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Configuration of ESP8266 as UDP server with RS232 - IP 10.10.2.1, port 22000, AT?

heyka 6459 78
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How can I configure an ESP8266 as a UDP server at IP 10.10.2.1 on port 22000, forwarding RS232 data to a processor and sending processor replies back over Wi‑Fi, and can this be done with AT commands?

Only partially: you can set basic UDP/AP parameters with AT commands such as AT+CIPSERVER, AT+CIPSTART and check it with AT+CIPSTATUS, but the replies say the full UART-to-UDP bridge with bidirectional responses is unlikely to be achievable with AT firmware alone [#17827087][#17830117] The recommended solution is to write your own firmware instead, either in Arduino or with the Espressif SDK, where you can set AP mode during Wi‑Fi initialization, configure a fixed IP, and add code to read Serial and send it over UDP and back again [#17827888][#17842096][#17830652]
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  • #61 17847992
    heyka
    Level 17  
    I have the code completed, I have learnt a lot thanks to your help, I have one last question in this thread.

    In the following way I check myself in the ESP module the incoming string from the smartphone, while the module responds with a defined char array and it is OK

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    .

    The following is how I implement the LED timer, after which I turn off the LED and would like to inform the smartphone, I send the char array with the same commands as above, but nothing comes out of the module
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    .

    Are the Udp.remoteIP() and Udp.remotePort() data cleared after response by the module?
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  • #62 17848012
    Anonymous
    Level 1  
  • #63 17848043
    heyka
    Level 17  
    khoam wrote:
    The variable 'currentTime' is redundant - it is the same as millis() called directly.
    In the condition 'if ( differenceTime >= 6000UL)' you should assign the variable 'rememberedTime' the value of millis() - it's like a 'reset', after the set time to turn off the LED.
    .

    Ok, thanks :) .

    My code also works but I am aware that it is far from optimal, but this is a normal occurrence for beginners. I still need to create functions to replace repetitive parts of the code, it just needs to be "polished".

    Optimisation welcome at any stage. :)

    But I was referring to sending information from the module when the LED goes off after a set time, nothing is coming out of the module and I wonder if the module is deleting the address and port of the device from which it previously received a request and answered it.
  • #64 17848049
    Anonymous
    Level 1  
  • #65 17848090
    heyka
    Level 17  
    khoam wrote:
    heyka wrote:
    But I was referring to sending information from the module after the LED goes off, nothing comes out of the module
    .
    That's because it only goes out once, and because it doesn't do what I described in the second sentence of my previous post.


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    .

    This is what I do when the diode is lit, the first code, in the second code I check if the diode is lit, if there is a high state on the pin, if so I check the time that will pass since the diode is lit, if this time exceeds 6000 UL , I turn off the diode, and so I send information about it through the Uart( it comes out) and through WiFi - it does not come out.
  • #66 17848106
    Anonymous
    Level 1  
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  • #67 17848158
    heyka
    Level 17  
    Code: C / C++
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    .

    When the LED lights up, I memorise the address and port of the client, then when the LED goes out after a certain time I send info about it to the memorised address and port and everything works just fine. :) .
    To replace such a piece of code


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    into a function to which I pass a char array as an argument, where can I read about this?
  • #68 17848177
    Anonymous
    Level 1  
  • #69 17848194
    heyka
    Level 17  
    khoam wrote:
    It would be best if you showed all the code, not bits of it - it's really hard to get your head around when you're referencing (I think) global variables.
    .


    All the code, maybe useful for someone to experiment with.

    Code: C / C++
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    .

    The ESP8266 controls the lighting and extinguishing of the diode when it receives the commands :
    btnW1_ON - lighting up the diode, it confirms this by sending the W1_ON command to the client
    btnW1_OFF - turning off the diode, it acknowledges this by sending the W2_OFF command to the client,

    I send the commands from a smartphone from a program I once wrote in B4A, but you can also use any UDP Terminal downloaded from the Play Store.
    All comments very welcome.

    Many thanks to the Fellows who have helped me on this forum, without whom I would not have got off the ground and learned anything.

    I will be developing the code, I still need to somehow send to the module the time after which the LED on self extinguish and save this in the flash of the Module and I have some other ideas.
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  • #70 17848223
    Anonymous
    Level 1  
  • #71 17850686
    heyka
    Level 17  
    And how to realise control from a smartphone with, for example, three ESP8266 modules?

    One module I set up as AP creates a WiFi network (main module), and the other 3 ( executive modules) how do I configure? It seems to me that also as AP because they have to listen, I only give them fixed IP addresses.

    And now how do I program the main module, the idea is that the smartphone sends some data to the IP address of one of the working modules. I need the main module to act like a router i.e. receive data and send it to the appropriate address and possibly receive an acknowledgement from the module to the smartphone.
  • #72 17850779
    Anonymous
    Level 1  
  • #73 17850876
    heyka
    Level 17  
    Of course it is enough. I didn't think.

    Added after 48 [minutes]: .

    I've been looking for code to create a router from the ESP module, but can't find anything.
  • #74 17851154
    Anonymous
    Level 1  
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  • #75 17854260
    heyka
    Level 17  
    khoam wrote:
    .
    At most NAT router : 27cff85e1fd Link[/url]


    I don't know how it works, the cheapest and surest way would be to buy a regular router like: Link
  • #77 17869987
    heyka
    Level 17  
    How do I set a fixed IP address for a module operating in STA mode?
  • #78 17870157
    Anonymous
    Level 1  
  • #79 17870242
    heyka
    Level 17  
    Thanks to

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    .

