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https://github.com/mecparts/RetroWiFiModem

An ESP8266 based RS232 <-> WiFi modem with Hayes AT style commands and LED indicators
https://github.com/mecparts/RetroWiFiModem

esp8266 hayes kicad modem openscad retrocomputing rs-232 rs232 vintage wifi

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An ESP8266 based RS232 <-> WiFi modem with Hayes AT style commands and LED indicators

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# Retro WiFi modem



## An ESP8266 based RS232 \<-\> WiFi modem with Hayes AT style commands and LED indicators



### (And yes, this version makes the noises)



![Front Panel](images/Front%20Panel.jpg "Front Panel")



This project grew out of a desire to get an old Ampro LB+/Z80 hooked up

to the Internet.



Right from the start, I knew I wanted a row of LED indicators at the

front of the modem so that it would be reminiscent of an old Hayes

Smartmodem. (I briefly considered finding an old Smartmodem on eBay, but

soon remembered that the case had in fact been made of metal; they don't

build 'em like that anymore.)



Since the modem was going to be hooked up to the Little Board's

serial port, I needed an actual RS-232 level serial port, with either a

DB-25 or DE-9 connector.



And finally, since I wanted the Hayes style LEDs, I thought it would be

handy to have the Hayes AT commands too, at least as close as I could

manage.



That was all I started with. I couldn't tell you how I stumbled across

the whole WiFi modem thing; I can't even remember what terms I searched

with but very quickly I came across the message thread at [WiFi232's

Evil

Clone](http://www.vcfed.org/forum/entry.php?740-WiFi232-s-Evil-Clone&bt=1056).

Inspired by that, and [Paul Rickards'

WiFi232](http://biosrhythm.com/?page_id=1453), and [Daniel Jameson's

ESP8266 based virtual modem](https://github.com/stardot/esp8266_modem) I

got started.



I had a preliminary version put together and working by the first

evening. Then the wholesale changes to the software began. And for the

longest time, it looked like they'd never end. Eventually though, they

calmed down and "wholesale changes" downshifted to "another tweak I'd

like to make."



The hardware didn't change nearly as much from beginning to end. I did

the development on a Wemos D1 R1 and a little half length solderless

breadboard mounted together. The plan for the final hardware was always

to use a [Wemos D1 mini](https://docs.wemos.cc/en/latest/d1/d1_mini.html).

A MAX3237 took care of the 3.3V <-> RS-232 level shifting, and a

74HCT245 was used to drive the indicator LEDs.



![Prototype](images/Prototype.jpg "Prototype")



The only major additions to the hardware during development was an OR

gate on the serial output from the ESP8266 and the addition of a

DFPlayer Mini for the dialing and connection sounds.



On startup, the ESP8266 sends out some debug information

(at an oddball baud rate) through the serial port. It shows up as

garbage characters to whatever's hooked up to the serial port. It

annoyed me enough that I fed the Tx signal through the OR gate, with the

other input hooked up to an output pin that I could count on remaining

high (thereby masking off the Tx signal) until after the sketch had

started and set it low.



And while it didn't make the cut the first time around, there's a

DFPlayer Mini in this version for faux dialing and connection sounds.

They really do complete the whole retro feel (but they can be turned off

too).



## The Hardware



![Interior](images/Interior.jpg "Interior")



The second time around, I decided that I was going to bite the bullet

and go with some surface mount stuff, starting with the MAX3237. Having

a full suite of RS-232 control signals seemed worth it. I stuck with

through hole components where I could (I already had most of them in my

parts box) but adding the DFPlayer Mini meant that the 74HC32 and

74HCT245 had to be surface mount just to make them fit.



In keeping with the retro theme, the modem uses classic Hayes style

blinking LEDs and a DE-9F for the RS-232 connector. Everything is

displayed and brought out to the DE-9F connector: RTS, CTS, DSR, DTR,

DCD, RI, TxD and RxD.



