this one is odd. with the nextion's RX pin connected to the esp8266-01's TX pin the ESP module will not boot up. the Nextion TX pin connected has no effect.
if I unplug only the RX wire, power on, wait for the ESP's blue light to blink and stop, then plug in the RX wire, everything works great.
any idea why this hardware issue exists and how I can work around it? if it matters, I'm using this ESP-01 adaptor board https://www.tindie.com/products/blkbox/esp8266-esp-01-programming-and-development-board/
I am looking into this type of chip as well (specifically the ESP-8285).
From what I have been reading, the ESP can be turned on/off. I guess this would be for being able to power down the radio when not needed to save power. Not too different from turning off the radio in your cell phone.
So, now we want to use this radio as our main MCU, yet would we not have to acknowledge that the ESP is traditionally a wireless chip that is traditionally a slave to another MCU? (I am waiting for my ESPs to arrive, they have been shipped - plug in for iTead's ESP-8285 inserted here).
I don't have a definitive answer, perhaps the Nextion is reporting successful bootup over RX and your ESP is just booting itself. Perhaps the ESP needs to get to full ready mode before powering the Nextion or start the ESP with TX/RX disabled and enable them after a delay once the ESP is fully running.
As I stated, I am still waiting for mine - but certainly interested in what you find out
How have you wired the other GPIOs?
Maybe you are falling into an alternative mode
GPIO 0 and 2 are not connected. eventually I'll use one of them for PJON but right now that's not implemented.
the only thing connected is RX and TX, and unplugging TX makes it boot. I don't see anything relevant on that "pin magic" page. it seems that whatever circuit the nextion has is causing the esp to lock up in the boot process. If I connect that TX pin to a FTDI RX to "listen" I don't see the boot reason or anything.
poked around and find the nextion has a 10K pulldown resistor on RX, which seems odd. shouldn't it be a pullup since serial is active low?
I added a 4.7K pullup and now it boots fine. as I understand it, this may cause problems at higher serial speeds, but should be fine at 9600. am I going to have long term issues with this? should I remove the 10K on the nextion and use a 10K pullup instead?
to clarify, the 4.7K pullup is to 3.3V since the ESP's RX is not level shifted.
I have found http://bbs.espressif.com/viewtopic.php?t=796 which shows why the pulldown is a problem.
Can someone at itead please explain why there is a 10K pulldown on RX? the more I research the more I think it should not have one.
unless there's some really good reason to have it, I'm going to remove it from mine.
Your 10K pulldown question is best posed to the Engineers. Open a New Support Ticket at the top. I am mostly certain that in their interest of functionality and profitability they didn't merely toss resistors randomly on the PCBs. I could be wrong. Removing it is a good experiment, though I am not certain it would keep your warranty intact. In the interests of Science, please keep us up-to-date as to the outcome.
I am also going to toss this thought out there. There are those that love when they get to heat their soldering irons up, and there is no stopping them when the urge becomes too great. But, I have to admit, in all the posted threads I have read through on this board, no one else seemed to have this difficulty in interfacing their Nextion and showcasing their projects. It is because of that lack of "remove pulldown before use" with all the other successful Nextion projects that leads me to believe that this is not only unnecessary, but probably not wise. Logic would dictate that if the product was unusable with the pulldown in place, there would not be successful projects and it would not be there in the first place as Itead would have had to revise their boards to ensure a working product for continued sales.
However, I may be wrong.
I agree patrick, which is why I'm hesitant. I'm guessing if I used a level shifter on that pin, which isn't technically necessary, I wouldn't have a problem. it's also possible that others are using software serial on other pins and avoiding the issue, but an -01 doesn't have that luxury.
Just a thought about the other project argument: Are there other ESP8266 projects as reference?
And refering to other projects only prooves that the pulldown doesn't harm the functionality. It doesn't proove that it is required tho'.
Not directly Scruff.r,
though Itead does deal with the 8266, and now the 8285.
Nextion Gallery has Pete's second place award winning link to the 1st Annual ESP8266 Design Contest
and Searching 8266 in the search Bar brings up other threads, though I haven't checked them all.
I am not saying there isn't an issue with ESP-01's and Nextion, just I haven't seen anyone else needing to pull resistors to make it work - and I have read too many threads, though not all of them
Pete's is using software serial.