Tag Archives: forum

How much you can hang off a Trinket (ATtiny85)?

Adafruit’s Trinket platform – based on Atmel’s versatile ATtiny85 microcontroller (MCU) – has been used to power a number of diverse projects in recent months, including an audio playerflickering candle in a jar, a knock drawer lock, a sound-reactive LED color organ and even a rover.

Today, we’re going to take a closer look at an Adafruit forum post by Pocketmoon who wanted to demonstrate just how many components can be hung off the 3.3v ATtiny85-powered Trinket.

Over I2C

  • DS1307 Real Time Clock (includes 24C32 32K Bit I2C EEPROM memory which is also visible on the I2C bus)
  • HMC5883L 3 Axis Compass Magnetometer
  • PCF8574 – Remote 8-Bit I/O Expander for I2C-Bus

Over SPI

  • OLED 128×64 SSD1306
  • 23K256 SRAM Chip – 32K of lovely SPI accessible memory.

“The SRAM provides a screenbuffer for the OLED module, which has no built in RAM. To draw the buffer to the display I read a ‘page’ worth of data (128 Bytes) at a time from the framebuffer and push these to the OLED, both over SPI. So a local 128 byte buffer is needed in the Trinket. All the Trinket pins are in use so I use a small switch to disconnect #3 and #4 during programming,” Pocketmoon explained.

“With SPI you need a separate Slave Select line for each device. These are provided by the PCF8574 which is an I2C IO Expander. I write to this first (over I2C) to select one of the output pins which act as Slave Selects for each SPI device. The outputs (I’m using 2) are then AND’ed with a single Master SS (on #3). This allows the individual SS’s to be driven low by the master SS. Code eequires a bit of jumping between I2C mode and SPI mode and both are using the serial hardware on the ATtiny.”

The display in the photo above shows the time, a compass reading and a time per frame in milliseconds. Pocketmoon says the display is running at about 13fps, with additional room for optimization.

Interested in learning more? You can check out the original forum post here and pick up a Trinket from Adafruit’s official store here for $7.95.