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The heart of our Controller PCB 10 is a 32-bit ARM Cortex-M4F micro-controller. This controller has 1 MB Flash, 192 KB RAM, and is running with a clock frequency of 168 MHz. Controller PCB 10 uses the STM32F4DISCOVERY board which also includes an ST-LINK/V2 programmer. The use of this breakout board is only a temporary solution. If the controller works fine with the breakout board then in a later version we will place the ARM Cortex-M4F micro-controller on our controller board.

The ARM Cortex-M4F micro-controller has three 12-bit analog-to-digital converters. These converters are capable to provide a throughput of up to 1,000 ksps = 1,000,000 samples per second even if both input jacks of the controller board are multiplexed. The DMA of the controller is used to store continuously the converted signals into the memory such that we can read out the signal samples stored before the signal reaches a threshold.

The block diagram, circuit diagram, printed circuit board, and an assembled circuit board of Controller 10.4 are shown in Figure 42, 43, 44, 46, and 47, respectively.

Electronic parts

The electronic parts necessary for Controller 10.4 are listed in Table 7.

Breakout board STM32F4DISCOVERY
Display LCD 122DIP
GPS module GlobalTop PA6H (MT3339)
Ethernet Controller ENC28J60
Voltage transformer LF33CV
Transistors T40, T41 BC338
LEDs GPS fix LED LED 3mm (green)
Diodes D40, D41, D42, D43, D44, D45, D46, D47, D48, D49, D50, D51 1N4148
Resistor, metal 1% R47, R55, R56, R65 10kΩ
R46, R50, R52, R53 2.2kΩ
R62, R63, R64 1kΩ
R40, R41, R57 680Ω
R54 470Ω
R58, R59, R60, R61 330Ω
R42, R43, R44, R45 49.9Ω
R48 47Ω
R49, R51 10Ω
Resistor network, star, 8-9 RN42 10kΩ A103
Resistor network, 2 x 3-6 2 x RN41 1kΩ B102
Resistor network, star, 8-9 RN40 100Ω A101
Capacitors, electrolytic, 5mm C45 470 µF
Capacitors, electrolytic, 2.5mm C44, C48, C55, C56 100 µF
Capacitor, ceramic, 2.54mm C57, C58, C59, C60, C62, C63 220 nF (224)
C40, C43, C46, C47, C49, C50, C51, C52, C53, C54, C61, C64 100 nF (104)
C41, C42 18 pF (18)
Inductances, HBCC L40, L41, L42 10 µH
Crystal 25 MHz

Table 7: The electronic part list for the controller board 10.4


This board board is placed piggyback on the controller board. It has two push buttons, a black reset button and a blue user defined button. The functionality of the blue push button depends on the state of the program. The four user defined LEDs, LED3 (orange), LED4 (green), LED5 (red) and LED6 (blue) are used to indicate the received signals, the GPS state, the 1PPS signal, the interference mode and other problems.

The other additional hardware of the STM32F4DISCOVERY board is not used by the controller. This especially concerns the motion sensor, the accelerometer, the microphone, and the audio DAC.


When booting up, the different combinations of the four glowing LED show the steps of the initialization phases. They may be helpful for investigating problems. There are other LEDs on the STM32F4DISCOVERY. One big red/green LED left to the mini-USB connector for the ST-Link firmware programmer and a small red LED on the opposite site as power indicator. Both LEDs cannot be controlled by the CPU, so the ST-Link LED is blinking all the time when no USB connection is available. There is another red LED close to the micro USB connector. It can light up when using the analogue user input.


The LCD DIP122 graphic display provides a 122 x 32 dot matrix and is used to show several peaces of information about the system. The dot matrix allows displaying graphical symbols and illustrations beside letters and digits. The user can see the state of the network, the state of the GPS module, the state of the amplifiers, and many other useful notes. The display is available with different LED backlight colors. We recommend the most robust and cheapest green display whose size is only 67mm x 27mm. However, the contrast and brightness is more brilliant on the amber display than on the green and blue display. The amber and blue displays have a size of 75mm x 27mm and are a little bit more expensive than the green displays. The green backlight has a higher power consumption than the other ones. The backlight is driven through a transistor, which is connected to a PWM output of the controller. Thus, the brightness can be adjusted by software. A charge pump, which is driven by another PWM of controller, converts 3V to around -5V for the contrast voltage. The correct voltage depends of the display type, supply voltage and temperature. The LCD has an integrated temperature compensation, so the contrast should be stable even when you use the LCD outside.


The buzzer of the controller board can be used to indicate different states and events by different sound signals. For example, every received signal can be indicated by a beat sound. The buzzer can output an alarm if the system enters the interference mode or if the network connection is lost. The buzzer can also be used as a loudspeaker to output the received VLF signals. This provides a very useful tool to locate sources of interferences and thus to find the best place of the antennas in a noisy environment. In any case, the buzzer can also be turned off.

