In the brand new issue of HackSpace magazine, out now, we show you how to bring an old phone into the 21st century by adding a Raspberry Pi to turn it into a networked assistant.
Delving into history
The first task was to open the telephone and check the amount of space available for the new innards. Figure 2 shows the printed circuit board (PCB) inside the phone. This design was one of the first times a PCB had been used in a UK telephone.
The author would have liked to have kept the internal components in place so that the phone could be returned to its original state if required. Unfortunately, this turned out to be impossible.
Wiping the slate clean
The circuit board was cleared of components, and a 3D-printed holder for the Raspberry Pi Zero with prototyping board was inserted into the space, as shown in Figure 3, below. The phone will use a 12-volt power supply, and it was found that a power supply socket fits into the cord holder for the exchange connection with an appropriate washer.
Figure 4, below, shows the circuit for the telephone. The two devices in the centre are two ‘buck converters’. The one on the left converts the 12-volt power input into 35 volts to power the bell. The second converts 12 volts into 5 volts to power the Raspberry Pi. The handset switch is connected to the handset cradle and indicates whether the handset is on the phone. The dial pulse and dial active switches are in the telephone dial, of which more later.
Ring the bell
HackSpace magazine issue 73 out NOW!
Read the full tutorial when the free PDF version of the latest issue becomes available on December 14th.