kopia lustrzana https://github.com/bazjo/RS41_Hardware
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README_EN.md
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README_EN.md
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@ -24,7 +24,7 @@ Pull requests with improvements, translations and bug fixes are welcome!
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# Introduction
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The sonde is to be divided into six functional blocks, which are highlighted in the following picture.
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* [Power Supply](#Power Supply)
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* [Power Supply](#Power supply)
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* [Microcontroller](#microcontroller)
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* [Front end](#frontend)
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* [GPS](#gps)
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@ -50,25 +50,132 @@ TVS70030](http://www.ti.com/lit/ds/symlink/tlv700-q1.pdf) from TI are used. `U50
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## Hard wired logic
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The P-channel MOSFET Q501 discussed above is controlled by an N-channel MOSFET `Q502`.
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* The probe is on when this transistor is closed, so its gate is HIGH.
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* The probe is off when this transistor is open, so its gate is LOW.
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* The sonde is on when this transistor is closed, which means its gate is HIGH.
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* The sonde is off when this transistor is open, which means its gate is LOW.
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Via `R506` and `D502` a one-way rectified signal of the NFC coil reaches the gate. This allows the probe to be switched on via NFC. Furthermore this signal is also used for communication with the RI41 Groundcheck Device via the voltage divider `R510` and `R514`/`C525` to the MCU.
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Via `R506` and `D502` a one-way rectified signal from the NFC coil reaches the gate. This allows the probe to be switched on via NFC. Furthermore this signal is also used for communication with the RI41 Groundcheck Device and via the voltage divider `R510` and `R514`/`C525` brought to the MCU.
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Once the probe is switched on, it is kept in this state by the switched battery voltage, which is fed to the gate via `R505`.
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Once the sonde is switched on, it is kept in this state by the switched battery voltage, which is fed to the gate via `R505`.
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To switch it off again, the MCU can close the N-channel MOSFET `Q503`, which brings the gate from `Q502` to LOW.
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The button at the bottom of the probe `S501` also switches the gate from `Q502` via `R507` to HIGH. So that the microcontroller can also query the status of the button, the gate voltage of `Q502` is fed via the voltage dividers `R506` and `R512`/`C524` to an ADC input of the MCU. The lower voltage drop via `R507`, which leads to a higher gate voltage when this is pressed, is evaluated here.
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The button at the bottom of the probe `S501` switches the gate from `Q502` via `R507` to HIGH. The microcontroller can also query the status of the button, the gate voltage of `Q502` is fed via the voltage dividers `R506` and `R512`/`C524` to an ADC input of the MCU for this purpose. The lower voltage drop via `R507`, which leads to a higher gate voltage when this is pressed, is evaluated here.
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Finally, the battery voltage itself can also be evaluated via the voltage dividers `R508` and `R512`/`C524`.
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Finally, the battery voltage itself can also be evaluated by the MCU via the voltage dividers `R508` and `R512`/`C524`.
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# Microcontroller
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The microcontroller is a [STM32F100C8](https://www.st.com/resource/en/datasheet/stm32f100c8.pdf) `U101` from ST in LQFP48 package, which gets its clock from the 24 MHz crystal `X101`. Apart from the fact that all IO pins are occupied, it is only worth mentioning that RC low pass filters are present at many outputs.
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The microcontroller is a [STM32F100C8](https://www.st.com/resource/en/datasheet/stm32f100c8.pdf) `U101` from ST in LQFP48 package, which gets its clock from the 24 MHz crystal `X101`. Apart from the fact that all IO pins are used, it is only worth mentioning that RC low pass filters are present at many outputs.
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# Measuring frontend
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Translated with www.DeepL.com/Translator
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## Circuit arrangement
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Mechanically, the front end consists of the sensor boom, which is made of Flex PCB material covered with silver paint and connected to the board with a 20-pin FPC connector. The sensor boom includes a PT1000 temperature sensor, which is designed as a wire (the characteristic 'hook'), and a ceramic hybrid module to measure humidity. It combines three functions
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* Measurement of air humidity using a capacitive hygrometer (dielectric constant of the hydrophilic dielectric changes and thus the capacitance of the capacitor over the measuring range.
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* Measurement of the temperature of the module using a PT1000 as a feedback variable for controlling the module heating.
