- Data type: UINT16 (type index = 0)
- Read-only
The Digit is a battery powered temperature and light logging device, which collects data in a remote location, and stores it to internal memory. When finished, the data can be downloaded via the convenient USB connector. Each data point is associated with a time stamp, so you know when it was collected.
Using the provided Otero software, starting, stopping, and downloading from the Digit is simple and easy. Data is summarized in the program view screens, or can be exported to .csv for further analysis. Temperature can be viewed in °C or °F, and real-time data is visible when connected over USB.
The Digit also supports field programmed firmware upgrades, just download the latest firmware file from the firmware page, and upgrade using the software package provided.
General
Memory | 260,000 Readings |
Logging rate | 10s, 30s, 1m, 10m, 30m, 1h, 6h |
LED Alarms | 2x user-defined thresholds |
LED indicators | Green, Red |
Battery life | 3.3 Years @ 25°C, 1m interval |
Battery type | 3V CR1632 coin cell, replaceable |
Software | Free, Windows only |
Communication | USB |
Real-time clock | ±2 seconds per day @ 25°C |
Memory-Wrap | No |
Single/Multi-Use | Multi-use |
Conformal Coating | Yes |
Operating Temperature | -35°C to +85°C (-31°F to +185°F) |
Solid-lid Plastic Enclosure (-TL) | IP67 - Water Resistant when properly closed * |
Aluminum Enclosure | IP68 - Not hermetically sealed ** Depth: 1.5m ** Duration: ** |
Unlike many battery powered loggers in its class, the Digit does not require a special base to download stored data. Simply connect the Digit to an available USB port, and download stored information using the Otero software. The circuit board is protected by a thin film of conformal coating, which makes the Digit resistant to moisture, static discharges, and fingerprint oils. Still, it is recommended to take ESD precautions when handling the circuit board directly.
Note: Foreign objects inside the enclosure present a risk of damaging the board when the base is twisted off because they can catch and bind.
Note: For applications where the digit may be exposed to water or excess humidity that may condense onto the PCB consider placing a small desiccant packet in the case along with the Digit to prevent moisture build up inside the case. Remember to replace the packet when necessary.
* The plastic enclosure is hard to close properly. The rubber o-ring has a tendency to not properly seat itself in between the case lid and case body. Customers have reported humidity building up inside the plastic enclosure during long term testing resulting in failed measurements.
** We have not done thorough water resistance depth or duration testing other than our digit pond tests so we do not have exact depth or duration specifications to go along with the IP68 water resistance rating. These are two additional specifications that CNET recommends manufacturers also supply when indicating that devices have an IP68 rating. Our tests indicate that the aluminum enclosure is more water resistant than the plastic enclosure which we have rated for IP67 when properly closed so if a Digit-TL is being used in continuous submersion experiments we highly recommend the use of the aluminum enclosure. The case has an extra indentation so that the O-ring is more likely to seat itself properly in between the case lid and the case body resulting in a more water tight seal.
SPECIFICATION | MIN | TYP. | MAX. | UNIT |
---|---|---|---|---|
Temperature range* | -35(-31) | +85(185) | °C(°F) | |
Temperature resolution | 0.067(0.12) | °C(°F) | ||
Temperature accuracy at +25°C (+77°F) | ±0.1(0.2) | ±0.5(0.9) | °C(°F) | |
Temperature accuracy from 0°C to +65°C (+32°F to +149°F) | ±0.25(0.45) | ±0.5(0.9) | °C(°F) | |
Temperature accuracy from -35°C to +85°C (-31°F to +185°F) | ±0.5(0.9) | ±1(1.8) | °C(°F) |
*Temperature readings are not restricted to the operating range, however continuous operation beyond the limits specified is not guaranteed.
Note: When connecting a Digit that has been exposed to temperature extremes (below 32 degrees F or above 100 degrees F) it is recommended to let the digit adjust back to room temperature for approximately 5 minutes before connecting the device to your computer.
The Digit uses a Texas Instruments TMP112 to record temperature. The TMP112 chip returns calibrated 12-bit readings which are saved to memory within the Digit-TL/TLH. For more information about this temperature sensor, see the TMP112 datasheet.
