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I have an RPI 4 Model B running the raspios bullseye 1.1.0 created by Cycling74 to use it in conjunction with RNBO. Found here: https://rnbo.cycling74.com/resources

All required libraries for this project are installed (liblo-dev, pyliblo3, which ibcludes gpiozero). The following python code returns no error:


from gpiozero import MCP3008
import liblo as OSC
import sys

// send all messages to port 1234 on the local machine
try:
    target = OSC.Address(1234)
except OSC.AddressError as err:
    print(err)

    sys.exit()


// start the transport via OSC
OSC.send(target, "/rnbo/jack/transport/rolling", 1)


// read from last two channels
potA = MCP3008(channel=0)


while True:
    print("Pot A", potA.value)
    OSC.send(target, "/rnbo/inst/0/params/cutoff/normalized", potA)

I have connected an MCP3008 to my RPI and connected an LDR according to this schematic: enter image description here

These are the connections between the MCP3008 and the RPI:

MCP3008 Connection
VDD 3.3V
VREF 3.3V
AGND GND
CLK SCLK
DOUT MISO
DIN MOSI
CS PIN5
DGND GND

The LDR is connected with a 10kOhm resistor to the first channel of the MCP3008.

Unfortunately all pins the same value: 0.0004885197850512668 without the desired value change.

I can get an LED to blink and measure an LDR with a capacitor, but somehow, the MCP3008 does not communicate with the RPI. I thought it could have been the MCP3008 and ordered a new one. I have verified the LDR: When measuring the resistance in the LDR with a potentiometer, it shows that it changes values from 0.1 - 1.0 measured in voltages.

What did I do wrong? What do I miss? Python version inconsistency, broken MCP3008?

For more info about the circuit: pibits.net/amp/code/read-ldr-raspberry-pi-using-mcp3008.php

Please disregard the OSC for now. I am just checking the prints in the terminal, which prints the same value roughly 4000 times a second.

I have activated the SPI in the sudo raspi-config, but I think it was already enabled by default.

Maybe something to do with hardware vs software SPI Connection? Source here: https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters/mcp3008

sjoerd
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    There is no such thing as "raspios bullseye 1.1.0". It is unclear from the fritzing diagram what you have connected (I COULD look up the datasheets and draw a circuit BUT you should do this rather than expect others to do so) – Milliways May 03 '23 at 12:02
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    Have you enabled SPI? You don't seem to have connected SPI CS. – Milliways May 03 '23 at 12:34
  • I use the raspios created by Cycling74 to use it in conjunction with RNBO. Found here: https://rnbo.cycling74.com/resources

    I am unsure what you mean by the unclarity of the diagram. More info, for example here: http://www.pibits.net/amp/code/read-ldr-raspberry-pi-using-mcp3008.php

    Please disregard the OSC for now. I am just checking the prints in the terminal. Which prints the same value roughly 4000 times a second.

    I have activated the SPI in the sudo raspi-config, but I think it was already enabled by default. Anyway, it didn't do the trick.

     – sjoerd May 03 '23 at 13:33
  • The spio-sclk (pin 11) of the rpi is connected with the clk pin of the mcp3008. Is that not enough? The MISO and the MOSI are connected and I use pin 5 for the sync and channel=0 for the resistance reading.

    Thanks for looking into this and taking the time!

     – sjoerd May 03 '23 at 13:37
  • If you haven't connected CS then SPI will do nothing because you haven't enabled the device. MCP3008 is not the easiest device to use (there are few examples on line) – Milliways May 03 '23 at 22:53
  • You need to adopt a systematic approach to testing. The first thing I would do is connect ground and then 3.3V to one of the ADC inputs you are monitoring. If the readings don't change that suggests a fault in the wiring. – joan May 04 '23 at 07:25
  • @Milliways Thanks, corrected. – joan May 04 '23 at 07:26
  • @Milliways Thanks for your suggestions and help in creating proper posts around here. – sjoerd May 04 '23 at 14:33

1 Answers1

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See https://gpiozero.readthedocs.io/en/v1.6.2/api_spi.html?highlight=#module-gpiozero.spi_devices which details the necessary connections.

The MCP3008 CS pin must be connected to the SPI CE0 pin - GPIO8
as listed in the link above.

Milliways
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