Roast Meter

ESP32 LOLIN32 board instead of the recommended one.
https://www.sparkfun.com/products/15663 You could use this ESP32 version of the Thing Plus, and probably not need to solder any wires.

https://www.sparkfun.com/products/16474 max30101 breakout
https://www.mouser.com/ProductDetail/474-SEN-16474 alternate source I used

https://www.sparkfun.com/products/14426 50mm cable x 2
https://www.mouser.com/ProductDetail/474-PRT-14426 alternate source I used

https://www.sparkfun.com/products/14427 100mm cable
https://www.mouser.com/ProductDetail/474-PRT-14427 alternate source I used

OLED. Screen Size: 64x48 pixels (0.66" Across)
https://www.mouser.com/ProductDetail/713-104020248 alternate display $5.50 from Mouser
OLED Info Link
I used this cheaper alternate, but it has a different connector so soldering is required.
When I was trying to assemble everything, I pushed the OLED too hard into the case, and broke off a piece of the OLED. After that, only every other line lights up. To compensate I use the largest font, so it still works and is easy to read.

Normal OLED from project
https://www.sparkfun.com/products/14532 oled $18

Case
Case needs to be 3d printed
Files here
Someone from Home Barista printed a bunch out and sent one to me.
Otherwise I would have used treatstock to get it made. I saw pretty reasonable prices there.

lab slides (to make sampling window) My case already had the glass installed.
You would need to cut it to size to make a square from a rectangular thicker piece, and then superglue it in place.
https://www.amazon.com/AmScope-BS-72P-100S-22-Pre-Cleaned-Microscope-Coverslips/dp/B00L1S93PS/ref=sr_1_6?crid=363P8HPSXU7IV&keywords=lab+slides+7105&qid=1678640185&sprefix=lab+slides+7105%2Caps%2C251&sr=8-6

If you are building the battery powered version:

Building/Assembly

ESP32

I used a generic lolin32 type ESP32 as pictured below. They are cheap, and it fits in the case. I was only able to put in one screw though, but it is held in place fine. I had to file the opening for the usb connection some, because the USB connector is off to one side.
I also soldered power wires to the ESP32, and use OTA programming so I no longer plug into the USB. If you plugged/unplugged a lot, then maybe the one screw could cause a problem. If you, I'd glue to board down to keep it in place.

I2C interface to MAX30101 and OLED

SDA GPIO 21

SCL GPIO 22

Ground GND

VCC 3V

Front of ESP32 LOLIN32 board used for this project.

MAX30101

Used the TBD cable to connect from MAX30101 board to ESP32

Cut connector off one end of the cable, strip all wires, and solder wires to ESP32

SDA GPIO 21

SCL GPIO 22

GND GND Black

3.3V 3V Red

Back of OLED board

MAX30101 board

OLED

Use the cable the comes with the OLED board.

Cut one connector off, make cable long enough to reach from OLED to MAX30101 board

Strip wires, and solder into holes on edge of MAX30101 board

SDA SDA White

SCL SCL Yellow

Ground GND Black

3.3V 3V Red

INT and 1.8V are not connected

Power

I decided to use a USB cable with one end cut off to make a more permanent power connector.

Made it a few feet long, strip red and black wires. But strip back the outer sleeve and foil so a few inches of red and black wire are exposed.

I also added a toggle switch I had in my junk drawer, so I can easily turn on and off. Had to drill a bigger round hole where the rectangular switch cutout is. Make sure hole is far enough from edge so switch doesn't hit edge of case. When I did, the switch just makes it.

Drilled a hole in case to run this wire through, and put a tie wrap around the cable by the hole to provide strain relief and protect the solder joints if you pull the cable.

USB Red goes toggle switch. Other side of switch to 5V pin on ESP32, which is on lower left of board above the white battery connector.

USB Black goes to GND pin below the 5V pin

Pics of how I soldered the cables to the boards.

Battery

Thought about, but decided I didn't need a battery.

But info below if you want to try it.

