Author Topic: Building 16-step sequencer with 74hc154, new to digital  (Read 4473 times)

cloudscapes

Building 16-step sequencer with 74hc154, new to digital
« on: April 26, 2008, 03:38:13 PM »
hey all,
I *think* this is considered digital as it involves binary decoding and stuff like that. if I'm wrong, my appologies and feel free to move. anyways. I built this circuit:

http://www.electronics-project-design.com/DisplayLED.html

..minus the start/stop logic. it's permanently on. instead of using 16 resistors before each led, I just stuck one resistor after them to the ground. saves on parts. anyways, as-is, the thing works great! it sequences up or down! now comes the issue. I want to substitute the 4514 with a 74hc154 because the packaging is much smaller (those really large 24-pin ICs vs really narrow 24-pin). from what I understand they're basically the same thing (though different pinouts). I substituted that IC, rearanging the pinouts, but it unfortunatelly does not work. the 16 leds are all lit up at once when I power the whole thing on. I've confirmed that I have the 40193's outputs lined up correctly to the decoder's inputs, I used 4 leds to confirm it was outputing binary.

the datasheet for the 4514 (the chip I DON'T want to use) is this:
http://www.standardics.nxp.com/products/hc/datasheet/74hc4514.pdf

and the datasheet for the one I want, the 74hc154 is this:
http://www.classiccmp.org/rtellason/chipdata/mm74hc154.pdf

have I missed something?
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{DIY blog}
{www.dronecloud.org}

cloudscapes

Re: Building 16-step sequencer with 74hc154, new to digital
« Reply #1 on: April 26, 2008, 03:44:34 PM »
grounding G1 and G2 (pins 18 and 19) as instructed in the 74hc154 datasheet "truth table" gets the sequencer going, however it's inversed to what I want it to be. instead of being a LED chaser with one LED on, 15 of the LEDs are on with one going dark sequentially (hopefully that made sense)
~~~~~~~~~~~~~~~~~~~~~~
{DIY blog}
{www.dronecloud.org}

cloudscapes

Re: Building 16-step sequencer with 74hc154, new to digital
« Reply #2 on: April 26, 2008, 03:55:23 PM »
okay, I missed the part about "one of the 16 normally HIGH outputs will go low" in the datasheet. looks like I'll have to go for the larger 4514 afterall :(
~~~~~~~~~~~~~~~~~~~~~~
{DIY blog}
{www.dronecloud.org}

SISKO

Re: Building 16-step sequencer with 74hc154, new to digital
« Reply #3 on: April 27, 2008, 03:02:55 PM »
You could invert those led and conect the leds resistor to 12v
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