SPECIFICATION | MIN | TYP. | MAX. | UNIT |
---|---|---|---|---|
Light range | 10 | 12,000 |
Light readings are determined based on reverse leakage through the green LED, and thus have the strongest response to the green component of light. The readings are returned in a Lux range, but should not be considered accurate Lux values, and the values can vary greatly from device to device. Light readings are also dependent on temperature as we don't do a full light calibration process while manufacturing the devices.
Although not intended for calibrated light measurements, the light readings are useful to monitor changes in light levels. The most common application is simply monitoring whether some light source is on or off.
Because the light readings can vary greatly from device to device, the recommended usage is to take a particular device, see what it reports at different light levels in an environment of interest, and then use that information to interpret future readings.
The example below demonstrates a possible operating sequence for the Digit.
The moment the Digit is connected to a USB port, it will signal if a user threshold alarm has been triggered. If any alarms have been triggered the red LED will illuminate for 5 seconds. If the alarms are configured, but no alarms have been triggered, the Green LED will illuminate for 5 seconds. If user-alarms are disabled (set to None in software), the LEDs will not turn on. Additionally, while connected to USB, and for 6 log events after disconnect from USB, each read of temperature will cause the green LED to blink once.*
LEDs OFF: Alarm(s) are disabled.*
Green LED: Alarm(s) configured, but not yet triggered.
Red LED: Alarm(s) triggered.
Green and Red LEDs Blink: Two rapid blinks of both LEDs indicates that the device has recovered from a system error, such as a power failure from changing the battery.
There are no buttons on the device (to save on space, and make the enclosure more simplistic) so instead the LEDs are activated with USB power.
*LED behavior changed slightly starting with firmware v1.21, see firmware revision history for details.
Battery life
Logging at a rate faster than one reading per minute doesn't decrease battery life dramatically, but it does have a small impact. Take note of the table below if you are using the Digit in hot temperatures.
LOG (1M) \ TEMPERATURE | -35°C | 23°C | 85°C |
---|---|---|---|
Temperature | 3.4µA | 3.9µA | 11.4µA |
Temperature, Light | 3.8µA | 4.4µA | 11.8µA |
*3 year lifespan calculated: 140mAh / 0.0048mA = 31818hr = 3.33yr
Notice that at cold temperatures the power consumption is actually lower than at room temp, but some batteries have reduced overall capacity at low temperatures, which can offset the reduction in power usage. High temperatures have the most dramatic impact on battery life, as the processor and peripherals simply consume more power when hot.
Memory
Memory will not run out for at least 15 days, at a log interval of 10 seconds, while logging temperature, and light. The memory lasts much longer if you select fewer log items, and change the logging to happen less frequently. For example, if you log temperature and light once per minute, the memory will last for 90 days.
Ex: 260,000(readings) / 2(log items) / 1(per minute) / 60(minutes) / 24(hours) = 90.277 days of memory
Reference the table below to find how long it will take to use up memory space.
10S | 30S | 1M | 10M | 30M | 1H | 6H | |
---|---|---|---|---|---|---|---|
Temperature | 30d | 90d | 181d | 4.9yr | 14.8yr | 29.7yr | 178yr |
Temperature, Light | 15d | 45d | 90d | 2.6yr | 7.4yr | 14.8yr | 89yr |
When the Digit runs out of space to store new readings, it will not wrap-around and erase older data, it will simply not store new information. When the Digit reaches 262,144 stored readings, the very last data point is repeatedly overwritten.
Alarm conditions
Threshold alarms are useful for applications where the data set is not important, as long as a specific threshold is not exceeded. There is no button on the Digit to check if an alarm occurred, so alarms can be checked by plugging it into a 5V adapter, or 5V USB battery as shown in the images below. Adapters are in-expensive, and can be purchased through a number of retailers. Shown below is a simple 5V adapter and a 11200mAh External USB Battery Pack, this smaller one would also work.
The concept is that the "checking station" will have a 5V USB power supply (battery or adapter). Simply plug the Digit in for a brief moment to check LEDs, and then place it back into the measurement environment. Also, only a single 5V USB supply is required to check as many Digits as desired.