The PCB is laid out for a

[Wemos D1 mini](https://docs.wemos.cc/en/latest/d1/d1_mini.html) and the

software expects to see just that. If you're just using the software and

not the PCB, there's no reason you couldn't use another kind of ESP8266

board; I used a D1 R1 myself when I was developing the modem. You'd just

need to add pin definitions for your board in RetroWiFiModem.h.



A separate 3.3V regulator is used to power the MAX3232 IC and 74HC32

quad OR gate. Some (most?) D1 mini clones have the smallest 3.3V

regulator on board that they can get away with to power the board, and

they don't have a lot of mA's left over to power anything else. Better

safe than sorry.



![Back Panel](images/Back%20panel.jpg "Back Panel")



The power connector expects a 2.1mm I.D. x 5.5mm O.D. barrel plug,

delivering 5 volts, centre positive.  I used a Tri-Mag L6R06H-050 (5V,

1.2A), [DigiKey part#

364-1251-ND](https://www.digikey.com/product-detail/en/tri-mag-llc/L6R06H-050/364-1251-ND/7682614).

If you plug in a 9V adapter like you'd use for an Arduino, you *will*

let the magic smoke out and have an ex-modem on your hands.



![Schematic](images/RetroWiFiModem.sch.png "Schematic")



On the off chance that there's someone else out there with a well

stocked parts box and a burning desire to put together their own WiFi

modem, there's a [BOM](kicad/RetroWiFiModem-bom.csv) in the kicad

sub directory. If you actually had to go out and buy all the parts, it

really wouldn't be cost effective.



Then again, how practical is getting an Ampro Little Board on the

Internet? Practicality isn't always everything. Sometimes nostalgia is

worth the effort.



## The case



Like I said at the start, I would have loved to have used an old Hayes

Smartmodem case, but they were metal and wouldn't have allowed the WiFi

to work particularly well.



In the end I went with a Hammond 1593N case (DigiKey part #

[HM963-ND](https://www.digikey.com/en/products/detail/hammond-manufacturing/1593NBK/1090774)

or [HM964-ND](https://www.digikey.com/en/products/detail/hammond-manufacturing/1593NGY/1090775)

depending on whether you like black or grey). STL and OpenSCAD

files are included for the front and back panels. You could use the

proper Hammond red panel for the front (DigiKey part #

[HM965-ND](https://www.digikey.com/en/products/detail/hammond-manufacturing/1593NIR10/1090776)),

*but* they're only available in 10 packs and their price is highway robbery.

I ended up using a slightly smaller red panel (DigiKey part #

[HM889-ND](https://www.digikey.com/en/products/detail/hammond-manufacturing/1593SIR10/409899))

that was ~much~ cheaper (it has recently increased in price by 500%)

and available in single units.



The labels are unbelievably low tech. I print them on a piece of inkjet

transparency film. I then cut that down to size so that it will fit

under the LED opening. Then I attach the trimmed down transparency piece

to a length of matte finish, invisible tape and carefully position it in

place. A bit of careful work with an x-acto knife and you've got

yourself a label that looks like it's part of the panel. If you look

closely at the front panel image you can see the edges of the

transparency film and the tape, but in practice they both essentially

disappear.



## The PCB



The PCB includes cutouts for the two columns that join the case

together, and mounting holes for the 6 standoffs. Also, there's an oddly

shaped cutout in back end to allow a particular IDC DE-9F I had on hand.

It's available from DigiKey (or a very close clone is) but it's fairly

pricey. But there's plenty of room for an ordinary solder cup DE-9F.

You'd most likely want to omit the 10 pin header and just wire the DE-9F

right to the board.



## The Software



In a nod to its popularity, the command set I used largely follows that

used in [Paul Rickards' WiFi232](http://biosrhythm.com/?page_id=1453)

modem. Even if the innards are completely different, it made sense to

make it *work* like what people were already used to. There's a reason

everyone's been copying the Hayes command set for almost 40 years!



