.00mil 20.8910mm 10.00mil 20.00mil "clearline"]
@@ -1327,7 +1318,6 @@ Layer(1 "top")
        Line[520.00mil 768.00mil 506.00mil 782.00mil 10.00mil 20.00mil "clearline"]
        Line[714.48mil 823.00mil 714.48mil 923.52mil 10.00mil 20.00mil "clearline"]
        Line[714.48mil 923.52mil 703.00mil 935.00mil 10.00mil 20.00mil "clearline"]
-       Line[703.00mil 935.00mil 620.00mil 935.00mil 10.00mil 20.00mil "clearline"]
        Line[687.00mil 910.00mil 657.00mil 910.00mil 10.00mil 20.00mil "clearline"]
        Line[657.00mil 910.00mil 648.00mil 901.00mil 10.00mil 20.00mil "clearline"]
        Line[648.00mil 901.00mil 629.00mil 901.00mil 10.00mil 20.00mil "clearline"]
@@ -1374,6 +1364,8 @@ Layer(1 "top")
        Line[648.00mil 817.00mil 648.00mil 796.48mil 25.00mil 20.00mil "clearline"]
        Line[648.00mil 796.48mil 677.00mil 796.48mil 25.00mil 20.00mil "clearline"]
        Line[677.00mil 796.48mil 677.00mil 817.00mil 25.00mil 20.00mil "clearline"]
+       Line[703.00mil 935.00mil 606.00mil 935.00mil 10.00mil 20.00mil "clearline"]
+       Line[606.00mil 935.00mil 574.00mil 903.00mil 10.00mil 20.00mil "clearline"]
 )
 Layer(2 "bottom")
 (
@@ -1620,7 +1612,8 @@ NetList()
        Net("unnamed_net11" "(unknown)")
        (
                Connect("C5-2")
-               Connect("R7-1")
+               Connect("R5-2")
+               Connect("R6-1")
                Connect("U4-3")
        )
        Net("unnamed_net12" "(unknown)")
@@ -1705,18 +1698,12 @@ NetList()
                Connect("U2-2")
        )
        Net("unnamed_net31" "(unknown)")
-       (
-               Connect("R5-2")
-               Connect("R6-1")
-               Connect("R7-2")
-       )
-       Net("unnamed_net32" "(unknown)")
        (
                Connect("R8-1")
                Connect("R9-2")
                Connect("U4-4")
        )
-       Net("unnamed_net33" "(unknown)")
+       Net("unnamed_net32" "(unknown)")
        (
                Connect("C2-2")
                Connect("R9-1")

diff --git a/chaoskey.sch b/chaoskey.sch
index 4e77f953b6a69b37d522861c560b1d5d11dd058a..2304a97b1cf7400fe9de5deb7faa2195c7fb06e0 100644 (file)
--- a/chaoskey.sch
+++ b/chaoskey.sch
@@ -475,55 +475,55 @@ N 73200 67500 75000 67500 4
 N 73500 67500 73500 67200 4
 N 74700 67500 74700 67200 4
 C 74600 65900 1 0 0 gnd.sym
-N 75900 67500 76800 67500 4
-C 75100 69500 1 270 0 capacitor.sym
+N 75900 67500 77800 67500 4
+C 77500 69500 1 270 0 capacitor.sym
 {
-T 75800 69300 5 10 0 0 270 0 1
+T 78200 69300 5 10 0 0 270 0 1
 device=CAPACITOR
-T 75400 69200 5 10 1 1 0 0 1
+T 77800 69200 5 10 1 1 0 0 1
 refdes=C4
-T 76000 69300 5 10 0 0 270 0 1
+T 78400 69300 5 10 0 0 270 0 1
 symversion=0.1
-T 75400 68800 5 10 1 1 0 0 1
+T 77800 68800 5 10 1 1 0 0 1
 value=1uF
-T 75100 69500 5 10 0 1 0 0 1
+T 77500 69500 5 10 0 1 0 0 1
 footprint=0402
-T 75100 69500 5 10 0 1 0 0 1
+T 77500 69500 5 10 0 1 0 0 1
 loadstatus=smt
-T 75100 69500 5 10 0 1 0 0 1
