This project is created during Praktikum Raumfahrtelektronik - Lehrstuhl für Raumfahrttechnik at the Technische Universität München (TUM). This board carries out submillimeter measurement of an actuator displacement, which is part of a test-setup to transport Regolith via hoppers. As a sensing unit an LVDT is used, that is driven by a Signal Conditioner which gets read by a 24-bit ADC to a MCU where the Experiment data is then delivered via USB.
Without any additional filtering a 3 sigma precision of 0.000161 mm was achieved.
Contributors: Beatriz Mas Sanz, Thilo Witzel and Sven Julius Steinert
The Python app gives easy access to the recording functionality while autodetecting the device Port, saving the downloaded lines in data.csv and direct plotting via pyplot.
However, the MCU can also be controlled directly via COM Terminal at baudrate = 921600 with the following commands
| CMD | HEX | FUNCTION | ANSWER |
|---|---|---|---|
| '0' | 0x48 | start recording | RECORDING\nEND |
| '1' | 0x49 | stop recording | STOPPED\nEND |
| '2' | 0x50 | start download | <.csv file> END-OF-FILE-SEQUENCE\n |
| '3' | 0x51 | enable stream | Stream Data Enabled < values > |
| '4' | 0x52 | disable stream | Stream Data Disabled |
The stream mode is supporting a higher sample rate at 500 sps (instead 200 sps in recording). We recommend to use the streaming mode via SerialPlot v0.12 where baudrate = 921600, and Data Format = ASCII have to be set before sending a '3' as starting Command.
The PCB has to be connected to the LVDT sensor and a computer to operate. The power and data transmission for the LVDT are provided by a micro-USB connection.
| PCB Label | LVDT Cable | FUNCTION |
|---|---|---|
| PYRD | Yellow - Red | Primary Coil |
| PYBK | Yellow - Black | Primary Coil |
| SBK | Black | Secondary Coil |
| SRD | Red | Secondary Coil |
| SBL | Blue | Secondary Coil |
| SGN | Green | Secondary Coil |
Since the linearity of the LVDT is proven in its factory test inspection and that linearity is conserved by the ADC a real calibration is not really meaningful. Especially at this precision level, different kind of hardware than a digital Caliper is needed.
However, maximum positive and negative displacement of ± 1.27 mm can be verified by its Voltage of 12.785418 mV and 4362.785418 mV.
If observed differently these mV values can be set in the MCU code.
The zero position of the sensor can be set through spinning the LVDT core on its positioning threaded screw.
| Mfr. No | Manufacturer | Description | Qty. | Price [EUR] |
|---|---|---|---|---|
| 02560389-000 | TE Connectivity | Linear Displacement Sensors HR 050 LVDT .05in | 1 | 166,31 |
| AD698APZ | Analog Devices Inc. | Sensor Interface LVDT SIGNAL CONDITIONER | 1 | 54,27 |
| ADS1220IPWR | Olimex | BB-ADS1220 4 Channel Sigma Delta Precise 24-Bit ADC Breakboard | 1 | 13,00 |
| ESP32-S3-DevKitC-1-N8 | Espressif | WiFi Development Tools - 802.11 ESP32-S3 General-Purpose Development Board, ESP32-S3-WROOM-1-N8, with Pin Header | 1 | 15,00 |
| ERJ-8ENF1742V | Panasonic | Thick Film Resistors - SMD 1206 17.4Kohms 1% AEC-Q200 | 3 | 0,18 |
| ERA-8AEB1692V | Panasonic | Thin Film Resistors - SMD 1206 16.9Kohm 25ppm 0.1% AEC-Q200 | 3 | 0,66 |
| TNPW12066K26BEEN | Vishay | Thin Film Resistors - SMD 6.26Kohms .1% 25ppm | 3 | 0,92 |
| HV732BTTD1004D | KOA Speer | Thick Film Resistors - SMD 0.25W 1M 0.5% 500 VOLTS | 3 | 0,563 |
| C1206C104J1RACAUTO | KEMET | Multilayer Ceramic Capacitors MLCC - SMD/SMT 100V 0.1uF X7R 1206 5% AEC-Q200 | 13 | 0,199 |
| 12065A102GAT4A | KYOCERA AVX | Multilayer Ceramic Capacitors MLCC - SMD/SMT 50V 1000pF C0G 1206 2% Tol | 3 | 0,65 |
| 12065C334JAT2A | KYOCERA AVX | Multilayer Ceramic Capacitors MLCC - SMD/SMT 50V 0.33uF X7R 1206 5% | 7 | 0,491 |
| 12062A102GAT2A | KYOCERA AVX | Multilayer Ceramic Capacitors MLCC - SMD/SMT 200V 1000pF C0G 1206 2% Tol | 3 | 0,87 |
| PX-28LCC | Kycon | IC & Component Sockets LCC 28P PBT | 2 | 1,75 |
| CR1206-FX-47R0ELF | Bourns | Thick Film Resistors - SMD 47ohm 1% | 11 | 0,045 |
| CR0402-FX-4533GLF | Bourns | Thick Film Resistors - SMD CHIP RESISTOR | 10 | 0,058 |
| B41888C4228M000 | EPCOS / TDK | Aluminium Electrolytic Capacitors - Radial Leaded 16VDC 2200uF 20% STD Leads | 4 | 1,89 |
| C1206C685K4PACTU | KEMET | Multilayer Ceramic Capacitors MLCC - SMD/SMT 16V 6.8uF X5R 1206 10% | 5 | 0,87 |
| NMA0515SC | Murata | Isolated DC/DC Converters - Through Hole 1W 5-15V SIP DUAL DC/DC | 2 | 5,08 |
| 12063A103FAT2A | KYOCERA AVX | Multilayer Ceramic Capacitors MLCC - SMD/SMT 25V 0.01uF C0G 1206 1% | 3 | 0,96 |