This is my last week project: a Simple Yet Powerful Handheld CO2 Meter. SYPHCOM (name in progress ..)

The use for a portable CO2 meter is to be able to measure air quality in closed spaces (i.e. the office). The higher the number (usually above 1200~1500) the worst ventilation, which means higher chances to get
the Covid-19.

CO2 Meter Front View

With this is possible to know when is time to open the windows and ventilate.

It’s main guts are:

• Arduino Pro Micro, Leonardo Atmega32u4 based.
• SenseAir S8 LP CO2 sensor.
• Vintage HP HDSP-2000 ceramic LED matrix display, manufactured week 20 year 1984. NOS.

Back view of handmade CO2 meter

The capacitor stands for when the CO2 sensor does a read cycle (every 2s): both the display and the SenseAir S8 uses so much power that you can see the display and leds in the Arduino Pro Micro sighly dim off when powered from standard USB 0.5A when a read is made in the SenseAir CO2 Sensor. Without the capacitor, the arduino can’t stand for the display refresh and does a glitch in the display.

CO2 Meter glitch

Also there’s a UDN2981A source driver to drive the columns in the HDSP-2000 display and a small momentary press button with 10K pull down resistor to launch sensor callibration if pressed on powerup (use with caution!!).

CO2 Meter first working stage

The components that makes it portable are:

• Lithium battery charger (Like this one).
• Recycled Li-Po cell (250mAh)
• Pololu s7v8a adjustable step-up DC-DC (adjusted to 5V).
• Switch.

Making CO2 Meter porable with lipo charger and battery

I use the same components to make projects portables. The good thing about the pololu s7v8a is that it is both a step-up and a step-down DC-DC converter. This is handful if a project work 3.3v as it will give 3.3v always even if the battery is reading 3.0v. Unfortunally the recicled 250mAh battery is not much for the power needs so only lasts 30m on thi battery cell.

CO2 Arduino HDSP-2000 SenseAir Schematic

Code available here.

In the video the leds seems to be dimmer than they really are because of the high light, but actually they are pretty much visible.

Overall all makes a nice looking portable and easy to use CO2 meter and Covid prevention tool in closed spaces.

I’ve had this Omega2+ with minidock and soldered Oled SDD1306 lying around naked and decided to make a 3D printed custom enclosure for it.

Both halves snaps together to keep it closed.

I recently came across with moononournation’s libraries and code on Arduino IDE for ESP8266 and ESP32, which includes a demo of WiFi 2.4G air scanner.

As iOS user I can not have a WiFi Explorer so having this keychain hanging in my backpack was a nice idea. However moononournation did a tutorial and printer STL files for a TTGO VT7 v1.0 that is no longer available, so I designed my own enclosure for a TTGO T7 v1.4.

Link to the file here.

When I contracted my internet line with spanish ISP Pepephone they installed me a ZTE F680 router with embedded ONU/ONT. I didn’t wanted the router thing so I hacked it to achieve the ONU/ONT password and replaced with a classic ZTE F601.

Now I finally managed to get rid of the ZTE F601 by using a SFP with integrated ONU/ONT. The SFP I bought is DFP-34X-2C2 but DFP-34G-2C2 model should work as well.

DFP-34G-2C2 SFP ONU/ONT

This is an ARM v7 (ZX279125) running at 600Mhz and nearly 1200 bogomips, 32Mb integrated RAM and 16Mb of external (SPI?) flash (source) running linux ZTE flavour 2.6.32 in a SFP form factor. PDF

To be able to configure it there has to be some link in the optical connection, otherwise the SFP interface in your switch/router might not linkup and the SFP internal IP might not be reachable.

The default connection info is as follows:

• IP: 192.168.1.1
• VLAN: 1
• URL: http://192.168.1.1
• User: admin
• Pass: admin

In its web page you can configure PON settings and even routing mode. By default, there is no WAN connection (this means there’s no routing mode, only bridge with all vlans through the SFP interface port). You can make the SFP a router to route you house/office traffic by making a WAN connection but I prefer to keep it as bridge.

Once in the web configuration page we can configure LOID, SN and their passwords as per our ISP requirements:

DFP-34G-2C2 LOID web

DFP-34G-2C2 SN web

There is also telnet access with the following credentials:

• User: root
• Pass: Pon521

Telnet access is for linux advanced users and is not recomended to tamper with.

I bougth mine here: https://es.aliexpress.com/item/4000296796422.html

I have this SFP directly plugged to my C2960G switch and my router is a Debian virtual machine inside a synology DS218+ NAS which receivec VLAN20 traffic from the ONU/ONT through the switch and then the VM routers the traffic to VLAN1.

Is been long since the original proyect was made and I’ve been keeping it ‘naked’ until I got the guts to design a simple yet useful case.

STL can be downloaded HERE.

The original proyect was published in my blog here: http://karman.cc/blog/archives/746

Original Youtube video showing working navigation:

Here is the custom Hardware by Mike: http://karman.cc/blog/archives/861