GPS Module

The controller needs a GPS device with a serial TTL level interface and a 1PPS signal. We recommend to use the on-board GlobalTop PA6H GPS module. This module allows you to connect an external antenna with an SMA connector. Most external antennas have a connection cable between 2 and 5 meter. The longer the cable the larger the loss. The green LED beside the GPS module stops blinking when the GPS has found its position. The LED will then light continuously on boards prior to version 10.3b and switched off on newer boards.

If you do not want to use the GlobalTop PA6H GPS module, we recommend to use the NaviLock or GlobalSat EM-406A GPS module. The pin assignment of the GPS connector on the controller board is shown in Table 8. This pin assignment is identically to the pin assignment of the EM-406A. Other GPS modules may be used too, but the firmware of the controller currently only supports the MediaTek MT3339 and SiRF chip sets.

Pin EM-406A module signal GPS Connector Pin
1 ground 1
2 +5 Volt 2
3 serial input TTL 3
4 serial output TTL 4
5 ground 5
6 1PPS output 6

Table 8: Pin assignment of the EM-406A module and its connection to the GPS connector

Amplifier connectors

The Controller has two RJ45 connectors for two amplifiers with maximal 3 channels each. The firmware automatically detects to type of the connected amplifier. Both connectors can be used independently. Do not connect version 5.x amplifiers or earlier!


The controller board is connected to a local area network by a shielded CAT network cable from the RJ45 network connector. This jack has integrated transformers and LEDs. There are only very few compatible jacks, so have a close look into the datasheets when you want to use another connector! Although the ARM Cortex M4 based STM32F4 micro-controllers already have an internal Ethernet controller, they do not include an Ethernet Physical Layer Transceiver (PHY). For experimental reasons, we additionally have placed the Ethernet controller ENC28J60 on the board of Controller 10.x. The ENC28J60 a very widely used “all-in-one” ethernet controller, but it can only handle 10Mbit/s ethernet connections. With around 150mA current drawn it has a relatively high power consumption. The ENC28J60 is connected to the processor via SPI. In a forthcoming version, we intend to remove the ENC28J60 and to replace it by an Ethernet Physical Layer Transceiver on the controller board. Then we will use the internal Ethernet controller of the processor, which uses DMA and can also handle 100MBit/s connections.


The receiving system should have a good ground to operate effectively. The ground of the amplifier and thus also the ground of the controller board should be connected to a large expanse of metal such as a safety hand rail around a roof or a heating core. Note that the ground of the system should never be connected to the ground wire of the electrical supply system. Usually some grounding is already given if the shielded network cable is connected to the router.

In some situations, grounding can inject even more noise in your system. Grounding on both, controller and amplifier, can also produce some negative side effects. If grounding is needed for your system, we suggest connecting it on the controller only, as it has a special terminal block for that purpose. See also Figure 44.

Serial interface

The board has a 3.3V TTL level serial interface which is 5V tolerant. This interface can be used for debug purposes. The connector also provides the power supply for a TTL to RS232 or TTL to USB converter. The pin assignment is printed on the board and can also be found in the schematic.

First hardware check

For the first hardware check, do not connect anything. Remove the STM32F4DISCOVERY board and remove the display. After connecting a 5V USB power supply, the green GPS fix LED should start blinking, if you are using the GlobalTop PA6H GPS module. Next, remove the power supply and mount the STM32F4DISCOVERY board and the display. Close Jumper 1 only if you are using the green display, otherwise, if you are using the amber or blue display, open Jumper 1. Then connect the power supply again at the mini USB connector of the controller board, not at the mini USB connector of the STM32F4DISCOVERY board. Some of the LEDs on the STM32F4DISCOVERY board should start blinking. The display should not show anything, because the STM32F4DISCOVERY board does not contain our firmware yet. The next step is to upload the firmware. Note that the USB connectors on the STM32F4DISCOVERY board are only used to program the board, not for power supply.

Controller PCB change log

Revision Change
10.2 First release
10.3 Added ground connector, Added MP joint
10.3b Changed polarity of GPS LED by request of manufacturer to prevent malfunction
10.4 The power supply for the display is changed from 5V to 3.3V

Table 9: Change log of controller 10

Figure 42: Block diagram of Controller 10.x

Figure 43: Circuit diagram of Controller 10.4

Figure 44: Printed Circuit Board of Controller 10.4

Figure 45: Assembly Diagram of Controller 10.4

Figure 46: Assembled Controller 10.3

Figure 47: Assembled Controller 10.3 with STM32F4DISCOVERY board and display