Homini Complete Room Sensor Module?

[Samuel235]

@scalz, it is a good thing i didn't think it was that simple and why i don't like using that method for the adc of voltage monitoring. From the other topic on here with the voltage monitoring you can see i was having a lot of issues with understanding the theory behind it. I don't like to do something because that is how it needs to be done, i'm the person that actually wants to underatand the reason and method of doing it and why.

Normally, old school is the best way to learn. The new methods are mostly better, but for the method the old school way is better. So thank your father!

I don't think these boards of mine will need the type of intricacies like you're having to do, but i'm always learning the methods and theories on why they need to be done like that.

[scalz]

cool, I think you will get this sensor working...even if now you don't need all these advice, maybe in future you will remember about it when needed ;)
humm, maybe at lunch I will try to make a basic and small childboard for this one..so I will be able to add it to my pir multisensors..very tempting, and so I would be able to help you..

[Samuel235]

@scalz Oh, no doubt about it i need this advice and i thank you for it. I definitely need it as i wouldn't be asking here ;)

From my findings i need a fair bit of help on the sensors them selves and their calibrations too.

A daughter board for which board? I'm intrigued to see what you come up with. I'm planning on having this split in two boards stacked on top of each other inside of the enclosure. One for power distribution and one for data and sensor connections.

[sundberg84]

:+1: Gas/Smoke/Temp/Hum/Light/Motion in one would be great!
For me its tempting when you are aiming at a celing mounter 3d case like a smoke detector.

I hope it can all be fitted inside a normal size case - you see, there are other aspects of it like esthetics according to my wife.

[Samuel235]

@sundberg84, i'm with your wife here. It must look appealing to the eye, hense why i wanted in a custom enclosure fashioned like that smoke detector/sprinkler image i included. Since its something being mounted on the ceiling, its got to be subtle and not in your face ugly.

I'm glad you're very interested in following this production, thank you 👍

[scalz]

@sundberg84 nice catch :)
@Samuel235 : this one (I showed you in post above) http://forum.mysensors.org/topic/2951/my-mysx-multisensors-board
On daughter board, the sensor would be on the left side of the pic because others sensors are on right (little dirty hack but like this I could have everything I need per room..depending of the sketch size too). I would add mosfet to cut power on daughterboard etc...a thing to try, I just need to make a tiny daughter board, oshpark and voila!

[Samuel235]

@scalz, ahh sorry i forgot you linked that. Yeah that would make that a nice little setup!

[scalz]

@Samuel235 : here what could look my small childboard...first pass, I will change few things before order it. 3.35$ for 3 boards at oshpark :) It could be smaller, it is because now I like/try to have everything ontop (but there are two smd jumpers on bottom), that made me hungry! time to eat :)
@tbowmo: here an idea for a childboard ;)

[Samuel235]

@scalz I like it! A quick side step, how do you make these 3D models? Are they generated by your eagle designs or do you manually build them in a 3d model program?

[scalz]

@Samuel235 thx. actually, I still use eagle 6.5, I know there are things in 7.x but not tried yet. so for the moment, sometimes I make my own model, or find some where I can..for 3d preview, google sketchup eagleup. So for pcb preview I use sketchup, for custom enclosure solidworks (I prefer it than sketchup) then I export box to sketchup (as I can't do the opposite). Have fun :)

[Samuel235]

@scalz, thank you. I'll spend many hours playing now ;)

[tbowmo]

@scalz

Nice :) I'm preparing a board with various sensor types on, that one could populate as one wishes..

[Samuel235]

@tbowmo, cool! Be sure to include the information or links in here for us to check out please :)

[tbowmo]

@Samuel235

It would be added as a MysX add-on module (have some space left on a panel, that I'm preparing)

[Samuel235]

@tbowmo now i'm even more intrigued 🤔

[Samuel235]

I'm still on the man hunt for the right sensor to use for air quality, I've narrowed my search down to two parameters to monitor; Carbon Monoxide and Smoke. If you guys would like to see any other gases being monitored please give me your feedback, this is all that i would want, but i have no idea of the other countries and their interests to gases. What about carbon dioxide?

So i have roughly chosen two sensors, the CCS801 for Carbon Monoxide and the MP503 for Smoke. I know there are a few sensors out there for smoke and to be honest, i'm yet to study those in comparison to the MP503 due to being very busy at the moment. Could anyone give any input on my choices here and if i should use another sensor out of the MP range from Winsen-Sensors for my smoke one? What about the Carbon Monoxide choice, that look good enough for you guys?

CCS801 - Carbon Monoxide:
Power Consumption: 1.8v 0.9mW (In pulse mode)
Rough Price without shipping costs: £5.49
Datasheet: http://www.ccmoss.com/sites/default/files/documents/CC-000015-DS-8-Datasheet for CCS801.pdf

MP503 - Smoke:
Power Consumption: 5v <300mW
Rough Price without shipping costs: £N/A at the moment
Datasheet: file:///C:/Users/Desktop%20System/Downloads/MP503%20(Ver1.4)%20-%20Manual.pdf

[Samuel235]

Sensor Choice

From further research, I have learnt that there are two main types of sensors out there; electrochemical and semiconductor. The information displayed below explaining each are extracts from Wikiedia.

Electrochemical:
Electrochemical gas detectors work by allowing gases to diffuse through a porous membrane to an electrode where it is either chemically oxidized or reduced. The amount of current produced is determined by how much of the gas is oxidized at the electrode,[3] indicating the concentration of the gas. Manufactures can customize electrochemical gas detectors by changing the porous barrier to allow for the detection of a certain gas concentration range. Also, since the diffusion barrier is a physical/mechanical barrier, the detector tended to be more stable and reliable over the sensor's duration and thus required less maintenance than other early detector technologies.