### First time setup



The default serial configuration is 9600bps, 8 data bits, no parity, 1

stop bit.



Here's the commands you need to set up the modem to automatically

connect to your WiFi network:



1. `AT$SSID=your WiFi network name` to set the WiFi network that the

modem will connect to when it powers up.

2. `AT$PASS=your WiFi network password` to set the password for the

network.

3. `ATC1` to connect to the network.

4. Optional stuff:

   * `AT$SB=speed` to set the default serial speed.

   * `AT$SU=dps` to set the data bits, parity and stop bits.

   * `ATNETn` to select whether or not to use Telnet protocol.

   * `AT&Kn` to use RTS/CTS flow control or not.

   * `AT&Dn` to set up DTR handling.

5. `AT&W` to save the settings.



Once you've done that, the modem will automatically connect to your WiFi

network on power up and will be ready to "dial up" a connection with

ATDT.



### Command Reference



Multiple AT commands can be typed in on a single line. Spaces between

commands are allowed, but not within commands (i.e. AT S0=1 X1 Q0 is

fine; ATS 0=  1 is not). Commands that take a string as an argument

(e.g. AT$SSID=, AT$TTY=) assume that *everything* that follows is a part

of the string, so no commands are allowed after them.



Command | Details

------- | -------

+++     | Online escape code. Once your modem is connected to another device, the only command it recognises is an escape code of a one second pause followed by three typed plus signs and another one second pause, which puts the modem back into local command mode. The character used can be set with `ATS2=n`.

A/      | Repeats the last command entered. Do not type AT or press Enter.

AT      | The attention prefix that precedes all command except A/ and +++.

AT?     | Displays a help cheatsheet.

ATA     | Force the modem to answer an incoming connection when the conditions for auto answer have not been satisfied.

ATC?
ATC*n* | Query or change the current WiFi connection status. A result of 0 means that the modem is not connected to WiFi, 1 means the modem is connected. The command ATC0 disconnects the modem from a WiFi connection. ATC1 connects the modem to the WiFi.

ATDS*n* | Calls the host specified in speed dial slot *n* (0-9).

ATDT[+=-]host[:port] | Tries to establish a WiFi TCP connection to the specified host name or IP address. If no port number is given, 23 (Telnet) is assumed. You can also use ATDT to dial one of the speed dial slots in one of two ways:

    

  • The alias in each speed dial slot is checked to see if it matches the specified hostname.
    • 

  • A host specified as 7 identical digits dials the slot indicated by the digit. (i.e. 2222222 would speed dial the host in slot 2).
    • 

Preceding the host name or IP address with a +, = or - character overrides the ATNET setting for the period of the connection.

    

  • **+** forces NET2 (fake Telnet)
    • 

  • **=** forces NET1 (real Telnet)
    • 

  • **-** forces NET0 (no Telnet)
    • 

Once the dial attempt has begun, pressing any key before the connection is established will abort the attempt.

ATE?
ATE*n* | Command mode echo. Enables or disables the display of your typed commands.

    

  • E0 Command mode echo OFF. Your typing will not appear on the screen.
    • 

  • E1 Command mode echo ON. Your typing will appear on the screen.
    • 



ATGET*http://host[/page]* | Displays the contents of a website page. **https** connections are not supported. Once the contents have been displayed, the connection will automatically terminate.

ATH | Hangs up (ends) the current connection.

ATI | Displays the current network status, including sketch build date, WiFi and call connection state, SSID name, IP address, and bytes transferred.

ATL?
ATL*n* | Query or set the volume of the speaker (0-3).

ATM?
ATM*n* | Query or set whether the speaker is enabled or disabled. ATM0 disables the speaker. ATM1 enables it.

ATNET?
ATNET*n* | Query or change whether telnet protocol is enabled. A result of 0 means that telnet protocol is disabled; 1 is *Real* telnet protocol and 2 is *Fake* telnet protocol. If you are connecting to a telnet server, it may expect the modem to respond to various telnet commands, such as terminal name (set with `AT$TTY`), terminal window size (set with `AT$TTS`) or terminal speed. Telnet protocol should be enabled for these sites, or you will at best see occasional garbage characters on your screen, or at worst the connection may fail.

