Tekbots Data Logger 3.0 User Manual
Overview
The Tekbots Data Logger device can sample a 0 to 3.3 volt signal with 10 bit precision, allowing eight
channels of to be sampled simultaneously. The data_lgr.3 device can store more than 10,000 samples,
and can sample at periods from 200 micro seconds per channel to 200 seconds. Multiple sessions can
be stored on the data_lgr.3 device, and each session will be stamped with the time the session began.
The user interface also allows the device to be used in an 8 bit live session mode, where the data is
stored on the computer rather than the device.
Usage
The Data Logger 3.0 software can configure and read from the data_lgr.3 board. When the Data Logger
3.0 program is first started, the screen will appear as in Figure 1 below.
Figure 1 - Data Logger 3.0 User Interface
In Figure 1, no data_lgr.3 board is connected to the computer. The current Data Logger state is
indicated by the status label at the bottom of the screen. If a data_lgr.3 device is connected to any USB
port on the computer (no driver is required), the device will be recognized and the Set Settings, Erase
Datalogger, and Start Live Session buttons will become enabled.
Setting up a Sampling Session
By default, the data_lgr.3 board will sample with a period of 0.02 seconds using ADC input channels 0
and 1. If other settings are required, follow these steps:
1. Connect the data_lgr.3 board to a computer
2. Run the Data Logger 3.0 software on the computer
3. Click the Settings button on the Data Logger 3.0 user interface.
At this point, a dialog will appear which resembles Figure 2 below.
Figure 2 - Data Logger Settings Dialog
In the Settings Dialog, simply check the channels to use, and select the desired sampling period (in
seconds). Press OK, and the settings will be stored on the data_lgr.3 board. If an invalid sampling
period is selected, the Sampling Period box will appear red and the OK button will be disabled. The
minimum sampling period per channel is 200 micro seconds, and the maximum is 200 seconds.
The data_lgr.3 board is designed to sample from a source with and output impedance no greater than
20K ohms, but can sample from higher impedances if High Input Impedance Mode is selected. In this
mode, the sample and hold circuitry is connected to the input for 100 micro seconds to allow the
voltage levels to stabilize. In some applications, it may be important to note that on any sampling
interval, each successive channel sampled will be phase shifted by 125 micro seconds from the prior.
For example, if channels 0, 1, and 4 are chosen, channel 1 will be sampled 125 micro seconds after
channel 0, and channel 4 will be sampled 125 micro seconds after channel 1.
Once the OK button is clicked, the settings will be applied to the data_lgr.3 device. Sliding the run/stop
switch to the RUN position will begin a sampling session with the most recent settings. Sliding the
switch back to the STOP position will refresh the sample list in the Data Logger 3.0 software, and the
new session will be visible in the session list.
Downloading and Saving a Sampling Session
To download and save a sampling session, follow these steps:
1. Connect the data_lgr.3 device to a USB port on the computer
2. Run the Data Logger 3.0 software on the computer
3. Have at least one session stored on the Data Logger
Figure 3 below shows the Data Logger software with four sessions recognized from the device.
Figure 3 - Data Logger 3.0 With Four Sessions Recognized
The software will automatically recognize the sessions, but does not automatically load them. To load a
session from the device, click the Load button for the respective sample. The progress bar will display
the load progress. Load time will vary from a small fraction of a second to 30 seconds. When the load is
completed, the Load button will change to Save, and the data set will be displayed in the chart. Figure 4
below shows the Save button and graphed data.
Figure 4 - Data Logger 3.0 Software with one Session Saveable
Clicking Save at this point will open a Save File dialog. Enter the location and filename, and the data set
will be saved as a comma separated values (.csv) file, which can be opened and manipulated with
programs like Matlab or Excel.
Running a Live Session
To run a live session, first ensure the following:
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
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A data_lgr.3 device is connected to the computer
The Data Logger 3.0 software is running
The data_lgr.3 device is set to Stop
To begin the live session, first click the Start Live Session button and the settings dialog will appear. Set
the desired settings (live sessions have a minimum sampling period of 200 micro seconds per channel),
and click OK. At this point, the sampling will begin and the results will be displayed live in the chart. A
maximum of 1000 data points will be displayed during a live session, and the total number of points is
only limited by the memory capacity of the computer.
To stop a live session, click Stop live Session. The data will be stored in memory on the computer until
Save is clicked on the data set. Be aware that exiting the program will cause all unsaved live session
data to be lost.
