Homini Complete Room Sensor Module?

[Samuel235]

Another little bit of progress. I'm really struggling with time at the moment, had another 15 minutes to get some schematics done today. The power circuitry is coming along now, just the external programming power to sort out.

[Samuel235]

And the first of many to arrive is the Figaro Carbon Monoxide sensor.

[Samuel235]

There is a topic (here) being discussed regarding the use of IR LEDs and receivers to determine the circuit needed before i get some hardware. I will be ordering parts before the end of this week so if there is no suggestions i will be purchasing materials to trial and test the best setup for this.

Another subject to be discussed is powering while programming. I do propose to have the module fully powered up while programming and debugging to allow the monitoring of the sensor readings to allow debugging methods to be carried out with the best precision possible. However, this means that we need to have some sort of external connector on board to provide power while we're plugged into our programming systems. There would be two ways to go around this, one will allow full powered up mode for the board and the other will just allow power to the MCU and Radio while programming.

1. Add external connector (I'm feeling maybe a USB Mini-B simply due to its popularity). This would then power up the board completely while programming is completed, allowing full debug viewing through serial monitor.
2. Add a jumper on the power line of the MCU and Radio module to allow the programmer to provide enough power for the MCU and Radio while programming. This would mean that the only debugging we can do through the serial monitor would be MCU and Radio related.

Any input would be greatly appreciated.

[Samuel235]

The remaining parts have been ordered to get the prototyping under way. Plan of attack will be:

1. Prototype each circuit on breadboards separately to make sure each is working as intended and giving the correct results.
2. Combine all of the circuitry apart from the powering options onto breadboard as one working module, get some software written up with the help of a few guides, tutorials and a fellow member of our community being interested in joining me on this module.
3. Generate PCB designs and have them manufactured.
4. Test the AC/DC conversion circuitry for a few weeks while the PCB is on order.
5. Receive the PCBs and populate with the breadboarded circuit.
6. Fashion some sort of enclosure, hoping to have purchased a 3d printer by then.

Does anyone have any experience with a prusa I3 3d printer?

[Samuel235]

Infrared smoke detection circuitry has changed now. It is now going to running as a single IR LED coming from the MCU pin since we do not need any sort of frequency for a newly implemented photo transistor rather than the IR receiver. However, I may have it coming through the 555 time to just turn the LED on for 1 second every 10 seconds or so to stop excessive power draw for no reason. If it detects smoke 10 seconds later than it was first present inside of the chamber, that is fine for the needs of a smoke detector. In my opinion. If you feel otherwise please state so!

I have chosen to do this outside of software to save having to do multitasking in software. This way all that the MCU needs to know is if the photo transistor has detected any smoke, which we can monitor on every loop of the MCU.

I'm still not sure whether to go down the 555 timer route for the siren to sound or to use some soft of PWM function on the MCU. The way i'm thinking is that if we go down the timer route it releaves the MCU of another job and therefor it doesn't have to stall in the loop while its powering the buzzer. However, I personally feel that if the module detects smoke, the last thing that we will be worried about is if its taking readings from the other sensors. But then that would be a cool feature to be able to look back at the measurements on.

[Samuel235]

I would like to separate the 3v3 to the MCU and the radio from the rest of the components, this way i can safely power the MCU and Radio with the programmer when uploading software with just the programmer attached. But i want it so if it is powered externally i would like the board to use that power.

I'm proposing the use of diode(s) on the power lines in between the MCU and radio to stop the flow going out to the rest of the circuit. I'm hoping that by using the diode(s) to stop the 3v3 from the programming feeding to the whole 3v3 circuit it will not draw enough current to damage the programmer and the PC. By using this diode i believe that the MCU and Radio will draw the strongest voltage of whatever is connected, if nothing is connected other than the FTDI or ISP programmer then it will only power on the MCU and Radio. A quick hand drawn sketch below:

Do you feel i'm going about this the correct way rather than separating the MCU and radio with a hardware jumper? One less thing to care about while programming in my opinion.

[Samuel235]

And the prototyping begins! Pretty much all of the breadboard versions of parts have arrived and i will be prototyping each circuit individually then wrapping it all together. A few mods need to be done to the light sensor to make it breadboard friendly but its doable!

[Dwalt]

@Samuel235 Did you source a breakout version of the OPT3001? It is hard to find.

[Samuel235]

@Dwalt, unfortunately no mate, i will need to solder leads to the pads for prototyping needs 😞

[Samuel235]

@Dwalt, this is the one i was looking at but then decided to just solder leads to the sensor itself instead. If i were to get some breakout boards made and maybe solder the sensors on myself, i wonder what the demand would be like, just thinking if its worth doing to help us out.

