HEM Data Support


Please look for your question in the Frequently Asked Questions below. If you are already using HEM Data products, and don’t see your question, you may fill out the Technical Support Form.

Database / Vehicle Data

What parameters are standard to cars (OBD-II)

List of OBD-II parameters

What parameters are standard to heavy duty trucks (J1939)?

List of J1939 parameters

Is it possible to configure the CAN bus logger using a .DBC file?

Yes. You can import the DBC file into our DawnEdit software. Also you can add your own messages.

For light/medium duty vehicles, how do I log all of the data that is broadcast on the CAN network?

The DAWN OBD Mini Logger will log broadcast (Normal) messages when placed in the vehicle with no config.txt file. In addition, adding “|EFFFFFFFF” to the end of the first line of the config.txt file will log all Normals along with requests.

Is the OBD Mini Logger capable of being reconfigured for any of the proprietary CAN buses available on the vehicle – beyond the standard OBD CAN bus?

Yes. It also supports various CAN baud rates.

Pricing / License

What is the pricing for the DAWN Mini Loggers?

The Mini Logger pricing is volume dependent. Please contact sales@hemdata.com.

Does the software have an expiration date?

There is no expiration date for the software. The software is supported for 1 year unless you purchase an Extended Support Policy (ESP). Contact HEM Data for more about ESP.

Are you delivering in the EU?

HEM Data sells and supports its products worldwide from our U.S. office.


What frequency is used for CAN sampling?

Frequency is adjustable. CAN data can be acquired at the maximum rate it is transmitted on the bus. 250 samples/sec is the fastest any message is transmitted.

What is the maximum logging period for highest and lowest sampling frequency?

The standard microSD card is 4GB and should last for many months and possibly up to 2 years. Data is stored as a compact binary file. A file is a trip – it starts when ignition is on and ends when ignition is off.

Can I acquire CAN and analog simultaneously?

Yes. The DAWN J1939 and OBD Mini Loggers can acquire CAN data along with any number of ADAQ units.

Does the logger write timestamps?

Yes, there is a real time clock (RTC) on the logger. Also, the file name uses the start date and time. There is a time stamp for each data point.

The ADAQ logger does not have any digital inputs, how would you recommend recording data from a speed sensor, ie. to measure fan speed?

We recommend using a frequency to voltage signal conditioning unit that will output 0-5V for frequency.

How many parameters/messages can the OBD Mini Logger log simultaneously?

This is limited only by the vehicle’s controllers; the logger is not the limitation.

Can the logger be used as an event logger, so that it logs after a trigger?

DawnEdit can post process so you only see the data that meets the criteria.

The logger isn’t working with a 2015 Volvo or Mack Truck.

Volvo has moved to the OBD-II 16-pin connector and uses 500kbaud for CAN1 and 250kbaud for CAN2. Mack now uses 1Mbaud on CAN1 and 500kbaud on CAN2.

Logger Troubleshooting

Red Lights

Not reading microSD card or memory properly.
Remove card and reinsert. If still blinking try another card or format existing card.
If still failing
Sometimes the loggers go bad and can’t read the memory. HEM Data can ship a replacement if still under warranty.

No Lights

No power or no data
Make sure logger is powered. If powered, make sure the data requested in the config file is coming across the network. LD network must be OBD compliant.
If still failing
Logger may be dead. If logger does not work with a simple config file on multiple vehicles, it may have died. HEM Data can ship a replacement if under warranty.

Blue-Green Lights

Bad baud rate
Use CAN1Baud=250000 (for 250kbuad in this example) in the prefs.txt file.

Continuous Green After Successful Logging

Network continues to send data
Create a config file that doesn’t log the messages that send after ignition off. Use Message Monitor or “Create message file from binary IOS” to look at the end of an IOS file to see which messages continue to send. Sometimes it is a useful message but on a non-useful controller. In this case, specify the proper Target ECU in the DawnEdit Messages Tab.
Logger can be removed while blinking green if the above solution is not preferred.

Data Storage/Retrieval

When should we use the USB cable versus just inserting the microSD card into the computer?

The cable is only used to update firmware and and config the Mini Logger. To download the files use the microSD card.

What is the data format when downloaded to the PC?

The OBD/J1939 messages are stored in a binary IOS file and the analog in a CSV file. As a batch post process both files are merged into a single CSV file with the CAN messages being converted to scaled engineering parameters

How do I estimate the file size?

