SIG-CON-01

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Tindie-larges-v2.png

SIG-CON-01 is a Six-Channel RC filter with an 74AC14 Schmitt Trigger buffer/inverter.

SIG-CON-01-CAD.PNG

Filter Design

  • Each channel has an RC filter
  • The Resistor is in series with the input of the buffer
  • The capacitor is to ground on the input of the buffer
  • The front of the board has resistors in 0805 footprints
  • The rear of the board has capacitors in 0805 footprints
  • Time constant = RC
  • Input part is a 74AC14 Hex Inverter
  • Flexible Supply Voltages (2-6V)
  • 24 mA drive (High or Low level)
  • Schmitt Trigger Threshold Voltage Levels

SIG-CON-01-74AC14-ThresholdVoltages.PNG

RC Selection

  • Input current levels to the 74AC14 are very small (on the order of 1uA) - consider them as negligible
  • At Vcc = 5V
    • The typical positive going threshold is about 2V
    • The typical negative going threshold is about 1.6V
  • Decay (5V to 0V drop)
    • V(t) = Vo*E^(-t/RC) values
    • T = -RC * [ln(V(t)/Vo)]
    • Solving for typical values, V(t) = 2V, V(t=0) = 5V
    • R=10K, C=.1uF, T=500uS
    • R=4.7K, C=100pF, 240nS

RC Filter Simulation in LTSpice IV

SIG-CON-01-SimulateRC.PNG

Version 4
SHEET 1 880 680
WIRE -48 32 -144 32
WIRE 80 32 32 32
WIRE -144 64 -144 32
WIRE 80 64 80 32
WIRE -144 160 -144 144
WIRE 80 160 80 128
WIRE 80 160 -144 160
WIRE 80 176 80 160
FLAG 80 176 0
SYMBOL res 48 16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 4700
SYMBOL cap 64 64 R0
SYMATTR InstName C1
SYMATTR Value 100pF
SYMBOL voltage -144 48 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 5 1uS 20nS 20nS 2uS 0 1)
TEXT -178 200 Left 2 !.tran 6uS

Annotated Waveform

SIG-CON-01-SimulateRC-Wave-Annotated.png

Connectors

  • The board has a separate 2-pin power connector
  • The input signals are on the left side of the board
  • The output signals are on the right side of the board
  • Pin 1 of each connector is adjacent to the reference designator silkscreen

P1 - Input Connector

  • Note P1 and P2 have a different orientation
  • Both P1 and P2 have channel 1 at the top of the connector
  1. Input Channel 8
  2. Input Channel 7
  3. Input Channel 6
  4. Input Channel 5
  5. Input Channel 4
  6. Input Channel 3
  7. Input Channel 2
  8. Input Channel 1

P2 - Output Connector

  • Note P1 and P2 have a different orientation
  • Both P1 and P2 have channel 1 at the top of the connector
  1. Output Channel 1
  2. Output Channel 2
  3. Output Channel 3
  4. Output Channel 4
  5. Output Channel 5
  6. Output Channel 6
  7. Output Channel 7
  8. Output Channel 8

P3 - Power Connector (2V-6V)

  1. +5V
  2. GND

Rev X1 Rework

  • Missing power connection on U1
    • Add wire U1-14 to +5V pin of power connector