ELF Software Improvements

At the request of a fellow roaster I'm adding some clicking capabilities to the ELF control panel. I've already made the power button toggle the power when clicking on it and I'm working on adding some new buttons to increase and decrease the temperature. When I first designed the control panel I thought it would be easier to use keyboard shortcuts instead of looking for the mouse pointer in the middle of roasting. However, some folks, to my surprise, are running ELF on tablets and phones so using keyboard shortcuts is difficult. I should have the temperature buttons done in the next week or two. It doesn't take long, I just have to find the time to do it.

ELF Software Improvements

I've recently completed a couple of improvements to the ELF roasting software.

Previously, roast profiles needed to be reloaded before each roast. Now, after stopping a roast, restarting will automatically reload the roast profile at the beginning. This makes it quicker to do back-to-back roasts.

Also, the temperature gauge is now a single background image with a needle image that rotates to point to the correct temperature. Before, there were over 150 images that were used to indicate different temperatures by having the needle point to a different temperature in each picture. With this change, the web page loads much faster and the needle rotates smoothly between temperature changes instead of "jumping". It looks much more like an analog gauge.  This was fun to work on and I am pleased with the result.

Download the latest and let me know what you think.

ELF now has roast profiles

I've finally finished writing the software that allows ELF to run a roast profile automatically.

Here is how it works:

Colombian Santa Barbara (Happy Mug) with new ELF features

The following new features were added to ELF:

1. The temperature chart starts with an x-axis scale of 12 minutes and a y-axis scale of 0-500F. The chart will expand the scale if the roast goes longer than 12 minutes or if the temperature exceeds 500F. Most of my roasts are finished within 10 minutes. This fixed axis allows me to compare roasts since they will all be using the same x-axis and y-axis scales.
2. Ability to export the roast log as an image and include the notes section as part of the image.
3. Markers can be added to the chart to indicate significant events like first crack start/stop, second crack start/stop, etc..  The markers are blue vertical lines. I will make them thicker so they are easier to see. When roasting press ALT-M to create a marker.

Now that I've settled on a temperature profile for both the Colombian and Sumatra beans I will begin working on the next ELF feature: automated roasting profiles.

Colombian Santa Barbara (Happy Mug), next features for ELF

After many roasts I've finally settled on a roast profile for Colombian beans that I like. First crack occurs around the seven (7) minute mark while the beginning  of second crack occurs around the ten(10) minute mark, at which point I stop the roast.

Electric Lights and Fire (ELF) Raspberry Pi Coffee Roaster

Here is a video of the ELF roaster in action:

I stumbled upon a video of someone using a popcorn popper to roast coffee. It seemed simple and a used popper can be acquired cheaply at a thrift store. This was the start of ELF, a roaster designed to produce the world's best cup of coffee.

My first visit to my local Goodwill produced two Poplite Poppers for the whopping total of $8. I immediately started to use one and experienced beans blowing out of the popper. An extended chimney, made from 3” ductwork from the local hardware store, resolved that issue.



First Roaster

The first batch roasted in under 5 minutes. To slow down the roast I began unplugging the unit for 30 second intervals during the roast. This allowed me to extend the roast to 7-8 minutes.

Tired of unplugging the popper I decided to retrofit the second popper with a thermocouple, ac relay, a raspberry pi, and some web code and the Electric Lights and Fire (ELF) roaster was born.




ELF

EFL LED flame

ELF with web controller

The major components, along with a schematic, of ELF are described below. A parts list is also provided at the end of the article.

Thermocouple

This thermocouple from SainSmart is ideal as the small probe end allows it to be installed directly underneath the screen where the heated air is blown. The MAX31855 breakout board is also needed as it reads the thermocouple temperature and provides it to the Raspberry PI via a SPI interface.

To install the thermocouple:
First, remove the fan/heater module from the popper by removing the bottom, top, and the wiring nuts. Next unscrew the four screws holding the fan/heater module together. This will allow access to the area underneath the screen. Insert the thermocouple through the hole as shown in the diagram and reassemble the fan/heater module.



Thermocouple threaded through hole below heater screen

Thermocouple wire (gold colored) routed along side ac power wires

 AC Relay

This AC relay works well for cycling the power to the heater on and off. I initially connected a GPIO pin from the Raspberry Pi to the relay. This failed as the GPIO pin does not provide enough current to activate the relay. I discovered, however, that the 5V power from the Raspberry Pi would activate the relay. Thus, I used an NPN transistor connected to a GPIO pin that, when set high, will apply the 5V power from the Raspberry Pi to the relay which powers the Poplite heater.

Temperature Control

A python process is started on powerup that controls the roaster. It reads configuration values from a file to get the desired temperature and attempts to achieve the desired temperature once the roaster is activated though the web page controls. It applies the temperature setting every second. Within that second it will read the thermocouple temperature every 10 milliseconds. If the temperature is above the set value the heater is turned off. Conversely, the heater is turned on if the temperature is below the set value. This process also logs all relevant data to a comma separated file that can be exported to Excel.

Flickering Flame

The flickering flame on the front is produced using four LED’s: two yellow and two red. Each LED is connected its own GPIO pin on the Raspberry Pi with a 330 Ohm resistor to limit the current. The intensity of the LED is controlled using pulse-width-modulation (PWM). A PWM cycle frequency of 22 Hz was chosen as it produces a nice flickering effect. A higher value reduces the flickering and a lower value makes the flickering too slow. When the heater is turned on a random value is chosen for the red and yellow LEDs. This makes it appear more like a fire with occasional flare ups.

User Interface

The UI was developed using django, a framework for developing web pages using python.  The UI is made up of mostly images. The old-style LED numbers are image files with an image file for each digit. The temperature gauge was made by rotating the dial image on the gauge background in 5 degree increments and saving a file for each increment. The gauge can show temperatures between 140 and 550 in 5 degree increments requiring 82 image files for the temperature gauge. All the images must be loaded by the browser before the UI can be used to control the roaster. This takes between 30 and 60 seconds. This allows the browser to run smoothly with no delay which could be caused by waiting for an image to download.

If you would like a copy of the code please send me an e-mail.

Inside of ELF

ELF Bottom

Raspbery Pi breakout and AC relay

ELF Top

Schematic

Parts List Here

ELF was featured in issue #46 of "Mag Pi" magazine (page 38).
ELF was also featured in issue #18 of "Raspberry Geek" magazine.

ELF Parts List

One (1) Raspberry Pi, $35
One (1) Raspberry Pi Power Supply, $10
One (1) Raspberry Pi Breakout Board, $7.50
One (1) Type K Thermocouple, $10
One (1) MAX31855 Thermocouple Breakout Board, $15
One (1) AC Relay, $8
One (1) NPN Transistor, $0.06
One (1), AC outlet, $3
One (1), AC outlet box, $1

One (1) Poplite Popper, $4 (from Goodwill)

Other miscellaneous parts:
AC wire with male plug
Two red LED's
Two yellow LED's
18 AWG wire
20 AWG wire
10K ohm resistors
300 ohm resistors
Spray Paint
Wood box

Total Price: $90

With miscellaneous parts the total price will be around $100.