# Handheld Carbon Monoxide Detector

#### panther12

Joined Aug 3, 2022
3
Hello Community,

I'm looking for a handheld co detector and after much research, I've found one but I'm confused with its specifications. Here are its details:
Handheld carbon monoxide (CO) detector with high accuracy sensor, pump suction type, selectable measuring range of 0 to 500 ppm, 0 to 1000 ppm, 0 to 2000 ppm, gas leak alarm with audible, visual and vibrating, compact size and light weight, long working time, easy to carry and operation. Is it okay to go? Should I buy it? Looking for your recommendations.

#### Ya’akov

Joined Jan 27, 2019
6,260
Welcome to AAC.

To decide if something is suited to a particular use, characterizing the thing is half the job, and secondary to characterizing the use.

What will you be using it for? What are the requirements for that use?

#### panther12

Joined Aug 3, 2022
3
Welcome to AAC.

To decide if something is suited to a particular use, characterizing the thing is half the job, and secondary to characterizing the use.

What will you be using it for? What are the requirements for that use?
Hi,

I will use it for to warn us of any unusual build-up of CO in our home.

#### panther12

Joined Aug 3, 2022
3
Hello Community,

I'm looking for a handheld co detector and after much research, I've found one but I'm confused with its specifications. Here are its details:
Handheld carbon monoxide (CO) detector with high accuracy sensor, pump suction type, selectable measuring range of 0 to 500 ppm, 0 to 1000 ppm, 0 to 2000 ppm, gas leak alarm with audible, visual and vibrating, compact size and light weight, long working time, easy to carry and operation. Is it okay to go? Should I buy it? Looking for your recommendations.

I think we use co detector for home use or there's something else for it?
I've read several blogs that focus on co detectors on the issue that I'm facing since one year. Is there anything separate for it?

#### Ya’akov

Joined Jan 27, 2019
6,260
Why would you think a health and safety focused CO detector would not be appropriate for your use? If an instrument is designed to measure something for a particular purpose—in this case CO gas for human safety—where does the question come in?

Also, why not use dedicated CO alarms, or CO/Smoke combination alarms, which are readily available and constantly monitoring?

#### Alec_t

Joined Sep 17, 2013
13,036
As CO is slightly less dense than air it tends to accumulate above head height in a room. If you're moving around the room with a hand-held sensor you are likely to cause room air to mix with and dilute any accumulations of CO, so the sensor might not then detect it. IMO, a static sensor high up on a wall would be more effective than a hand-held one.

Joined Jan 15, 2015
6,813
For general home safety I guess we figure:

What level of CO is toxic to humans?
As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible.
The above quote taken from here. A good read on the subject.

Next:
As CO is slightly less dense than air it tends to accumulate above head height in a room. If you're moving around the room with a hand-held sensor you are likely to cause room air to mix with and dilute any accumulations of CO, so the sensor might not then detect it. IMO, a static sensor high up on a wall would be more effective than a hand-held one.
Our home CO detector is a wall mount about 6 feet off the deck in an area close to the thermostat. Also an area where the ambient air is about as still as it gets. Now if you really want to know how good or accurate a CO detector really is you can buy calibrated gas to test units.

On an unrelated side note. I spent a good part of my career with global travel living in many countries. I worked for the US DoD. I spent 3 years living in the Naples, Italy area. Every winter despite warnings I watched US servicemen die unnecessarily. CO poisoning. While Naples is not brutal cold the winters are cold sometimes. Americans living in non-military housing would run heaters using propane or kerosene. Less ventilation newcomers who were not savvy could and too often would end up dead. You go to sleep and simply never wake up. This is why today I take having a good CO detector necessary.

Ron

Joined Jan 15, 2015
6,813
You can make one with Arduino and MQ-9 or MQ-7. You can add a display too if you wish. MQ-7 and MQ-9 both can detect carbon monoxide. You can follow this design: https://www.pcbway.com/project/shareproject/Mq_sensor_Base_Staion_f272b685.html
While the Arduino can be a fun experimenter / hobby micro-controller I have to strongly recommend against your link. While the MQ series of gas sensors are plentiful and inexpensive they are far from a good accurate sensor, especially where safety is a concern. If I were to put together something using an Arduino I would choose an MQ7, this is a MQ-7 data sheet. This data sheet is all over the web. It reads in part:
"The sensor’s conductivity is more higher along with the gas concentration rising. When high temperature (heated by 5.0V), it cleans the other gases adsorbed under low temperature. Please use simple electrocircuit, Convert change of conductivity to correspond output signal of gas concentration". The author's code sample will tell a user nothing as the numbers are not mapped to for example the PPM concentration of the measured gas sample. I can buy one of these for about $28.00 USD and feel much safer than cobble together something homebrew. Again, the link is fine for a hobby experiment but not something I would use as a safety device in my home. Ron #### bidrohini Joined Jul 29, 2022 66 While the Arduino can be a fun experimenter / hobby micro-controller I have to strongly recommend against your link. While the MQ series of gas sensors are plentiful and inexpensive they are far from a good accurate sensor, especially where safety is a concern. If I were to put together something using an Arduino I would choose an MQ7, this is a MQ-7 data sheet. This data sheet is all over the web. It reads in part: "The sensor’s conductivity is more higher along with the gas concentration rising. When high temperature (heated by 5.0V), it cleans the other gases adsorbed under low temperature. Please use simple electrocircuit, Convert change of conductivity to correspond output signal of gas concentration". The author's code sample will tell a user nothing as the numbers are not mapped to for example the PPM concentration of the measured gas sample. I can buy one of these for about$28.00 USD and feel much safer than cobble together something homebrew.

