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3x4_4pin.sch

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+v 20130925 2
+N 46300 41900 46300 48000 4
+N 43500 43700 43500 48000 4
+N 44300 47200 48300 47200 4
+N 44300 46200 50000 46200 4
+N 44300 45200 50000 45200 4
+N 44300 44200 49100 44200 4
+N 44900 43000 44900 48000 4
+B 46800 48400 1200 400 3 0 0 0 -1 -1 0 -1 -1 -1 -1 -1
+T 47100 48500 9 10 1 0 0 0 1
+buttons
+T 41700 44700 9 24 1 0 0 0 7
+1  2  3
+
+4  5  6
+
+7  8  9
+
+*  0  #
+C 43300 48000 1 270 0 switch-diag.sym
+{
+T 43700 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 47700 5 10 0 1 270 0 1
+clock=clk
+T 43900 47800 5 10 1 1 0 0 1
+refdes=S1
+}
+C 44700 48000 1 270 0 switch-diag.sym
+{
+T 45100 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 47700 5 10 0 1 270 0 1
+clock=clk
+T 45300 47800 5 10 1 1 0 0 1
+netname=S2
+}
+C 46100 48000 1 270 0 switch-diag.sym
+{
+T 46500 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 47700 5 10 0 1 270 0 1
+clock=clk
+T 46700 47800 5 10 1 1 0 0 1
+netname=S3
+}
+C 43300 47000 1 270 0 switch-diag.sym
+{
+T 43700 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 46700 5 10 0 1 270 0 1
+clock=clk
+T 43900 46800 5 10 1 1 0 0 1
+refdes=S4
+}
+C 44700 47000 1 270 0 switch-diag.sym
+{
+T 45100 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 46700 5 10 0 1 270 0 1
+clock=clk
+T 45300 46800 5 10 1 1 0 0 1
+netname=S5
+}
+C 46100 47000 1 270 0 switch-diag.sym
+{
+T 46500 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 46700 5 10 0 1 270 0 1
+clock=clk
+T 46700 46800 5 10 1 1 0 0 1
+netname=S6
+}
+C 43300 46000 1 270 0 switch-diag.sym
+{
+T 43700 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 45700 5 10 0 1 270 0 1
+clock=clk
+T 43900 45800 5 10 1 1 0 0 1
+refdes=S7
+}
+C 44700 46000 1 270 0 switch-diag.sym
+{
+T 45100 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 45700 5 10 0 1 270 0 1
+clock=clk
+T 45300 45800 5 10 1 1 0 0 1
+netname=S8
+}
+C 46100 46000 1 270 0 switch-diag.sym
+{
+T 46500 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 45700 5 10 0 1 270 0 1
+clock=clk
+T 46700 45800 5 10 1 1 0 0 1
+netname=S9
+}
+C 43300 45000 1 270 0 switch-diag.sym
+{
+T 43700 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 44700 5 10 0 1 270 0 1
+clock=clk
+T 43900 44800 5 10 1 1 0 0 1
+refdes=S*
+}
+C 44700 45000 1 270 0 switch-diag.sym
+{
+T 45100 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 44700 5 10 0 1 270 0 1
+clock=clk
+T 45300 44800 5 10 1 1 0 0 1
+netname=S0
+}
+C 46100 45000 1 270 0 switch-diag.sym
+{
+T 46500 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 44700 5 10 0 1 270 0 1
+clock=clk
+T 46700 44800 5 10 1 1 0 0 1
+netname=S#
+}
+L 51200 48000 50000 48000 3 0 0 0 -1 -1
+L 50000 48000 50000 42200 3 0 0 0 -1 -1
+L 50000 42200 51200 42200 3 0 0 0 -1 -1
+L 49900 43100 50000 43000 3 0 0 0 -1 -1
+L 50000 43000 49900 42900 3 0 0 0 -1 -1
+T 50200 42700 9 10 1 0 0 0 22
+uP
+
+
+
+D0_out
+
+
+
+
+D1_out
+
+
+
+
+
+
+D3_in
+
+
+
+D4_in
+
+N 43500 43700 50000 43700 4
+N 50000 43000 50000 43100 4
+N 44900 43000 50000 43000 4
+N 46300 41900 48300 41900 4
+C 48600 44200 1 90 0 diode-1.sym
+{
+T 48000 44600 5 10 0 0 90 0 1
+device=DIODE
+}
+C 49300 44200 1 90 0 diode-1.sym
+{
+T 48700 44600 5 10 0 0 90 0 1
+device=DIODE
+}
+C 47400 42800 1 270 0 diode-1.sym
+{
+T 48000 42400 5 10 0 0 270 0 1
+device=DIODE
+}
+C 48100 42800 1 270 0 diode-1.sym
+{
+T 48700 42400 5 10 0 0 270 0 1
+device=DIODE
+}
+N 48300 42800 48300 43700 4
+N 47600 43000 47600 42800 4
+N 48400 45200 48400 45100 4
+N 49100 45100 49100 46200 4
+L 49900 43800 50000 43700 3 0 0 0 -1 -1
+L 50000 43700 49900 43600 3 0 0 0 -1 -1
+L 50100 45100 50000 45200 3 0 0 0 -1 -1
+L 50000 45200 50100 45300 3 0 0 0 -1 -1
+L 50100 46100 50000 46200 3 0 0 0 -1 -1
+L 50000 46200 50100 46300 3 0 0 0 -1 -1
+B 43100 43900 4400 4400 12 1 0 2 100 75 0 -1 -1 -1 -1 -1
+L 41800 43500 41800 42200 3 0 0 2 50 10
+C 48100 46900 1 0 0 ground.sym

