update

nrf52-stepper/index.html

@@ -15,7 +15,9 @@ pre code {
 <a href='nrf52-stepper-layout.png'><img src='nrf52-stepper-layout.png' height=300px></a>
 <a href='nrf52-stepper-traces.png'><img src='nrf52-stepper-traces.png' height=300px></a>
 <a href='nrf52-stepper-interior.png'><img src='nrf52-stepper-interior.png' height=300px></a>
-<p>This is a stepper motor controller built around the DRV8825 and the nRF52.</p>
+<p>This is a stepper motor controller built around the DRV8825 and the nRF52.  The nRF52 receives commands over the radio and controls the motor, which means we only need to deliver power to the motor, no data lines.</p>
+
+<p>This board uses a PWM output and a low pass filter to deliver a voltage level to control the current limiting value for the DRV8825.  A 10K resistor and a 1uF capacitor do a reasonably good job smoothing the 10kHz PWM into a constant voltage level.</p>
 
 <p>Some sample firmware is available below (or as files: <a href='nrf52-drv8825/nrf52-drv8825.ino'>nrf52-drv8825.ino</a> and <a href='nrf52-drv8825/radio.h'>radio.h</a>).  This code defines a command set issued over the radio for moving a number of steps, changing stepping speed, setting microstepping parameters, and setting a current limit value.</p>