Circuit diagram of SDS011 PM sensor

Is there a circuit diagram available for the SDS011 sensor like the one for PPDns given here?

I have a number of broken SDS011. Some of them are known to be broken by reversing + and -. Maybe it is possible to fix them easily?

Haven’t found a schematic but the MCU appears to be a STM32F038K6 so power might not be connected directly to the MCU,

Have to take down a sensor today so will have a look at the power supply side of things if I get a chance.

Found this interesting information with some internals:

This is for the plant power device but it gives an idea, it’s probably the power regulation that’s blown as he said he’s repaired one by replacing a low dropout regulator.

U24 marked DK7y is a LDO and probably what has given out the magic smoke.

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You might want to replace the 5V6 zener diode and the 68uF capacitor at these locations too image When one of my SDS011s or someone can supply a dead SDS011m I’ll have a go at doing a full reverse engineering.

I don’t think this is a capacitor :slight_smile:
If I am not mistaken D17 is a Schottky diode in SOD-123 package. Marked as SL {YM}. Part number probably 1N5819HW.

Directly below you will have D30 Zener diode in SOD-123 package. Marked as W8 so it may be BZT52-C5V1.

Than J34 - fan terminal.

C61 - 20µF capacitor

And E2, E3 and E4 in fact may be UDZ5V6B Zener diodes in SOD-323 package. Marked as W8. Exactly as you described.

U24 - marked as DK 8P - LDO in SOT25 package.
Probably AP131-25W

There are two components I have problem with identifying:

R4 - Photo Sensor with size 4,5 x 4mm
Marking on botom 7C 23.

U1 - Transimpedance amplifier (TIA)
8-pin, 3x3mm
Makings on top: TI 13F6
On bottom: 87A P2XR

Designation Type Package Marking Part number Value Remarks
R4 Photo Sensor 4,5 x 4mm From bottom 7C 23
C1 Capacitor 0603
C2 Capacitor 0603 Not populated
C3 Capacitor 0603
C4 Capacitor 0603
C5 Capacitor 0603
C7 Capacitor 0603
C12 Capacitor 0603
C14 Capacitor 0603
C32 Capacitor 0603
C50 Capacitor 0603
C51 Capacitor 0603
C53 Capacitor 0603
C58 Capacitor 0805
C59 Capacitor 0805
C61 Capacitor 0603 20µF
C71 Capacitor 0603 Not populated
C72 Capacitor 0603
D17 Schottky diode SOD-123 SL {YM} 1N5819HW
D25 LED 0805 Red LED
D30 Zener diode SOD-123 W8 BZT52-C5V1
E2 Zener diode SOD-323 BC UDZ5V6B
E3 Zener diode SOD-323 BC UDZ5V6B
E4 Zener diode SOD-323 BC UDZ5V6B
J26 Terminal Laser terminal
J31 Terminal XH-2.54-7P UART interface
J34 Terminal Fan terminal
R1 Resisor 0603 01F 10MΩ 1%
R2 Resisor 0603 472 4,7kΩ
R3 Resisor 0603 01B 1kΩ 1%
R7 Resistor 0603 302 3kΩ
R8 Resisor 0603 511 510Ω
R9 Resisor 0603 01C 10kΩ 1%
R10 Resistor 0603 30X 20Ω 1%
R16 Resisor 0603 30E 2MΩ 1%
R28 Resistor 0603 01D 100kΩ 1%
R47 Resistor 0603 224 220kΩ
R78 Resisor 0603 01C 10kΩ 1%
R82 Resisor 0603 01C 10kΩ 1%
R83 Resistor 0603 30X 20Ω 1%
R84 Resistor 0603 01D 100kΩ 1%
R85 Resistor 0603 512 5,1kΩ
R86 Resisor 0603 30X 20Ω 1%
R87 Resisor 0603 30X 20Ω 1%
U1 TIA 8-pin 3x3mm Top: TI 87 13F6 / Bottom: 87A P2XR Transimpedance amplifier (TIA)
U17 MCU UFQFPN32 5x5mm F031K6 STM32F031K6 Main MCU
U22 Transistor TSOP-6 HOYA 14 AO6800 MOSFET
U24 LDO SOT25 DK 8P AP131-25W
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Here is some work in progress: NovaFitness SDS011 V2.18 Reverse Engineering – Google Drive

You will find there BOM, IC datasheets, photos and additional resources.

