For a few good reasons most sensors, microcontroller development boards, and single-board computers operate at 3. However, quite a few very useful components and boards that operate at 5V still exist. Whereas we typically include some form of level shifting onboard our custom-designed products to make life easier for our customers, there are plenty of cases where shifting signals is still necessary in order to work with other components and boards. For this reason, we keep a batch of these breadboard-friendly level shifters in our inventory for those needing to convert signals between two different voltage levels.
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Remember Me? What's New? Results 1 to 22 of Thread: What is the difference between the 74HCT and sparkfun's logic level converter? What is the difference between the 74HCT and sparkfun's logic level converter? I'm still getting up to speed on making sense of schematic's and data sheets, so I'm having trouble understanding the difference between these two chips. I know they aren't the same exact thing, but I would like to understand how they differ and are they interchangeable in regards to communicating with led strips from a teensy?
They are a bit more practical in shape and size for use with out a breadboard. This is the post that measured various logical level converters and found that the 74HCT was the only one to handle a a lot of WS leds without problem. The TXS shifter appears to work for just a few leds, though there was one failure with a so-called grumpy strip. Yeah I saw this post a few days ago, I was curious if it was as simple as one just not being compatible.
Seems like it is! I have a few of the 74HCT's on the way. Thanks for the confirmation! Originally Posted by visualSound.
That's super helpful, thank you for explaining. Do you know of any wiring diagrams or images that show how to set that up? Thanks again. Got it! It also has the ohm series line matching resistors, and RJ jacks to plug in CAT6 cable which exactly matches the ohm resistors and offers excellent signal quality.
For a large LED project, I highly recommend you follow the wiring advice on that page, especially locating the power supplies as close as practical to the LEDs and use short, large diameter wires for the LED power.
Those passive level converters, using a N-channel mosfet and 2 resistors, are really only good to use for I2C. Their big weakness is the high level output on either side is only due to the weak pullup resistor, so the low-to-high output is very slow. Because high-to-low is much faster, they result in a distorted waveform output, which is terrible for WS LEDs where the width of the pulses matters.
They're unable to source any substantial current into a load, so troubleshooting by connecting a LED to "see" the signal causes trouble. Even just connecting extra wire to the output, especially when experimenting on a breadboard, can really alter the low-to-high speed. Unfortunately, Adafruit, Sparkfun and others have sold that level convert circuit as a general purpose solution, which though it performs really well only with certain protocols like I2C. Adafruit revised their description a few month ago from an overly optimistic "good for everything" sales pitch to a much more conservative approach.
Likewise, the active bi-directional converters, like TXB, have often been promoted to hobbyists with overly optimistic descriptions. Those TXB chips work similarly to the passive approach, except a circuit detects any unexpected change at the "output" and very briefly drives the other side high very strongly for a brief moment. Thereafter, the output voltage is maintained with only a weak pullup. The momentary strong drive solves the slow low-to-high transition.
But the detection circuit is a ticking time bomb, ready to go off and cause incorrect behavior. Those TXB tend to work well when the signals are on short wires between digital chips on the same circuit board. When driving long wires to LED strips, where huge changes in current also happen along shared ground paths, those drivers can easily become a liability. A unidirectional buffer or able to buffer with way, but hard-wired for the intended direction is the right way to buffer WS data signals.
It really is the right approach. Wow, thanks for the break down Paul, Yeah I will be investing in some of those adapters for the next project, right now I'm kind of keeping things small and getting educated on all this stuff as it's my first time playing with these led strips. I ordered a dozen of the 74HCT's, so I should be in much better standing when those arrive! Thanks again! A somewhat related question, is there a chip with less channels that would do the same job as the 74HCT?
I only need 2 channels It's slightly smaller and maybe slightly less expensive, but still pretty similar. Originally Posted by PaulStoffregen. Why would an AND gate not function as a level shifter? The HCT08 output is specified at 4 mA currents instead of 6 mA, but it's still a true 5V push-pull drive that's plenty strong enough for a line through a series termination resistor to the LED strip.
Both chips have the same TTL level logic input circuit a specific ratio of mosfet sizes: an oversized N-channel so the logic threshold is nominal 1.
Even though the ' is depicted as a pair of buffers, inside the chip is it certainly implemented as several logic gates based on the 3 input signals which create 2 internal logic signals that drive the 2 big mosfet transistors connected to the output pin.
Thanks Paul! And could something like an ULN also work? I'm asking because I have a bunch of those chips around. Last edited by TechAlex; at PM. Yes, OctoWS is unidirectional. Even the ones which emulate DMX protocol are unidirectional. If you want data both ways, first you need things that actually communicate both directions!
Let's talk of this in terms of specific protocols or devices. Details matter. Whatever you do, don't believe the maker myth that you can buy a cheap bidirectional level shifter as a universal solution to all 3 vs 5 volt interfacing needs. Especially the mosfet plus resistors circuit in of limited use, mainly only for I2C, and nearly useless for high speed communication! Worked fine. Last edited by Michael Ward; at PM. Good info - this is the difference between buying parts and real engineering Thanks for the info!
Another thumbs up. I am using the CD74HCTE to drive 12x5m of 12v ws strips over 30 feet of cheap thermostat cable and it works great. This little chip solved a problem I have been having for some time. Also note - if you are running over very long distances you need to account for voltage drop. I am using 18ga with a starting voltage of 13v to end up around 12v at the strip. I will probably move to 16ga wire. Low voltage presents a lot like a degraded signal - so check!
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74HC/HCT245 Octal Bus Transceiver; 3-state