74164 Shift Register

Forum 2005-2010 (read only) Hardware Interfacing
1

I've been working with a 74HC164 SIPO shift register - just experimenting to expand the outputs. I have a row of 8 leds as outputs.

I'm using code from here: arduino + monome + ?: Test 74HC164 SHIFT OUT with LED
(apparently can't post live url as this is my first post - sorry)

Which sets the byte and shifts it down the line.
In the code above there's a delay between each shift and you can see the bits being moved down the line of outputs.

My problem is I want to display a given pattern without the 'shifting' being visible. Currently, if I remove the delay, the lamps are still lit momentarily as the bit passes through.

EG - For a demo I adapted the code above to do a binary count, so set the byte, shift it into the register, increment by one and shift the next byte in. At full speed it appears that all the leds are lit briefly during the shift cycle.

How do I eliminate the flicker? Or ensure outputs are off whilst the data is shifted?

Many thanks for any help!
Simeon

2

It will require using an additional Arduino digital output pin, but the chip linked below allows one to shift in new data without changing the output pins until you 'latch' in the new value after shifting it in.

http://www.nxp.com/acrobat_download/datasheets/74HC_HCT595_4.pdf

Lefty

3

OK - that makes sense. Thanks.

I'm an absolute noob to all this and the differences/advantages of types of shift registers isn't/wasn't all that clear to me when I picked up the 164s.

Would a small cap in line with each led help? How would I work out a suitable value?

Simeon

4

Would a small cap in line with each led help?

No if you do it properly with the latch you won't need anything. Putting a capacitor to catch a spike is only papering over the cracks in a bad design.