Shimmer Shimmer3 Manuel utilisateur

Realtime Technologies Ltd IMU User Manual

Shimmer3

Bridge Amplifier+ Expansion Board

User Guide

Revision 1.6

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

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Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

Table of Contents

1. Introduction .........................................................................................................................4

2. General Information .............................................................................................................5

2.1. Pre-Requisites .........................................................................................................................5

2.2. Bridge Amplifier+ Expansion Board Specification...................................................................5

3. Hardware Considerations...................................................................................................... 6

3.1. Board Layout and Connections...............................................................................................6

3.2. Output Signals.........................................................................................................................7

4. Using the Bridge Amplifier+ Module...................................................................................... 8

4.1. Load Cell Calibration: Calculating Load...................................................................................8

4.2. Resistance Calibration: Calculating Resistance.......................................................................8

5. Firmware Considerations ......................................................................................................9

6. Hardware Customisation .................................................................................................... 10

7. Troubleshooting ................................................................................................................. 11

7.1. Verifying Your Shimmer Bridge Amplifier Works..................................................................11

7.2. Secure connection between Shimmer and expansion board...............................................11

8. Appendices......................................................................................................................... 12

8.1. Assembly ...............................................................................................................................12

Opening the Bridge Amplifier+ enclosure.....................................................................................12

8.2. Recommended accessories...................................................................................................12

Philips 21091A Technical Data......................................................................................................12

8.3. How to Connect a Wheatstone Bridge to the Shimmer Bridge Amplifier ............................13

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

1. Introduction

This document is an accompaniment to the Shimmer Bridge Amplifier+ Expansion Board. Its purpose

is to aid the user in getting started with Shimmer Bridge Amplifier+ Expansion Board.

The Shimmer Bridge Amplifier+ Module contains a bridge amplifier, excitation source, and connector

enabling force measurement with Shimmer. The expansion board is ideal for all load, weight, force,

torque, and pressure measurements through the connection of a user-supplied strain gauge based

bridge sensor or load cell. One application area is muscle capacity testing including pinch-grip, lift-

bar, and grip-strength.

The Bridge Amplifier circuitry detects variance in resistance values when force is applied to the load

cell. The small, lightweight, wearable form factor allows for measurements free from wired

constraints to allow for natural range of motion, and measurement outside of a dedicated lab

setting.

Additionally, the board has a connector and amplifier for Resistance measurement. For example, this

can be used to measure data from a temperature sensor, like the Philips 21091A, or other

resistance-based sensors with a range of 1k- 20k.

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

2. General Information

2.1. Pre-Requisites

A Shimmer3 device programmed with appropriate firmware.

oLogAndStream (v0.6.0 or greater) can be used to simultaneously log data to SD card

and stream data over Bluetooth.

oSDLog (v0.12.0 or greater) can be used to log data to the SD card.

oBtStream (v0.7.0 or greater) can be used to stream data over Bluetooth.

oAll are available for download from www.shimmersensing.com.

A Shimmer Bridge Amplifier+ Expansion Board.

A suitable strain gauge load cell or resistance-based sensor.

2.2. Bridge Amplifier+ Expansion Board Specification

Bridge Amplifier:

oGain1: 183.7 ± 1% (Normal Channel), 551 (3x Normal) ± 1% (High Gain Channel)

oFrequency Range1: DC..1kHz (Normal Channel), DC..100Hz (High Gain Channel)

oCommon Mode Rejection1: higher than 110dB

oInput Impedance1: 50MOhm

oInput Signal Range: ±7mV, ±2.5mV/V (Normal Channel), 0-4mV, ±1.43mV/V (High

Gain Channel)

oZero-load Noise: 12mV RMS both outputs, < 1% full-scale (Normal Channel), < 0.5%

full-scale (High Gain Channel)

oExcitation Voltage2: 2.8V ± 5%

oInput Protection: Current limiting, EMI/RF suppression

Resistance Amplifier

oGain1: 10.1 +/-2%

oPull-up/Input Impedance: 200kOhms to +3.0V

oFrequency Range1: DC..408Hz (2nd Order)

oSignal Range: 280mV or 20kOhms (1k-20kmeasurement range recommended)

oZero-load Noise: 0.1 mV RMS at output.

Connections: Two 3.5mm jacks (headphone type) for 4 conductor shielded cable for Bridge

Amplifier and Resistance Amplifier,

Current Consumption: < 100µA (Excitation disabled), 17mA (Excitation enabled3)

EEPROM memory: 2048 bytes.

1Calculated specification, exact value subject to environmental and component variation.

2The Excitation source is software controlled.

3This value is load-cell dependant, to estimate use the formula I = 1 + 2.8/(RSGin || RSGout); RSG data is

available from the load-cell manufacturer.

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

3. Hardware Considerations

3.1. Board Layout and Connections

The board layout for the Bridge Amplifier+ Expansion Board is illustrated in Figure 3-1, whilst

connections for the 3.5 mm jacks on the board and their corresponding functions are listed in Table

3-1 and Table 3-2. For details on the connections for J6 and J7, which connect the board to the

Shimmer3 mainboard, please refer to the Shimmer User Manual, which can be downloaded from the

Shimmer website.

