This project was contributed by Andy Fundinger, a professional Python developer and trainer. Andy built this integration as a way to teach his students how to make calls to their mothers on Mother’s Day, using Plivo and a keypad attached to a Raspberry Pi.
Raspberry Pi is a single-board computer that comes with
  • A Linux-based operating system
  • 700 MHz ARM11 CPU
  • 256MB (or 512MB) RAM
  • SD card storage
  • 2 USB ports
  • Composite and HDMI video out
  • Stereo audio out
  • 8 GPIO pins
  • Wired Ethernet

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Build a Raspberry Pi call button

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1. RasPi Circuit Diagram and inputs flow via GPIO

I hooked up a four-button keypad to four of the Raspberry Pi GPIO pins as inputs,  then run a continuous loop to check whether the buttons have been pushed. Circuit diagram #1
Circuit diagram #2

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2. Call flow via Plivo Voice API

Plivo normally expects that you’ll be using it for a web app, so I had to fake that somewhat. Rather than building a full web app, I had each student create a single page that had at least the minimum viable XML to dial a specified number in response to the call being answered. We also played with having a little more in that XML file. But basically we told Plivo that it was a web service and Plivo was OK with that. 
params = {
'from': "14245550100",
'to': '12015550164',
'answer_url':"https://example.com/static/call_mom/answerThenCallMom.xml",
'answer_method': "GET"
}
p.make_call(params)
Then you execute a script that makes an HTTP GET request for “answerThenCallMom.xml”, which could be as simple as: 
<Response>
    <Dial>
        <Number>14245550100</Number>
    </Dial>
</Response>
Get the code for my Raspberry Pi project on GitHub. Contributed by Andy Fundinger