A key in understanding threshold alarms is to realize that the act of checking an alarm would trigger the alarm, if it the alarm always occurred on the first out-of-threshold reading. Alarm arming must also be considered: what if it takes some time before the Digit reaches equilibrium with the measurement environment? The Digit has three ways to customize arming and triggering behavior, which allows for flexible alarm control.
1. Arm after time delay. Say it takes ~30 minutes to reach equilibrium with the measurement environment, and after this amount of time, you want to know if a specific threshold in temperature is exceeded. Configure the alarm arming condition for a pure time delay of 30 intervals, at a 1 minute log interval. Once configured, the alarm will not arm until 30 minutes have elapsed, and thus the alarm cannot be triggered until at least 31 minutes have elapsed.
2. Arm according to thresholds. If the amount of time to reach equilibrium is unknown, it is possible to delay arming until the Digit reaches a specific threshold condition. Once below/above the defined threshold(s), it will become armed, and thereafter the alarm will trigger if the threshold is exceeded. Threshold arming is particularly useful for refrigeration applications. Accommodate environment noise by setting the arming delay to a few intervals.
3. Trigger delay. Just like a security system, the alarm cannot be triggered until it is armed. But then what if you want some time to check the LEDs, without concern for triggering the alarm? Also, what about environment noise? Will a single stray data point cause the alarms to trigger? Set an appropriate trigger delay to resolve these issues. A trigger delay of 1 will trigger the alarm on the first alarm-causing data point. A trigger delay of 5 means that 5 consecutive alarm-causing data points must occur before the alarm is triggered. Use the trigger delay to account for environment noise, and give yourself time to check the LEDs, and return the Digit to the logging environment.
The Digit does not have an accurate method of determining how much battery life is remaining, it does not have any battery detection circuitry in place. Instead, Otero uses a mixture of the number of logged data points collected since the battery install date and the validity of the temperature sensor's data to determine the battery's remaining battery life. If the battery install date is not accurate or if it has been changed then the remaining battery life indicator will be wildly inaccurate. If the real-time temperature data shown in the "data" tab of Otero is displayed as "NaN" the battery voltage is below the operating level of the device and the battery therefore dead. The Digit will report Brown-Out, Power Failure, Low Voltage, and other errors in the logged data set more frequently as the battery ages and will eventually become un-able to log any data. As a general rule of thumb, if the device is being set out to log for a long period of time it is wise to replace the battery beforehand.
Enclosure: 60mm x 21mm (2.362" x 0.826")
Circuit board: 40mm x 17mm x 9mm (1.57" x 0.67" x 0.35")
You can see that the circuit board is close to the size of a USD Quarter. Slip it into a jacket pocket, or toss it in the glove box to monitor temperature on the go. The rubber o-ring provides a highly water resistant seal. Included with the aluminum enclosure are two extra o-rings that can be used as backup or spare seals. Remove the extra O-rings from the enclosure before use.
Back in January when we first started selling Digit devices, someone decided to stow one outside partially under a rock to see how it'd hold up. Well after about 7 months, the results were collected, and you can see them below. The rock covered about half of it, so the discoloration on the enclosure is from the sun on the exposed half.
Temperature data for Colorado from January to late July.
Data was collected at a 10 minute interval, and only temperature was being logged. Each day is a small spike, and then within each day (can't be seen at this zoom level), it is possible to see when the sun passed from direct contact with the Digit, to only hitting the rock above (shaded).
As the season changes from winter to summer, the average temperature increases, nothing too surprising, but it's always good to verify that the hardware is reliable, even in outdoor conditions. Read more on the related blog post.
The Digit-TLH is a battery powered temperature, light, and humidity logging device, which collects data in a remote location, and stores it to internal memory. When finished, the data can be downloaded via the convenient USB connector. Each data point is associated with a time stamp, so you know when it was collected.
Using the provided Otero software, starting, stopping, and downloading from the Digit is simple and easy. Data is summarized in the program view screens, or can be exported to .csv for further analysis. Temperature can be viewed in °C or °F, and real-time data is visible when connected over USB.
The Digit also supports field programmed firmware upgrades, just download the latest firmware file from the firmware page, and upgrade using the software package provided.
