USER MANUAL - singletact.com
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1. Baselin capacitance SingleTact Output gt 255 Digital scaling value The digital scaling value is a2 byte number stored at register locations 10 and 11 Table 7 For increased precision the digital scaling value resolution is in 0 01 increments This means that 100 equals unity scaling The 255 offset provides the facility for a negative swing The internal capacitance to digital converter CDC operates at 140 to 4000 Hz depending on the capacitance sensor settings in particular the number of accumulations Each time the CDC completes a measurement the output register is updated the frame index increases by one and a pulse is produced on the frame synchronization output pin A timestamp is calculated on the CO851F717 but since there is no crystal oscillator on the SingleTact interface board this timestamp is not stable and should only be used as a course estimate Copyright 2015 www SingleTact com 10 gt SingleTact MINIATURE FORCE SENSORS Table 7 Sensor settings layout in main register These are stored in flash and loaded each time the SingleTact is powered on 1 Please consult C8051F717 datasheet for more information Copyright 2015 www SingleTact com 11 lt SingleTact MINIATURE FORCE SENSORS Table 7 Sensor readings layout in main register These are updated at gt 140Hz depending on capacitance sensor settings The frame sync digital output pulses each time these change 1 This should only be2. 0 8 Table 2 The SingleTact interface board pinout Parameter Value Supply Voltage 3 6 12V I2C Clock 100kHz or 400kHz Analog Range 0 2 V FSR output from 0 5V to 1 5V Digital Logic 3 3V Sensor update rate 1 C or Analog gt 140Hz depends on C8051F717 settings Table 3 Electrical parameters Copyright 2015 www SingleTact com 6 gt SingleTact MINIATURE FORCE SENSORS 2 2 ANALOG INTERFACE As shown in Figure 3 the analog output swings from O to 2V with valid outputs ranging from 0 5V to 1 5V As pressure increases beyond the full scale range FSR the output increases to 2V and then saturates An output below 0 5V may indicate negative pressures which occur when the sensing area is under tension This should be avoided since it can damage the internal structure of the sensor Note that if the sensor is unloaded and the output is still under 0 5V then a shift in the sensor s baseline has occurred You can reset the baseline using the sensors digital 0 FSR interface which is specified in Section 3 Analog Output Force or Pressure Figure 3 SingleTact analog output SingleTact com Figure 4 SingleTact configuration The analog output connections are detailed here below Connection Pin Number Connection No connection 5 4 No connection No connection No connection No connection Analog output 2V swing 0 5 to 1 5V full scale range Ground Vo 3 7V to 12V Table 4
3. gt SingleTact MINIATURE FORCE SENSORS USER MANUAL EXPERIENCE INCREDIBLE PERFORMANCE CONTENTS 1 2 Introduction Interfaces 2 1 Pinout 2 2 Analogue Interface 2 3 PC Interface 2 4 12C Interface Source Code and Examples 3 1 Flashing an Arduino 3 2 An Arduino Example 3 3 NET Example 3 4 Interface Board Source Code Copyright 2015 www SingleTact com gt SingleTact MINIATURE FORCE SENSORS 0 N O Ol 11 12 16 20 22 gt SingleTact MINIATURE FORCE SENSORS 1 INTRODUCTION The SingleTact is a single element sensor that accurately and reliably measures force The interface board features a 2V analog output for easy DAQ integration and an I C interface for embedded systems This document provides all the information necessary to interface with SingleTact including a sample Arduino digital interface and a PC data acquisition app The open source code can be downloaded from https goo gl zRDBsk An overview of the Arduino based SingleTact system is shown in Figure 1 The SingleTact can be used in a number of ways outlined in Table 1 MCU SingleTact com Capacitive Measurement Electronics SingleTact Interface 9999 00009 SingleTact Capacitive Force Sensor Board USB to PC Figure 1 Arduino based SingleTact System Overview USB Interface Arduino Uno Use Case System Overview 1 Force Measurement Analog output Connect to multimeter lt gt gt oscillos
4. used as a course estimate as it is liable to drift IC transmissions are limited to 32 bytes The packet layout is detailed below Table 8 I2C Packet layout to sensor There are only two master to slave I C commands read request and write which are encoded in the first byte of the outgoing I C transmission The second and third bytes represent the read location and length respectively An I C slave read transmission is typically preceded by a master to slave read request command that sets the read location If no such read command is issued the read location defaults to 128 the sensor output location Data can be read from anywhere in the register addresses 0 191 but can only be written to the first 128 bytes Reading or writing out of this valid range will fail Bytes 3 to N 1 where N is the packet length contain any data to be written to the main register This command updates the internal flash memory so the new settings are persistent beyond a power cycle The final byte must be OxFF to signify the end of the packet Copyright 2015 www SingleTact com 12 gt SingleTact MINIATURE FORCE SENSORS 12C slave read commands simply contain the main register data up to the number of requested bytes 32 max BYTE From Sensor 0 31 Main Register Data Table 9 I C Packet layout from sensor The frame synchronization output pin 7 see Figure 2 goes high when a new measurement is available Th