3x4_5pin.sch

@@ -0,0 +1,184 @@
+v 20130925 2
+N 46300 42300 46300 48000 4
+N 43500 43700 43500 48000 4
+N 44300 47200 48300 47200 4
+N 44300 46200 50000 46200 4
+N 44300 45200 50000 45200 4
+N 44300 44200 49100 44200 4
+N 44900 43000 44900 48000 4
+B 46800 48400 1200 400 3 0 0 0 -1 -1 0 -1 -1 -1 -1 -1
+T 47100 48500 9 10 1 0 0 0 1
+buttons
+T 41700 44700 9 24 1 0 0 0 7
+1  2  3
+
+4  5  6
+
+7  8  9
+
+*  0  #
+C 43300 48000 1 270 0 switch-diag.sym
+{
+T 43700 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 47700 5 10 0 1 270 0 1
+clock=clk
+T 43900 47800 5 10 1 1 0 0 1
+refdes=S1
+}
+C 44700 48000 1 270 0 switch-diag.sym
+{
+T 45100 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 47700 5 10 0 1 270 0 1
+clock=clk
+T 45300 47800 5 10 1 1 0 0 1
+netname=S2
+}
+C 46100 48000 1 270 0 switch-diag.sym
+{
+T 46500 47900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 47700 5 10 0 1 270 0 1
+clock=clk
+T 46700 47800 5 10 1 1 0 0 1
+netname=S3
+}
+C 43300 47000 1 270 0 switch-diag.sym
+{
+T 43700 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 46700 5 10 0 1 270 0 1
+clock=clk
+T 43900 46800 5 10 1 1 0 0 1
+refdes=S4
+}
+C 44700 47000 1 270 0 switch-diag.sym
+{
+T 45100 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 46700 5 10 0 1 270 0 1
+clock=clk
+T 45300 46800 5 10 1 1 0 0 1
+netname=S5
+}
+C 46100 47000 1 270 0 switch-diag.sym
+{
+T 46500 46900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 46700 5 10 0 1 270 0 1
+clock=clk
+T 46700 46800 5 10 1 1 0 0 1
+netname=S6
+}
+C 43300 46000 1 270 0 switch-diag.sym
+{
+T 43700 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 45700 5 10 0 1 270 0 1
+clock=clk
+T 43900 45800 5 10 1 1 0 0 1
+refdes=S7
+}
+C 44700 46000 1 270 0 switch-diag.sym
+{
+T 45100 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 45700 5 10 0 1 270 0 1
+clock=clk
+T 45300 45800 5 10 1 1 0 0 1
+netname=S8
+}
+C 46100 46000 1 270 0 switch-diag.sym
+{
+T 46500 45900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 45700 5 10 0 1 270 0 1
+clock=clk
+T 46700 45800 5 10 1 1 0 0 1
+netname=S9
+}
+C 43300 45000 1 270 0 switch-diag.sym
+{
