Please, help to figure out the pinout of microwave motion sensor FC1816.

The seller "doesn't understand" what it is required on queries to provide the pinout for the module. The module is the smallest microwave motion sensor I found, so it's very welcomed to run it.

I followed traces to find the function of 4 pins of 5. Please, help me to understand last pin. UPD: This question solved. Other question arose below...

FC1816 microwave motion detector

From left to right:

  • Pin 1: Out, connected to pin 2 of BISS0001.
  • Pin 2: Vcc, connected to pin 8 of BISS0001.
  • Pin 3: Enable, connected to pin 9 of BISS0001. Short it to GND should run the BISS.
  • Pin 4: Gnd, connected to pin 7 of BISS0001.
  • Pin 5: UPD: Vcc of microwave generator.

I have tried to connect both Vcc together to +5V, Enable to Vcc via 2k resistor (pullup), ground as regular. The out gives always logical 1.

What voltage should be supplied? BISS0001 supports up to 5V.

  • \$\begingroup\$ You should draw out a schematic as best you can. \$\endgroup\$
    – uint128_t
    Apr 2, 2016 at 16:25
  • \$\begingroup\$ The BSS0001 seems to be for PIR, not microwave. Many of the cheap boards sold on the grey market are little more than reproductions of the manufacturer's data sheet application circuit, or else clones of some existing hobbyist-oriented design - so having the schematics of those on hand will be a huge aid to understanding what you are looking at. \$\endgroup\$ Apr 2, 2016 at 17:24
  • \$\begingroup\$ @ChrisStratton, the fact BISS is for PIR confuses me too. Reverse engineering of the module is complicated: it is made with Chinese industry SMT components. I can't find their specs and even type of component. SOT-23 component on the front side can be FET or EJT or regulator or something else. Capacitors not marked as usual. Hoping someone encountered this module. \$\endgroup\$ Apr 2, 2016 at 18:26

3 Answers 3


First things first. Grab yourself a copy of the BISS0001 datasheet.

To understand what was going on I traced the signal line from the microwave IC to the BISS

  1. signal comes from top left corner (green)
  2. then enters preamp stage on pin14 (green)
  3. goes from pin 16 to pin 13 .. 2nd amplification stage (blue)
  4. goes from 2OUT to internal comparator

The comparator does following ..

  • signal should be around V2 ~ (1/2 VCC)
  • if the signal goes above VH or VL (i guess 0.3*VCC and 0.7*VCC) the output is triggert

hand crafted schematic of the FC1816 ;-)

But .. what the hell is wrong? Why does the output stay always high? The problem (in my oppinion is the output amplitude of the 2nd amplification stage which higher then expected, maybe due to some noice or whatever).

To understand what is going on the 2OUT I got my arduino and connected 2OUT to an analog input via 1megohm resistor.

The following picture already shows my modified circuit.

arduino @ 2OUT

  • startup and stabilization is .. fine .. this would explain the first long phase of the led staying high
  • 2 = min value
  • 3 = max value
  • 4 = avg value (all during 50ms period)
  • 1 = output value (aka LED)
  • 5 = std-deviation (just for testing)
  • scale 0-1023 is analogRead (aka 0-5V)

During the retrigger-inhib period the signal gets very eradic, even after replacing the amplification resistor (2nd Amplification stage) from 105 to a 150k (154). Before doing this the max signal would spike VH (0.7*VCC) and the output would instantly toggle again at the end of the inhibition period.. rendering the module useless.

EDIT: Try a variable resistor with maybe 200k Ohm to find the best value for your application

After replacing the amplification resistor I got the module working!


  • Replace amplification resistor from 105 to eg. 154 (lowering the amplification) or put one in parallel
  • (optional) Replace output pulse time resistor from 103 to 471 (10kohm 470ohm) (30sec -> 6 seconds)
  • (optional) Lift pin 1 and connect to ground to prevent retriggering

Some additional ideas that worked very very well for me:

  • Power the FC1816 VCC and UDP through an RC-Section (100Ohm Resistor and after that (on the side of the FC1816) an capacitory ~100-220µF)

My final solution I am currently using:

  1. Replace the 2nd stage-amplification resistor with a 150k resistor
  2. Disable the trigger (PIN3 low) all together and grab the signal at 2OUT and feed it directly to an arduino for further processing
  3. Use a 150 ohms series resistor and after that an 1000µF cap. The 150 ohms are crucial .. i tried 80 ohms and this was way too low.

To do so I used the statistics library and had very good results with max/min/std-dev

  • \$\begingroup\$ Thank you, @cimba007. I have memorized the spec of BISS0001 ;-) There are too many options to tweak the module. Thanks for your ideas, i'll try them. Just to be sure, in addition to resistor replace I am connecting the pins as following: - Pin 1 - to LED and resistor to GND. - Pin 2 + Pin 5 - To Vcc 3.3V. - Pin 3 - to resistor 2kOhm to Vcc. - Pin 4 - to GND. Is that correct? \$\endgroup\$ Apr 25, 2016 at 12:50
  • \$\begingroup\$ It works perfectly with proposed changes and suggested wiring. Thank you very much, cimba007! \$\endgroup\$ Apr 26, 2016 at 17:18
  • \$\begingroup\$ @Ivy: Yep, that is what I am doing. Have a look at the additional points I added at my "solution". ( de.wikipedia.org/wiki/RC-Glied#/media/File:Tiefpass.svg ). Note: The RC-Lowpass should provide enough current (R = U/I) to power up your LED AND the FC1816. Something like this (R = U/I with U = 0,5 I = 0,003 or maybe I = 0,020=> 25-160Ohms). Choose the resistor lower like maybe 10Ohm with led or 100ohm wihtout). This will lower the noise in the power supply for the FC1816 further. Note that I used 5V as VCC and 5-0,5 = 4,5V is still plenty. So be carefull if you only use 3.3V \$\endgroup\$
    – cimba007
    Apr 30, 2016 at 10:44

I found China patent CN 203951457 U. It uses BISS0001 for microwave detection. Blindly guessing that you should connect pins as a standard PIR module, and the microwave part (on the opposite side of PCB) is connected to the BISS0001 input instead of the PIR sensor.


I drew the schematic of an FC1816 I bought s couple of years ago. Unfortunately this device does not seem to be available any more. FC1816 schematic


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