Derek Woodroffe's Pi Tele Cow Aims to Turn a Raspberry Pi Pico W Into a Portable VOIP Handset

With a 15-key keypad, microphone, speaker, and display, this battery-powered handset could deliver low-cost VOIP calls on the go.

Extreme Electronics' Derek Woodroffe is working on a device that turns a Raspberry Pi Pico W microcontroller board into a portable phone — complete with 3D-printed handset: the Pi Tele Cow.

"[The Pi Tele Cow is] a simple VOIP/SIP [Voice-Over-IP/Session Initiation Protocol] portable Wi-Fi telephone handset, running off a [Raspberry Pi Pico W] using the [board's] Wi-Fi for connectivity," Woodroffe explains of the gadget. "Built to be as basic as possible, but to have [a] working 'usable' hand held phone."

The Pi Tele Cow, the name and logo for which is inspired by the classic British Telecom design and the Raspberry Pi Pico W's "PiCow" nickname, is built around the Raspberry Pi Pico W and its dual-core RP2040 microcontroller. To this, Woodroffe has added an SD card for storage, a microphone, speaker, 15-key keyboard, SSD1306-based I2C LCD display, and a 15-key telephone keypad, along with an internal battery chargeable over USB.

Despite its appearance, though, the Pi Tele Cow is neither designed for use with landline connections nor offers cellular connectivity. Instead, it's designed to use the Wi-Fi radio on the Raspberry Pi Pico W to connect to a network — storing credentials for up to nine access points on the SD card — and link to a SIP server to make Voice-Over-IP calls.

The project is a work-in-progress, with Woodroffe admitting that there is "intermittent no speech, can't cancel [an] outgoing call before answer, [it can] lock-up after calls, requires reboot to make [a] second call, [and there are] NAT calling issues," but as an initial proof-of-concept it has demonstrated that the Raspberry Pi Pico W is powerful enough to at least attempt to drive a handheld VOIP phone.

The source code for the project has been published to GitHub under the permissive BSD 3-Clause license, with Woodroffe planning to sell the PCB on the Extreme Kits site once the design has been finalized and the firmware to-do list whittled down.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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