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Topic: SN74LS164N don't work (Read 5762 times) previous topic - next topic

Techone

Nice to hear everything work out fine.

My rule about any type of "reset" or "clear" in FF , counters, CPU, PIA , etc... any chips that use a FF inside, will need a reset circuit. All PC - MCU - CPU - Cell phone - iPad - have a reset circuit. 

Here why :  At power up, the FF are in "whatever" state, so a long enough reset pulse - LOW reset or HIGH reset pulse is done at power-up, place all FF at the same state, and place the CPU - MCU at Program Counter 0 <-- on Intel anyway. And all systems is ready to go. Even the ATMEGA329P have a reset pin.   

CrossRoads

Hmm, yes 74LS164 can only source 0.4mA (hi output), and sink just 8mA (low output).

http://www.ti.com/lit/ds/symlink/sn74ls164.pdf

Should have looked that up sooner. Obvlous solution would have been to reconnect things to have the LS164 driving the cathodes instead of the anodes.

74HC164 works because it can source 4mA.
http://www.ti.com/lit/ds/symlink/sn74hc164.pdf
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Techone

Thanks CrossRoads for those links. It look like I have to use a transistor to help switch ON / OFF the leds with the 74LS164.

CrossRoads

Or,
Change your wiring to have the anodes at +5 and the resistor/cathodes pulled low by the shift register to turn them on.
The 8mA sink current of the LS164 will drive the LEDs easily.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Techone

OK...sinking current... got it. With 470 ohms as a limiting resistor, the current will be below the 8 mA LS164 current limit. Assuming the led voltage is about 2 V, the limiting current is about 6 mA. Safe...

Thanks CrossRoads.  ;)

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