“Did I turn the electric range (stove) off?!?” Are you tired of having to rush back home when you are already late for appointment, to find your stove was actually off? Or tired of the shockingly high bills at the end of the month due to the hours that the stove was left on by mistake”

Here is an easy hack for you that is cheap and easy to do…

Even though most ranges are not smart enough to warn if they are kept ON for an extended period of time, they do have two LED indicators that will be the key for this hack. Usually one LED is for the hot surface – which stays ON as long as the surface of the cooktop is hot. The other one gets turned ON whenever any of the switches/heating elements are turned ON and gets turned OFF as soon as all the switches/heating elements are turned OFF. That’s our trigger. A photocell can be used to detect the status of this LED, update the status of a device in a controller (Vera Edge in this case) and also set an alarm after a user-specified/default time period.

Key Functions:

This device has the following unique functions:

1. Checks the status of the range (ON/OFF)
2. Activates a timer whenever the range is ON
3. Sets off a buzzer (beeps until range is off or change timer time) after the timer expires
4. User can choose different times for the timer (based on cooking time)
5. Sends update to a Vera device through an Ethernet Shield Gateway
6. Ability to check the status of range (ON/OFF) on your phone
7. Ability to receive email notification when the timer expires (Vera Scenes)

Operation:

The photocell is placed on top of the status LED to detect the light from the status LED of the range. With the range ON/OFF it sends a HIGH/LOW signal to the attached Nano. The Nano then sends this information to the Vera device through an Ethernet Shield Gateway and the device status gets updated. It sends email/notification to the user based on the set Scenes in Vera. It also actives a timer in the Nano and sets off a buzzer (beeper) after the set time expires. By default, the buzzer gets activated after an hour from the time the range is turned ON. User can change the timer time to a greater value (2, 3, 4 or 5 hours) by using a single push button switch. A LED indicates which time the timer is set to.

If the range is kept ON for the time period that was set, the buzzer gets activated and status gets updated in Vera device. Once the range is turned OFF everything gets reset and Nano waits for next trigger. The photocell sensor is placed on the stove using a magnetic housing allowing for an easy removal during cleaning.

Materials:

The following materials were used in this project:

1. ATmega328 (Arduino Nano) x 2 (One for gateway, one for this sensor)
2. A temperature / humidity sensor AM2320 (was not required for this project but used it for monitoring temperature / humidity of our main floor / kitchen) x 1
3. Photocell x 1
4. Pushbutton x 1
5. Buzzer (4-12V) x 1
6. NRF24L01 x 2 (One for gateway, one for this sensor)
7. 100k trimmer pot, few other resistors
8. LED x 5
9. Capacitor 10uf, 25V or 4.7uf, 16V x 2
10. 2N3904 x 2 or BC547 or similiar
11. WizNET (W5100) Ethernet module x 1

Setup Instructions:

1. Setup an Ethernet gateway using a Nano, NRF24L01 and WizNET (W5100) following the instruction at https://www.mysensors.org/build/ethernet_gateway
2. Build the circuit as per the diagram/schematic
3. If the controlling / knobs housing surface of the range is metal a magnetic housing for the photocell (this case) can be used. For other type of surfaces, a housing with sticky tape can be used.
4. Upload the sketch (see comments in code for operation details)
5. Place the photocell on top of the status LED and turn ON/OFF the range
6. You have a range monitoring device!!

Opportunities to Improve:

A couple of opportunities to improve include:

• Use an AC detection device to work with ranges without the indicator LEDs
• Develop the ability to remotely turn OFF the range
• Need to find/make a suitable box for the device

Demo: For demo/video the alarm time was changed to 10 seconds for the default alarm (check code for comments). After verifying first alarm, time was changed to 30 seconds using pushbutton. Second alarm was verified in about 30 seconds. Stove was then turned off and controller reset everything to default.

Thanks for reading.