Question about Microwave Presence sensor

I am trying to understand how this Microwave presence sensor actually works. I have watched Big Clive’s video on it, however, mine seems to act a little different. Its almost like its a lot less sensitive.

Basically, mine pretty much only activates, or goes high on the output pin, when I almost have my hand like, 2mm away from where the boards antenna is. Moving in the room doesn’t work or anything. It did seem to do this before, but only for a short amount of time. I am feeding it 5v from an esp32, so it’s not being underpowered, or overpowered.

If anyone has any suggestions, that would be greatly appreciated. If more info is needed, please let me know!


Hi @Maddie188056
Welcome back.

Full disclosure I have not used this device before but I did notice this on jsdesbonnet’s github deep dive.

Above I red squared the relevant section.
I think he’s talking about this circled section of the PCB.


Does your board have a resistor soldered into that those R-GN pins?

Pix :heavy_heart_exclamation:

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No it does not. When it says 7 metres, does that mean it only detects motion 7 metres away from it (like around the 7m range) or anything from 0 metres, to 7 metres?

I think the author means ranging from 0 meters to 7 meters (exclusive). :thinking:

Hmm that would imply you should be able to get HIGH outputs at the full range of the device.

I’m not sure this is relevant, but what do you have attached to the CDS pin?
That’s apparently used in lighting applications.
Have you left CDS floating or did you tie it to something?

Maybe there is a short at the R-CDS pins.
If some rogue solder or copper has bridged the pins for instance it would set the threshold so high almost nothing would count as a detection.

Just some thoughts :slight_smile:

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Thank you for your response. Clears up the question. None of my contact pins on the back are touching anything. I am curious though, should I leave the CDS pin floating, or pull it to ground/3.3v/5v to disable it?

Hi Maddie
Interesting little device. I note from the description this is a “Doppler” radar so as such the target will have to be coming toward the unit or going away. If stationary it will not detect.
I also note the statement.
“Unlock the ability to sense people, animals and other water-y beings through walls and without any light (including infra-red)”
I would question that. No radar I have had dealings with would do that. My main experience is with pulse echo (or what has recently been called “Time of Flight”) types but any signals that get around walls would be so scattered as to be pretty useless for radar. Also the reflected signal would be very minute if any existed.
Cheers Bob

I’m really struggling to find an official datasheet on this online.
Even the author of the github repository says he can’t find much on it.
So weird!

I did manage to find this schematic on here

And this schematic here

Both of these imply to me that the CDS is tied to the ENABLE pin of the PCWL9196 integrated circuit chip

Both these datasheets agree that the ENABLE pin of the PCWL9196 is active HIGH.
It’s tied to 3.3v through some 1 mega ohm resistors but it’s also tied to ground via a … I think that’s a photo-resistor(?), controlled by the CDS pin.

Look, I’m new to this hobby, and there are some other people here that might need to fact-check me here. The way I read this is that the CDS pin needs to tied HIGH in order to ensure the internals are enabled and the board works.

The numbers online say you only need 0.7v or higher at the CDS to ensure the ENABLE pin stays HIGH. I can’t find something official looking to back that up.

Two parallel 1,000,000 ohm resistors is equivalent to one 500,000ohm resistor which is inline to power. That seems to line up, it implied the resistor to ground is 100000ohms. That’s a nice round number you’d find in a commercial board I guess. :man_shrugging:

( 0.0070ma = 0.7v / 100,000ohm ) > ( 0.0066ma = 3.3v / 500,000ohm )

… hmmm gosh I’m actually not sure about myself here.
Maybe someone else with more experience will chime in and correct me?
(nothing gets you quality information faster than being wrong on in internet :laughing: )

That’s the best I have without being overconfident and unhelpful.
I hope someone else can assist.
Pix :heavy_heart_exclamation:

0.7V is typical for the maximum voltage that will register as a logic LOW. So the spec you quote is defining the low state. A high state isn’t necessarily anything above 0.7V - there will likely be a minimum voltage for a logic HIGH, typically 2V. Big Clive would be the best source for an explanation of the schematic, but I think he concentrated more on the antenna circuitry. He may have mentioned someone else who looked at the module.

1M is high for a pullup but Enable might have an internal pullup and the 1M resistors are just for some additional stability.

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Hi Pix

Also very conveniently “preferred values”. Or in other words commonly available.
For all practical purposes 0.007mA is the same as 0.0066mA rounded up 1 decimal place. We are getting down to not very much current at all here, 7µA
Cheers Bob

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Found it.

Project and discussion:

Circuit analysis and explanation:

It appears that the datasheet to work from is the BISS0001:
High Performance PIR Motion Detector IC


NICE ONE! :clap: