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Step 3The Interface
For the first version of the interface i wanted to use only parts that I already had in my lab. I decided to build an interface that should be connected to the parallel printer port of my pc. There are 24 keys on the phone that I liked to simulate. I decided not to connect to the loudness control switch.
To connect to each button I needed a latched port expander using 74LS259 and 74LS138 TTL ic's. To press the buttons I used some old CD4066 analog switches.
See the attached logic plan. I soldered the parts on an evaluation board with small wires. On the borad I put also a voltage regualtor LM78L05 and some capacitors. The power regulator is a standard application to get a regulated power for the ic's. I connected a old, unregulated AC-DC charger.
You can see the setup on the attached pictures.
To connect to each button I needed a latched port expander using 74LS259 and 74LS138 TTL ic's. To press the buttons I used some old CD4066 analog switches.
See the attached logic plan. I soldered the parts on an evaluation board with small wires. On the borad I put also a voltage regualtor LM78L05 and some capacitors. The power regulator is a standard application to get a regulated power for the ic's. I connected a old, unregulated AC-DC charger.
You can see the setup on the attached pictures.
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