Found an alternate, slightly cheaper battery that should work.

battery charger datasheet 500ma max charging current

PH2.0 JST connector

3.7V 522332 400mAh Lipo

1 1/4 x 1 3/16

AKZYTUE 3.7V 400mAh 802030

Software

See Gitlab page. to get source code, and some more comments on software.

https://gitlab.com/randytsuch/roast_meter

MAX3010x library

https://github.com/sparkfun/SparkFun_MAX3010x_Sensor_Library

From arduino program, go to Tools, Manage Libraries, search for "MAX3010x"
Select and Install Sparkfun MAX3010x library in the Library Manager.

OLED Info

Link

esp32 oled library https://github.com/ThingPulse/esp8266-oled-ssd1306

From arduino program, go to Tools, Manage Libraries, search for "esp oled"
Select and Install library shows below by ThingPulse in the Library Manager.

Recommended library for Seeed OLED board, but didn't work for me with ESP32

Another OLED library that didnt' work for me. Main project uses this library.

I2C scan results

I2C device found at address 0x3C

I2C device found at address 0x57

Found this is the Sparkfun docs

The ADDR jumper (highlighted below) can be used to change the I2C address of the board. The default jumper is open by default, pulling the address pin high and giving us an I2C address of 0X3D. Closing this jumper will ground the address pin, giving us an I2C address of 0X3C.

The released code is

#define PIN_RESET 9

#define DC_JUMPER 1

MicroOLED oled(PIN_RESET, DC_JUMPER);

Need to change DC_JUMPER to 0, and then Sparkfun library will use the 0x3C address.

Library

#define PIN_RESET 9

// From version v1.3, we can instantiate oled like this (but only for I2C)

MicroOLED oled(PIN_RESET);

// This is the new way of initializing the OLED.

// We can pass a different I2C address and TwoWire port

// If 0x3D does not work, try 0x3C

oled.begin(0x3D, Wire); // Initialize the OLED

if (oled.setFontType(4) == 0) // Set font to type 4 (fontlargeletter31x48)

{

Serial.println(F("Could not enable font 4 (fontlargeletter31x48)!"));

Serial.println(F("Have you changed the #define INCLUDE_FONT_LARGELETTER to 1 in SFE_MicroOLED.cpp?"));

Serial.println(F("Freezing..."));

while (1)

; // Do nothing more

}

// Demonstrate font 0. 5x8 font

oled.clear(PAGE); // Clear the screen

oled.setFontType(0); // Set font to type 0

Program uses font 1 now for please load sample, and font 3 to display readings

// Demonstrate font 1. 8x16. Let's use the print function

// to display every character defined in this font.

oled.setFontType(1); // Set font to type 1

// Demonstrate font 2. 10x16. Only numbers and '.' are defined.

// This font looks like 7-segment displays.

oled.setFontType(2); // 7-segment font

// Demonstrate font 3. 12x48. Stopwatch demo.

oled.setFontType(3); // Use the biggest font

Find i2c addresses

I used code from this page https://randomnerdtutorials.com/esp32-i2c-communication-arduino-ide/

In the section "Scan I2C Address with ESP32"

It found this:

I2C device found at address 0x3C

I2C device found at address 0x57

OTA

Software includes AsyncElegantOTA library to support Over The Air Programming

Random Nerd OTA Tutorial

In the Arduino program, select Sketch, Export compiled Binary.
After a min or two, you will see "Done Compiling" message at bottom of window. File is saved for OTA loading.

If you connect to the serial port when ESP32 boots up, IP Address of ESP will be displayed.

Enter the IP address in a browser and you will see

Hi! I am ESP32. add /update for ota

Enter ip address/update, 192.168.xxx.xxx/update

and you will see a page to upload the program.

From the OTA page in your browser, navigate to to the directory where your .ino file is stored

You will see a file with a name similar to this:

roast_meter_05.ino.d32.bin

Select it, and start upload. Wait for upload to complete.

Thats it.