diff --git a/docs/Measuring_Resonances.md b/docs/Measuring_Resonances.md
index e346a178..481f5cea 100644
--- a/docs/Measuring_Resonances.md
+++ b/docs/Measuring_Resonances.md
@@ -8,6 +8,12 @@ Note that using ADXL345 requires some soldering and crimping. ADXL345 can be
 connected to a Raspberry Pi directly, or to an SPI interface of an MCU
 board (it needs to be reasonably fast).
 
+When sourcing ADLX345, be aware that there is a variety of different PCB
+board designs and different clones of them. Make sure that the board supports
+SPI mode (small number of boards appear to be hard-configured for I2C by
+pulling SDO to GND), and, if it is going to be connected to a 5V printer MCU,
+that it has a voltage regulator and a level shifter.
+
 
 Installation instructions
 ===========================