# MQ2
High sensitve multiple gas sensor especially for LPG, Propane and Hydrogen.

If you are using just MQ2(not module), Then prepare load resistance around 2k ohm.

This sensor need pre-heating. To get stable output, wait for heat-up, minimum 2 minutes.

This library get analog voltage from a sensor. Output voltage will increase regarding gas level. When you need actual level (ppm), you should do calibrate the sensor and prepare a formula.

![](./image.jpg)

## wired(obniz,  { vcc, gnd, do, ao});

name | type | required | default | description
--- | --- | --- | --- | ---
vcc | `number(obniz io)` | no |    | VCC or H on MQ2.
gnd | `number(obniz io)` | no |    | GND or H on MQ2.
do | `number(obniz io)` | no |    | digital out
ao | `number(obniz io)` | no |    | analog out


```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.onchangeanalog = function(voltage) {
  console.log(voltage);
}
```

## startHeating()

It start heating.

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
mq2.startHeating();
```

## [await] heatWait(sec: number)

It start heating and wait for a while.
You can update wait time.

name | type | required | default | description
--- | --- | --- | --- | ---
sec | `number` | no | 120 | seconds for wait

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.onchangeanalog = function(voltage) {
  console.log(voltage);
}
```

## onchangeanalog = function(voltage: number)

Specified function will be called every voltage change.

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.onchangeanalog = function(voltage) {
  console.log(voltage);
}
```

## onexceedvoltage = function(voltage: number)

Specified function will be called only when a voltage exceed voltageLimit variable.

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.voltageLimit = 1.0
mq2.onexceedvoltage = function(voltage) {
  console.log(voltage);
}
```

## voltageLimit = number

It define the level of onexceedvoltage call.

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.voltageLimit = 1.0
mq2.onexceedvoltage = function(voltage) {
  console.log(voltage);
}
```

## onchangedigital = function(voltage: number)

This function only be called when do was specified at wired function.
do output high/low regarding output. It compared in a module.
This function will be called every change of do.

```Javascript
// Javascript Example
var mq2 = obniz.wired("MQ2", {vcc:3, gnd:2, do:1, ao:0});
await mq2.heatWait();
mq2.onchangedigital = function(value) {
  console.log(value);
}
```