In using the Pi2Grover - Raspberry Pi to Grove Connector Interface Board I noted that neither the Grove nor Adafruit PIR sensoes worked. I measured the logic levels. Detached from the board the levels were 0 & 3V when attached they are 2.6V low and 3.2V high. Is there a fix for this?
I looked at the schematics for the seeedstudio board (and suspect the same problem on the adafruit board).
Before I talk about what to do, give me the exact product page for the Adafruit device you are using so I can verify this.
The problem on the seeedstudio board is they have a 10K Ohm resistor in line with the D1 output. This is a poor way of converting a 3.3V to 5V compatible line and will screw up the bi-directional I/O circuitry on the Pi2Grover board as well as many other circuits and voltage translators. Bad boys!
I thought they might have done this. I've seen this design practice before on other of their products. It would cost about $0.10 to do it right.
So, what do to? You can either add your own buffer between the D1 on the PIR board and the Grove input line, or you can use one of our Grove PowerDrive buffers to fix the problem without screwing around soldering and breadboarding.
The data sheet for the HC-SR501 PIR is here www.mpja.com/download/31227sc.pdf and as you suspected there is a 1k resistor in series with the output. This also explains why neither pull up nor pull down port controls worked. I bought several of the Grove PowerDrive buffers. Thanks for the assist and info. I will look for the series resistor cheap fix in the future should similar problems arise.