The difference between *real* and *fake* telnet protocol is this: with *real* telnet protocol, a carriage return (CR) character being sent from the modem to the telnet server always has a NUL character added after it. The implementation of the telnet protocol used by some BBSes doesn't properly strip out the NUL character. When connecting to such BBSes (Particles! is one), use *fake* telnet.

When using *real* telnet protocol, when the telnet server sends a CR character followed by a NUL character, only the CR character will be sent to the serial port; the NUL character will be silently stripped out. With *fake* telnet protocol, the NUL will be passed through.

ATO | Return online. Use with the escape code (+++) to toggle between command and online modes.

ATQ?
ATQ*n* | Enable or disable the display of result codes. The default is Q0.

    

  • Q0 Display result codes.
    • 

  • Q1 Suppress result codes (quiet).
    • 



ATRD
ATRT | Displays the current UTC date and time from NIST in the format *YY-MM-DD HH:MM:SS*. A WiFi connection is required and you cannot be connected to another site.

ATS0?
ATS0=*n* | Display or set the number of "rings" before answering an incoming connection. Setting `S0=0` means "don't answer".

ATS2?
ATS2=*n* | Display or set the ASCII code used in the online escape sequence. The default value is 43 (the + plus character). Setting it to any value between 128 and 255 will disable the online escape function.

ATV?
ATV*n* | Display result codes in words or numbers. The default is V1.

    

  • V0 Display result codes in numeric form.
    • 

  • V1 Display result codes in text form.
    • 



ATX?
ATX*n* | Control the amount of information displayed in the result codes. The default is X1 (extended codes).

    

  • X0 Display basic codes (CONNECT, NO CARRIER)
    • 

  • X1 Display extended codes (CONNECT speed, NO CARRIER (connect time))
    • 



ATZ | Resets the modem.

AT&F | Reset the NVRAM contents and current settings to the sketch defaults. All settings, including SSID name, password and speed dial slots are affected.

AT&D?
AT&D*n* | Display or set the handling of DTR going inactive. The default is &D0 (ignored).

    

  • &D0 Ignore
    • 

  • &D1 Go to command mode
    • 

  • &D2 End call
    • 

  • &D3 Reset modem
    • 



AT&K?
AT&K*n* | Data flow control. Prevents the modem's buffers for received and transmitted from overflowing.

    

  • &K0 Disable data flow control.
    • 

  • &K1 Use hardware flow control. Requires that your computer and software support Clear to Send (CTS) and Request to Send (RTS) at the RS-232 interface.
    • 



AT&R?
AT&R=*server pwd* | Query or change the password for incoming connections. If set, the user has 3 chances in 60 seconds to enter the correct password or the modem will end the connection.

AT&V*n* | Display current or stored settings.

    

  • &V0 Display current settings.
    • 

  • &V1 Display stored settings.
    • 



AT&W | Save current settings to NVRAM.

AT&Zn?
AT&Z*n*=*host[:port],alias* | Store up to 10 numbers in NVRAM, where *n* is the position 0-9 in NVRAM, and *host[:port]* is the host string, and *alias* is the speed dial alias name. The host string may be up to 50 characters long, and the alias string may be up to 16 characters long.

Example: `AT&Z2=particlesbbs.dyndns.org:6400,particles`

This number can then be dialed in any of the following ways:

    

  • `ATDS2`
    • 

  • `ATDTparticles`
    • 

  • `ATDT2222222`
    • 



AT$AE?
AT$AE=*startup AT cmd* | Query or change the command line to be executed when the modem starts up.

AT$AYT | Sends a Telnet "Are You There?" command if connected to a Telnet remote.

AT$BM?
AT$BM=*server busy msg* | Query or change a message to be returned to an incoming connection if the modem is busy (i.e. already has a connection established).