This information describes the Digit-TLH's humidity sensor additions and what features users are given on top of the Digit-TL device. This information should be used in conjunction with the information found on the Digit Datasheet page. Due to the Digit-TLH being discontinued, a copy of the original Digit-TL and Digit-TLH datasheet can be found in .pdf form.
General
Vented Enclosure (H) | IP53 |
Specification | Min | Typ. | Max. | Unit |
---|---|---|---|---|
Humidity range | 5 | 95 | %RH | |
Humidity resolution | 0.75 | %RH | ||
Humidity accuracy* 15 to 60%RH & 25°C | ±3.5 | %RH | ||
Humidity accuracy* 10 to 90%RH & 25°C | ±5 | %RH | ||
Response time τ (63%) | 30 | sec | ||
Response time τ (63%) (inside enclosure) | 240 | sec |
*Humidity accuracy can be improved to ±2% with high accuracy calibration chamber. See Offset and Slope discussion below.
The Digit-TLH uses a Honeywell HCH-1000 to record humidity. The 10-bit ADC and current source work together on the Digit to record the capacitance value of the HCH-1000, which is then adjusted in software to produce a calibrated humidity reading. Due to the limited resolution of the on-board ADC, the humidity resolution is limited to about 0.75% humidity per step.
The humidity version of the Digit is called the Digit-TLH, meaning that it is capable of logging all 3 types of data: Temperature, Light, and Humidity. Touching the wires of the HCH-1000 sensor during a reading will cause the reading to be wrong, but this is only an issue when holding the unit in your fingers to plug it in.
The -TLH version of the Digit is factory calibrated to meet the above specifications. If higher accuracy is necessary, it may be possible to improve calibration by adjusting the parameters listed below. There is typically no need to adjust the factory offset, or slope, they are provided for advanced users to improve accuracy.
There are two main parameters to adjust the calibration of Digit humidity. Use the calibrate humidity section in software.
To verify correct calibration, simply download the data after new settings are stored, and software will use the new calibration adjustments. The calibration images below illustrate humidity data collected by nine different Digit-TLH devices in two fixed-humidity reference chambers. The single-point calibration shows the factory calibration quality.
The factory calibration is a single-point calibration adjustment, but higher accuracy can be achieved with a two-point calibration as demonstrated in the image below.
The dew-point temperature can be calculated from the relative humidity and temperature. The dew-point temperature is the temperature to which the air must be cooled to reach saturation. Basically when the temperature cools to the dew point, fog or dew can occur, because ambient water vapor will condense. A well-known approximation used to calculate the dew point, given just the air temperature, T and relative humidity (in percent), RH, is the Magnus formula:
Dew Point = (243.12*[ln(RH/100)+( (17.62*T) / (243.12+T) ) ] ) / (17.62 - [ln(RH/100)+( (17.62*T) / (243.12+T) ) ] )
RH = Relative Humidity (in percent)
T = Temperature (in Celsius)
Spreadsheet program users can copy and paste the above formula into their spreadsheet software to generate a column for dew point (substituting RH and T with corresponding cell contents). Alternatively, use an online calculator. There are some other more complex ways to calculate dew point, see the Wikipedia Dew Point topic if interested.
Logging at a rate faster than one reading per minute doesn't decrease battery life dramatically, but it does have a small impact. Take note of the table below if you are using the Digit in hot temperatures.
Log (1m) \ Temperature | -35°C | 23°C | 85°C |
---|---|---|---|
Temperature | 3.4µA | 3.9µA | 11.4µA |
Temperature, Light | 3.8µA | 4.4µA | 11.8µA |
Temp, Light, Humidity | 4.2µA | 4.8µA* | 12.5µA |
*3 year lifespan calculated: 140mAh / 0.0048mA = 31818hr = 3.33yr
Notice that at cold temperatures the power consumption is actually lower than at room temp, but some batteries have reduced overall capacity at low temperatures, which can offset the reduction in power usage. High temperatures have the most dramatic impact on battery life, as the processor and peripherals simply consume more power when hot.
Memory will not run out for at least 15 days, at a log interval of 10 seconds, while logging temperature, and light. The memory lasts much longer if you select fewer log items, and change the logging to happen less frequently. For example, if you log temperature and light once per minute, the memory will last for 90 days.
