Many Attiny85s and 828s as I2C slaves

Projects Programming
1

Hi all, I'm working on a project where I'm making an array of panels with different knobs and buttons on each of them, which will be hot-swappable on I2C communication and all controlled by a master uno or mega.
I've chosen the attiny828 as it's large amount of analog pins and small price is perfect for most of the panels.

I bought some attiny85 chips just to test if my idea is feasible, however after many videos and tutorials i am unable to get the attiny85 chip to send information over I2C to an arduino uno, let alone reading a potentiometer's state and then sending it.

My question is: is it doable to use attiny chips (especially 828s) as I2C slaves in this way? Realistically, i only need to send 1-2 states of analog pins back at a time per panel. The master can handle all logic and processing of those states as far as I'm concerned. I just haven't seen attiny chips used in this larger and unique way often, so I'm having my doubts.

here's an example of one of the codes used for the attiny. I followed tutorials using arduino uno as an ISP for the chip and it went well as far as i could tell:

#include <TinyWireM.h>

#define pot_pin1 A2
#define I2C_SLAVE_ADDRESS 0x10

void setup() {
  TinyWireM.begin(I2C_SLAVE_ADDRESS);
}

void loop() {
  int potValue = analogRead(pot_pin1);
  
  TinyWireM.beginTransmission(0x08);
  TinyWireM.write(potValue);
  TinyWireM.endTransmission();

  delay(100);
}

Any help is appreciated. Thanks!

2

Then use slave code on the ATTiny, using onRequest().

3

You realize the I2C protocol maximum wire length is measured in centimeters. Not in meters.
The protocol is designed for communication between devices on the same PCB.

4

It is also not considered hot swappable.

5

Is that sketch of post #1 for ATtiny85 or ATtiny828?

6

I had much better luck with I2C code on a Tiny85 talking to an Uno when using the ATTinyCore core by Spence Konde. >> GitHub - SpenceKonde/ATTinyCore: Arduino core for ATtiny 1634, 828, x313, x4, x41, x5, x61, x7 and x8.
For the core, here is a version of Wire and some exampes that may help.

1 Like
7

Is there another form of communication I can use with these chips that does? Assuming I am just sending analog pin states?

8

The most distanced panel from the master will be shorter than a meter. I only chose I2C to continue with the idea because of its ability to use only 2 pins across several devices.

9

It’s for the 85. I’m assuming there won’t be too much difference in the code when and if I start using 828s, other than pins.

10

Many bus systems do the same (RS-485...).

1 Like
11

What about USB? Do attiny chips, along with minimal extra hardware, have the ability to communicate this way? It would solve the hot-swap issue and I could find some way to process the oncoming information on a computer, which an uno or a mega was going to do anyways.

12

Checking the Functionality of I2C Bus between UNO and ATtiny85
1. Build the following setup (Fig-1) between Arduino UNO and Digispark Attiny85 Dev Board using I2C Bus. Do not connect the wiper of Pot with (PB5)ADC0-pin of ATtiny85.

i2cUnoAttiny85
i2cUnoAttiny85959×356 34.4 KB

Figure-1:

2. Upload the following sketch in UNO.

#include<Wire.h>
#define slaveAddress 0x23

void setup()
{
  Serial.begin(9600);
  Wire.begin();
  pinMode(13, OUTPUT);
  //--------------------
  Wire.beginTransmission(slaveAddress);
  byte busStatus = Wire.endTransmission();
  if (busStatus != 0)
  {
    Serial.println("Slave is not found.");
    while (true); //wait for ever
  }
  Serial.println("Slave is found.");
}

void loop()
{
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
  //----------------
  Wire.requestFrom(slaveAddress, 2);
  unsigned int y = Wire.read() << 8 | Wire.read();
  float testVolt = (5.0 / 1023.0) * y;
  Serial.print("Voltage received fromm Slave: ");
  Serial.println(testVolt, 1);
  delay(1000);
}

3. Upload the following sketch into ATtiny85 of the Digispark ATtiny85 Dev Board.

#include<Wire.h>
#define slaveAddress 0x23

void setup() 
{
  Wire.begin(slaveAddress); 
  Wire.onRequest(sendEvent);  
}

void loop() 
{
  delay(5);
}

void sendEvent()
{
  unsigned int y = analogRead(A0);
  Wire.write(highByte(y));
  Wire.write(lowByte(y));
}

4. Press RESET Button of Arduino UNO. Check that the following message has appeared on SM1.

Slave is found.

5. Connect wiper of Pot with (PB5)ADC0-pin of ATtiny85.
6. Rotate the Pot and check that the following readings do appear on SM1.

Voltage received fromm Slave: 3.0
Voltage received fromm Slave: 3.0
Voltage received fromm Slave: 2.7
Voltage received fromm Slave: 3.9
Voltage received fromm Slave: 4.6
Voltage received fromm Slave: 4.9
Voltage received fromm Slave: 5.0
13

Thanks, I’ll try this out. It’s just a raw attiny chip, but I assume it’ll work the same.

14

It is very convenient to work if you have a Digispark ATtiny85 Dev Board.

15

Yes, however I am only using 85s for testing, I will be switching to probably 828s for more analog pins. Trying to keep it affordable as I may have up to 20 of these panels.

The wire library doesn’t work on a raw attiny85. Will wireS or wireM work interchangeably?

16

I am simply using Wire.h Libray that works for Attiny85. Please, see my post #12.

How many analog channels do you need for each MCU?

17

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