Oven Temperature Checker - 2nd generation

🔲The original Spacerlabs "Oven Temperature Checker - OTC" appeared on this blog on📅 6 December 2021; but it's development actually began in 📅September 2017. To recap, it's purpose is to measure the air temperature🌡 of the internal cavity of a domestic oven ( non microwave ) to compare with the user set 🌡temperature. This 📮post describes the next generation OTC, and the differences. Many features are, however, retained; for example 2.4GHz BluetoothⓇ wireless 🛜connectivity ( using Bluetooth Low Energy - BLE*) is still used.

The OTC now has a custom 3-D printed case compatible with a terminated ( plug-in ) or unterminated ( hardwired ) Type-K thermocouple. The OTC is powered from an external power source, e.g., power bank, via the micro-usb socket.

Custom case, any colour possible, usb socket on rear, note thermocouple inputs

There is no integral display. The User Interface ( UI ) is the SpacerLabs custom app "OTC_Ui_v1.x" for a BluetoothⓇ enabled Android device. The OTC functions as a BluetoothⓇ server, advertising itself as "SPACERLABS_OTC". Connecting to the server with a paired BluetoothⓇ client device, ( e.g. smart phone having the app installed ), enables the OTC ready for use.

App icon attributed to 'Freepik'

App screen showing a completed measurement run

The App displays the version of the software uploaded to the OTC, real time 🕖clock ( RTC ), status of BluetoothⓇ connection, and received signal 🛜strength indication ( RSSI ) of the BluetoothⓇ signal. A pop-up ⚠alert appears if the 🛜signal is too weak. A measurement cycle, maximum duration ⏲10 minutes, can be started, paused or cleared by tapping the appropriate button. A 🌡temperature measurement is made every ⏲second and plotted. Instantaneous oven 🌡temperature, OTC 🌡temperature, elapsed ⏲time and average oven🌡 temperature over time are numerically displayed. The oven 🌡temperature, up to 240C, is plotted 📈against🕰 time. Any thermocouple faults which might occur are ⚠flagged; OC (open circuit), SCV (short to volts) & SCG (short to ground). Temperature measurements in serial form, data rate 115200Baud, can be accessed by connecting a pc running terminal emulation software to the micro-usb socket.🔳

 

The OTC 📖User Guide can be downloaded 🔗here.

*BLE is the low power variant of classic BluetoothⓇ.

Oven Temperature Controller

This usb dongle style temperature controller has been successfully used to control the temperature of an oven during reflow-soldering electronic circuit boards. It incorporates the MAX31855 14bit 0.25C resolution thermocouple to digital converter chip, and connects to a Type-K thermocouple and solid state relay (SSR), which together with a mini-oven form a self-assembled reflow soldering setup.

The SSR (not shown) connects to the screw-terms

It can also be used simply to measure the internal temperature upto 255C of any domestic oven (not microwave), by omitting the SSR.

Custom pc software for either purpose has been written using Visual Basic language.

Clear style dongle enclosure - cover removed

The temperature controller has also been designed to fit a typical dongle enclosure.

 

 

Oven Temperature Checker

Measuring temperature using a MAX31855K thermocouple to digital converter chip and Lilygo TTGO T-Display ESP32 board. To be used as an "Oven Temperature Checker" ( OTC ) for comparing actual air temperature inside a domestic oven with the set value.

Type-K thermocouple connected to MAX31855 breakout board

The OTC is unusual as it also acts as a BluetoothⓇ server ( SpacerLabs_OvenCheck ) using the 'Bluetooth Low Energy'  ( BLE ) variant of BluetoothⓇ. Connecting to it with a paired BluetoothⓇ client device ( e.g., a smart phone 📱), having a suitable App installed enables the OTC ready for use. The BLE features of the OTC have been modelled on the standard service and characteristics of the BluetoothⓇ "Environmental Sensing Service", having just the one characteristic for "Temperature" exposed.

SpacerLabs "Oven_Check" App

Many general purpose BLE client App's are available. However, here at SpacerLabs, we have built our own custom App for Android devices, called 'Oven_Check', to make the process of accessing the functions of the OTC quick and easy.