Ex: 260,000(readings) / 2(log items) / 1(per minute) / 60(minutes) / 24(hours) = 90.277 days of memory
Reference the table below to find how long it will take to use up memory space.
10s | 30s | 1m | 10m | 30m | 1h | 6h | |
---|---|---|---|---|---|---|---|
Temperature | 30d | 90d | 181d | 4.9yr | 14.8yr | 29.7yr | 178yr |
Temperature, Light | 15d | 45d | 90d | 2.6yr | 7.4yr | 14.8yr | 89yr |
Temp, Light, Humidity | 10d | 30d | 60d | 1.6yr | 4.9yr | 9.9yr | 59yr |
When the Digit runs out of space to store new readings, it will not wrap-around and erase older data, it will simply not store new information. When the Digit reaches 262,144 stored readings, the very last data point is repeatedly overwritten.
There are two different hardware versions for the Digit-TL/TLH. The primary difference is that the current version has an easily replaceable CR1632 battery, and the old version has a solder mount battery which required a soldering tool for replacement. Hardware version 1.11 is no longer in production, as v1.20 is a fully compatible improvement. They are both compatible with Otero(software), and should be considered interchangeable.
Hardware version 1.20 on the left, and v1.11 on the right, the table below describes the notable differences.
Hardware v1.20 | Hardware v1.11 | |
---|---|---|
Battery style | Replaceable CR1632 | Solder mount BR1632 |
Battery life | 140mAh (3.3yr) | 120mAh (3.0yr) |
Operating temp (T, L) | -35 to 85°C | -35 to 85°C |
Operating temp (H) | -35 to 85°C | 10 to 85°C |
Humidity slope stability | ±0.01%RH/°C | ±0.04%RH/°C |
Default enclosure | Clear plastic* | Aluminum |
Al Enclosure Orientation** | USB opposite to keyring | Either orientation OK |
* The clear plastic enclosure includes both a vented and watertight base option. Unlike the aluminum enclosure, the clear plastic enclosure allows the device to collect light readings. The rugged aluminum enclosure can be purchased as an add-on item.
** Both hardware versions fit inside the aluminum and clear plastic enclosure variants, but the battery holder makes HW 1.2 a bit too large to fit both directions in the aluminum case. The aluminum enclosure is watertight and airtight, so response time of the Digit temperature readings is not impacted by orientation within the case.
The battery in HWv1.11 was a 120mAh Panasonic BR-1632A, and can be found on DigiKey, part number P022. With a soldering tool it is possible to both replace the battery, or install a different battery.
Note: If extreme harsh temperatures are expected to last for a long time, a custom battery can be installed to handle the conditions. Acceptable battery voltage range is 3.0V to 3.6V. Our top pick is a Tadiran TL-5101/P, which will work continuously for more than 3 years at even the most harsh of conditions (-55C to +85C). The Digit shown below is stored inside our office refrigerator.
On old Digit-TLH devices, the humidity accuracy below 10°C was subject to battery voltage. Often times the battery voltage would drop at cold temperatures, and the humidity readings were low if the battery voltage was less than 2.73V. Humidity readings on new hardware (v1.2+) operate normally over the full temperature and battery voltage range.
When the Digit is connected to a powered USB port, battery usage is suspended. Therefore, it is possible to prolong battery life by connecting the Digit to a 5V USB adapter, or USB hub when it's not being used. Another good method to prolong battery life is to disable all log items when the Digit is not in-use. When nothing is being logged, it stays in a low-power sleeping state.
Use the instantaneous readings to grab a reading from each of the sensors while the Digit is connected via USB. The conversion equations used to convert each of these from a raw representation are described below. Alternatively, download the C++, or LabVIEW example code attached at the bottom of this page.
Temperature on the Digit is stored as an unsigned 12 bit value, this value needs to be converted into a signed number, and multiplied by a conversion factor before it will look like degrees C. The raw value is a 16-bit number, the 4 lowermost bits being system flags.
Raw Temperature 16-bits:
Xxxx xxxx xxxx rrrr
r's are reserved for flags.
x's are the temperature information.
X is the most significant temperature bit, discussed in step 2.
