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I am trying to understand a part of the schematic for a relay based multiplexer. Basically the relays are triggered by

RESET :continuous signal of 3.5VDC <voltage < 16 VDC holds device in an active state

CLOCK: on the transition from <1.5 V to >3.5V, relays advance on the leading edge of the clock; clock must be a minimum of 5 ms in width

I just want to understand what are the purpose of resistors,capacitor & diodes in this circuit. More specifically R1 & R3.

As far as I understand:

  1. R2& R4: pulldown resistors. Making sure that these inputs are not floating? BTW both connected to different pins of the same schmitt trigger IC.So why are the resistors values different?
  2. R1 & R3 in series to limit the current? Not sure about them? Also why different values again?
  3. C1 & C2 :decoupling capacitors to ensure smooth signal voltage levels?
  4. D1 & D2: 1.5KE20A transzorbs limiting clock & reset to 16V.This is pretty straightforward i think.

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  • \$\begingroup\$ R1 & R3 makes the delay needed, "probably" to slow down commands. Have you made a simulation to show it? Will be clear after. Values of components are not really critical. \$\endgroup\$
    – Antonio51
    Jun 18 at 8:39

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Depending on the "pulse", D1 & D2 are perhaps not needed.

R2 & R4 pull-down resistors to make sure C1 & C2 discharge at the "same" time.

R1 & R3 fix the delays of waves at the output.
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