Board Indicators and Connectors
Power Indicators
The data_lgr.3 device can be powered from USB or from four AA batteries. When the batteries are low,
a red indicator LED will turn on. There are two indicator LED’s: One for the output power (V+ and GND),
and one for the microcontroller power. When battery voltage is too low, one or both of the power
indicator LEDs will light up red. The Output Power Indicator will turn on before the MCU Power
Indicator. The power indicators will also turn on if too much current is drawn from the V+ and GND
pins: the current limit is 0.15 amps.
Sampling Indicators
When the device samples a channel, the Channel Indicator LED will flash. This provides a convenient
method for ensuring the configuration is correct. Note that if the sample period is small (high frequency
sampling), the Channel Indicator LED’s may appear to be on continuously.
Memory Full Indicator
When the flash memory onboard the data_lgr.3 device is full, the MCU State Indicator LED will flash on
and off, and every other Channel Indicator LED will be on. In this state, the data_lgr.3 board must be
reset and the memory must be erased before any more data can be stored (be sure to download and
save the data before erasing the data logger!). To reset the data_lgr.3 device, simply disconnect USB
and battery power momentarily.
Memory Corrupt Indication
A corrupt memory state is signaled by the MCU State Indicator LED blinking rapidly and the Channel
Indicator LEDs all turned on. If the data_lgr.3 device enters this state, the data stored in the device
memory is inconsistent with what is expected. The raw data in the memory chip can be recovered by
running the raw data downloading tool. The device can be put back into a usable state by resetting the
data_lgr.3 and erasing memory.
General Error Recovery
If the data_lgr.3 board is ever in a state where samples cannot be taken (the MCU State Indicator led
flashes and the Channel Indicator LEDs are constantly on to some state), all state holding variables can
be reset by the following procedure:
1. Disconnect all power from the data_lgr.3 board
a. Remove at least one battery
b. Disconnect the USB connector
2. Reconnect the data_lgr.3 board to the computer
3. If the data must be recovered, run the data recovery utility on the computer
4. Run the Data Logger 3.0 software and choose Erase Datalogger
At this point, all state holding memory in the data_lgr.3 board is cleared and the data_lgr.3 device will
be ready to sample data again.
Hardware Overview
The data_lgr.3 board uses an at90usb162 microcontroller as an interface between the computer USB,
memory chip, and ADC chip. The microcontroller will communicate using the Serial Peripheral Interface
protocol (SPI) with the ADC and memory, requesting a sample from the ADC and storing the result in the
external flash memory.
Microcontroller Operation
The at90usb162 microcontroller uses the LUFA USB code for a Generic HID device. Generic HID devices
use drivers built into the operating system, so no driver installation is required. The microcontroller
operates at 8Mhz on 3.3 volts, and all I/O lines to the microcontroller are 3.3 volts as well. If the
data_lgr.3 device must be reprogrammed, simply connect the HWB (hardware boot) pin to ground and
momentarily connect the reset pin to ground. The microcontroller will load the default Atmel boot
loader and the chip can be reprogrammed with the Atmel Flip utility.
Memory Chip Operation
Samples and session data are stored on the external flash memory SST25VF010A device. This device has
1048576 bits of storage capability. Before a sampling session begins, the microcontroller will write a 20
byte header to the flash memory, and sample data will be stored afterwards. When a sampling session
is complete, the number of samples will be written to the header. If a sampling session is terminated
unexpectedly (power is removed), the size will be stored as 0xFFFFFF and the true size will be detected
and written to the header before the next sampling session begins.
ADC Chip Operation
The ADC chip is an MCP3008 8 channel, 10 bit, 2.7v to 5v, 200ksps analog to digital converter. At 3.3
volts, the chip can sample at around 75ksps. Using the microcontroller at 8Mhz limits SPI clock rates to
4Mhz, which in turn limits actual sampling frequency to around 5Khz. Faster sampling rates could be
obtained if samples were stored in 8 bit format instead of 10, and if the output impedance of the
sampled signal is guaranteed to be small (less than 1K).
The input of the ADC chip is a sample and hold circuit which connects to the channel input when a
sample is taken. When the sample and hold connects, a hold capacitor must charge up to a stable
voltage. The precision of the sample and hold measurement is a function of the sampling time and input
impedance: a longer sample time will allow for a larger input impedance. Currently, normal samples are
taken with a sample time of 10 micro seconds, which allows for accurate measurements with input
impedances up to 20K ohms. In high input impedance mode, the sample time is increased to 100 micro
seconds, allowing for accuracy with input impedances up to 500K ohms. Note that the increased sample
time when using high impedance mode will cause increased phase shift between successive samples on
the same sampling interval.