AT$MDNS
AT$MDNS=*mDNS name* | Query or change the mDNS network name (defaults to "espmodem"). When a non zero TCP port is defined, you can telnet to that port with **telnet mdnsname.local port**.

AT$PASS?
AT$PASS=*WiFi pwd* | Query or change the current WiFi password. The password is case sensitive. Clear the password by issuing the set command with no password. The maximum length of the password is 64 characters.

AT$SB?
AT$SB=*n* | Query or change the current baud rate. Valid values for "n" are 110, 300, 450, 600, 710, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 76800 and 115200. Any other value will return an ERROR message. The default baud rate is 1200. The Retro WiFi modem does not automatically detect baud rate like a dial-up modem. The baud rate setting must match that of your terminal to operate properly. It will display garbage in your terminal otherwise.

AT$SP?
AT$SP=*n* | TCP server port to listen on. A value of 0 means that the TCP server is disabled, and no incoming connections are allowed.

AT$SSID?
AT$SSID=*ssid name* | Query or change the current SSID to the specified name. The given SSID name is case sensitive. Clear the SSID by issuing the set command with no SSID. The maximum length of the SSID name is 32 characters.

AT$SU?
AT$SU=*dps* | Query or change the current number of data bits ('d'), parity ('p') and stop bits ('s") of the serial UART. Valid values for 'd' are 5, 6, 7 or 8 bits. Valid values for 'p' are (N)one, (O)dd or (E)ven parity. Valid values for 's' are 1 or 2 bits. The default settings are 8N1. The UART setting must match your terminal to work properly.

AT$TTL?
AT$TTL=*telnet location* | Query or change the Telnet location value to be returned when the Telnet server issues a SEND-LOCATION request. The default value is "Computer Room".

AT$TTS?
AT$TTS=*WxH* | Query or change the window size (columns x rows) to be returned when the Telnet server issues a NAWS (Negotiate About Window Size) request. The default value is 80x24. For terminals that are smaller than 80x24, setting these values appropriately will enable paging on the help (AT?) and network status (ATI) commands.

AT$TTY?
AT$TTY=*terminal type* | Query or change the terminal type to be returned when the Telnet server issues a TERMINAL-TYPE request. The default value is "ansi".

AT$W?
AT$W=*n* | Startup wait.

    

  • $W=0 Startup with no wait.
    • 

  • $W=1 Wait for the return key to be pressed at startup.
    • 




### Updating the Software



While I liked the idea of being able to update the software OTA, it

seemed to make more sense in my situation to be able to *push* a new

version as I built it rather than have the modem *pull* it. So that's

what I did. It uses the default OTA upload capability built into the

Arduino IDE.



**Jan 24/22:** It's been reported that the ESP8266 core is slightly

snafu'd at the moment, and that it's breaking things in the modem

software. As a workaround, I've added the bin file that gets uploaded

to the modem in the repository. I haven't updated my ESP8266 core in

ages; "if it isn't broken, don't break it", and everything still works

for me. The bin file can be uploaded with the *espota.py* tool in the

ESP8266 tool directory tree.



(If TPTB have deleted/renamed/moved that tool in the current core,

you'll have to figure out how to do a manual OTA update.)



### RTS/CTS handshaking and a dead spin loop issue



Something I noticed with ESP8266 software that puzzled me was the

number of places I saw a series of Serial print statements being broken

up with calls to yield(), like so:



```

   Serial.print("Hello world!\n");

   yield();

   Serial.print("How are you today?\n");

   yield();

```

It didn't take long to figure out what was going on; The print() call

was blocking, and at lower baud rates, even printing a few relatively

short strings was enough to cause the watchdog to bark and cause a

reset. So the repetitive yield() calls were an attempt to feed the

watchdog often enough to keep it from barking.



What does this have to do with RTS/CTS handshaking? Simply put,

lowering RTS for more than a few seconds was causing the watchdog to

bark as well. So I started digging.



