Differences to System GREEN

original source¹⁾

Below is a list of comparisons between technical data of the old GREEN and newer RED systems. The old system produced (and still produces) good results, but the hardware was maxed out. RED is much more flexible, precise and has several new features, while staying in a similar price range.

GREEN
The amplifier had a huge delay. The antennas didn’t have damping resistors and thus, also self-resonances. The high and low-pass-filters were simple and had a low cutoff frequency.

RED
Reduced delay and antennas with damping resistors. This minimizes self-resonances of the antennas. The filters are better and have a higher cutoff frequency, so we get more information from the signal. All those things are one of the most important improvements on SystemRED!

GREEN
Gains have to be set by jumpers or potentiometer on the amplifier. Threshold for signal trigger were fixed on the controller board.

RED
Gains and thresholds can be changed individually for each channel by software. This gives the possibility of automatic gain/threshold configuration by the server to maximize the detection rate of the whole network. There’s still a potentiometer on the amplifier board, mainly for testing purposes.

GREEN
ATMega644 with 20MHz, 64kB flash, 4kB RAM, no DMA, 2 USARTs. One of the main limitations were the missing DMA capabilities.

RED
STM32F4 ARM Cortex M4F technology with 168MHz, 1MB flash, 192kB RAM, several DMA channels, 6 USARTs. This MCU fits perfect for our needs. There are still resources left, for example the integrated DSP. We could use it to examine a signal closer before sending it. The unique processor-ID gives us the possibility to identify each hardware.

GREEN
Two independent external 8-bit converters with around 500ksps, which have to be polled by the CPU. There was no other configuration possible.

RED
Three independent 12-bit converters integrated in the MCU with up to 2200ksps each, which write their data into memory by themselves (DMA). So we can now see the signal before the trigger, which is important for a better position computing. The A/D-converters can be configured by the CPU in different ways, i.e. sampling time, resolution, threshold. Each A/D-channel has a multiplexer, so one converter can be used for different amplifier channels. All three converters can be joined to sample one input with almost 12000ksps. So the 1PPS signal can be checked for accuracy or the voltages for bad power supplies. The A/Ds are also acting as a hardware monitor by checking voltages and temperature.

GREEN
Needs serial or USB cable connected to a running computer or embedded device, where the tracker has to be installed.

RED
Uses direct Ethernet connection, so no other device/computer is needed. Thus, the system runs almost “out-of-the-box”.

GREEN
Only buttons for a test-signal and a reset-button. Real status could only be checked from connected PC.

RED
Buttons, Buzzers and LCD for checking status, easy installation, signal pass-through and several other useful things.

GREEN
Only basic functionality. A firmware update needs special hardware.

RED
Uses a much more complex firmware, but with a lot of possibilities. Update is easily possible via web-interface and with two different programmers on-board. New features or bugfixes are easily possible.

GREEN
Not available. Some trackers (like XLT) had a simple implementation. But there was no possibility to talk to the controller itself.

RED
The return channel through HTTP-protocol is a main feature of the new system. It allows automatic remote configuration of the controller and amplifier by the servers. It has several fallback functions, if there are problems with our servers.

GREEN
12V power supply. The system itself had a very low power consumption around 1.5W, but a running PC was needed. If a special router was used instead, the overall power consumption was around 2.5W.

RED
5V power supply through USB jack. This is a common standard today. The voltages are checked by the MCU and can be shown on LCD/web-interface. The power consumption is 2-3W, mainly depending on LCD color and brightness.