I wanted to control my ZEQ25 (now CEM25) with SkySafari Pro but didn't want to pay the high price for a SkyFi or Starseek. $150+ seemed a bit nuts to me.
I started by building a WiFi to Serial converter using a Raspberry Pi. That worked fine but required external power and more wires going into the hand controller.
I then started working with the ESP8266. It's a small WiFi enabled chipset that has a built in microcontroller. People have done amazing things with the ESP8266. A bare board costs about $3.00 and you need a few external components to make it run / program. Instead of using the a bare module, I decided to pay twice (!!) the price and buy an ESP8266 board that had all the external parts built in. The best board I could find is the WeMos D1 Mini.
It requires no external components to program via USB and has all the built in SMD parts to make the ESP8266 run when programmed. For software a project called ESP-Link by jeelabs already did exactly what I wanted. It creates a WiFi to serial bridge and also puts a webserver on the ESP8266 that allows you to change the settings from a webpage. Neat!
The next step was to open up the iOptron 8408 hand controller. There is a ton of extra space inside the hand controller. I found a bare spot on the board and used some double sided tape to secure the D1 Mini board. Initially the board was to thick to fit inside the case so once programmed, I removed the micro-usb connector to make the D1 Mini board thinner. That gave me enough room to tape the board down and still screw the hand controller back together.
I traced out the RJ9 connector on the board to a Max3232 clone chip that converts RS232 to TTL for processing by the ARM microprocessor that is in the hand controller. Since the ESP8266 puts out TTL level signals I bypassed the RS232 converter and soldered the Tx and Rx lines to the TTL side of the Max3232 that went straight to the ARM chip.
All that was then required was to find 3.3 volts and route power to the ESP8266. I checked the specs on the switching power supply that is used to convert 12 volts from the battery powering the mount to 3.3 volts for the ARM and MAX3232. It's rated up to 1.5 amps which means there is plenty of spare power. The ESP8266 takes about 170ma at max transmit power.
You can see in this picture a small bluetooth to serial module that would do the same thing only over bluetooth. You'd power it and hook it up to the same lines as the ESP8266. I haven't tried it since I use apple devices and bluetooth control won't work with SkySafari, so do that at your own risk.
After I buttoned it all back up, everything works exactly as it should. I can control my mount from my iPhone with no additional power supplies or wires, all for less than $10.00 and a few hours of work.