The DAC controller board features 160 individually controllable 16-bit DAC output. It can output voltage ranging from 0-20V on each channel.

The PCB contains 10 DAC81416RHAT- 16-channel 16-bit high-voltage output DAC with integrated internal reference from Texas Instruments. All ten DACs are daisy-chained and controlled using a single central microcontroller. All outputs are accessible from the 20 IDC connectors placed at the edges of the PCB. Each IDC connector will have 8 DAC channel outputs and 8 ground connections.

The controller also features a 10x16 LED matrix to indicate the status of all 160 channels. The LED matrix is controlled by 20 of 74HC595 8-bit shift registers so we only need three GPIO pins to control the entire LED matrix.

An Atmega328P is used as the main controller. The Atmega328P is flashed with a specific AT firmware. The MCU will accept AT commands from the control software through the USB and will control the precision DAC chips though high-speed SPI.

We have also included an ESP32 SoC on board for wireless control. This allows us to control the DAC controller over WiFi or Bluetooth. The ESP32 has a specific control firmware for this. Now, let's look at the schematics.

The above schematic diagram shows the entire circuit with extensive details. For easy understanding let's look at each section of the circuit.

Main Control Section

This section contains all the necessary circuitry for the AT command-based wired and wireless communication and control.

As you can see the first subsection in this control section is the USB input. This type C USB port is used not only for PC communication but also for firmware flashing and debugging. An AMS1117 3.3V regulator is used to generate the 3.3V for the onboard wireless SoC. The 20V from the DC input jack is stepped down to 5V using a low-noise buck converter for the logic circuitry. A CH340K USB to UART converter chip is used for PC communication, flashing and debugging purposes. Then you can see two different microcontrollers. The Atmega328P is used for wired control through the USB port and the ESP32 can be used if both wired and wireless communications are needed.

Daisy Chained 16-bit High Precision DACs

The next main section is obviously the DAC. Here we have used a total of ten DACs, and each DAC has 16 channels.

We have used the DAC84146 DACs from Texas Instruments. The DAC84146 is a 16‑channel, buffered, high-voltage output digital-to-analog converter (DAC) with a 16‑bit resolution. The DAC81416 include a low-drift, 2.5‑V internal reference, eliminating the need for an external precision reference in most applications. These devices are specified monotonic and provide a high linearity of ±1 LSB INL. The full-scale output range for each DAC channel is independently programmable. The integrated DAC output buffers can sink or source up to 25 mA, thus limiting the need for additional operational amplifiers. Each pair of channels can be configured to provide a differential output with offset calibration. The three dedicated A-B toggle pins enable dither signal generation with up to three possible frequencies. The DAC81416 incorporate a power-on-reset circuit that connects the DAC outputs to ground at power up. The outputs remain in this state until the device registers are properly configured for operation.

All ten DACs are connected in a daisy chain configuration so that we can control all of them with a minimal number of GPIOs, through the high-speed SPI interface.

LED Matrix for Visual Feedback

As mentioned earlier the status of each channel ( power state) can be monitored through the onboard LED matrix.

I have gone with a 10x16 matrix format so that each row will represent the output from an individual DAC chip. The LEDs are controlled using the 74HC595 shift registers. The use of shift registers not only reduces the number of control pins but also makes the control easier since there is no need for constant display updates, which will utilise a lot of MCU processing. Whenever a channel is turned on the corresponding LED on the matrix will light up indicating that the channel is turned on. and as soon as the channel is turned off the LED will also be turned off.

PC Controller Software

The control software is written for Windows OS and is written in Visual C# in Visual Studio Community Edition. Here is the control UI.

The control software UI is very easy to use. The indicator near the connect button will indicate whether the board is pulled in or not. This logic is pinned to the VID and PID of the USB to UART controller chip. Next, we have the connect button, which can be used to start or stop the connection to the controller board. Next is the mode selection, in mode 1 the output voltage configuration will be common for all 160 channels. But they can be individually turned on or off. In mode 2, the output voltage of each channel can be set individually.

Then we have the global power button which can be used to control the entire board at once. The export button can be used to export the current setting to a CSV file. The import button can be used to import the saved configuration, which will make it easier to load predefined configurations with ease. Even though the project was primarily developed for testing beam-controlling antennas, it is very useful in many other testing procedures because of its versatility and capabilities.

The entire project source including hardware design files, firmware source code and the PC control software source code can be found on the project repo along with the precompiled binaries.