However, the sensors are subject to corrosive elements or chemical contamination and may last only 1–2 years before a replacement is required. Electrochemical gas detectors are used in a wide variety of environments such as refineries, gas turbines, chemical plants, underground gas storage facilities, and more.

Semiconductor:
Semiconductor sensors detect gases by a chemical reaction that takes place when the gas comes in direct contact with the sensor. Tin dioxide is the most common material used in semiconductor sensors, and the electrical resistance in the sensor is decreased when it comes in contact with the monitored gas. The resistance of the tin dioxide is typically around 50 kΩ in air but can drop to around 3.5 kΩ in the presence of 1% methane. This change in resistance is used to calculate the gas concentration. Semiconductor sensors are commonly used to detect hydrogen, oxygen, alcohol vapor, and harmful gases such as carbon monoxide. One of the most common uses for semiconductor sensors is in carbon monoxide sensors. They are also used in breathalyzers. Because the sensor must come in contact with the gas to detect it, semiconductor sensors work over a smaller distance than infrared point or ultrasonic detectors.

So while the electrochemical is the better of the two in terms of power consumption, they do required to be changed on average every 2 years. However, while that is a downside, you do have to re-calibrate the semiconductor type if its needed to remain the accuracy it did when installed. I'm not sure which would be better, to replace or to re-calibrate? One side of the argument is that the semiconductor range is much easily available, at least for the UK market anyway, and cheaper to purchase. But then you have the power consumption of the internal heater to consider, they reportedly get up to anywhere in the region of 60 degrees Celsius, this would cause issues for my temperature sensor (unless i some how shield my temp sensor off from the area of the gas sensors, possible to do with a custom enclosure.

---

I'm proposing that if we wanted to go down the route of the electrochemical sensors, we could mount these on daughter boards and mount these either ribbon cables or pin headers to then enable us to swap out the sensors with ease in the future. I'm tempted with the idea of having the daughter board that holds the sensor externally accessible, but inside its own enclosure that attaches to the main enclosure so you would just pull off a side enclosure and either replace the whole thing or replace the sensor board inside of this side enclosure and then push the side enclosure back onto the main enclosure. Interesting prospect. By the time I get some feedback i might be able to use a 3d modeler to possibly mock up some 3d sketches of what i mean.

But then the semiconductor type is a simple calibration using a 'calibration test' that you purchase from the manufacturers and adjust to meet the known concentration of the given gas. This can take several days depending on the heat-up time. I do not like the sound of this. The whole idea of this module is to be ease of use and to leave it running on its own without worrying about if its accurate or not.

Current Thoughts

As you can see i'm really starting to favor the low power, high cost, hard to find electrochemical sensors. However, like I've stated many times over, they're proving very hard to get my hands on. If anyone knows of any, please link them in here.

What're your thoughts on the sensing sides of things, would you rather:

1. Low component cost, higher running costs, higher maintenance. Electrochemical.
2. High component cost, low running costs, possible high maintenance. Semiconductor.

[Samuel235]

Due to the electrochemical sensors being so hard to get my hands on it would seem i have very little choice but to order off of AliExpress.

I have found a decent price for the ME2-CO here: AliExpress.

I'm very tempted to get some normal MQ-7's just to try them out or even the high quality Figaro TGS2442's, but i just don't like the 24-48 Hour warm up period on those, that coupled with the power consumption is just putting me off of the 'normal' Semiconductor types. However, they are pretty cheap compared to the Electrochemicals.

Datasheets:

ME2-CO
MQ-7
TGS2442

Questions

1. Could i get some of your opinions on this, do you feel i'm being a little over the top with the power consumption issue?
2. Whats your thoughts on the warm-up times? Don't forget they do apply when it comes to calibrating the sensor, you would have to make the calibration alterations, then wait another 2 days for it to warm and settle before testing again....

[Samuel235]

I've nearly compiled the full list of sensors for this module as follows:

• Carbon Monoxide Sensor - ME2-CO
• Smoke Sensor - 1 IR emitter & 1 Receiver to create a photoelectric sensor
• Humidity & Temp Sensor - SHT21
• Motion - HC-SR501 Module
• Light - APDS-9300-020

I'm now left with sourcing a low cost buzzer for this module and some LED's for status updates for debugging and notifications of working states. I'm tempted to have the device sleep with the smoke and carbon monoxide sensors connected to interrupt pins if possible and only have the motion sensor detecting in certain situations such as night time and alarm enabled status maybe. Its not something i want on permanently if not needed due to the current usage in busy areas such as hallways and main rooms, it will draw power consistently and the idea is to keep the power consumption down as low as possible.

As usual I appreciate all thoughts and suggestions for this and welcome them to the comments. I'm not the best at software/coding so if anyone would like to help in that aspect, i wouldn't say no when the time comes to do such a task. It will be a few weeks before that happens though as i'm yet to design the hardware. I need to purchase a few tools before this can go a head, including a hot air reflow station and a 3D printer for the custom case.

[Samuel235]

With all the parts for this module on order now, just for a discussion;

1. What would you hardware guys rather have in terms of ambient light sensors? Digital (I2C device) or Analogue that performs like a NPN transistor? What is easier to configure/setup? (APDS-9300-020 OR TEMT6000X01)

2. Low power motion detector daughter board or HC-SR501 Module?

3. I'm yet to make my voltage supply schematic, i'm looking at a few topics around here regarding this, does anyone have any information to educate me further in this area, power supply is not my most confident area ;)