The TMP112 datasheet also explains this process. See page 8: http://www.ti.com/lit/ds/sbos473b/sbos473b.pdf
Invalid Measurement = 32768
If the battery is dead, the TMP112 has failed, or a communication line between the temperature sensor and the microprocessor is damaged. the Digit will return a value of 32768. A value of 32768 converts into -128C, but normal operation will never return -128C, so it's a unique indication of an invalid reading.
bit0 (0x01) = Warning Detected
bit1 (0x02) = Power Failure Detected
bit2 (0x04) = Reset Detected
bit3 (0x08) = 'On USB' flag, to indicate processor heat influence
Raw light readings are saved as a number of timer counts in memory, ranging from 18-65535.
Raw Light 16-bits:
xxxx xxxx xxxx xxxx
In software the calibrated light value is generated through interpolation along a 3D surface (with some simplification). The temperature (to nearest 1°C) at the time of the light reading is used as an index, then the Digit's raw light value (timer counts) points to a region in-between Lux values, so interpolation is performed between the nearest 2 points in Lux.
Due to the simplification of 1°C resolution, the interpolation is merely done on a 2D surface, the whole 3D surface does not need to be analyzed in software.
If converting raw light readings sounds overwhelming, don't worry too much-just look at the C++ example code attached on this page. The 3D calibration surface is simply a header file[LightCalibration.h] with 3 static arrays. The light conversion code uses temperature as the first lookup index in the header file, which reduces the three large(1792 datapoint) arrays down into two 14 datapoint arrays that represent possible values of calibrated lux and raw light counts at the given temperature.
Next, the raw light reading (DGT_LIGHT_RAW) is compared to each of the raw readings in the 14 datapoint array that contains raw values. Simple linear interpolation between the two nearest raw values will yield a fractional index of where the raw reading resides relative to the available calibration points. Finally, this fractional index is applied to interpolate between the nearest Lux values which yields the light reading in Lux.
Invalid Measurement = 1
If the Digit is plugged/un-plugged from USB during a light reading in-progress, the reading is interrupted, and a 1 is saved instead of the timer value. A value of 1 converts to roughly 12000 Lux, but normal operation will never return a value of 1, so it's a unique indication of an invalid reading.
Humidity readings are performed by an HCH-1000, which is a capacitive humidity sensor. A constant current source and a 10-bit ADC on the Digit-TLH work together to read the capacitance value, which is the raw humidity reading.
Raw Humidity 16-bits:
rrrr xxxx xxxx xxxx
x - measurement of raw capacitance (humidity)
r - reserved.
Master Equation
%RH = (DGT_HUMIDITY_RAW - DGT_HUMIDITY_CAL_OFFSET + ( (DGT_HUMIDITY_CAL_T_SLOPE)(DGT_TEMPERATURE_LATEST_RAW) -
(DGT_HUMIDITY_CAL_T_SLOPE)(-38) )(DGT_HUMIDITY_CAL_SLOPE)
*In the case of downloaded data, use whatever temperature reading happened at the same time as the humidity reading (adjacent in memory).
Invalid Measurement = 1
If the Digit does not have a humidity sensor, or the humidity sensor is broken, the raw humidity reading will be a value of 1. Normal operation will never return a value of 1, so it's a unique indication of an invalid reading.
There is also a command (DGT_HUMIDITY_CAL_I_SOURCE) to initiate calibration of the constant current source, which is used during factory calibration, but it is not recommended to write to this register, unless you plan to re-calibrate the other parameters.
Use the _DATASET, and START_TIME parameters to interpret downloaded data. Logged data must always be saved in one of the following sequences: T, TL, TH, THL, so downloading code simply reads the logged items, and interprets data space in segments of unsigned 16s. There are no timestamps saved with the data. Instead, use the DGT_LOG_START_TIME and the DGT_LOG_INTERVAL_INDEX_DATASET to determine when data was collected.
Change the configuration of the Digit with the following registers. Changes are applied when data is erased with DGT_FLASH_bkERASE. It is recommended that the Digit RTC is synchronized with the host computer with DGT_RTCC_TIME immediately prior to applying changes to configuration (calling DGT_FLASH_bkERASE).
Alarm thresholds, changing factory settings, and upgrading firmware are not covered in this doc. If you need information about these topics please contact [email protected] for more details.