MH-Z19 (PWM) CO2 sensor support package

[mbz4]

This item focuses on building a support package for the MH-Z19 CO2 sensor using PWM protocol.

Testing w/ this PWM Async library:

No results so far:

Tried several wiring configs:

Useful docs here:

• MH-Z19B @revspace.nl
• interesting multi-lib
• winsen official mh-z19b user manual

Pin	Definition
Vin	Vin
GND	GND
Vo	Analog output (0.4～2 V) or (0~2.5V)
PWM	PWM
HD	HD (zero calibration, low level lasting for over 7s under low level is effective)
Rx	UART (RXD) TTL Level data input
Tx	UART (TXD) TTL Level data output

[mbz4]

PWM Async example working:

Testing w/ exhale on-to sensor:

On to preparing iotempower driver draft...

[ulno]

What prevents you from using the built-in pwm functionality of IoTempower? This would then allow to run on all esp32 and esp8266 platforms?

[mbz4]

What prevents you from using the built-in pwm functionality of IoTempower? This would then allow to run on all esp32 and esp8266 platforms?

not sure mhz19 supports writing over pwm
docs show this PWM output definition for ppm measurements:

will test w/ native iotemp pwm library first, setup.cpp:
pwm(CO2, D2, 2000); ... again, doubt it supports writing over pwm unless undocumented

[ulno]

ah it is for reading pwm - not writing Reading might be impossible until the buffered async reader works - so you might need to help me fix that one first. But all depends on timing. So the serial communication port is just bogus and useless?

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[mbz4]

@ulno pwm(CO2, D2, 2000); gave this:

ah it is for reading pwm - not writing Reading might be impossible until the buffered async reader works - so you might need to help me fix that one first. But all depends on timing. So the serial communication port is just bogus and useless?

ok

i figured i'd try w/ PWM since serial also unsupported
guess one thing at a time, will push back to Todo/Backlog

Do you have an open issue already for async pwm reader?