Estimate the file size using the following equation. Note messages not parameters. There can be multiple parameters per message:
16 * (# of messages) * sampleRate * (time in sec) / 1024 = kB

For example, if you take 5 messages at 1 sample/sec for 1 hour:
16 * 5 messages * 1 sample/sec * 3600 sec / 1024 = 281 kB

For OBD use 11.5 instead of 16. 16 is the byte size of a J1939 message in our IOS format.

For EOBD, the messages are longer. We suggest running a short test and multiplying for an estimate.

What happens when logger memory is full?

The standard microSD card is 4GB and should last for many months. When memory is full, it overwrites the oldest file.

When the OBD/J1939 Mini Logger is interconnected with the ADAQ Mini Logger how does it store data?

If you used separate units, initially it would store data on its own card but a radio could transfer the data so it is written to one. The best solution is to do it all on the ADAQ.

Can I acquire both analog data and CAN (J1939 or OBD) data on one MicroSD card?

Yes, the ADAQ Mini Logger is capable of both analog and CAN inputs.

What size microSD card should I use?

Newer loggers (since 2011) can use up to 32GB microSD cards. Older loggers must use the 2GB microSD cards.

Why am I getting a January 2000/2001 start date?

This means that the real-time clock battery is dead. If your logger has GPS, it has a rechargeable battery. If you do not use the GPS logger for very long or very often, the battery will lose charge. For non-GPS, HEM Data will replace the battery for no charge if covered under the 1-year warranty. Contact HEM Data.

How do the files get downloaded with WiFi?

Files can be uploaded to your local server or our website using the HTTP POST method. If you use your own server, we will provide sample code. DAWN Dashboard is an option if you want HEM Data to convert, store, and display the data as you specify.

Data Conversion

Is my J1939 data coming from multiple controllers?

You can view the raw data by using the “Create message file from binary IOS” checkbox when converting. If you know the correct controller for a particular message, you can enter it in the Messages Tab. Refer to c:\DAWN\User’s Guides\Appendix A DawnEdit.pdf for more information.

I have noticed parameters alternating between their maximum values and a real value. Is this something the logger does when a response is missing?

Yes, if it only has the maximum value it means the parameter is part of the message where other parameters are available but those are not available.

Why is my sample rate incorrect?

Newer loggers are capable of 10x faster speeds than the older models and must be configured differently. If you are using an older Mini Logger (2011 or older) and DawnEdit2 version 3.2 or later, you need to multiply your sample rate by 10 in the Create Mini Logger Config File Dialog. For example to take 10 samples/sec enter 100.

How is Fuel Economy calculated by DawnEdit?

FuelEconomy = (lambda * 7.107 * speed / MassAirFlow);
Fuel Economy in MPG
Speed in KPH
MAF in g/s

After converting the IOS file, I get an empty CSV file with only the parameter names.

In this situation it is likely that you did not use the correct config.txt file or (for OBD) there is no config file on the card. Copy the correct config file and log data again.

How do I change the units in the converted CSV file?

In DawnEdit, find the parameter you want to edit. You can directly edit it or click Duplicate Record. Change the unit in the Units column. Also, change the Factor and Offset appropriately. You can also change the Min/Max but it is only for reference and is not necessary. The example below shows how to convert from Celsius to Fahrenheit:

Name Scale Offset Min Max Unit
Ambient Air Temperature 0.03125 -273 -273 1735 C
Ambient Air Temperature 2 0.03125 * 1.8 -273 *1.8 +32 -273 *1.8 +32 1735 *1.8 +32 F
Ambient Air Temperature 2 0.05625 -459.4 -459.4 3155 F
I am using Absolute Time and it is not formatted correctly in Excel

The converted CSV file has no formatting associated with it. In Excel, select the entire Time column and open the Format Cells dialog. Choose Custom and enter m/d/yyyy hh:mm:ss . For decimal places make it m/d/yyyy hh:mm:ss.0 . If you save the file in Excel as a CSV the file will become corrupt. Save it as an xls/xlsx.


How is the time synchronization done between CAN and GPS data?

GPS data is sampled at 1 Hz and is written to a CSV file. The CAN messages are written to a binary file. They are merged as a post process using DawnEdit or Dashboard. Both start acquisition in less than 1 second.

What is the internal GPS resolution of the DAWN Mini Logger?

a) Basic – 3-5m
b) DGPS – 1-2m
– Automatically supports this if a DGPS/WAAS satellite/tower is available.