5. Analog connections Copyright 2015 www SingleTact com 7 gt SingleTact MINIATURE FORCE SENSORS 2 3 PC INTERFACE An Arduino UNO board can be used to provide a USB interface to SingleTact Download the PC Interface from https goo g 40CqZB The demo application is available from Github https goo gl L6kKYCs Connect the sensor to the Arduino board as follows SingleTact com 3 8 2 SingleTact Capacitive a IC board Capacitive Measurement Force Sensor Electronics SingleTact Interface USB to PC Board Figure 5 SingleTact configuration USB Interface Arduino Uno 9999 SingleTact Connection Pin Number SingleTact Connection No connection 5 4 No connection Arduino UNO A4 Arduino UNO A5 No connection No connection An Arduino GND pin An Arduino 5V pin Table 5 Shows connections between SingleTact and Arduino UNO The SingleTact is powered from an Arduino 5V line and is connected to the Arduino I2C bus Please refer to Section 3 1 for instructions on flashing the Arduino Copyright 2015 www SingleTact com 8 gt SingleTact MINIATURE FORCE SENSORS Run SingleTact exe to bring up the demonstration application Settings On Hash IC Address x05 Reference Gain 01 4 Baseline 54511 Scale Factor 500600 Full Scale Range Update Hash 12C Address 005 Output 512 Reference Gain x Scale Factor A 5 00 y Sa cone opine sas 65 hi Figure 6 Demo PC DAQ sof
6. E SENSORS 3 2 AN ARDUINO EXAMPLE This section details the Arduino firmware required for the PC DAQ outlined in Section 2 3 The PC to Arduino interface is setup to mirror the I C interface keeping the Arduino code as simple as possible The structure is shown in the following diagram 1 Arduino Uno N SingleTacts Request data USB UART Request data 12C Read output Scan buffer sensors Send sensor data 4 Send new data to PC Transfer to If new data compare itr output buffer and timestamp update Graph repeats repeats repeats Processes not Figure 8 Arduino example communication architecture synchronised Copyright 2015 www SingleTact com 16 gt SingleTact MINIATURE FORCE SENSORS ommand needs I2C result The Arduino firmware functions as follows o ioe Da N New Command Y y 1 Note the Arduino contains a crystal Y Read po over oscillator so it is able to produce a od more accurate timestamp than the packet il N SingleTact interface board Timestamp reading 1 Relay commands l over I2C Send result ack to PC Figure 9 Arduino firmware flow diagram The PC DAQ code functions as follows GUI Thread Acquisition thread intere ston On user click ne Start acquisition thread Start acquisition
7. Tact interface is as simple as arduinoSingleTactDriver nitialise COMport Start Arduino driver singleTact_ l2cAddressForCommunications 0x04 Set 12C address singleTact_ Initialise arduinoSingleTactDriver Start sensor The sensor is read using the following SingleTactFrame newFrame singleTact_ ReadSensorData Get sensor data if null newFrame If we have data Process result Settings can be pulled from the sensor using singleTact_ PullSettingsFromHardware and sent to the sensor using singleTact_ PushSettingsT oHardware The sensor settings can be modified using commands like singleTact_ Settings ReferenceGain Copyright 2015 www SingleTact com 20 gt SingleTact MINIATURE FORCE SENSORS 3 4 INTERFACE BOARD SOURCE CODE The interface board source code can be downloaded from GitHub using https goo gl Qjs62D Programming the C8051F717 requires a 8 bit programmer which can be purchased from Digikey 336 1182 ND Programming requires the Silicon Labs IDE and a free Keil compiler which can be downloaded from http goo gl yJLZh2 The hardware connections are as follows Connection Pin Number Connection Programming Clock Programmer 5 CG Programming Data Programmer pin 7 pin 4 None 6 3 None None 7 2 None Ground Programmer pin 2 or 4 or V Programmer pin 10 9 SL Table 12 Programming connections For convenience the Silicon Labs 8 bit programmer conne