In cores/esp8266/uart.cpp I found the following function:



```

static void

uart_do_write_char(const int uart_nr, char c)

{

    while(uart_tx_fifo_full(uart_nr));



    USF(uart_nr) = c;

}

```



This is the low level function that everything calls to send a character

out the serial port. The cause of the watchdog barking is in the dead

spin while loop. It waits until there's room in the transmit FIFO to add

another character. So if RTS/CTS handshaking is enabled, and RTS is low

for longer than the watchdog likes: woof.



What I did to quiet the watchdog down both when sending long strings at

low baud rates and during long waits for RTS to come active again was to

add a yield() call to the dead spin while loop, like so:



```

static void

uart_do_write_char(const int uart_nr, char c)

{

    while(uart_tx_fifo_full(uart_nr))

      yield();



    USF(uart_nr) = c;

}

```



This way, no matter how long the code has to wait for space in the

transmit FIFO, the watchdog is kept well fed and quiet.



## Status



As I said way back in 2020, is a personal project like this ever

*really* finished? I've had two units assembled and in use since the

spring of 2020, and a third since 2022, and while there's

been some software changes since then, and a second rev of the hardware

to bring out all the RS-232 control signals and add in the faux dialing

and connections sounds, I really don't expect any more changes. But I've

said that before! There are no outstanding bugs that I'm aware of, and

no new features on my wish list. For the time being at least, I think

it's complete.



### Linux, Telnet, Zmodem and downloading binary files



Have you used the modem to 'dial' into a Linux box? And have you done a

`sz binary_file` on the Linux box? And at a completely reproducible

point in the file, has the connection dropped? But other binary files

work just fine? Then read on.



This drove me slightly batty for months. I finally narrowed it down to

trying to send blocks of binary data with a large number of FF bytes. I

eventually created a test file consisting of 2K of FF and used that to

test with. I could download it through the modem with Xmodem just fine.

Ymodem also worked if I kept the block size down to 128 bytes - but the

connection would drop instantly if I tried sending 1K blocks. Same thing

with Zmodem.



In fact, if I just tried `cat binary_file`, the connection would

drop. Which eventually got me thinking. Sitting at the console on my

main Linux box, I telnet'd to the same box and logged in. No WiFi modem

involved anywhere, just a telnet session on the console to the same box.

I then did a `cat binary_file`. The telnet connection dropped, and I

was back in my original session.



It's the Linux telnet daemon. Not the modem at all.



To prove it to myself, I hooked up WiFi modems to two systems on their

serial ports and had one dial into the other. I could send the all FF

binary file back and forth with Zmodem and Ymodem, no trouble at all.



But you really, really need to download that binary file through the

modem from a telnet connection to a Linux box? You're not going to be

able to use Zmodem. Ymodem will work (the sy command defaults to 128

byte blocks), as will Xmodem. But not Zmodem.



Oddly enough, the telnet daemon has no trouble *receiving* the all FF

binary file. Only sending it. Your guess as to why is probably better

than mine.



## References



* [WiFi232 - An Internet Hayes Modem for your Retro Computer](http://biosrhythm.com/?page_id=1453)


* [WiFi232's Evil Clone](https://forum.vcfed.org/index.php?threads/wifi232s-evil-clone.1070412/)


* [Jussi Salin's Virtual modem for ESP8266](https://github.com/jsalin/esp8266_modem)


* [Stardot's ESP8266 based virtual modem](https://github.com/stardot/esp8266_modem)


* [Roland Juno's ESP8266 based virtual modem](https://github.com/RolandJuno/esp8266_modem)



## Acknowledgements



* A whole lot of people owe a big vote of thanks to Jussi Salin for

releasing their virtual modem code for the ESP8266 and starting the

ball rolling.

* Paul Rickards for an amazing bit of hardware to draw inspiration from.

* All the Stardot contributors for their work.

* And, of course, Dennis C. Hayes for creating something so simple and

elegant that has stood the test of time.