+T 77500 69500 5 10 0 1 0 0 1
 vendor=digikey
-T 75100 69500 5 10 0 1 0 0 1
+T 77500 69500 5 10 0 1 0 0 1
 vendor_part_number=490-10017-1-ND
 }
-N 75300 69900 75300 69500 4
-N 75300 69700 77300 69700 4
-N 76500 69700 76500 69500 4
-N 77300 69700 77300 67700 4
-C 75100 70800 1 0 0 3.3V-plus.sym
-C 76400 64100 1 0 0 gnd.sym
-C 75200 68300 1 0 0 gnd.sym
-N 77800 67300 79200 67300 4
+N 77700 69900 77700 69500 4
+N 77700 69700 78300 69700 4
+N 76500 69700 76500 68400 4
+N 78300 69700 78300 67700 4
+C 77500 70800 1 0 0 3.3V-plus.sym
+C 77400 64100 1 0 0 gnd.sym
+C 77600 68300 1 0 0 gnd.sym
+N 78800 67300 80200 67300 4
 {
-T 78200 67400 5 10 1 1 0 0 1
+T 79200 67400 5 10 1 1 0 0 1
 netname=randombits
 }
-C 75200 70800 1 270 0 inductor.sym
+C 77600 70800 1 270 0 inductor.sym
 {
-T 75700 70600 5 10 0 0 270 0 1
+T 78100 70600 5 10 0 0 270 0 1
 device=INDUCTOR
-T 75500 70500 5 10 1 1 0 0 1
+T 77900 70500 5 10 1 1 0 0 1
 refdes=L3
-T 75900 70600 5 10 0 0 270 0 1
+T 78300 70600 5 10 0 0 270 0 1
 symversion=0.1
-T 75500 70100 5 10 1 1 0 0 1
+T 77900 70100 5 10 1 1 0 0 1
 value=bead
-T 75200 70800 5 10 0 1 270 0 1
+T 77600 70800 5 10 0 1 270 0 1
 footprint=0402
-T 75200 70800 5 10 0 1 270 0 1
+T 77600 70800 5 10 0 1 270 0 1
 vendor=digikey
-T 75200 70800 5 10 0 1 270 0 1
+T 77600 70800 5 10 0 1 270 0 1
 vendor_part_number=240-2554-1-ND
-T 75200 70800 5 10 0 1 270 0 1
+T 77600 70800 5 10 0 1 270 0 1
 loadstatus=smt
 }
 C 73300 65800 1 0 0 nc-bottom.sym
@@ -903,123 +903,113 @@ T 67500 66400 5 10 0 1 0 0 1
 vendor_part_number=P27.0KLCT-ND
 }
 N 67600 66400 67600 66500 4
-C 76600 68600 1 90 0 resistor.sym
+C 76600 67500 1 90 0 resistor.sym
 {
-T 76200 68900 5 10 0 0 90 0 1
+T 76200 67800 5 10 0 0 90 0 1
 device=RESISTOR
-T 76700 69200 5 10 1 1 0 0 1
+T 76700 68100 5 10 1 1 0 0 1
 refdes=R6
-T 76600 68600 5 10 0 0 0 0 1
+T 76600 67500 5 10 0 0 0 0 1
 footprint=0402
-T 76700 68800 5 10 1 1 0 0 1
-value=33k
+T 76700 67700 5 10 1 1 0 0 1
+value=27k
 }
-C 76800 66100 1 0 0 resistor.sym
+C 77800 66100 1 0 0 resistor.sym
 {
-T 77100 66500 5 10 0 0 0 0 1
+T 78100 66500 5 10 0 0 0 0 1
 device=RESISTOR
-T 77100 66400 5 10 1 1 0 0 1
+T 78100 66400 5 10 1 1 0 0 1
 refdes=R8
-T 76800 66100 5 10 0 0 0 0 1
+T 77800 66100 5 10 0 0 0 0 1
 footprint=0402
-T 77100 65900 5 10 1 1 0 0 1
-value=47k
+T 78100 65900 5 10 1 1 0 0 1
+value=470k
 }
-C 75600 68500 1 0 0 resistor.sym
+C 76600 66600 1 90 0 resistor.sym
 {
-T 75900 68900 5 10 0 0 0 0 1
+T 76200 66900 5 10 0 0 90 0 1
 device=RESISTOR
-T 75900 68800 5 10 1 1 0 0 1
+T 76700 67200 5 10 1 1 0 0 1
 refdes=R5
-T 75600 68500 5 10 0 0 0 0 1
+T 76600 66600 5 10 0 0 90 0 1
 footprint=0402
-T 75900 68300 5 10 1 1 0 0 1
-value=33k
+T 76700 66900 5 10 1 1 0 0 1
+value=27k
 }
-C 76600 65300 1 90 0 resistor.sym
+C 77600 65300 1 90 0 resistor.sym
 {
-T 76200 65600 5 10 0 0 90 0 1
+T 77200 65600 5 10 0 0 90 0 1
 device=RESISTOR
-T 76000 65900 5 10 1 1 0 0 1
+T 77000 65900 5 10 1 1 0 0 1
 refdes=R9
