Pages: . Hello all. I've just acquired two 74LSs and need help understanding the datasheet. The output pins are pretty obvious, and I can GUESS at the clock, data and latch pins, but would totally appreciate if someone more knowledgeable could tell me which are the clock, data and latch. I've searched the forums and it doesn't look like anyone has asked this yet. Many thanks.
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Pages:  2. Hi all, Id really appreciate some input on this one Its like a big cable harness tester i suppose but I'm not worried about multiple pins being shorted, it would only ever be one output connected to one input. The only thing I'm concerned about is resources, I haven't got a great deal of experience with handling lots of IO - so for example, if I wanted to test x pins, I'd need 12 of these ICs, so far so good - the datasheet says that 64 address are available for this chip.
I'm thinking the programme would work in very simplistic terms by holding the first output to a know state high , and then scan all the inputs to see which one is also high, and then do the same with the second, output etc etc.
Also, can anyone tell me if the wire. Thanks for reading, Joel. The wire lib will "support" this chip as the wire lib just do the very low protocols. Hi, Yes, the Wire library should support those chips. But your whole design sounds over-complicated, if I understand your requirements and I'm not certain I do.
Sounds like you only need to set one output high at any instant, and read one input at any instant. Can you clarify how many? Hi Paul, Thanks for your reply. You are correct in that I only need to set one output high and read that input in any one instant - apologies if my description wasn't very clear. The result I need to end up with is something like: Out 2 is connected to Input 12 Out 26 is connected to Input 55 Out 40 is connected to Input 3 etc I would need outs and ins so yes, 57, combinations sounds alot now!
I had looked at the demultiplexer and multiplexer chips but wasn't sure if enough could be cascaded to give the required IO count. Cheers, Joel. Quote from: jhauxwell on Dec 29, , am. I think I'm right with saying connections. If all possibilities are to be tested then it must be x as output 1 could be connected to input 1,2,3, or any other input up to , and then the same would be true for output 2, and all the other outputs up to I'm not sure what you mean by second-tier demux, would you mind elaborating?
I can see that I'd need 30 x mux and 30 x demux chips to get the required ins and outs, just not entirely sure how to connect it up - like I said, I've found people cascading 2 or 3 but not 30! Forget de multiplexors. How about shift registers? Should be simpler overall I think. Daisy-chain 30 x 74hc for outputs.
Daisy-chain 30 x 74hc for inputs Use the Arduino's built-in SPI hardware to read from the 's at high speed. That way you can read in 8 bits at a time and check for a non-zero bytes efficiently. For the outputs s , you don't need to use the SPI bus, since you simply want to clock-in a single "1" and shift it along times, so you can just toggle the clock line to do that. To reduce the chip count, there are bit shift registers such as 74ls and 74ls, but they might cost more than double the 8-bit chips!
I think you're right - simpler, and cheaper! I've looked at a few examples of the 74hc and the 74hc in use and they're very well documented.
As far as hooking them up is concerned, presumably ill need to pull all of the inputs of the 's down to ground via 10K resistors so that nothing is floating. As for the outputs of the 's, usually in the hook-up examples I've found, these are shown driving LEDs via ohm current limiting resistors. In my application, the outputs of the 's will basically be driving into the inputs of the 's - is this OK or would I need current limiting resistors on all of the output pins?
Now with Unlimited Eagle board sizes! The ' outputs will be connected to the ' inputs via the cable, yes? Maybe even do 30 highs at a time, so only 8 passes are needed.
Use SPI. Then read all High inputs except for the 1 low input. If pins are shorted, one output can pull multiple 1K resistors low with no issue.
Quote from: jhauxwell on Dec 29, , pm. Quote from: CrossRoads on Dec 29, , pm. Hi Paul, There could theoretically never be a short, however it is possible that pins would be not connected and I'd have to be able to pick this up.
This is why I thought that I'd need pull-down resistors actually, of them! As for the possibility of a short ever happening then it would be good to have some protection built in so I take it I'd need a resistor in series on every pin of the 74HC's Ill draw up something in Eagle shortly and post so you can take a look and let me know if you think it should work. Just thought of a small problem.
The clock lines, the one to the 30 output registers, the one to the 30 input registers, and the latch line to the 30 input registers. They would each be driven by a single Arduino output. But the fan-out would need to be 30, which may be asking too much. So maybe a few buffer gates would be needed, e.
Controlling 60 LEDs
This project describes the plans to build a RFID based scalable doorlock. Participants: wouter, JG, Askarel, You? This software bring the shift register and input multiplexer contraption to life. It consist of 3 modules coupled by a chunk of shared memory. The daemon forks and call an external script with a command line parameter whenever there is an event at the door. This architecture enable the system to be extended to do things that were not foreseen at the time of conception.
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74LS673 Datasheet PDF