[scalz]

@Samuel235
wow, soldering leads on opt3001!
That won't be easy I think, I hope you have very very thin wire and iron! and still not sure...it's a small 2mmx2mm, and delicate, I think you can easily skip this step, it's a simple i2c sensors, no surprise...or maybe you will waste some money if no good tools. I prefer to design evalboards than soldering leads on tiny dfn (doable sometimes but very tricky), it's easier to breadboard and reusable ;)

@dwalt
One thing I could do is to release some evalboards I have designed. As it's small, it's cheap at oshpark...I have already made one for opt3001, and have some for others sensors, boosters, buck, buckboost..but I'm little busy actually!
But if I do this you would still have to solder it on pcb, or I should look at the new pcba service...

[Samuel235]

@scalz It seems you have beat me to it with creating a breadboard friendly breakout board for them. If you're confident in the use of this sensor could you double check my schematic and let me know if i have connected it correctly please?

I might get a breakout board for breadboard friendly use designed if you're too busy yourself. Not sure how much call there is for them though.

[scalz]

@Samuel235 it's few months I did this. like I said I make breakout boards for testing, so I have a small collection now!
This was a breakout with opt3001 and si7021, regulator onboard (with smd jumper to power directly with 3.3v), and few pullups. Same pinout as common chinese sensor boards + interrupt pin for ambiant light:

I will upload at openhardware asap ;) that's lot of things to upload lol!

[Samuel235]

0_1462204198812_capturedvideo.MOV

Currently prototyping the optical smoke sensor. I have the buzzer circuit working fine, i also have the circuitry for the optical sensor working. But i can't get it to reflect its IR Light off of smoke and onto the phototransistor.

Waiting on some feedback regarding the Figaro sensor and using with a mosfet from another forum, will post updates when recieved.

[Samuel235]

UPDATE!

Figaro TGS5042 Electrochemical Carbon Monoxide Sensor - Working.

Prototype work complete for the carbon monoxide sensor, using the OP AMP style measurement system which includes just 1 Resistor, 1 Capacitor, an OP AMP (Model featured above) and the Sensor itself.

Improvements?

Currently reading through the appnotes given by Figaro for this sensor, heck its a long but interesting read! While it would be great to run with this current setup of 4 components for this circuit, there are things like polarity precautions on the sensor to be taken into consideration. So, with this being said, I'm currently in the process of maybe adding another OP AMP or just a resistor to the keep the sensor shorted out incase the device is isolated from power for any reason. Then there is the accuracy to take into account...

Question

I'm very tempted to amplify the sensors output enough to get to a PPM that is dangerous and then send the alarm off, meaning that at 5v out of the OP AMP it would be enough to send the sensor off and therefor we have a much a higher accuracy between safe and dangerous readings but it would not be able to go over what would be deemed as 'unsafe' levels. OR would you rather me have it so it can read to quite high CO levels despite the 'dangerous' level being around 2/3v out rather than 5v? So, would you rather a high range of readings but lower accuracy or a more accurate but lower range, still enough to detect the dangerous level?

I will be posting images and schematics for the completed parts of the module ASAP for you guys to check out.

[epierre]

@Samuel235 said:

IONISATION METHOD

I'm very tempted to just use a MQ2 sensor with its circuit on my board rather than a separate board.

MQ2 consumes a lot of energy as every MQ. Also don't rely on your life on this kind of sensors...

Have you tried the bottle of perfume around ?

[Samuel235]

@epierre, you're correct in thinking they are pretty high energy and inaccurate. Would you advise any other sensor at all for this method? I'm currently working on my own custom made optical smoke sensor unit using a IR LED and Phototransistor, but i would like a ionisation method sensor as well.

[epierre]

@Samuel235 the ionisation for smoke ensor was the old method with radioactive elements.

maybe a particle sensor but you would need to simulate a smoke to set levels, compared to a dusty room I think. Maybe a barbecue test (beware of greasy dusts !)

[Samuel235]

I'm encountering some issues regarding my MOSFET enabled PIR sensor. I'm currently using a n-channel MOSFET in a high side switching setup. The issues that i'm getting are that while the gate is pulled low, the sensor is alternating between a HIGH and LOW output, false triggering and when the gate is 5v, high, it is not powering at all.

I'm attempting to get my hands on a p-channel MOSFET to put in a low side switching application to attempt to fix this. I'm assuming that its acting like this because its producing false triggers while the GND is not connected through to ground. I've tried to connect a 10k resistor from drain to gate to eradicate the 'floating' connection, no hope either. If anyone has a link to any p-channel MOSFET that i can get in the UK that would be much appreciated.

[Samuel235]

There is currently discussions going on over on the forums at allaboutcircuits.com with myself and a few others regarding this OP AMP and the sensor output readings. I thought i would let you guys know in case you're interested in following the build.