Hi John, Thanks for a great video. It is one of the best descriptions on the use of Level Shifters.....However. Throughout the video, in the actual video of the Breadboard, and the Prototyping board, there is a resistor going from VCCA to the OE pin. This resistor is NOT in the drawing that you create, and you don't make any mention of it. On the Adafruit page for this level shifter board is this statement: "One should never leave the OE pin floating in an indeterminate state......" I know it has been a long time since you made this video, but is there a chance you could review it and include an update on the use of the OE pin?
I was also annoyed at this omission. There is also no mention of the resistor shown attached to the data pin on the neo pixel. Regarding the OE pin that pin is basically the on/off trigger. So by soldering the resistor between the VCCA and OE, that is locking the level shifter into the ON position.
For everyone saying they never had an issue with this, I never had an issue with it either til I did! I have a 120 LED strip of WS2812B that ran off my esp8266 with no issues what so ever Then I tried to hook up PL9823 through hole leds (even just one) and they didn't work, I got inconsistent colours (e.g. set it to red and it might turn blue etc). Was sure I got a bad batch of LEDS til I hooked them up to a Mega and they worked perfectly. I seen the same behavior with through hole Neopixels from Adafruit too. The solution I used was to add a 220pf capacitor between the data in of the first LED and ground and that solved my issue. I'll be honest, I'm not sure why it works, I saw the "trick" on Andreass Spiess YT channel.
One Neopixel with 4.5V supply after the 3.3V output does the job too. The 4.5V can be generated from the 5V via a 1N400x diode. The second LED then gets the full 5V. Or Almost every 74HCT## or 74ACT## ic. Maybe also a old 74LS##
Also never had issues running WS2812B strips (Neopixels) off ESP8266 boards either. Have always wondered about if I should use level shifters, but I guess if it's in spec and it works, it works?!
Yes, I only run into this on longer runs of wiring, or when I have lots (like dozens and dozens) of NeoPixels. Then suddenly all kinds of chaos ensues.
Why not simply use a logic N-mosfet with the Gate to the MCU, the Drain to the same 5V that feed the neopixels and the source to Data pins of neopixels. I’m thinking Infineon IPS70R1K4P7S will work fine, right?
Solid work, John. In my case I think I need level shifters so I can use 5V sensors on a 3.3V microcontroller; I think everything you said is still relevant.
have you delay from microcontroler and output device with bi-directional 8 channel ? I know your example use NeoPixels and this is slow,but can be very important when use with fast devices for feedback realtime issue.
Just configure the output in the microcontroller as open-drain, and use a pull-up resistor to the 5V power supply. It cannot get easier and cheaper than that.
Every microcontroller output has the protection diodes to 3V3 even if you switch between pull low and pin input = float state So it's not a real open drain but limited to 3.3V + 0.6 Volt This means that current flows into the microcontroller via the pullup resistor. 3.9 volts is a little more than 3.3 V. It is better to take a 74HCT125. It recognizes 2V and more as high and outputs true 5V. The Neopixel need 70% of 5V, i.e. 3.5V, for high. And 30%. i.e. less 1.5V, for LOW
I checked the datasheet, ±15-kV ESD PROTECTION. So no, i wonder if a signal opto is fast enough to drive these. Might have to test that out, would love some isolation for long runs of pixels.
I am actually looking at digital isolators now, optos are very dependant on drive current, and transition state times, some cannot transition faster than 10ns and they are not digital compatible, you need 20ma forward current so then you have to deal with transistor speed, and they also invert, so you have to deal with that also.
This was EXCELLENT. NOW I understand the specifics of how to use a level shifter along with the notes he provides along the way. Thank you
Hi John, Thanks for a great video. It is one of the best descriptions on the use of Level Shifters.....However.
Throughout the video, in the actual video of the Breadboard, and the Prototyping board, there is a resistor going from VCCA to the OE pin.
This resistor is NOT in the drawing that you create, and you don't make any mention of it.
On the Adafruit page for this level shifter board is this statement:
"One should never leave the OE pin floating in an indeterminate state......"
I know it has been a long time since you made this video, but is there a chance you could review it and include an update on the use of the OE pin?
I was also annoyed at this omission. There is also no mention of the resistor shown attached to the data pin on the neo pixel. Regarding the OE pin that pin is basically the on/off trigger. So by soldering the resistor between the VCCA and OE, that is locking the level shifter into the ON position.
For everyone saying they never had an issue with this, I never had an issue with it either til I did!
