Seed Grove Gas Sensor(MQ2) module. What does the chip do? - Page 1
Forum section: electronics / projects

author: 741
author_rank: Frequent Contributor
timestamp: July 19, 2019, 09:36:19 am
content: I have one of these modules, and I am interested to know the function of the 6-pin i.c, whick looks like SC-70/SOT-323, (marking "19AHK"), located on the back of the PCB.The sensor heater needs 5V +/-0.2.The supply to the PCB is listed as 5V. This surprises me because the chip "looks like" a switch-mode regulator. Maybe it is a SEPIC type, and I can feed in VDD under or over 5V? I found a circuit diagram (http://www.highcube.org/files/Gas_Sensor_Schematic.pdf) but not a chip part number.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 19, 2019, 02:45:56 pm
content: I don't see any IC on the pictures though:https://www.seeedstudio.com/Grove-Gas-Sensor-MQ2.html* perplexed *

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 19, 2019, 03:28:34 pm
content: Could that be a boost converter for a 3.3V version?

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 19, 2019, 03:53:33 pm
content: Maybe a version that's not sold anymore, or something.Anyway: judging by the schematic you provided, the capacitor between the SW and OUT pins would IMO suggest a SEPIC indeed. I couldn't find this IC based on the SMD marking you gave though.

author: 741
author_rank: Frequent Contributor
timestamp: July 20, 2019, 08:23:43 am
content: I see the back of the PCB is just tracks on the image. The one I have has the same "SKU" 101020055 but has PCB v1.5.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 20, 2019, 02:13:35 pm
content: I see. Looks like Seed's web site is not up to date as they are only showing v.1.3b!No documentation talks about it either. Seed sells undocumented stuff?I actually only found the schematic you posted for the MQ5 version. We can assume the power supply section would be the same. There are Eagle files too, I opened them, and this is the same as on the PDF: absolutely no reference for the regulator IC. Both the symbol and PCB layout show a SOT23-5 package though, and not a SOT23-6. What a mess.Seeing your picture though, I think the marking may be 9AHK instead of 19AHK (the 'I' being a bar that shows pin 1's side IMO). I didn't have more luck finding the reference from this marking though... it would probably be best to directly ask Seed's support? (Unless they have as poor a support as their documentation?)

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 20, 2019, 05:06:35 pm
content: That does appear to be a boost converter for the 3.3V version.

author: floobydust
author_rank: Super Contributor
timestamp: July 21, 2019, 02:07:24 am
content: Winsen gas sensorsthe majority use a heater resistor. It's a high power load, 170-200mA at 5V.MQ-2 flammable gas sensor uses 172mA at 5V for its heater.MQ-7B CO sensor needs a high/low heater where high heat (5V 172mA) burns off impurities and low heat (1.5V 52mA) to take a reading.The problem is the Seeed Studio"Grove Connector" shieldfits on an Arduino Uno and has a 3.3V or 5V switch for VCC to who knows.So using 3.3V power, the gas sensor and heater need 5V so there is a need for a boost-converter. The IC smt marking code I9AHK is SOT23-6, Foster Semiconductor but no datasheet on it.Either way I would expect the main board voltage reg to get overloaded from the high drain, up to ~325mA with a 3.3V feed.The module it's not a good design, it should take raw 9V or something in on another connector. No schematic for the shield either.