8. cope or data acquisition card a gt PC acquisition software I C digital uutput Interface to customer electronics 2 Evaluation Force o ty Measurement 2 9009 3 Customer Integration 4 Customer Customer reads capacitance using 3 Integration Q their own circuitry Table 1 The four SingleTact use cases 1 In addition to the data acquisition software a NET library is provided for simple integration into a customer s own software suite 2 Supports over 100 SingleTact interface boards Customers can modify interface board firmware as needed Source code is provided in Section 2 4 3 Customer may choose to use the Silicon Labs C8051F717 Capacitance to Digital converter that is used in the SingleTact Interface The source code is provided in Section 3 4 Copyright 2015 www SingleTact com 4 gt SingleTact MINIATURE FORCE SENSORS 2 1 Pinout The sensor is plugged into the FFC connector on the green interface board the sensor connector pads should face upward The connections are outlined in Table 2 The electrical parameters are outlined in Table 3 SingleTact com Figure 2 SingleTact configuration Connection Pin Number Connection Programming Clock O 4 Programming Data 12C Interface SDA 12C Interface SCL Analog output 2V swing 0 5 to 1 5V full scale range Frame Sync Pulse for each new measurement Ground Vec 3 7V to 12V 0 9 O
9. ctor pinout is shown below For more information consult http bit ly 1V6sCm J Figure 11 Silicon Labs 8 bit programmer pinout Copyright O 2015 www SingleTact com 21
10. is can be used to synchronize the I C communications channel to the capacitance sensor Alternatively since the frame index increments with each new frame the sensor can be polled as quickly as possible over I C throwing away duplicate data where the frame index has not incremented Copyright 2015 www SingleTact com 13 gt SingleTact MINIATURE FORCE SENSORS 3 1 FLASHING AN ARDUINO This process outlines how to flash Arduino with SingleTact firmware 1 Download and install the Arduino Software from https goo gl hhQIOK 2 Download the Arduino firmware from GitHub https goo gl mZ03Uu 3 Connect the Arduino to the PC using the supplied USB cable 4 Open the Arduino IDE software Moo sketch_may11b Arduino 1 6 4 DEN File Edit Sketch Tools Help fa sketch mayi1b old setupt A ff put your setup code here to run once void loop put your main code here to run repeatedly Arduino Uno on COMMS Figure 7 Arduino integrated development environment L Go to File gt Open and open SingleTactDemo ino 2 Go to Sketch gt Include Library gt Add zip Library and select Timer1 zip 3 Go to Sketch gt Verify Compile If you receive an error make sure the Arduino is selected under Tools gt Port You are now ready to run the demonstration application detailed in the previous Section Copyright 2015 www SingleTact com 15 gt SingleTact MINIATURE FORC
11. thread o Stop acquisition y On receipt of Sync settings with measurement sensor Post to GUI y thread Displayed on Restart acqusition screen Figure 10 PC DAQ example code Copyright O 2015 www SingleTact com 17 gt SingleTact MINIATURE FORCE SENSORS On the PC the Arduino appears as a virtual serial device Data is sent to from the Arduino using serial interface such as the one available in NET The serial commands which encase the raw I C commands shown in blue are outlined in the following tables Headers and footers are added to easily deliminate serial packets A timeout can be specified for 1 C transfers The Arduino calculates a timestamp for each packet using the Arduino s crystal controlled oscillator Table 10 Serial packet structure to Arduino Copyright 2015 www SingleTact com 18 gt SingleTact MINIATURE FORCE SENSORS Table 11 Serial packet structure from Arduino Ha Copyright O 2015 www SingleTact com 9 gt SingleTact MINIATURE FORCE SENSORS 3 3 NET INTERFACE This section details an example NET DAQ App Download the NET Interface and demo application from GitHub https goo gl CAZP88 For convenience the low level PC interface is encapsulated in two NET components 1 ArduinoSingleTactDriver The basic Arduino interface The user must create one of these 2 SingleTact There can be multiple SingleTacts each with their own I C address Creating a Single
12. tware The demonstration application can be used to change the sensor s I C address and modify its capacitive sensing settings For more information on these settings please refer to Section 3 Copyright 2015 www SingleTact com 9 gt SingleTact MINIATURE FORCE SENSORS 2 4 C INTERFACE The SingleTact I C interface supports standard 100 kbits s and high speed 400 kbits s clock rates and a 7 bit address width The SCL and SDA lines should be pulled up to the bus voltage which can be between 3V and 5V The SingleTact software architecture is based on a 192 byte register which is detailed in Table 6 The first 127 bytes of memory are used to store settings in flash and are therefore persistent after a power cycle The sensing results are available from byte 128 A more detailed breakdown of the register is shown in Tables 7 and 8 The interface board will always respond to two I C addresses 0x04 and the address specified in flash Since the default flash setting is 0x04 the interface board flash address has to be changed before multiple boards can be used on the same I C bus 0 Sensor Setting Saved to flash 127 128 Output Sensor Data 191 Table 6 Register layout The capacitive sensor settings are outlined in the C8051F717 datasheet Internally the CO851F717 measures capacitive to 16 bit precision This is scaled to a 12 bit digital and 2V analog output as per the following calculation Raw capacitance
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