I would like to measure exact values of all capacitors and identify all components. Than I will draw schematics in EasyEDA, and design prototype PCB. I will add some new features to this board - like ability to flash own firmware.

With deep understanding of construction and proper schematics repairing broken SDS011 should be easy. Also we could experiment with improving this device. And maybe in future NovaFitness would like to talk with us - right now (despite of selling thousands of theirs sensors) they treat us like idiots. Which is unfortunate.

There is one guy in our local community who is doing quite the same work. Forwarded information to him. Hope he will manage to register on the forum and add something valuable.

U1 seems to be TLV2376IDG in VSSOP (8) package

Got two units marked as: TI 87 13F6, TI 01 13F6

13F6 is the same across different years.

I tried to reverse old one. In that device V2-008 they use OA TI OPA2376 and LDO TX6211B.
TLV2376 seems almost same characteristics.
Also draw some schematic in EasyEDA for it and measure signals after first stage TIA and second stage amplifier, there are very noisy with 100 mV needles with 5 ms period, I think because they didn’t use rc-filter and signal buffer before STM’s ADC.

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I wounder is it possible to load new firmware to STM processor over standard connection of SDS? Or it must be done via connector pad located on the PCB?

The biggest drawback of the closed source FW is that you don’t know how it works. If the measurements are raw one or some sort of a math model… If it could be “opened” then there will be more information…

Yes. I think “rx”, “tx” and “nc” as boot0 are enough for it.

Indeed. It might be possible.

This is exactly what I want to do. I will also replicate PCB to make a open source version with experiments in mind.

I’ve just measured values of capacitors.

Designation Package Value Measured value
C1 0603 ??? ???
C2 0603
C3 0603 100nF 120nF
C4 0603 10nF 9nF
C5 0603 100nF 120nF
C7 0603 100nF 120nF
C12 0603 100nF 120nF
C14 0603 10µF 8,7µF
C32 0603 100nF 120nF
C50 0603 100nF 120nF
C51 0603 4,7µF 4,53µF
C53 0603 100nF 120nF
C58 0805 20µF 20µF
C59 0805 20µF 20µF
C61 0805 20µF 20µF
C71 0603
C72 0603 10µF 8,6µF

I didn’t got any readings on C1 capacitor.

I think capacitor in feedback of this TIA will be 100-1000 pF, 300 pF most plausible.
I’ll try to desolder and measure.

Do you want make a better one sensor or fully compatible board?

We will see :slight_smile: I always want to push designs to it’s limits. Understanding design is one thing, improving another. I would like to try write own firmware for SDS011.

STM32 power rail runs on 3.3V. LDO TX6211B and AP131-25W have similar package markings, but I don’t think we found exact LDO used in SDS011.

“DK” in case of TXSemi TX6211B means 3.0V variant link

“DK” on AP131 means 2.5V variant

So I don’t think we know exact part number and manufacturer of this LDO.

In my device there are 3.3V “DE=A1D”, and I think this part is not very important.
Most important to understand is there any calculations with amplitude of impulses or stupid counting impulses above some level at first and second stages of amplifier and produce pm10 and pm2.5 respectively.
But stm could work from 2.0 to 3.6 volts, OpAmp too, main question is laser and how it works from different voltages.

Perfect! I will put TX6211B in schematics. I think I will read a datasheet to be sure that this part is not very important and may be swapped for another with similar characteristics.

So basically it looks like poor and noisy design which works only because of proper calibration.