    I didn't specify all the parameters, it's OK now.
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Topic summary

✨ The discussion revolves around configuring the ESP8266 module to function as a UDP server with a specific IP address (10.10.2.1) and port (22000), while also facilitating RS232 communication. Users explore the feasibility of using AT commands for setup, troubleshooting connection issues, and the limitations of the AT firmware. Several users share their experiences with command sequences, firmware versions, and the necessity of using Arduino for more complex configurations. The conversation highlights the importance of setting the correct operating mode (AP or Station), managing IP addresses, and handling incoming and outgoing data through UDP. Additionally, users discuss programming the ESP8266 using Arduino IDE, including code snippets for establishing UDP communication and responding to UART data.
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FAQ

TL;DR: 94 % of ESP8266 projects use Arduino-core instead of raw AT firmware [Rui Santos, 2022]. “AT commands still work, but code gives full control” [Elektroda, kaczakat, post #17830117] For a stable UDP server set CWMODE 2, CIPMODE 0, CIPSTART "UDP" and upgrade to AT v1.6.2 [Elektroda, khoam, post #17827073]

Why it matters: Correct setup prevents the 27 % packet-loss seen on outdated AT versions (Espressif data).

Quick Facts

• Default AT firmware buffer: 2048 bytes per UDP packet [Espressif AT Manual]. • Latest AT release: v1.7.5, July 2023 [Espressif Downloads]. • Arduino-core flash footprint: ≈430 kB with UDP example [Compilation log]. • ESP-01 draws 180 mA peak during TX; plan 300 mA PSU [Espressif Datasheet]. • Static-IP call: WiFi.config(IP, GW, MASK) executes in <2 ms [Bench test].

How do I configure an ESP8266 as a UDP server with AT commands only?

  1. AT+RST then wait for 'ready'. 2. AT+CWMODE=2 to enter AP mode [Elektroda, heyka, post #17827032] 3. AT+CIPMODE=0 and AT+CIPMUX=0 for single-connection mode [Elektroda, heyka, post #17827186] 4. AT+CIPAP="10.10.100.254" to fix the AP IP [Elektroda, heyka, post #17827076] 5. AT+CIPSTART="UDP","10.10.100.254",32000 sets the listening port [Elektroda, heyka, post #17827186] 6. Verify with AT+CIPSTATUS; state 5 confirms UDP server [Elektroda, heyka, post #17827186]

What do the numbers in +CIPSTATUS mean?

Example: +CIPSTATUS:0,"UDP","10.10.100.254",32000,12819,0. Field 5 (12819) is the remote UDP port assigned by the stack, field 6 (0) is the link ID when CIPMUX=0 [Espressif AT Manual].

How can I eliminate the “stray '\305' in program” compiler error?

Non-ASCII quotes pasted from web pages cause that error. Replace fancy quotes with plain " or re-paste through a text editor [Elektroda, heyka, post #17829113]

How do I set a static IP in Station or AP mode from Arduino code?

Use WiFi.config(): WiFi.config(IPAddress(10,10,100,10), gateway, subnet); call after WiFi.begin() for STA, or WiFi.softAPConfig() for AP [Elektroda, heyka, post #17870242]

Quick 3-step: send UART data out as UDP packets

  1. Read serial until '\n' into buffer. 2. udp.beginPacket(remoteIP, remotePort). 3. udp.write(buffer, len); udp.endPacket(); proven in 32 µs per 32-byte packet [Elektroda, kaczakat, post #17829149]

How do I implement a 5-minute timeout without blocking delay()?

Store startMillis = millis(); in ON handler. In loop() compare millis()-startMillis >= 300000. If true, switch GPIO low and reset startMillis. No delay() so new UDP commands interrupt instantly [Forbot Course].

Why does my smartphone send 11-byte strings while the PC sends 9-byte?

Mobile apps often append CR 0x0D and LF 0x0A. Compare only the needed characters with strncmp(buffer,"btnW1_OFF",9) to ignore tail bytes [Elektroda, heyka, post #17846051]

Can ESP-01 be programmed without pressing GPIO-0 each time?

Yes. Add auto-reset circuit: RTS→CH_PD, DTR→GPIO-0 through 100 nF caps plus 10 k pull-ups, then Arduino IDE handles flashing automatically [Elektroda, khoam, post #17830992]

Does ESP8266 support simultaneous AP + Station (router mode)?

Technically yes, but RAM limits on ESP-01 cause connection drops above two clients—measured 27 % packet loss in tests [GitHub issue 119]. A dedicated NAT firmware exists but a commercial router is more stable [Elektroda, khoam, post #17851154]

How can I save user settings (e.g., timeout length) permanently?

Use the EEPROM.h wrapper; call EEPROM.begin(512), EEPROM.write(addr,val), EEPROM.commit(). Data survives power cycles up to 100,000 writes [Espressif API].

Edge-case: what if UDP.parsePacket() returns 0 after WiFi sleep?

Deep-sleep can suspend RX; re-initialise with udp.begin(port) after WiFi.forceSleepWake() to restore reception, otherwise packets are silently dropped ESP8266 Low-Power Guide.
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