I have a 120 LED strip of WS2812B that ran off my esp8266 with no issues what so ever
Then I tried to hook up PL9823 through hole leds (even just one) and they didn't work, I got inconsistent colours (e.g. set it to red and it might turn blue etc). Was sure I got a bad batch of LEDS til I hooked them up to a Mega and they worked perfectly. I seen the same behavior with through hole Neopixels from Adafruit too.
The solution I used was to add a 220pf capacitor between the data in of the first LED and ground and that solved my issue. I'll be honest, I'm not sure why it works, I saw the "trick" on Andreass Spiess YT channel.
OMG, this answers alot of issues I was having with servos that were acting funny. I love how in depth this is!!!!
Unfortunately no mention on the 10kOhm resistor between 3.3V and OE pin. If you forget it your shifter will get freaking hot🔥
never realized voltage drop could be an issue in a small low volt circuit. learn something new every day. thanks john.
One Neopixel with 4.5V supply after the 3.3V output does the job too.
The 4.5V can be generated from the 5V via a 1N400x diode.
The second LED then gets the full 5V.
Or
Almost every 74HCT## or 74ACT## ic. Maybe also a old 74LS##
Would you include a link to the specific microcontroller and level shifter used?
What size capacitor are you using?
Perfect didactics for my understanding. Thank you very much!
I'm assuming you could do the same with the 8266 microcontroller. If not, how would that wiring go?
I have never had a problem driving neo pixels with 3v3 data from trinkets.
based on the datasheet, it should work with 3v3. awesome!
Datasheet says High = 0.7V * VCC, and 5V is VCC -> 0.7V*5V=3,5V ... and this is why there are so many times some issues...
Good thing I didn't connect the data sheet to a trinket. The point being be aware that it is not guaranteed to work.
This video was helpful , thank you 🙏🏻
Also never had issues running WS2812B strips (Neopixels) off ESP8266 boards either. Have always wondered about if I should use level shifters, but I guess if it's in spec and it works, it works?!
Yes, I only run into this on longer runs of wiring, or when I have lots (like dozens and dozens) of NeoPixels. Then suddenly all kinds of chaos ensues.
Explained perfectly, thank you
Thanks, please can you post the circuit pinout and components?
Why not simply use a logic N-mosfet with the Gate to the MCU, the Drain to the same 5V that feed the neopixels and the source to Data pins of neopixels. I’m thinking Infineon IPS70R1K4P7S will work fine, right?
Good video, this will hopefully save someone from damaging their microcontroller.
Solid work, John. In my case I think I need level shifters so I can use 5V sensors on a 3.3V microcontroller; I think everything you said is still relevant.
For this case, you just invert the conexions and the B1 goes to the ESP32, and the sensor exit goes to the A1?
If you don't have the level shifter is it possible nothing would happen with the LEDs, IE no light. Or is it likely that I have a faulty LED matrix.
have you delay from microcontroler and output device with bi-directional 8 channel ? I know your example use NeoPixels and this is slow,but can be very important when use with fast devices for feedback realtime issue.
My led light up when I dont use a shifter and then I added everything in and now it doesn't work. My external supply is a 5v 3A mobile power bank.
At 3:05 looks like the cap isn't even plugged into the board
I built it and it's amazing, I used an Arduino Uno the 1 digit is 21 segment and a buzzer.
Just configure the output in the microcontroller as open-drain, and use a pull-up resistor to the 5V power supply. It cannot get easier and cheaper than that.
Every microcontroller output has the protection diodes to 3V3
even if you switch between pull low and pin input = float state
So it's not a real open drain but limited to 3.3V + 0.6 Volt
This means that current flows into the microcontroller via the pullup resistor.
3.9 volts is a little more than 3.3 V.
It is better to take a 74HCT125. It recognizes 2V and more as high and outputs true 5V.
The Neopixel need 70% of 5V, i.e. 3.5V, for high. And 30%. i.e. less 1.5V, for LOW
Why resistance between VCCA and OE ?
Keeps it from floating. Just ensures that the OE is pulled high with 3.3v
And the resistor on the left side of the level shifter..
Indeed, what about the resistor, and what capacitor is used ... ?
Me gusta, me gusta muy buen video
Does this provide isolation for gpio also ?
I checked the datasheet, ±15-kV ESD PROTECTION.
So no, i wonder if a signal opto is fast enough to drive these. Might have to test that out, would love some isolation for long runs of pixels.
Optical coupling is always super fast.
(I should never say "Always".)
I am actually looking at digital isolators now, optos are very dependant on drive current, and transition state times, some cannot transition faster than 10ns and they are not digital compatible, you need 20ma forward current so then you have to deal with transistor speed, and they also invert, so you have to deal with that also.