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* Module heating via a thick film resistor. During flight, the module is kept 5 K above ambient to prevent condensation. During the preflight check it is heated to remove impurities and to perform a zero humidity check. There is no on-site calibration in the Ground Check Device for temperature.
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In addition, two reference resistors `R208` and `R209`, one reference capacitor `C209`, five heating resistors `R201-205` and the MOSFETs `Q203-204,` required to control these resistors, as well as an unidentified component `R209`, which could be a thermistor, are available on an area delimited by milled slots from the rest of the printed circuit board. No heating of the references could be observed in tests at room temperature.
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## Circuit topology
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Electrically seen, the frontend consists of two ring oscillators for temperature and humidity, whose frequency is varied by variable impedances (e.g. the sensors) inserted into the feedback path with the help of analog switches.
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Each ring oscillator is formed by 3/6 of a [74HCU04](https://assets.nexperia.com/documents/data-sheet/74HCU04.pdf) Hex Inverter `U205`. Three inverters are connected in series. The first and third inverter are feedbacked directly via an RC series element `C207`/`R210`, `R214`/`C215`, `C208`/`R211`, `R215`/`C216`, the entire ring oscillator via a capacitor `C212`, `C213`. Both ring oscillators can be pulled to +3 V by a P-channel MOSFET `Q201`, `Q202` at the first inverter with separate control, which corresponds to ground at the output, to deactivate them. The heating resistors for the reference, which can be activated by closing `Q203`, `Q204` with closed P-channel MOSFETs `Q201`, `Q202`, are also located at the input of the inverters.
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The feedback path for the temperature measurement consists of 2/3 buffers of a [74LVC3G34] (https://assets.nexperia.com/documents/data-sheet/74LVC3G34.pdf) `U207` and two resistors `R219` and `R223`, which probably are used for the fine tuning of the resonance frequency. This is followed by four single pole single throw (SPST) switches [TS3A4751](http://www.ti.com/lit/ds/symlink/ts3a4751.pdf) `U201`, the NO of which is connected to the output of the buffer and which each switch one of the four possible measuring resistors (temperature/humidity/Ref1/Ref2) into the feedback path. The measuring tap is located between buffer and switch with a series resistor `R224`.
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In the feedback path of the humidity measurement there is a circuit formed by the remaining buffer and two resistors `R226` and R220. The measuring tap is made exactly like in the temperature measurement by a resistor `R225`. Furthermore in the feedback path there are three SPDT switches [TS5A9411](http://www.ti.com/lit/ds/symlink/ts5a9411.pdf) `U202-204`, which switch the measuring and reference capacitor either into the feedback network or to ground. U205 has no connection between COM and the input of the first buffer, where there should normally be a reference capacitor, so this switch does not serve any obvious purpose. However, since it is driven in software like the other two, it can be assumed that the switches have an example-independent non-linear effect on the feedback frequency measured at this switch to compensate for it. Parallel to the switches, fixed feedback is applied via the resistor `R212`.
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The two measurement outputs are converted in a NOR gate `U208` and the result is sent to the MCU so that only one measurement can be performed at a time. Measurements with a Logic Analyzer show that the temperature is measured twice per second and the humidity once per second.
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The heating of the humidity sensor is controlled by an unidentified component `U206`.
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# GPS
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The GPS module [UBX-6010](__used_asset__/gps_datasheet.pdf?raw=true) `U302` is connected to the MCU via a UART. Apart from the discrete SAW filter and LNA, the circuitry corresponds essentially to the typical application. The IC is not recommended for new designs.
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# Radio
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The radio interface is a one-chip solution with the [Si4032](https://www.silabs.com/documents/public/data-sheets/Si4030-31-32.pdf) `U401`, which is connected to the MCU via SPI. Worth mentioning are the secondary, unused antenna pad and two tracks at TX and XOUT, which purpose is currently unidentified.
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Two of the three GPIO pins are used. GPIO1 switches the N-channel MOSFETS to heat the reference. GPIO2 has not yet been identified.
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The IC is not recommended for new designs.
