PM reads -1 at all times

[K_Chen]

[EDIT - SOLVED - I removed a solder bridge between pins 5 and 6 of the PMS5003 cable socket, this some how solved the problem despite not being connected to anything.]

The PM2.5 is reading -1 on my DIY AirGradient Pro, PCB v 3.7. The dashboard doesn’t report a value at all. I have tried installing the software manually through the Aurdino IDE as well as through the web browser.

I also have a presoldered AirGradient Pro, PCB v 3.7 that I put together back in May. So I’ve done some testing as follows.

Kit 1

• May D 1 Mini
• Dec PCB
• Dec PM2.5
  Result: PM: -1

Kit 2

• May D 1 Mini
• Dec PCB
• Dec PM2.5
  Result: PM: -1

Kit 3

• Dec D 1 Mini
• May PCB
• May PM2.5

Result: PM: 9-11

Kit 4

• Dec D 1 Mini
• Dec PCB
• May PM2.5

Result: PM: -1

Kit 5

• May D 1 Mini
• May PCB
• Dec PM2.5

Result: PM: 6-9

I have tested the DEC PCB and have connectivity from the left most pin to VCC, the second leftmost pin to GND, the 4th to D6 and the 5th to D5.

[Achim_AirGradient]

A few things to check:

• What PM cable do you use? (Please note that PCB v 4.2 and v9 uses cross over PM cable. Previous versions uses a normal cable)
• Does the fan inside the PM module spin up?
• Is the cable plugged in deep enough in the socket?

[K_Chen]

• Normal as far as I can tell
• Dec PCB: No [Edit: Correction. It makes an aborted starting of the fan spinning ten stops ten starts again. about half a second]; May PCB: Yes.; checked with both d1 minis.
• See photos, also checked connectivity with multimeter with PM2.5 unplugged.

[K_Chen]

[Achim_AirGradient]

Thanks for the photos. Do I understand correctly that the issue has been solved?

[K_Chen]

As far as I can tell. the issue was a solder bridge between these two pins. Maybe it connected TX to the PM2.5 sensor’s case.

[Achim_AirGradient]

Yes that could be. Great that its solved.