I2C Communication between Arduino and RPi failing when Arduino is sending data

Question

I'm trying to read some data from the Arduino slave and when I receive the data it shows some numbers but not the correct ones.

I'm using node and i2c-bus module, also tried with wiringPi but got the same result.

I do the following thing in node.

const i2c = require('i2c-bus');
const bus = i2c.open(1, (err) => {
 setInterval(function() {
 var buf = new Buffer(4);
 bus.readI2cBlockSync(0x09, 50,4, buf);
 console.log(buf );
 }, 500);
});

And my Arduino code is:

#include <Wire.h>
int val = 0;
int receiveBuffer[9];
int toggle = 0;
void setup() {
pinMode(3, INPUT);
 pinMode(13, OUTPUT);
 Wire.begin(9);
 Wire.onReceive(receiveEvent);
 Wire.onRequest(sendData);
}
void loop() {
}
void receiveEvent(int howmany)
{
 int counter = 0;
 while(Wire.available()) {
 receiveBuffer[counter] = Wire.read();
 counter ++;
 }
}
void sendData(){
 if (receiveBuffer[0] == 50) {
 if (toggle == 0) {
 digitalWrite(13, HIGH);
 toggle=1;
 } else {
 digitalWrite(13, LOW);
 toggle = 0;
 }
 Wire.write(66);
 Wire.write(67);
 Wire.write(68);
 Wire.write(69);
 }
}

And the result in the RPi is this:

<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 08 bf ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>
<Buffer 10 7f ff ff>

See the at some point started to receive different numbers, but other times is mixed and show random things.

I try to do the same master/slave with 2 arduinos and I received the correct data.. I don't know why is failing in RPi and is driving me crazy.

I'm using a level shifter for the 5v i2c between the Rpi and the Arduino.

Also I know the i2c is working ok because I have 4 MCP23017 connected to the 5v i2c channel and they are working.

The arduino seems to receive the data okay as the led toggles alright.

Any ideas?

Answer 1

After hours of hitting my head against the wall I tried to connect it directly without passing through the level shifter and it worked... I don't understand exactly why it is, I suppose it's because of the pulldown resistors or something like that but can tell exactly.

• tlfong01: Perhaps your level shifter is not suitable for I2C. I tried more than 10 level shifters and still have not found one good enough. For now I mainly use TBX0102. I once tried TSX0102/04/08 but found them problematic. I recently found PCA9306 and might try it sooner or later. If you tell me what level shifter you are using, I might give some comments make a guess why it doesn't work. One other thing is that Rpi stretch python I2C has a bug,so I have heard, ...
• Milliways: You DO NOT need a level shifter with I²C to interconnect 3.3V & 5V logic - provided there is ONLY a 3.3V pullup (which is included on the Pi). Technically this results in marginal high levels, but I have never found problems. You CAN use a level shifter, but the need pullup on BOTH the 3.3V & 5V sides. The 10kΩ pullup on some level shifter is too high, and many cheap level shifters only have a voltage divider on the Rx circuit.
• Yind: @tlfong01 I don't know the exact model but it's exactly like this one. luisllamas.es/wp-content/uploads/2018/01/arduino-portada.png