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I am designing a PCB that controls 16-relay or more using micro-controller, but micro-controller does not have enough pins.I searched google and find solution of this problem is I/O expander, but that cost ~50 Rs and that increase PCB cost drastically high, so i want some alternative of I/O expander.

If possible/exist please suggest.

PS: The design is like as soon as supply high at input to relay circuit the load is "on" and if makes input low at relay circuit the load get off.

This is how design looks

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    \$\begingroup\$ Look in to something called a "Shift Register". One shift register (not suitable for driving most relays coils) is the 74HC595. There are others. \$\endgroup\$
    – pgvoorhees
    Nov 17, 2020 at 12:41
  • \$\begingroup\$ Shift register + ULN2003 \$\endgroup\$
    – Damien
    Nov 18, 2020 at 3:49
  • \$\begingroup\$ @Damien DC Output current per pin of 74HC595 is +/- 35mA, is still ULN2003 is req ? I am using self designed Solid state relay, whose opto-coupler requires nearly ~10mA for trigger. \$\endgroup\$ Dec 4, 2020 at 8:35
  • \$\begingroup\$ @Abhishekbhatia yes, I've put the comment as an answer \$\endgroup\$
    – Damien
    Dec 4, 2020 at 11:22

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Look into something called a "Shift Register". One shift register (not suitable for driving most relay coils) is the 74HC595. There are others.

If you drive solid state relays, if the per pin current is enough and that there are no inductance that would work.

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