The Apple IIc was in good enough shape to keep expanding, so I went ahead and added three things I wanted to try on it: a WiFi modem, an external floppy drive, and HDMI output. The first job was getting a serial modem connection working through the IIc’s port so I could dial into a few BBSes.
I used the other half of the cable from the previous Apple IIc work and built a separate adapter with a male 9-pin DIN on the end so it could be reused with other machines. The modem board itself used an ESP8266 module, a MAX3232 for RS-232 level shifting, pull-up and pull-down resistors for the ESP startup lines, a micro USB jack for power, and reset and flash buttons. I also broke out the serial control lines and added jumper options so signals like DTR/DSR and RTS/CTS could be looped back when software expected handshaking.
I spent some time in KiCad showing how the board was laid out and how the pin mapping matched the Zimodem firmware defaults for the ESP8266. The board was kept small, and I used KiCad’s 3D view to check clearances before building it. I also printed a simple case for it, and the finished modem looked tidy enough to use with more than just the Apple IIc.
For firmware, I used Zimodem on the ESP8266. It emulated classic AT modem commands, connected to WiFi, and translated telnet sessions so the Apple IIc saw what looked like a normal modem on the serial port. I showed the AT+CONFIG menu, phone book entries, echo settings, saved configuration, and the built-in firmware update command.
On the Apple IIc, I first tried Apple Access II because it was quick to get into terminal mode. The modem responded properly, and I dialed a stored number to connect to Particles BBS. That worked, but ANSI display wasn’t usable there, so I switched over to ProTERM. In ProTERM I set the baud rate to 9600, enabled a better terminal emulation mode, connected to Dura-Europos, and got a much cleaner result. I even loaded up a simple BBS game to confirm the setup was working end to end.
The external drive was an Apple Disk 2c I found on eBay listed as not working. Since the IIc already had its internal drive as the first drive, I used ADTPro to rescan volumes and see whether the external one responded. At first I got an I/O error, then I cleaned the heads with a cleaning disk and tried again. After that, the drive started reading disks, although one Summer Games disk still gave errors while other disks worked fine. I used Copy II Plus to copy an Oregon Trail disk from the internal drive to the external one, and the copied disk booted successfully.
I opened the Disk 2c to compare it with the internal IIc drive and found exactly what it looked like from the outside: the same mechanism, with the ribbon cable simply extended into the external enclosure. There wasn’t much mystery there.
To clean up the video output, I connected the Apple IIc’s composite signal to an RGBtoHDMI setup with a simple RCA lead and left the 5V connection unused. Once I selected the Apple II profile and set it for 60 Hz, the picture came right up. Oregon Trail displayed in color, 80-column text looked much sharper than composite, and a quick auto-calibration pass cleaned up the remaining sampling fuzz. I reconnected the modem and confirmed that BBS text over HDMI looked excellent.
The Apple IIc ended up with a working WiFi modem, a working second floppy drive, and sharp HDMI output.
— Aaron
Links
- My Retro Modem project with KiCAD files
- Zimodem Github Page
- RGBtoHDMI Github Page
- RGBtoHDMI Forum
- Music used by permission
- RGBtoHDMI from the Retro Hack Shack Shop
Timestamps
00:00 – Intro
01:58 – Wifi Modem First Look
04:25 – KiCAD
12:00 – Modem Software
16:05 – Access II
19:15 – ProTERM
23:10 – External Floppy Drive
33:23 – HDMI
40:44 – Wrap Up