-T 76600 65300 5 10 0 0 0 0 1
+T 77600 65300 5 10 0 0 0 0 1
 footprint=0402
-T 76000 65500 5 10 1 1 0 0 1
-value=470
+T 77000 65500 5 10 1 1 0 0 1
+value=4.7k
 }
-C 76600 67700 1 90 0 resistor.sym
+N 77100 68600 77700 68600 4
+C 77700 64400 1 90 0 capacitor.sym
 {
-T 76200 68000 5 10 0 0 90 0 1
-device=RESISTOR
-T 76700 68300 5 10 1 1 0 0 1
-refdes=R7
-T 76600 67700 5 10 0 0 0 0 1
-footprint=0402
-T 76700 67900 5 10 1 1 0 0 1
-value=33k
-}
-N 74700 68600 75600 68600 4
-C 76700 64400 1 90 0 capacitor.sym
-{
-T 76000 64600 5 10 0 0 90 0 1
+T 77000 64600 5 10 0 0 90 0 1
 device=CAPACITOR
-T 76000 65000 5 10 1 1 0 0 1
+T 77000 65000 5 10 1 1 0 0 1
 refdes=C2
-T 75800 64600 5 10 0 0 90 0 1
+T 76800 64600 5 10 0 0 90 0 1
 symversion=0.1
-T 76700 64400 5 10 0 0 0 0 1
+T 77700 64400 5 10 0 0 0 0 1
 footprint=0402
-T 76000 64600 5 10 1 1 0 0 1
-value=1uF
+T 77000 64600 5 10 1 1 0 0 1
+value=4.7uF
 }
-N 76500 67700 76500 67500 4
-N 76800 67100 76500 67100 4
-N 76500 67100 76500 66200 4
-N 76500 66200 76800 66200 4
-N 78100 67300 78100 66200 4
-N 78100 66200 77700 66200 4
-C 77200 66600 1 0 0 gnd.sym
-C 74900 68600 1 90 0 capacitor.sym
+N 77800 67100 77500 67100 4
+N 77500 67100 77500 66200 4
+N 77500 66200 77800 66200 4
+N 79100 67300 79100 66200 4
+N 79100 66200 78700 66200 4
+C 78200 66600 1 0 0 gnd.sym
+C 77300 68600 1 90 0 capacitor.sym
 {
-T 74200 68800 5 10 0 0 90 0 1
+T 76600 68800 5 10 0 0 90 0 1
 device=CAPACITOR
-T 74300 69200 5 10 1 1 0 0 1
+T 76700 69200 5 10 1 1 0 0 1
 refdes=C6
-T 74000 68800 5 10 0 0 90 0 1
+T 76400 68800 5 10 0 0 90 0 1
 symversion=0.1
-T 74200 68700 5 10 1 1 0 0 1
+T 76600 68700 5 10 1 1 0 0 1
 value=0.1uF
-T 74900 68600 5 10 0 1 90 0 1
+T 77300 68600 5 10 0 1 90 0 1
 footprint=0402
-T 74900 68600 5 10 0 1 90 0 1
+T 77300 68600 5 10 0 1 90 0 1
 loadstatus=smt
-T 74900 68600 5 10 0 1 90 0 1
+T 77300 68600 5 10 0 1 90 0 1
 vendor=digikey
-T 74900 68600 5 10 0 1 90 0 1
+T 77300 68600 5 10 0 1 90 0 1
 vendor_part_number=399-3027-1-ND
 }
-N 75300 69700 74700 69700 4
-N 74700 69700 74700 69500 4
-T 76400 70100 9 10 1 0 0 0 1
-To minimize input-bias-current errors, R8 = R7 + 1/2 R6
-T 77300 65000 9 10 1 0 0 0 1
+N 76500 69700 77700 69700 4
+N 77100 69700 77100 69500 4
+T 78300 65000 9 10 1 0 0 0 1
 * star ground
-T 77400 66700 9 10 1 0 0 0 1
+T 78400 66700 9 10 1 0 0 0 1
 *
-T 76600 64300 9 10 1 0 0 0 1
+T 77600 64300 9 10 1 0 0 0 1
 *
-T 75400 68400 9 10 1 0 0 0 1
+T 77800 68400 9 10 1 0 0 0 1
 *
-C 76800 66900 1 0 0 opamp.sym
+C 77800 66900 1 0 0 opamp.sym
 {
-T 77900 68200 5 10 0 0 0 0 1
+T 78900 68200 5 10 0 0 0 0 1
 device=IC
-T 77400 68000 5 10 1 1 0 0 1
+T 78400 68000 5 10 1 1 0 0 1
 refdes=U4
-T 77900 68800 5 10 0 0 0 0 1
+T 78900 68800 5 10 0 0 0 0 1
 symversion=0.1
-T 77400 67700 5 10 1 1 0 0 1
+T 78400 67700 5 10 1 1 0 0 1
 value=OPA356
-T 76800 66900 5 10 0 0 0 0 1
+T 77800 66900 5 10 0 0 0 0 1
 footprint=SOT23-5
 }
+C 76400 66300 1 0 0 gnd.sym
+T 76600 66200 9 10 1 0 0 0 2
+*
+