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# Interface
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The following interfaces are provided
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* EEPROM for the SGM version
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* XDATA and programming connectors
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* internal expansion connector
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* NFC interface
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## EEPROM
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On the back of the board there is a footprint for an SPI-EEPROM `U601` with generic pinout, which shares the SPI bus with radio and internal expansion connector. This is most likely used to implement the Radio Silence Mode in the military version RS41-SGM, but so far no such sonde finding is known to confirm this hypothesis. In Radio Silence Mode, the probe stores the ascent readings up to a certain altitude or time and sends them to the ground station alternating with the current frames. Since the internal memory of the MCU used, even in a configuration with more memory, is not sufficient for this purpose, the use of an EEPROM for this purpose seems to make sense.
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## EEPROM
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On the back of the board there is a footprint for an SPI-EEPROM `U601` with generic pinout, which shares the SPI bus with radio and internal expansion connector. This is most likely used to implement the Radio Silence Mode in the military version RS41-SGM, but so far no such probe is known to confirm this hypothesis. In Radio Silence Mode, the probe stores the ascent readings up to a certain altitude or time and sends them to the ground station alternating with the current frames. Since the internal memory of the MCU used, even in a configuration with more memory, is not sufficient for this purpose, the use of an EEPROM for this purpose seems to make sense.
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## XDATA and programming connectors
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On the 2x5 2 mm pinheader `J602` at the lower edge of the sonde the following connections are brought out
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* XDATA as a UART; the pins can also be configured as I2C in violence of the XDATA standard
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* SWD interface for flashing the MCU
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* Reset pin of the MCU
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* Battery voltage, 3.8 V boost voltage and 3 V MCU voltage
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```
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-------
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GND | o o | XDATA_RX(PB11)
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XDATA_TX(PB10) | o o | +3V_MCU
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- |
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V_Boost| o o | VBAT
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- |
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MCU_RST | o o | SWCLK(PA14)
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SWDIO(PA13) | o o | GND
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-------
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```
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## Internal expansion connector
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The internal expansion connector `J601` brings out the shared SPI bus and two GPIO/CS signals, one of which is shared with the EEPROM, as well as the 3.8 V boost voltage and 3 V MCU voltage. There are unused pins which can be used e.g. for programming the mezzanine board.
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The RPM411 barometric pressure module is the only mezzanine board in knowledge that uses this connection.
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The type of connector is unknown and not trivial to find out. The specs are
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* 2x8 poles
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* 0.5 mm pitch
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* 2 mm stacking height
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* male and female connectors have locking pins that require holes in the footprint.
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* The connector is mechanically loadable, there is no other mechanical connection between the two boards.
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It would be desirable to find out the connector type for own developments. The "Tough Contact" P5KF connectors from Panasonic Electric Works could be compatible at a first glance.
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## NFC interface
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The sonde can be switched on and parameterized via the NFC interface. The decoding takes place in the microcontroller, probably by bit banging, since there is no integrated NFC frontend available, which provides this wakeup functionality.
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NFC is essentially based on two mechanisms for sending and receiving data
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* When the Groundcheck Device sends data to the sonde, it pulses the 13.56 MHz carrier according to the data.
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* When the probe sends data to the groundcheck device, it modulates the load it pulls from the transmission antennas field according to the data.
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The received data is received differentially by the sonde. In parallel to the receiving coil there are two capacitors `C604` and `C605`, then the two connections are clamped in a double diode `D602/D607` against ground and one-way rectified. A connection is made to the voltage supply circuit described above.
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The other connection is clamped again to ground with `D603` and the one-way rectified signal is DC-coupled to ground with `R603` and AC-coupled with `C602`. `R601` and `R604` bias this AC coupling before the signal is filtered by an RC low pass `R602`/`C603` and clamped with `D601` against the supply voltage of the MCU.
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The modulation of the load resistor is carried out with the aid of a tap in front of the double diode to the voltage supply, by connecting the coil to ground via `R605` and the N-channel MOSFET `Q601`. This allows a current path over `R605`, `Q601` and `R603` to be established for one half of the AC voltage signal.
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# Last but not least
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Some project ideas, what to do with the gained knowledge
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* Expand Amateur Radio firmware to include its own NFC interface and use of existing sensors
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* alternative firmware for radiosonde use in the meteorological 400 MHz band
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* Use as IoT room climate sensors in the 433 MHz ISM band
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* Use as LoRaWAN nodes in the 433 MHz ISM band
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* Development of our own mezzanine boards for space-saving extension boards
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