spi/mcp3008 trouble with getting a reading from chip, all channels read 0 (zero)

Question

Pi model: Pi 3 A+

Os: Raspbian GNU/Linux 9 (stretch) <- it's stretch lite

SPI: On

Loop back test:

spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)
TX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D  | ......@....�..................�.
RX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D  | ......@....�..................�.

Wiring:

Code:

package main

import (
  "log"

  rpio "github.com/stianeikeland/go-rpio"
  "golang.org/x/exp/io/spi"
)

const (
  mosi = rpio.Pin(10) //physical 19
  miso = rpio.Pin(9)  //physical 21
  clk  = rpio.Pin(11) //physical 23
  ce0  = rpio.Pin(8)  //physical 24
  ce1  = rpio.Pin(7)  //physical 26

)

func main() {
  if err := rpio.Open(); err != nil {
    log.Println(err)
    return
  }

  defer rpio.Close()

  pins := []rpio.Pin{mosi, miso, clk, ce0, ce1}

  for _, pin := range pins {
    pin.Low()
  }

  dev, err := spi.Open(&spi.Devfs{
    Dev: "/dev/spidev0.0", Mode: spi.Mode0, MaxSpeed: 500000})

  if err != nil {
    log.Println("SPI error", err)
    log.Println("Did you forget to enable SPI interface?")
    return
  }
  defer dev.Close()

  out := []byte{1, 8 << 4, 0}
  in := make([]byte, 3)

  if err := dev.Tx(out, in); err != nil {
    log.Println("SPI read/write error. ", err)
    return
  }

  code := int(in[1]&3)<<8 + int(in[2])

  log.Println(code)
}

Voltage on ch 0 is 1.49, no conversion done by the chip. Returns 0 on ch 0.

Checked Vdd and Vref with multimeter using the analog and digital grounds.

Voltage reads 3.3

A year and a half ago the setup above worked with a pizero on jessie lite.

I tested 3 different mcp3008 chips with the same result.

Also tested on a pizero, no success.

Where is my mistake?

score 1 · Answer 1 · answered Jan 18 '19 at 15:04

Solved it.

MISO and MOSI were wired wrong.

Also the SPI package I used was a bit old.

Rewrote the code using this package "github.com/stianeikeland/go-rpio"

Here is the new working code:

package main

import (
  "log"
  "time"

  rpio "github.com/stianeikeland/go-rpio"
)

func main() {
  if err := rpio.Open(); err != nil {
    log.Println(err)
    return
  }

  defer rpio.Close()

  if err := rpio.SpiBegin(rpio.Spi0); err != nil {
    log.Println(err)
    return
  }

  rpio.SpiSpeed(1000000)
  rpio.SpiChipSelect(0)
  ticker := time.NewTicker(time.Millisecond * 1000)

  //change 0 from range 0 to 7 to read from different channels
  channel := byte(0)
  for range ticker.C {
    data := []byte{1, (8 + channel) << 4, 0}

    rpio.SpiExchange(data)

    code := int(data[1]&3)<<8 + int(data[2])

    //channels
    log.Println(code)

    //Vdd and Vref are at 5v. Change *5 to *3.3 if you are
    //powering the chip with 3.3v
    voltage := (float32(code) * 5) / 1024

    log.Println(voltage)

  }
  defer rpio.SpiEnd(rpio.Spi0)
}

spi/mcp3008 trouble with getting a reading from chip, all channels read 0 (zero)

1 Answers1