Again, the link is fine for a hobby experiment but not something I would use as a safety device in my home.

Ron
I got your point. Thanks for pointing out this matter. However, I only shared the link to show an idea about the PCB. The code was not actually my concern. Coding must be modified of course to show the results in ppm. Thanks for your valuable opinion and link. By the way, if we are to make something like the 'Kidde Battery Operated Carbon Monoxide Alarm with Digital Display' which sensor should we use? Do you have any suggestions? Thank you.

Joined Jan 15, 2015
6,813
I got your point. Thanks for pointing out this matter. However, I only shared the link to show an idea about the PCB. The code was not actually my concern. Coding must be modified of course to show the results in ppm. Thanks for your valuable opinion and link. By the way, if we are to make something like the 'Kidde Battery Operated Carbon Monoxide Alarm with Digital Display' which sensor should we use? Do you have any suggestions? Thank you.
OK, if I were to do this rolling my own and using for example an Arduino Uno I would do it this way. First we can try doing it with the MQ 7 since they are common and cheap. The sensor is a current output device so with that in mind I would try a 10 Ohm load resistance. Referring to the data sheet, The data sheet gives a range of 10-10000 ppm gas concentration. This is where problems begin. While the numbers are approximate depending on what we read they look about like this:

• 9 ppm (parts-per-million) is the maximum indoor safe carbon monoxide level over 8 hours
• 200 ppm or greater will cause physical symptoms and is fatal in hours
• 800 ppm of CO or greater in the air is fatal within minutes
OK, just for practice we need some numbers so we will use the link you provided. Since we are not a lab we will make a few assumptions.
"And the output voltage of the analog interface A0 increases with the raising of the gas concentration,A0 Output: 0.1-0.3V (relatively non-polluted)".
" he gas concentration being higher, the voltage can reach up to 4V".

So based on that and this gets very vague we figure it this way. Let's say 0.0 PPM is 0.2 Volt and 10000 PPM is 4.0 Volts. The only way to know the real truth is using calibrated gas mixtures. Those also need certified and come with a certificate.

Now let's look at the Arduino Uno analog in. We will also assume Vref is 5.00 volts. The Arduino A/D is a 10 bit A/D so we have 1024 bits or quantization levels or 0.0 to 5.0 volta becomes 0 to 1023 bits. The very best resolution becomes 5 / 1024 = 4.88 mV. The best resolution we will see is 4.88 mV. so back to our numbers 0.2 volts to 4.00 volts becomes .200 / .00488 = 41 counts. Then 4.00 / .00488 = 820 counts.

Here is the basic code sample:
Code:
int analogPin = 0;     // Signal to A0 pin
// outside leads to ground and +5V
int val = 0;           // variable to store the value read

int PPMValue = 0;

void setup()
{
Serial.begin(9600);          //  setup serial
}

void loop()
{
Serial.println(val);             // debug value

PPMValue = map(val, 39, 0, 827, 10000);
Serial.println(PPMValue);
delay (1000);
}
Here is what it looks like:

So we see the low and the high in bit counts.

We use the map function and we get on the high end

The problems become apparent. We have a 0 to 10,000 PPM range inside of 0.2 to 4.0 volt range and there is no way to get good resolution. All of this assumes way to much as to what real calibrated gas samples would yield. I'll post more later. Lunch is calling me.

Ron

Joined Jan 15, 2015
6,813
OK, moving right along. If I were building a CO detector rather than the 10 bit A/D in an Arduino I would be looking towards a dedicated 16 bit system. That gets us from 1024 quantization levels for a given range to 65, 526 bits. Bigger is better. I would also be looking for a sensor with a lower range like 0 or 10 PPM to maybe 1,000 PPM since we know a gas concentration of 800 PPM renders us dead in literally seconds. Next a good CO detection system will include both temperature and humidity compensation. Looking at sensor charts we know that the sensor output is not a straight line equation, we can live with slight non-linearity. However they are really subject to temperature shift and humidity shift so a good unit will have temperature and humidity compensation. Using an Arduino and what it has I would think about using a ADS1115 16 Bit A/D which is nice because it is not only 16 bit but offers up an I2C interface. Next I would add a DHT22 or similar to grab temperature and humidity and that also has an I2C bus capability.

If I want a good high quality sensor I will pay \$50 or more. The large scale manufacturers are buying maybe 500,000 pieces at a time. They are also buying a uC like an Arduino (Atmega 328P) at a few US dollars a piece in bulk. Since the chip does not need a bootloader installed and will go on their custom board.

Can I suggest a specific CO sensor? Nope since I never built a detector unit. I would likely start by contacting companies like Gas Lab in Florida (or equivalent) in your area (country) and talk to an applications engineer about sensors and then their sales people about buying thousands of sensors at a time for price break. Whoever sells you the sensors can also sell you certified gad samples and yo0u likely want 20% of range and 80% of range for your specific sensor. The gas will include certifications traceable to a standards lab. Manufacturing is a quagmire unto itself. A company with deep pockets can get started but for an upstart? Best wishes and good luck.

Can you just go buy a pile of MQ 7 sensors? Sure but you can see some of the problems above. A true product for market will have liabilities so it better be good and done right.

Least I get this poor thread anymore off topic I will let go at this. However, if you really wish to get into this I suggest you simply start your own thread.

Ron