Data Sheet

PYNQ-Z1 Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 16 of 25
12.1 Tri-Color LEDs
The PYNQ-Z1 board contains two tri-color LEDs. Each tri-color LED has three input signals that drive the cathodes
of three smaller internal LEDs: one red, one blue, and one green. Driving the signal corresponding to one of these
colors high will illuminate the internal LED. The input signals are driven by the Zynq PL through a transistor, which
inverts the signals. Therefore, to light up the tri-color LED, the corresponding signals need to be driven high. The
tri-color LED will emit a color dependent on the combination of internal LEDs that are currently being illuminated.
For example, if the red and blue signals are driven high and green is driven low, the tri-color LED will emit a purple
color.
Digilent strongly recommends the use of pulse-width modulation (PWM) when driving the tri-color LEDs. Driving
any of the inputs to a steady logic ‘1’ will result in the LED being illuminated at an uncomfortably bright level. You
can avoid this by ensuring that none of the tri-color signals are driven with more than a 50% duty cycle. Using
PWM also greatly expands the potential color palette of the tri-color led. Individually adjusting the duty cycle of
each color between 50% and 0% causes the different colors to be illuminated at different intensities, allowing
virtually any color to be displayed.
13 Microphone
The PYNQ-Z1 includes an omnidirectional MEMS microphone. The microphone uses a Knowles SPK0833LM4H-B
chip which has a high signal to noise ratio (SNR) of 63dBA and high sensitivity of -26 dBFS. The digitized audio is
output in the pulse density modulated (PDM) format. The component architecture is shown in Figure 13.1.
Figure 13.1. Microphone Pinout.
13.1 Pulse Density Modulation (PDM)
PDM data connections are becoming more and more popular in portable audio applications, such as cellphones
and tablets. With PDM, two channels can be transmitted with only two wires. The frequency of a PDM signal
usually falls in the range of 1 MHz to 3 MHz. In a PDM bitstream, a 1 corresponds to a positive pulse and a 0
corresponds to a negative pulse. A run consisting of all ‘1’s would correspond to the maximum positive value and a
run of ‘0’s would correspond to the minimum amplitude value. Figure 13.1.1 shows how a sine wave is
represented in PDM signal.
Figure 13.1.1. PDM Sine Wave.