Figure 3-1 Board Layout for Bridge Amplifier+ Expansion Board

The 3.5 mm 4-position jack connectors, J3 and J5, (indicated in Figure 3-1) have four connections

each, as labelled in Figure 3-2. Their connections are listed in Table 3-1 and Table 3-2.

Figure 3-2 Connector labels for 3.5mm 4-position jack

Connector

Pin #

Shimmer3

Label

Function / Notes

Sleeve (J3.1)

GND

Ground Connection

Tip (J3.2)

SGP

Signal (Positive)

Ring1 (J3.3)

SGN

Signal (Negative)

Ring2 (J3.4)

PV_SG

2.8V if GPIO_INTERNAL1 is high.

Table 3-1 Shimmer Bridge Amplifier+ Expansion Board connections for J3.

J5 indicated by yellow

colour on connector

tip

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

Important Note: Do not insert a two-position 3.5mm plug into the J3 connector as this may cause a

short-circuit between PV and GND.

Connector

Pin #

Shimmer3

Label

Function / Notes

Sleeve (J5.1)

GND

Ground Connection

Tip (J5.2)

SGN

RDIV1 (Signal)

Ring1 (J5.3)

GND

Ground Connection

Ring2 (J5.4)

GND

Ground Connection

Table 3-2 Shimmer Bridge Amplifier+ Expansion Board connections for J5.

Important Note: The pin-out of the J5 connector is not the same as that for other Shimmer3

expansion boards and is not compatible with Shimmer accessories, such as the Optical Pulse

Sensing Probe.

A high quality four-position 3.5mm jack with cable is available for purchase from Shimmer. You can

wire this connector to your load cell according to the connections in Table 3-1.

3.2. Output Signals

Table 3-3 below lists the ADC channel of the Shimmer3 to which each of the output signals from the

Bridge Amplifier+ Expansion Board is connected.

Signal

ADC channel

Function

Bridge Amplifier Low Gain

A14

bipolar pre-amplification

Bridge Amplifier High Gain

A13

additional 3x gain for unipolar load cells

Resistance Amplifier Output

resistance pre-amplification

Table 3-3 ADC channels for Bridge Amplifier+ Expansion Board output signals

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

4. Using the Bridge Amplifier+ Module

4.1. Load Cell Calibration: Calculating Load

To convert the output of the Shimmer to a quantifiable unit you require:

Output specification for the load cell device you are using in mV/V.

Knowledge of the daughter board gain (Normal or High Gain Channel, see specification

overview above).

The calculation procedure is:

1. Measure the ADC output difference (ADCDIFF) between a zero-load reading and the reading

of interest in your application. Referencing the actual zero-load reading obviates

consideration of DC offset error.

2. Convert the ADCDIFF into an analogue voltage difference (VDIFF) in mV using a ratio

3000mV / 4095bits = VDIFF (mV)/ ADCDIFF (bits)

where 4095 is the resolution of the Shimmer 12bit ADC

VDIFF (mV) / = ADCDIFF (bits) * 3000 mV/4095 bits

3. Divide the voltage by (2.8V x gain) to compute the load-cell output (LCOUT) in mV/V

LCOUT (mV/V) = VDIFF (mV) / (2.8V * gain)

4. Refer to the load cell calibration report or datasheet to determine the rated output (ROUT) in

(mV/V)/lb or (mV/V)/kg.

LOAD = LCOUT / ROUT

Example Calculation:

The high gain output has a zero-output ADC value of 230. In a grip test using a Futek LMD500 the

peak ADC value is 1430. What is the load in lbs?

(1) ADCDIFF = 1430 bits –230 bits = 1200 bits

(2) VDIFF = 1200 bits * 3000 mV/4095 bits = 879 mV

(3) LCOUT = 879 mV / (2.8V * 551) = 0.570 mV/V

(4) This calibration data for the LMD500 used has a rated output of 2.83mV/V @ 300lbs.

LOAD = 0.570 (mV/V) / (2.83(mV/V) / 300lbs) = 60.42lbs

4.2. Resistance Calibration: Calculating Resistance

For the Resistance amplifier channel, the relationship between the resistance at the input, , and

the voltage output, , is as follows:

   󰇛 󰇜

󰇛󰇜 

where  = 3V and  should be measured in volts.

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

5. Firmware Considerations

Note: This section is only of concern to persons wishing to modify the firmware.

Users with firmware development experience who wish to develop custom firmware for the Bridge

Amplifier+ Expansion Board should follow the example provided in the BtStream application, source

code for which is available on the Shimmer GitHub repository at

https://github.com/ShimmerResearch/shimmer3/tree/master/apps.

Users should note that the excitation voltage for the load cell connection is enabled via

GPIO_INTERNAL1. The amplifier for the Resistance input is enabled via Internal Expansion Power

(EXP_RESET_N). See the Shimmer3 User Manual for more details on these pins.

Realtime Technologies Ltd Shimmer3 Bridge Amplifier+ User Guide

6. Hardware Customisation

DISCLAIMER: We recognize the variation in gain and ranges of interest when performing

research with load cells. Hardware customization is best discussed with our engineers at the

time of order and executed by our factory.

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