Customer:
I want to use the MQ-138 easy-c with a Raspberry Pi. Is the easy-c voltage equal to Vcc on the pin on the bottom of the board?
Should I use a Vcc of 3.3 V with a Raspberry Pi? The diagram at MQ Gas Sensors – Hardware details | Soldered Documentation shows Vcc = 5 V but below it says Vcc = 3.3V - which is correct?
How much power does the Vcc pin on the bottom of the board require? The Winsen whitepaper for the MQ138 specifies 0.9 W at 5V = 200 mA.
Can I easily modify the Arduino drivers to work with CircuitPython? If I write a driver would you be interested in a copy?
Originally submitted via email support on 18 January 2026. Migrated to the forum for community visibility.
Soldered Support:
If you are using the Qwiic version, you just need to connect the Qwiic cable. The breakout comes with a 3V3 to 5V regulator as well as a boost converter. You don’t need to connect the VCC pin to the board, as those three pins are used for UPDI programming of the onboard ATTiny chip.
A port of the Arduino library to CircuitPython would be quite an undertaking, though with AI assistance it could be easier. We are currently more focused on developing MicroPython modules instead of CircuitPython.
Customer:
I made a calculation error. At 3.3 V, current = 900 mW / 3.3 V = 273 mA, which exceeds the capacity of Qwiic. Unless that is just peak current and the resistance of the heater is fixed.
Drawing 273 mA from the Raspberry Pi Zero 2 W’s 3.3V pin is not safe and will likely cause instability or damage, as the total current for all 3.3V pins is generally limited to around 50mA, with individual GPIOs around 16mA. For higher currents, use a separate, dedicated 3.3V regulator powered from the Pi’s 5V line. Drawing this much power from the onboard supply overloads its regulator, which can lead to voltage drops and system crashes, as the Pi itself consumes significant power.
So I need to connect the 5V output of the Raspberry Pi to a 3.3 V buck converter (no problem) and connect the Qwiic red and black wires to that and GND. The Qwiic SDA/SCL go directly to the Raspberry Pi.
Soldered Support:
I have talked to the hardware team. The Qwiic cable can draw more than 180mA. We have tested it at 250mA without a drop in voltage. If the cable itself is short there shouldn’t be any problems.
If you are concerned about stability, the best approach would be as you’ve described: connect the 5V output of the Raspberry Pi to a 3.3 V buck converter and connect the Qwiic red and black wires to that and GND. The Qwiic SDA/SCL go directly to the Raspberry Pi.