Fast I2C communication between ESP8266 & PCF8591

Question

I need faster communication between the ESP and the ADC, so I found this https://github.com/pasko-zh/brzo_i2c.

Original wire Example

#include "Wire.h"
#define PCF8591 0x48
byte a0;
void setup() {
 Wire.begin(13, 14);
 Serial.begin(115200);
}
void loop() {
 Wire.beginTransmission(PCF8591);
 Wire.write(0x04);
 Wire.endTransmission();
 Wire.requestFrom(PCF8591, 5);
 a0 = Wire.read();
 a0 = Wire.read();
 Serial.println(a0);
 delay(1000);
}

Brzo I2C example

#include "brzo_i2c.h"
uint8_t buffer[10];
uint8_t error = 0;
float temp = 0.0;
uint8_t ICACHE_RAM_ATTR get_temp(float *t) {
 uint8_t bcode = 0;
 brzo_i2c_start_transaction(0x48, 400);
 buffer[0] = 0x04;
 brzo_i2c_write(buffer, 1, false);
 brzo_i2c_read(buffer, 2, false);
 bcode = brzo_i2c_end_transaction();
 *t = ((buffer[0] << 8) | buffer[1]);
 return bcode;
}
void setup() {
 delay(500);
 Serial.begin(115200);
 brzo_i2c_setup(13, 14, 2000);
}
void loop() {
 error = get_temp(&temp);
 if (error == 0) {
 Serial.print("Temp = ");
 Serial.println(temp, 8);
 } else {
 Serial.print("Brzo error : ");
 Serial.println(error);
 }
 delay(500);
}

But I get always the same error.

1 : Bus not free

I rewrote it in different ways, changing the frequency, pins and doing multiple transactions. The main reason I don't get it to work is the difference in the API.

There is no Wire.requestFrom(); in the brzo_i2c lib. So I need to read the value with brzo_i2c_read(buffer,2,false);.

Answer 1

This line

brzo_i2c_start_transaction(0x48,400);

Sets the SCL frequency to 400kHz.

According to the Datasheet for the PCF8591 the maximum SCL clock frequency is 100kHz.

The other issue may be the "repeated_start" flag on brzo_i2c_write.

If you look at the examples, and "apply" that to your code, your would do something like:

uint8_t ICACHE_RAM_ATTR get_temp(float *t){
 uint8_t bcode=0;
 brzo_i2c_start_transaction(0x48,100); // changed 400 to 100
 buffer[0]=0x04; 
 brzo_i2c_write(buffer,1,true); // changed to true because 
 brzo_i2c_read(buffer,2,false);
 bcode=brzo_i2c_end_transaction();
 *t=((buffer[0]<<8)|buffer[1]);
 return bcode;
}

My understanding of the code is that you would set repeated_start to true in the write if you want to then immediately read - which in your case you want to.

Answer 2

I have no idea about Brzo but this looks wrong:

 brzo_i2c_start_transaction(0x48,400);
 buffer[0]=0x04; 
 brzo_i2c_write(buffer,1,false); // Write
 brzo_i2c_read(buffer,2,false); // Then a read ??
 bcode=brzo_i2c_end_transaction(); 

I think you end and read are the wrong way round, but like I say I've never done anything with this so I'm probably wrong.

• cocco: buffer[0]=0x04; brzo_i2c_write(buffer,1,false); sets the chip to return the analog values. after that i need to read the chip the first byte is analog input0 2nd = AIN1...
• cocco: Wire.write(0x04); // control byte - read ADC0 then auto-increment
• Code Gorilla: Like I said, I thought I might be wrong, I thought you had to end the transaction between writing and reading.