Smart Sensor AS8700A Carbon Monoxide Meter Teardown

AS8700A Meter
AS8700A Meter

Here’s a handy tool – a Carbon Monoxide meter that range to 1000ppm, with immediate update. Very handy for checking emissions of fuel burning appliances. There’s a large LCD on the front for displaying the reading, and the ambient temperature. There is a user-settable alarm if a high concentration of CO is detected in the air, and High/Low hold modes.

Rear With Belt Clip
Rear With Belt Clip

The rear of the unit has a belt clip, and the battery compartment which holds 3x AAA cells.

Sensor Cap
Sensor Cap

Under the decorative cap at the detector end is the sensor module itself, with a thick plastic cap covering the actual sensor.

CO Sensor Cell
CO Sensor Cell

The CO sensor cell is one of the smallest I’ve seen, a NAP-505 from Nemoto. Easily replaceable with a soldering iron if required after the quoted 7 year lifespan.

CO Sensor Module
CO Sensor Module

Connections to the main PCB are done through a small 3 pin connector & wiring loom.

Main PCB
Main PCB

Removing the 3 screws from inside the battery compartment allows the back cover to be removed. The belt clip screws into a pair of brass inserts, which is a nice touch. The sensor connects to the JST connector at the top of the boat.

LCD
LCD

The front of the PCB has only the buttons & the LCD itself, which is backlit with a pair of green LEDs.

Microcontroller
Microcontroller

There isn’t much to the actual circuitry. There’s an STM8 microcontroller, and a TP5532 zero-drift op-amp to deal with the sensor front end. Rather nicely, every single one of the test points is labelled! Handy for any hacking that needs to be done.

2 thoughts on “Smart Sensor AS8700A Carbon Monoxide Meter Teardown

    1. The Engineer says:

      Hi Antony,

      It does indeed work, however I’ve not managed to get around to testing it with a bottle of calibration gas I have lying around yet!

      Cheers

      Reply

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