I'm building a portable 8x8 LED matrix with an attiny85 and two SN74HC164s shift registers, powered off of two CR2450 coin cell batteries and having trouble determining where to put resistors in my design.

To test the SN74HC164, I connected and powered it directly to an arduino with resistors coming from the cathodes of the LEDs ( connected to the outputs of the shift register ) and nowhere else in the circuit, like shown in many tutorials.

Would there be any reason to add any resistors to the connections of the shift register, other than the outputs when powered off of the batteries or are all of the pins designed to consume only as much current as they need? I will have pins A, B and CLK connected to the I/O pins of the attiny85, VCC and GND connected directly the the batteries, with CLR connected to the voltage supply.

Do I need to limit the current through VCC and GND on the attiny85?

  • 3
    \$\begingroup\$ Post a schematic. The essential electrical engineering communications tool. \$\endgroup\$ – Michael Karas Jun 26 '17 at 3:58
  • \$\begingroup\$ 6V seems kind of high, 74HC4094 seems a better match for this application. it allows the outputs to be turned off during load - so you get blacker blacks. \$\endgroup\$ – Jasen Jun 26 '17 at 5:12
  • \$\begingroup\$ I'm planning on running the batteries in parallel.. The attiny85 doesn't really have enough pins to utilize other shift registers and a button... Unless I could use the shift pin for one of the shift registers to latch the other.. \$\endgroup\$ – Holden Jun 26 '17 at 16:37

no, resistors are not normally needed between logic chips.

Logic chips have high resistance inputs already, and the inputs consume very little current, adding more resistance in series is not needed.


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