Published March 3, 2019 © GPL3+

DigiSpark Thermostat with DHT12 and OLED

A thermostat with an OLED capable of plugging into a USB port.

BeginnerFull instructions provided11,985

DigiSpark Thermostat with DHT12 and OLED

Things used in this project

Hardware components

DigiSpark

I was not able to find genuine DigiSpark, bought Chinese clones which made the project so much harder

DHT12 Module

Digilent Pmod OLED

I use a 0.91' OLED with I2C

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

Soldering iron (generic)

Story

Couple of month earlier I made a thermostat using Arduino Pro Micro, a DHT22 sensor and a 0.96' OLED, which fit into a Wemos housing perfectly.

thermostat with DHT22

But I wanted something smaller that I can plug into the USB port on my screen. So I bought some DigiSpark clones, a spare DHT12 sensor (both prove to be unwise decision, I will explain later) and a 0.91' OLED.

All parts

The DHT12 module I have claim to support both I2C and single-wire communication, my initial thought was to use I2C since the OLED module supports that as well, however I was not able to find any DHT12 I2C library that is small enough to fit into the limited memory ATTiny85 has on DigiSpark.

To use the single wire comm mode, simply connect the SCL to GND, use the SDA as data pin.

Fritzing layout

OLED to DigiSpark

GND --> GND

VCC --> 5V

SDA --> P0

SCL --> P2

DHT12 to DigiSpark

GND --> GND

VCC --> 5V

SCL --> GND

SDA --> P3

(Note the P3 is shared with USB+, you need to unplug DHT12 when you upload the code to SigiSpark, it is pain in the bottom but sicne DigiSpark only has 4 analog pins, among them 2 are shared with USB, 1 shared with I2C, P5 does not work on the Chinese clone).

How to set up your DigiSpark is here:

http://digistump.com/wiki/digispark/tutorials/connecting

DigiSpark pin layout

Since the DigiSpark has only about 6KB of space for the code, I had to modify the library for both OLED and DHT, remove some unnecessary public variables and code to reduce the footprint from dht.h and dht.cpp (sadly you can only choose to read either temperature or humidity). Modified library files are attached.

Credit goes to RobTillaart for the DHT12 library and the person who created Tiny4kOLED Library.

The 0.91' OLED is capable of displaying both 8x16 and 16x32 size font, I find the 8x16 a bit small so I settled with 16x32(downside is no font for alphabet, only numbers), I tried creating some simple font with "The Dot Factory" but couldn't get it to display in my OLED.

You need to comment out the unused font in Tiny4kOLED.h to reduce footprint, I am using FONT16X32 so I have the rest commented out.

Tiny4kOLED.h

With all the libraries modified, code uploaded, you will get something like this:

I have designed a case to fit all the components

1 / 3

STL files are here: https://www.thingiverse.com/thing:3465493

Issue with DigiSpark Chinese clones (but they are dirt cheap!!)

1. Doesn't come with the latest version of bootloader, always goes into bootloader instead of code.

Resolution:

Download the micronucleus version 1.11 which has a compressed version for ATTiny85 from here: https://gist.github.com/Ircama/22707e938e9c8f169d9fe187797a2a2c
Run "micronucleus.exe /?" to check your bootloader version
Run "micronucleus.exe --run micronucleus-1.11-upgrade.hex" to load the ver 1.11 bootloader, after this, the DigiSpark will be good to go.

2. Doesn't like to work with all USB ports

Resolution:

Get a USB extension cable, connect it to your powered USB hub or USB port then connect DigiSpark to it. Sometimes it won't get recognized by Windows, download the micronucleus library, run the "Zadig" program with Administrator privilege and install "libusb". This worked on all my win10 laptop and Win7 desktop.

3. Pin P5 is a reset pin unless you set the fuse. Since we won't be using this pin, ignore it.

References:

https://github.com/RobTillaart/Arduino/tree/master/libraries/DHTstable

https://digistump.com/wiki/digispark/tutorials/basics

https://www.hackster.io/M-V-P/large-fonts-for-oled-128x32-driven-by-attiny85-715372

Code

/* Digispark ATtiny85 to small OLED 128x32 by I2C
 * https://github.com/datacute/Tiny4kOLED 
 * Tiny4kOLED.h: SSD1306xLED-Drivers for OLED 128x32 displays
 * @created: 2014-08-12  @author: Neven Boyanov
 * Source code available at: https://bitbucket.org/tinusaur/ssd1306xled
 * @ modified for 16x32 fonts: 2017-01-12 @author: Mihai Valentin Predoi 
 * Fits (2944 bytes) into Digispark  ATtiny85 (6012 bytes). 52 bytes of dynamic memory.
 *  ATtiny85(DigiSpark)			OLED
 *    <<------------------------>>
 *  PB0(DigiSpark P0)        	SDA
 *  PB2(DigiSpark P2)        	SCL
 *  5V         					VCC
 *  GND        					GND
 * 
 * FILE: dht.h
 * AUTHOR: Rob Tillaart
 * VERSION: 0.2.4
 * PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
 * URL: https://github.com/RobTillaart/Arduino/tree/master/libraries/DHTstable 
 *
 *	ATtiny85(DigiSpark)			DHT12
 *    <<------------------------>>
 *  DigiSpark P3	        	SDA
 *  GND				        	SCL
 *  5V         					VCC
 *  GND        					GND
 * 
 */

#include <Tiny4kOLED.h>
#include <TinyWireM.h>
#include <dht.h>

// ============================================================================

dht DHT12;
#define DHT12_PIN 3

void setup() {
  pinMode(3, INPUT); //Read DHT12 on P3 
  oled.begin();
  oled.on();
}

void loop() {
  
  oled.clear(); //all black
  oled.setFont(FONT8X16); // 2 lines of 16 characters exactly fills 128x32
  
  //next line: oled.setCursor(X IN PIXELS, Y - NO EFFECT since 32 bits is max height);
  oled.setCursor(0, 0);
  
  //oled.print(F(DHT_LIB_VERSION)); //wrap strings in F() to save RAM!

  // READ DATA
  int chk = DHT12.read12(DHT12_PIN);

  oled.print(DHT12.temperature, 1);

  delay(15000); //Change the delay to how often read the data.
}

Credits

Tfan

5 projects • 2 followers

IT Engineer, interested in 3D printing, Arduino, RaspberryPi and etc

Thanks to Micronucleus, RobTillaart, and Pre2.

DigiSpark Thermostat with DHT12 and OLED

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Schematics

Schematic

Code

Code for ATTiny85

Modified library for DHT12

Modified library for OLED

Credits

Tfan

Comments

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DigiSpark Thermostat with DHT12 and OLED

DigiSpark Thermostat with DHT12 and OLED

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Schematics

Schematic

Code

Code for ATTiny85

Modified library for DHT12

Modified library for OLED

Credits

Tfan

Comments

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