I am trying to use an SN74LS164 8-bit serial-to-parallel shift register with my Raspberry Pi, but I have some problems.
- VCC, A, B and CLR to +5V
- GND to 0V
- CLK to Raspberry Pi GPIO
When I power-on the circuit, all the LEDs are off. Then I send a clock pulse from the Raspberry Pi (go high for 100ms then go low). However instead of having the just first output (QA) go high, the first 3 or 4 outputs go high (QA, QB, QC and QD).
What am I doing wrong?
I took some photos of the scope, the first is the clock from the GPIO (without nothing) and the second is the clock connected to the register.
-- EDIT --
I added capacitors and MOSFETs to respect max output current. I re-added pull-down resitor on clock line because of the natural +1V offset (this offset come from the register not the pi)