MQ-3 Alcohol Sensor - Clarification on circuit

Other Hardware General Electronics
1

I have searched the forum, and google- but found conflicting information regarding the MQ-3 Alcohol sensor.

I will be using the following sensor from Sainsmart:

My question is:

What is the correct way to wire the ground connections on this circuit, when using an external power supply?

I saw one schematic where the Arduino had a wire connecting an analog input pin to the analog output pin on the sensor. There were no other connections made between the sensor and the arduino. The output pin on the sensor was connected to ground on the external power supply via a 10k resistor. The heater circuit on the sensor was also powered and grounded to the external power supply.

Doesn't there need to be a ground/power connection also for that input on the arduino? The attached diagram does not clarify whether or not the ground of the external power supply is connected to the ground on the arduino. Would this circuit work safely?

Also- I could not find any verifiable info specifically relating to the sainsmart sensor board. I also saw one schematic where all the pins were connected to the arduino. Is there something special about this board that prevents the sensors heater from drawing to much power?

2

There is only one ground in the circuit. (Connect all GNDs together.)

3

Thank you for the prompt reply.

And to clarify even more:

Shall I also connect the ground from the external power supply to the arduino ground pin?

4

Ganjaman:
Shall I also connect the ground from the external power supply to the arduino ground pin?

There is only one ground in the circuit. (Connect all GNDs together.)

5

Thank you

6

Would it not make more sense to connect the heater from the "external" (7805) supply to its ground and the sensor from the Arduino 5 V to the input terminal, not being too concerned how the two grounds were connected together?