Schematics

December 4, 2021

It used to be a matter of good form to include a circuit diagram or sketches with every electrical device. We are happy to continue this tradition, because what we could learn from circuit diagrams back then has ultimately benefited us all.

The electronics of the new hörbert, identifiable by the imprint V2.0, uses the ESP32 processor from Espressif. Many interfaces are led outward so that we can continue to offer expansions for hörbert in the future, as we have always done.

hörbert can be finely configured with our Playlist-Language PlaLa. We are constantly expanding PlaLa with more commands.

Tinkerport

Using the Tinkerport, we upload hörbert’s firmware during production. All the signals needed for programming are routed here. The board does not require additional power supply via the battery clips when a voltage of 3.3V is provided to VCC. We use an FT232R USB-Serial adapter to load the firmware onto all hörberts in our production via the Tinkerport.

Encoder

We use a rotary encoder with 24 positions and push function as a volume control and power switch. The signals go directly to the ESP32 so that we can wake hörbert from Deep Sleep Mode using an interrupt, without using the ULP.

Microphone

We use a PDM (Pulse Density Modulation) microphone SPH0644, whose power supply on our board is directly connected to an LED. If the LED does not light up, the microphone also does not have voltage, and therefore cannot make “secret” recordings.

On/Off + Analog Input

For external control using separate buttons, we provide a GPIO and an analog port to the outside. This allows us to wake up hörbert from deep sleep mode using an interrupt without using the ULP. In addition, additional control elements can be queried via the analog input.

Powerport

We have designed the Powerport for external power supply. Here, up to 6V can be supplied to VBAT_REVPROT, or directly 3.3V to VCC. Additionally, the i2c bus is available here along with an I/O line of the I/O Expander.

Expansion Port

The Expansion Port provides 2 I/O lines, one of which is connected to the ESP32 and the other to the I/O controller. The power supply of the Expansion Port is switchable, so external expansions do not have to be powered permanently. Of course, the I2C bus is also available here.

SD-Card Slot

The SD-Card Slot is equipped for 1-bit communication. The Card Detection Switch is connected but is no longer used in new firmware versions. The Write Protect Switch is not connected because SD-Card extensions and Micro-SD Cards do not support it anyway.
Attention, trap! Here lies IO2, so a programming cable on the Tinkerport can disrupt the function of the SD-Card.

Reverse Polarity Protection

The reverse polarity protection via FET saves us the voltage drop caused by a diode in series.

Power Supply

The highly efficient TPS62902 Buck Regulator provides 3.3V and eliminates the need for an additional LDO for low loads. That’s why the 3V3 LDO is also not populated.

A 1V8 LDO separately powers the audio amplifier.

Voltage Measurement

For the voltage measurement, we use an analog input of the ESP32 with a voltage divider. We only activate the voltage divider for measurement to save power.

I/O Expander

The I/O Expander SX1503 offers 2 ports with 8 GPIOs. Here the keyboard matrix (3 columns by 4 rows) is connected, as well as all the signals that did not fit on the ESP32.

Amplifier

The Class-D amplifier TLV320DAC3120 delivers its mono signal to the speaker(s) and to the wired headphone interface. An alternative configuration with a stereo amplifier is possible but untested.

Stereo headphones can be connected via Bluetooth.

Microprocessor

We are using the largest ESP32-WROVER module with 16MB Flash to have enough space for future expansions. The ESP32-WROVER module provides WiFi (2.4GHz), Bluetooth (BLE and Classic) through a built-in antenna. We use an i2c bus with 400KHz for communication on the PCB.