+T 43700 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 43300 44700 5 10 0 1 270 0 1
+clock=clk
+T 43900 44800 5 10 1 1 0 0 1
+refdes=S*
+}
+C 44700 45000 1 270 0 switch-diag.sym
+{
+T 45100 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 44700 44700 5 10 0 1 270 0 1
+clock=clk
+T 45300 44800 5 10 1 1 0 0 1
+netname=S0
+}
+C 46100 45000 1 270 0 switch-diag.sym
+{
+T 46500 44900 5 10 0 0 270 0 1
+device=SWITCAP-switch
+T 46100 44700 5 10 0 1 270 0 1
+clock=clk
+T 46700 44800 5 10 1 1 0 0 1
+netname=S#
+}
+L 51200 48000 50000 48000 3 0 0 0 -1 -1
+L 50000 48000 50000 41600 3 0 0 0 -1 -1
+L 50000 41600 51200 41600 3 0 0 0 -1 -1
+L 49900 43100 50000 43000 3 0 0 0 -1 -1
+L 50000 43000 49900 42900 3 0 0 0 -1 -1
+T 50200 42200 9 10 1 0 0 0 25
+uP
+
+
+
+D0_out
+
+
+
+
+D1_out
+
+
+
+
+
+
+D3_in
+
+
+
+D4_in
+
+
+
+D5_in
+N 43500 43700 50000 43700 4
+N 44900 43000 50000 43000 4
+N 46300 42300 50000 42300 4
+C 48600 44200 1 90 0 diode-1.sym
+{
+T 48000 44600 5 10 0 0 90 0 1
+device=DIODE
+}
+C 49300 44200 1 90 0 diode-1.sym
+{
+T 48700 44600 5 10 0 0 90 0 1
+device=DIODE
+}
+N 48400 45200 48400 45100 4
+N 49100 45100 49100 46200 4
+L 49900 43800 50000 43700 3 0 0 0 -1 -1
+L 50000 43700 49900 43600 3 0 0 0 -1 -1
+L 50100 45100 50000 45200 3 0 0 0 -1 -1
+L 50000 45200 50100 45300 3 0 0 0 -1 -1
+L 50100 46100 50000 46200 3 0 0 0 -1 -1
+L 50000 46200 50100 46300 3 0 0 0 -1 -1
+B 43100 43900 4400 4400 12 1 0 2 100 75 0 -1 -1 -1 -1 -1
+L 41800 43500 41800 42200 3 0 0 2 50 10
+C 48100 46900 1 0 0 ground.sym
+L 49900 42400 50000 42300 3 0 0 0 -1 -1
+L 50000 42300 49900 42200 3 0 0 0 -1 -1

README.md

@@ -0,0 +1,13 @@
+# Keypad Scanning
+
+The 3x4 and 4x4 matrix keyboards are commonly used for user input. Usually,
+the row and column wires are connected to GPIO pins on a microcontroller. A
+simple approach requires 7 wires for a 3x4 keypad.
+
+This article introduces a new technique wish reduces the number of GPIO pins
+down to 6, 5 and even 4, using software scanning techniques and diodes.
+
+Even though this reduces GPIO pin requirements in a manner similar to 
+[charliplexing](https://en.wikipedia.org/wiki/Charlieplexing), this is a
+*different* design.
+